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Spatial root distribution and water uptake of maize grown on field with subsoil compaction

Spatial root distribution and water uptake of maize grown on field with subsoil compaction J. Hydrol. Hydromech., 58, 2010, 3, 163­174 DOI: 10.2478/v10098-010-0015-z MARGARITA L. HIMMELBAUER1), WILLIBALD LOISKANDL1), SVETLA ROUSSEVA2) 1) University of Natural Resources and Applied Life Sciences, Institute of Hydraulics and Rural Water Management, Muthgasse 18, A-1190 Vienna, Austria; Mailto: ml.himmelbauer@boku.ac.at 2) "N. Poushkarov" Institute of Soil Science and Agroecology, Shosse Bankya Street 7, Sofia 1080, Bulgaria. Soil compaction in agricultural areas inhibits plant root growth through increased mechanical resistance, altered water and nutrient supply. The main objective of this study was to evaluate spatial distribution of roots and its effect on water uptake of maize grown on field with subsoil compaction. Two treatments were examined: complex melioration consisting of deep loosening in combination with drainage and control without applied meliorations. Root observations were conducted on vertical and superposed horizontal planes covered with a 2 cm grid short after silking. Root distributions expressed as index of density and/or dry mass density were estimated down to 1 m soil depth and with a distance to a plant base. For analysis of root distribution pattern on the horizontal planes, a Variance to Mean Ratio (VMR) test was applied. Soil water monitoring were conducted during the vegetation period. On the vertical planes, root densities were similar in the topsoil of both treatments, but the results were significantly higher in the subsoil of the meliorated one showing deeper allocation of root density. In contrast, the control had more squares with lots of roots (i.e. higher indexes) just at the top- subsoil boundary owing to bunching of roots in macropores. The horizontal planes in the control generally consisted larger areas without visible roots and thus great distances for water and nutrient transmission, especially in the subsoil. The estimated VMR also pointed toward different levels of root clustering. Consequently, an inhibited water extraction from the subsoil in the control, a delay in crop ontogenesis and a less biomass production was established during the observed period. KEY WORDS: Maize, Soil Compaction, Soil Amelioration, Root Spatial Distribution, Water Uptake. Margarita L. Himmelbauer, Willibald Loiskandl, Svetla Rousseva: PRIESTOROVÉ ROZDELENIE KOREOV A ODBER VODY KOREMI KUKURICE V PÔDE SO ZHUTNENOU PODORNICNOU VRSTVOU. J. Hydrol. Hydromech., 58, 2010, 3; 29 lit., 5 obr. 4 tab. Zhutnenie ponohospodárskej pôdy bráni rastu koreov; je to spôsobené zvýseným mechanickým odporom pôdy, a znízeným prítokom vody a zivín. Cieom tejto stúdie je zhodnotenie priestorovej variability koreov, ich vplyvu na odber vody koremi kukurice na poli so zhutnenou podornicnou vrstvou. Boli hodnotené dva spôsoby obrábania: komplexná meliorácia pozostávajúca z hlbokého podrývania v kombinácii s drenázou a obrábanie (kontrol bez melioracných zásahov. Identifikácia rozdelenia koreov bola vykonaná vo vertikálnych a horizontálnych rovinách s 2-cm sieou, krátko po metaní. Rozdelenie koreov bolo vyjadrené ako index hustoty alebo ako hustota suchej biomasy koreov do hbky 1 m; v horizontálnom smere az k susedným rastlinám. Bol pouzitý test ,,Variance to Mean Ratio" (VMR) na urcenie rozdelenia koreov v horizontálnom smere pocas vegetacného obdobia. Hustota koreov vrchnej vrstvy pôdy vo vertikálnej rovine bola podobná pre obidve varianty, ale pre meliorovanú pôdu boli hodnoty hustoty koreov v podlozí podstatne vyssie a korene zasahovali hlbsie. Ako protiklad, na kontrolnom pozemku bolo viac stvorcov s mnohými koremi (t.j. vyssie indexy) práve na hranici ornicnej a podornicnej vrstvy, pre enormný rast koreov v makropóroch. V horizontálnej rovine tento kontrolný pozemok obsahoval veké oblasti bez viditených koreov, a to znamená veké vzdialenosti pre prenos vody a zivín v podornicnej vrstve. Výsledky aplikácie VMR naznacujú tiez rozdielne úrovne zhlukov koreov. Z toho vyplýva znízený odber vody koremi rastlín na kontrolnom pozemku, ako aj pomalsia ontogenéza a nizsia produkcia biomasy, ktorá bola identifikovaná pocas sledovaného obdobia. KÚCOVÉ SLOVÁ: kukurica, meliorácia pôdy, priestorové rozdelenie koreov, odber vody koremi. Introduction Soil compaction, occurring naturally or a consequence of inappropriate land management, is a problem often established in agricultural areas. It can deteriorate structure, porosity and pore-size distribution, and decrease water permeability in soil (Horn et al., 2000). Many cultivated soils in Bulgaria are compacted, characterized by poor structure, and about 5 % of them are prone to waterlogging (Dilkova et al., 1998). In such soils, roots suffer due to increased mechanical resistance against root penetration, inhibited water, nutrient and oxygen supply. The negative impact depends on climate conditions as well as on particular root system characteristics. For efficient uptake of water by plants, the water "availability "as well as its "accessibility" to the roots is critical (Droogers et al., 1997). Water "availability" refers to soil ability to supply roots with water at a sufficient rate and is mainly a function of soil hydraulic characteristics. The water "accessibility", however, highly depends on root system extension and spatial distribution of roots. Root elongation is influenced by penetration resistance of the soil and thus by its bulk density, structure and pore system. In compacted soils, roots are often confined into large pores and are less efficient in uptake due to high intra-root completion. In addition, an insufficient supply of water and nutrients occurs owing to low hydraulic conductivity and diffusion rate in compacted soil spots. As a result of root clustering, water cannot be taken up at a rate useful for plants compared to soils with equivalent but uniformly distributed roots (Baldwin et al., 1972; Tardieu at al., 1992; Amato and Ritchie, 2002). Droogers et al. (1997) extended this approach, showing that not only extreme compaction but also different aggregates structure of soil, formed by various land management practices, leads to root grouping and influenced the uptake of water. Besides the root density parameter widely used for modeling and simulation of root uptake at a field scale (e.g. Novak, 2003), the root spatial distribution (rooting pattern) appears to be also important for water and nutrient acquisition by plants. This concept provides a basis for novel modeling of root uptake, however fitting data for validation is really still scarce (Lipiec et al., 2003; Pardo et al., 2000). The main objective of this study was to assess root spatial distribution and water uptake of maize 164 grown on field with subsoil compaction. A specific task was to examine the effect of amelioration practices against subsoil compaction on soil characteristics and thus on root development and crop productivity. Hydro-technical and ameliorative measures against soil compaction have been seldom applied, since they are costly and their long-term positive effects are arguable. Material and methods Climate and soil conditions The experiments were conducted on a research field of the "N. Pushkarov" Institute of Soil Science and Agro-ecology in Thracian lowland, semi-arid area of South Bulgaria. The climate is continentalMediterranean with a mean annual temperature of 12°C and a long-term annual precipitation of about 600 mm. A major rainfall maximum has been observed at the end of autumn -beginning of winter, a minimum precipitation- in late summer along with long periods of drought (Georgieva et al., 2007). The precipitation sums during the winter are often insufficient to complete even the lower limit of the readily available water for plants (Koleva and Alexandrov, 2008). The soil is fine textured Dystric Planosol (PLd, FAO soil classification) having elluvial-illuvial deep profile with high degree of textural differentiation (Boyadgiev, 1994; Dilkova et al., 1998). This textural differentiation, derived from the difference in clay content between two soil horizons, leads to compaction and low permeability for water of the subsoil. As a result, the soil is prone to surface waterlogging in early springs. Experimental setup, soil and root observations Soil meliorations using different hydro-technical and ameliorative methods to increase water permeability of the waterlogged soil were applied a few years ago following Shopski et al. (1998). In this study two main treatments were examined: deep loosening in combination with mole drainage and a control without ameliorations applied. The combined soil amelioration consisted of loosened soil zones to a depth of 60 cm and mole channels with a distance between furrows of 11 m. A durability of the channels depends on the soil, the climate and the local land management, but the positive effect on soil water permeability generally disappears in a course of ten years after the treatment. Experimental plots of 90 m2 were planted in the beginning of May with maize (Zea mays L. var. "Kneza"). Herbicides were applied shortly after planting, rest weeds were removed mechanically or hand pulled. Else, the both plots were managed according to the common local farming using mouldboard ploughing to about 30 cm depth. A series of soil physical and chemical characteristics were measured in advance to the experiment taking disturbed and undisturbed soil samples down to 1 m depth in both plots, i.e. particle size distribution, particle and bulk density, porosity, hydraulic conductivity at saturation, plant available water, pH, humus content, carbonates. For evaluation of the gravimetric soil water content, soil samples down to 1 m depth were taken continuously throughout observation period. Plant growth and development stages of maize were monitored, biomass production was measured at harvest. Root spatial distribution was examined using soil profile method shortly after silking maize stage (female flowering) when root systems are fully developed reaching their largest extension. First, representative areas completely free of weeds, having a regular crop spacing and development were selected. A trench was dug perpendicular to the crop rows to about 1 m soil depth. A profile (100 x 72 cm) covering one maize row and two half "between rows" distances left and right to the row was carefully smoothed. A few millimeters of roots was made visible from the adjacent soil using air and water under pressure in addition to hand tools. Next the profile was covered with a fine grid mesh of 2 x 2 cm. Root contacts were counted and indexes of density were introduced, accounting for a presence and an absence of fine and coarse roots in each square following Tardieu (1988. The indexes of root density equaled to 0 ­ absence of roots, 2 ­ one thin root visible, 4 ­ many thin roots visible, 8 ­ two and more thick roots > 2mm and thin branches visible. The indexes were related to root mass density per volume of soil taking small soil monoliths (cubes) with a face one mesh square from different depths and positions. The roots were washed out, their dry mass was measured, and thus the root mass density distribution down the soil profile was estimated indirectly. Two profiles (replications) were prepared in the same trench dug a few cm apart resembling a distance between single plants. Three horizontal planes (40 x 72 cm), covering the same row and the two half "between rows" distances, were dug on superposed depths intersecting the rooting volume in the middle of the topsoil (A1A2 horizon) at 13 cm, at the bottom of the topsoil at about 25 cm, and in the middle of the compacted subsoil (B horizon) at about 50 cm depth. The horizontal planes were prepared in a similar way as the vertical ones. The root density index here equaled the number of roots counts in each square. Data analyses Root density distributions expressed as indexes of density per square, percentage of squares consisting roots and root mass per volume of soil were calculated and plotted over the soil depth and with a distance to the crop row. Estimated results were compared with the measured soil parameters. Summary statistics, analysis of variance, and correlation analyses were conducted to find out the relations between different root, and soil parameters. For analysis of root distribution (pattern) on the horizontal planes, an additional Variance to Mean Ratio (VMR) test, called also index of dispersion, was used. The VMR test is proposed to characterize spatial distribution of points (Grieg Smith, 1983). The point distribution in a certain neighborhood may represent some interactions in-between, i.e. the points may occur in clusters, or there is a lack of interactions and the point distribution is completely random, or following deterministic pattern, thus the points are regularly distributed within the definite area. If the point distribution is random, it can be described by a Poisson process, where the variance and the mean values are equal and the approximated Variance to Mean Ratio is close to 1. VMR values larger than 1 point to existence of clusters, i.e. grouped or cluster distribution pattern which is mainly associated with a Negative binomial or Neyman type A theoretical distributions. VMR values below 1 suggest more uniform (regular) point distribution (Wulfsohn et al., 1996). In this study, the VMR was estimated for the root counts observed on the all horizontal planes in both treatments. Results and discussions Soil properties Essential soil characteristics are presented in Tab. 1. The soil is classified as clay loam in the topsoil and clay in the subsoil. The topsoil is acidified due to carbonate leaching down the soil profile. 165 Bulk density (BD) is a commonly used indicator for soil compaction (Bennie, 1996; Hakansson and Lipiec, 2000). BD values optimal for plant growth vary for different soils, but roots rarely enter soil if BD exceeds 1.6­1.7 g cm-3 (Russel, 1980). In this study, all BD measurements at field capacity were relatively high, but below the cited threshold value approximating 1.45 g cm-3 for the a good portion of the rooting depth in both plots (Tab. 1). However, the BD rose rapidly with the soil getting drier in the course of time. At the time of root sampling, the BD's reached a maximum of 1.64 g cm-3 at 30 cm depth (the topsoil- subsoil boundary) in the control plot. The BD's down to 50 cm depth in the meliorated plot did not change greatly compared to the values measured in spring and lay between 1.36 and 1.54 g cm-3 (data not shown). This seemingly was a subsequent effect of the hydrotechnical ameliorations against soil compaction. T a b l e 1. Major physical and chemical properties of the soil in the experimental field. T a b u k a 1. Najdôlezitejsie fyzikálne a chemické vlastnosti pôdy na experimentálnom poli. Field capacity (FC) Total porosity Wilting point (WP) Particle size distribution* Bulk density at FC Hydraulic conductivity saturation Dystric planosol Air filled porosity ** Plant available water Particle density Humus [%] 1.88 1.50 1.32 0.74 1.74 1.00 0.90 0.65 Depth [cm] Non-meliorated plot A1A2(0­22) 10­15 B1(t)(22­42) 35­40 B2(t) (42­72) 50­55 B3(t)(72­95) 80­85 Meliorated plot A1A2(0­28) 10­15 B1(t)(28­55) 40­45 B2(t) (55­78) 65­70 B3(t)(78­100) 85­90 Horizon Clay Silt Sand [%] [%] [%] [g cm-3] [g cm-3] [vol. %] [vol. %] [vol. %] 27.1 40.2 48.0 44.9 32.8 53.8 53.1 51.8 42.7 32.3 30.5 31.2 44.9 29.9 26.7 33.9 30.2 27.5 21.5 23.9 22.3 16.3 20.2 14.3 2.63 2.68 2.68 2.70 2.56 2.73 2.74 2.79 1.46 1.46 1.45 1.47 1.35 1.47 1.45 1.53 42.08 40.57 39.59 39.23 34.48 42.14 42.64 41.46 13.80 20.54 17.41 19.37 13.57 30.30 31.40 29.27 28.28 20.03 22.17 19.86 20.91 14.76 16.31 15.87 [%] 44.49 45.52 45.90 45.56 47.27 46.15 47.08 45.16 [%] 2.41 4.95 6.31 6.32 12.79 4.01 4.44 3.70 [cm d-1] 105.5 0.00 0.00 0.36 42.03 5.04 2.01 10.05 [­] 4.00 4.05 4.80 6.00 3.50 3.80 4.60 5.60 *Texture fractions: Clay (< 0.002 mm), Silt (0.002­0.05 mm), Sand (0.05­2 mm). *Klasifikácia textúry: íl (< 0.002 mm), prach (0.002­0.05 mm), piesok (0.05­2 mm). **Air filled porosity at field capacity is calculated after Vomocil (1965) as a difference between the total porosity and the volumetric water content at FC **Podiel pórov zaplnených vzduchom pri ponej vodnej kapacite pôdy, bol vypocítaný poda Vomocila (1965), ako rozdiel medzi pórovitosou a vlhkosou pri FC. Surprisingly, the water content assessed at FC level was higher in the topsoil of the nonmeliorated than in the meliorated one, and the WPwater contents were lower. Correspondingly, more plant available water (Allen et al., 1998) was estimated for the entire rooting depth in the control. The estimated total porosity was a bit higher in the meliorated plot, but the differences to the control were insignificant. Air-filled porosity represents the pore space filled with air after the soil has been drained and includes pores mainly larger than 0.05 mm. As critical limits for air-filled porosity, below which root growth and uptake are inhibited, are accepted values of 10 % (volumetric) for clay and 15 % for sandy soils (Arvidsson, 1999; Hakansson and Lipiec, 2000). In this study, the air-filled porosity at field capacity (FC) was calculated after 166 Vomocil (1965). The estimates were below the critical limits except of the meliorated topsoil, suggesting insufficient amount of (macro-)pores in the large part of the rooting zone (Tab. 1). The minimum of 2.4 % was found in the topsoil of the nonmeliorated plot (control). Therefore, even at optimal soil water conditions the plant roots here will be at a risk of suffering for aeration. In addition, only minor differences between the air-filled porosity measurements in the subsoil of the two plots were established. At the same time, the hydraulic conductivity measured at saturation was higher in the subsoil of the meliorated than the nonmeliorated plot, but the variation between single measurements was high. No significant differences in the rest of the evaluated soil parameters between non-meliorated and meliorated plots were found. Carbonates [%] 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 pH KCl Root density distribution At the time of root observation, the maize root systems already reached a soil depth of 1 m (Fig. 1). A high variability in root density (indexes) was observed between the single profiles (replications) in both treatments. Between the treatments, however, the measured indexes and the shape of distribution curves down the soil profile did not differ significantly (P < 0.05, ANOV. The highest den0,0 2 6 10 14 18 22 26 30 34 38 42 depth, cm sity index for the both plots was measured in the top 30 cm depth (topsoil). Below this depth, the root density in the control decreased gradually resembling an exponential curve typically observed for field grown crops (Himmelbauer et al., 2008). In the meliorated plot, however, the density index values were comparable between 30 and 60 cm soil depth (i.e. the melioration depth), and downwards decreased. 20,0 40,0 60,0 80,0 p 0,0 2 6 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 20,0 40,0 ) 60,0 80,0 46 50 54 58 62 66 70 74 78 82 86 90 94 98 Index > 4 Index > 0 Index > 0 Index > 4 Fig. 1. Percent distribution of squares consisting at least one root (index > 0) and with lots of roots (index > 4) averaged for the two profiles in the non-meliorated and meliorated plots. Obr. 1. Percentuálne rozdelenie stvorcekov obsahujúcich aspo jeden kore (index > 0) a stvorcekov s viacerými koremi (index > 4) spriemerované pre dva profily; nemeliorovaný variant, meliorovaný variant. As can be seen on the Fig. 1, between 60 and 90 % of the squares in the topsoil consisted at least one visible root (i.e. proportion of squares with index > 0), with small differences between the treatments. Close to the top-subsoil boundary, the proportion of squares with index > 0 was considerably higher in the meliorated than in the nonmeliorated plot, showing more homogeneous distribution of roots there. In the subsoil of the meliorated plot 50 % "full" squares were found in the upper 30 cm and 20 % underneath at 60 cm depth, against 30 % and 10 % in the control, respectively. Hence, the effect of the former meliorations with deep loosening to 60 cm depth on the root distribution was obvious. On the other site, the nonmeliorated plot had more squares consisting plenty of roots (index > 4), especially close to the topsubsoil boundary. Root growth in compacted soil is not completely restricted when macrospores or cracks are present, and a preferential root growth occurs in these pores (Laboski et al., 1998; Bingham and Bengough, 2003). In this study, the observed high root density indexes were a clear indication of root grouping into macropores crossing the top- and compacted subsoil. The results of the root mass density averaged for the two profiles (replications) are shown in Fig. 2. Values between 0.10 and 0.70 mg cm-3 were estimated for the topsoil with no considerable difference between the treatments (P < 0.05, ANOV. Between 30cm (topsoil) and 60 cm (subsoil), the values in the meliorated plot were close to 0.20 mg cm-3, and ap167 proximated the half of the root density in the nonmeliorated one. Below this depth, the root density in both plots decreased gradually to about 0.03 mg cm-3. Spatial variations in the soil bulk density along with the soil water content changes allowed roots to find paths to cross the compacted layer. In the control, about 28 % of the total root mass was found within the subsoil and 72 % in top. In contrast, the corresponding values in the meliorated plot were 36 % against 64 % showing apparently deeper allocation of the maize root mass at the time of observation. 0,00 2 6 10 14 18 22 26 30 34 38 depth, cm 0,20 0,40 0,60 0,80 mg cm -3 0,00 2 6 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 0,20 0,40 0,60 0,80 mg cm -3 1,00 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 mean dry mass mean dry mass Fig. 2. Root density distribution down the soil profile expressed as root dry mass density [mg cm-3] for non-meliorated and meliorated plots. Horizontal bars represent standard deviations. Obr. 2. Rozdelenie hustoty koreov vo vertikálnom smere, vyjadrené ako hustota suchej masy koreov [mg cm-3] pre: nemeliorovaný variant, meliorovaný variant. Horizontálne bodkované ciary reprezentujú standardné odchýlky. Concerning the horizontal allocation of root density, a concentration of roots near the maize row was observed in the topsoil, more evident in the meliorated plot than in the non-melioration one. In the subsoil, more homogeneous distribution with respect to the plant base was observed in both treatments: the density distribution shifted to the inter-rows, the differences to the row position were smaller and variability got higher. On the horizontal planes (Fig. 3), the proportions of the squares where at least one root contact was observed (index > 0) were between 60 to 90 % at 13 cm depth in the meliorated plot, demonstrating more homogeneous distribution with close distances between single root axes. The average value for the 25 cm plane was 56.4 % and 39.3 % for the lowest one at 50 cm depth. The corresponding val- ues for the three superposed planes in the control were 63.3 %, 31.1 % and 15.6 %, respectively. Some discrepancies in the root density results between the vertical and the horizontal maps were observed. They most probably resulted from the preferentially horizontal direction of the seminal roots in the topsoil and vertical in the subsoil as well as due to root branching pattern of maize (Koedjikov, 1975). Thus, the results of the vertical mapping seemed to be underestimated for the areas with more horizontal root growth and lack of branching in the topsoil, and just the opposite phenomenon happened underneath. Similar phenomenon was reported also by Chopart and Siband (1999). Different tests have been proposed for analysis of spatial root distribution (pattern), i.e. theoretical distributions such as Poisson, Negative binomial or 80,0 % 60,0 40,0 20,0 0,0 36cm R 36cm R 0 8 6 4 2 4 6 34 32 28 26 24 22 18 16 14 12 8 12 14 16 18 22 24 26 28 32 32 36cm-L 30cm 20cm 10cm 10cm 20cm 30cm 34 34 row 2 0 2 4 80,0 60,0 40,0 20,0 0,0 8 6 4 0 6 34 32 28 26 24 22 18 16 14 12 8 12 14 16 18 22 24 26 36cm-L 30cm 20cm 10cm 10cm 20cm 28 30cm row 2 0 13cm 25cm 50cm interrow L interrow R Fig. 3. Percent distribution of squares consisting at least one root (index > 0) observed on the three superposed horizontal planes at 13 cm, 25 cm and 50 cm in non-meliorated and meliorated plots. Obr. 3. Percentuálne rozdelenie stvorcekov obsahujúcich aspo jeden kore (index > 0), pozorované v troch superponovaných horizontálnych rovinách v hbke 13, 25 a 50 cm; nemeliorovaný variant, meliorovaný variant. the Neyman type A (Baldwin et al., 1972; Wulfsohn et al., 1996), a nearest neighbor test, a spatial autocorrelation test (Tardieu, 1988, a skewness test (Rogers, 1974), etc. The Variance to Mean Ratio (VMR) test has been proposed for ecological studies (Grieg Smith, 1983). Reported scales of the application of the VMR test (the chosen size of the tested unit are vary between different studies. According to Baddeley (2008), the power of the VMR test depends on the size and falls to zero for squares which are either very large or very small. Nevertheless, it gives an clear indication of important clustering processes occurred in soil. Baldwin et al. (1972) coupled it to diffusion coefficients of certain nutrients in soil and applied the test at a centimeter scale. Enlarging the quadrates to a decimeter scale, Tardieu (1988 came to the conclusion that their size will not significantly affect the VM Ratios in soils with relatively small structural impediments. This statement was confirmed by Wulfsonh et al. (1996). In this study, the VMR test was applied for the three superposed horizontal planes starting with the squares size of 2 cm (the mesh grid size) and increasing it to 10 cm in both trials. The square sizes corresponded to the dimension of soil aggregation and compacted clods observed in situ. The mean number of the root counts observed in each square (the root index on the horizontal planes) and the corresponding variances were calculated. Then the ratios between them, the VMR values were estimated for each depth position and treatment. T-test was used to compare the calculated VMR with the theoretical value of 1. The results are presented in Fig. 4 and Tab. 2. 8,0 7,0 6,0 5,0 VMR 4,0 3,0 2,0 1,0 0,0 0 2 4 6 quadrate size (cm) 8 10 12 13cm mel 25cm no mel 25cm mel 50cm no mel 50cm mel 13cm no mel Fig. 4. Results of the Variance to Mean Ratio (VMR) test applied for the root counts per square of 2, 4, 8 and 10 cm size for the three superposed horizontal planes in non-meliorated (no mel) and meliorated (mel) plots. Obr. 4. Výsledky testu ,,Variance to Mean Ratio" (VMR), aplikované na pocty koreov vo stvorceku s vekosou strany 2, 4, 8 a 10 cm pre tri superponované horizontálne roviny v hbke 13, 25 a 50 cm; nemeliorovaný variant, meliorovaný variant. The obtained results showed that the spatial patterns of roots did not follow a regular spatial distribution (assumed in the majority models of water uptake) either in the meliorated or in the nonmeliorated plot. Just the VMR value at 2 cm scale (square size) at the 13 cm depth in the meliorated plot equaled 1.0, suggesting a non cluster but random type of root distribution (Tab. 2). In addition, only at this depth statistically significant differences in the root counts number were established between the meliorated and non-meliorated plot. With increasing the square size to 8 cm, the VMR values rose rapidly larger than 1, stronger in the ploughed topsoil layer than below it. These scales of the testing most probably coincidence with the size of the soil aggregates and clods in the field. At a decimeter scale (10 cm), the VMR values dropped at all positions except of the topsoil in the control. In this case, the quadrates probably oversized the dimension of the soil clods. Surprisingly, in most cases the subsoil had lower VMR values compared to the topsoil, although that the visual examination in situ showed large structural barriers and root clustering at a transit to and within the compacted subsoil. Soil water monitoring Changes of the soil water content down the soil profile measured gravimetrically during the vegetation period are shown in Fig. 5. The values varied more rapidly and higher in the topsoil (0 ­ 30 cm) than in the subsoil, due to fluctuations in precipita170 tion, temperature and evaporation as well as due to the foremost root uptake, especially in the beginning of the growing period. End of June, when maize approached the end of the vegetative stage in the meliorated plot, an apparent decrease in the water content occurred also in the subsoil. In the control, the subsoil- water content values were still high. The maize plants just came to the 9 to 12 leaf stage and obviously did not extract lots of water from the subsoil. Until end of July matching the crop stage of silking in the meliorated plot, the soil in the 0­50 cm depth rapidly dried due to the enhanced root water uptake. There were two dry periods observed: in the middle of July and in August. Coming to harvest, the soil water content further decreased in all soil layers in both plots. In the control, the topsoil-water was almost depleted, while the subsoil remained much wetter than in the meliorated plot. The water uptake by root was obviously still restricted to the topsoil with low activity down the soil profile, although the high amount of plant available water estimated. This suggested some limitations for water uptake by the maize roots. In the meliorated plot, the subsoil water content depleted further and greater than in the control. This was attributed to the faster growth and the more extensive root water uptake there. In spring, the estimated soil water storage in mm was close to the field capacity level and after that it decreased more or less steadily(data not shown). As the plants come to silking, the water storage approached the wilting point in both treatments and at harvest it fell below the WP level, first in the meliorated plot and thereafter in the control. In general, the available water reserves in the meliorated depleted more rapidly than those in the control. Maize in the meliorated and non-meliorated plots developed differently. As it was also reported by Bingham and Bengough (2003), the growth of crop shoots was reduced when part of the root system was in compacted soil, although some compensatory adjustments in root growth. The plants in the meliorated plot were observed to grow more rapidly reaching the next growth stage one to two weeks earlier than those in the control. Accordingly, higher above-ground biomass production was found there. Crop parameters measured at root sampling and at harvest are presented in Tab. 3. The maize plants in the meliorated plots were much higher and developed twice as spasing before leaf area and biomass. Spatial root distribution and water uptake of maize grown on field with subsoil compaction T a b l e 2. Analyses of spatial arrangement of the root counts (indexes) on the tree superposed horizontal planes in the nonmeliorated and meliorated plots. T a b u k a 2. Analýza priestorového usporiadania poctu koreov (indexy) v troch superponovaných horizontálnych rovinách meliorovanej a nemeliorovanej pôdy. Root counts per square VMR 1.535*** 1.271*** 1.223*** 2.429*** 1.803*** 1.769*** 4.108*** 2.04*** 2.00*** 7.057*** 1.491* 1.397 Mean 1.93 B 1.06 A 0.58 A 7.71 B 4.23 A 2.32 A 30.78 A 16.96 A 9.27 A 50.42 A 25.96 A 14.21 A Melioration median Variance 2 1 0 7 4 2 27 17 9 49 27 13 2.12 b 1.37 a 0.72 a 16.54 b 9.93 a 3.81 a 142.60 a 70.63 a 21.65 a 177.80 a 74.91 a 26.52 a VMR 1.101 1.298*** 1.235*** 2.147*** 2.347*** 1.639*** 4.634*** 4.166*** 2.337*** 3.527*** 2.886*** 1.867** Depth 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm Nr squares Square size 720 720 720 Square size 180 180 180 Square size 45 45 45 Square size 24 24 24 Mean 1.33 A 0.43 A 0.19 A 5.06 A 1.73 A 0.76 A 20.13 A 6.89 A 3.00 A 35.33 A 10.50 A 4.88 A No melioration median Variance 2 x 2 cm 1 2.05 a 0 0.55 a 0 0.23 a 4 x 4 cm 5 12.29 a 1 3.12 a 0 1.34 a 8 x 8 cm 17 82.71 a 7 14.06 a 3 6.00 a 10 x 10 cm 31 249.4 a 10 15.65 a 5 6.81 a VMR-Variance: Mean Ratio, *** statistically significant differences from the theoretical value of 1 at 95%, 99% and 99.9% confidence level, respectively (T-test) ***Statisticky významné rozdiely od teoretických hodnôt 1 pre 95%, 99% a 99.9% intervaly spoahlivosti (T-test) Comparison between non-meliorated and meliorated plot: T-test for mean comparison: values followed by the same capital letter are not significantly different (P < 0.05); F-test for variance comparison, variances followed by the same small letter are not significantly different (P < 0.05) Porovnanir meliorovaných a nemeliorovaných variantov: T-test pre porovnanie priemerných hodnôt: Hodnoty nasledované tým istým vekým písmenom nie sú významne rozdielne (P < 0.05); F-test pre porovnanie variancií; Hodnoty variancií nasledované tým istým malým písmenom nie sú významne rozdielne (P < 0.05). 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 9.07. 12 leaf 15.07. 23.07. 31.07. 2.08. 8.08. 12.08. 19.08. milk rape 0-10cm 10-20cm 20-30cm 30-40cm 40-50cm 50-60cm 70-80cm 90-100cm g g-1 21.05. 27.05. 12.06. 14.06. 23.06. 26.06. 4.07. 10.07. 15.07. 23.07. 31.07. 2.08. 3-5 leaf 12 leaf dates silking root profiles 7.08. 12.8. milk rape 22.8. harvesting silking, root profiles dates Fig. 5. Soil water content measured at different soil depths during the vegetation period of maize in non-meliorated and meliorated plots. Obr. 5. Vlhkos pôdy meraná v rozdielnych hbkach pocas vegetacného obdobia kukurice; nemeliorovaný variant, meliorovaný variant. Correlation analyses Regarding the correlations between different root and soil parameters, dissimilar results were obtained for the two treatments. In the meliorated plot, the root density significantly correlated with the available soil water and the porosity (total and air-filled), and significantly but negative with the bulk density. In contrast, in the non-meliorated plot the root parameters correlated positively with the bulk density at sampling, but negatively with the porosity data. Looking at the correlation matrix (Tab. 4) one can recognize, that root density expressed as dry mass and percentage of squares consisting roots highly correlated with the hydraulic 171 T a b l e 3. Crop characteristics and biomass production of maize on meliorated and non-meliorated plots. T a b u k a 3. Charakteristiky porastov a produkcia biomasy kukurice na meliorovaných a nemeliorovaných variantoch. Occasion (Stage) Plant density Plot 1000 [pl. ha-1] 91.3 92.3 Height [cm] 141.9 230.9 At root observations (silking) Leaf area green [cm2] per plant 2247 4056 Biomass fresh [t ha-1] 19.9 44.5 Harvest (milk-dough stage) Biomass fresh [t ha-1] 25.6 48.0 No melioration Melioration T a b l e 4. Coefficients of correlation estimated between root density and different soil parameters. T a b u k a 4. Koeficienty korelácie medzi hustotou koreov a rôznymi pôdnymi parametrami. Depth [cm] RMD, mg cm-3 ­0.910 Index > 0, [%] Sq ­0.947 Index > 4, [%] Sq ­0.779 Porosity Bulk Available Hydraulic density* water conductivity Total Air-filled* [g cm-3] [vol. %] [cm d-1] [vol. %] [vol. %] ­0.590 ­0.624 ­0.484 0.557 0.414 0.644 0.785 0.682 0.811 0.061 0.184 ­0.079 0.300 0.323 0.235 pH Clay [%] Index RMD > 0 Index > 4 [mg cm-3] [% ]Sq [% ]Sq 1 0.961 0.954 1 0.837 1 ­0.755 ­0.744 ­0.873 ­0.750 ­0.558 ­0.655 *Parameters measured at filed capacity level, RMD ­ root dry mass density, percentage of squares (Sq) consisting at least one root (Index > 0) and a lot of roots (Index > 4). *Parametre merané pri vlhkosti pôdy na úrovni ponej vodnej kapacity; RMD ­ hustota suchej hmotnosti koreov, percentuálne vyjadrenie ,,stvorcov" (Sq) obsahujúcich aspo jeden kore (index > 0) a viac koreov (index > 4). conductivity, significant but negative with the clay content and the pH values at a certain soil depth. The strongest positive correlation (R = 0.7 to 0.8) was estimated between the root (index and mass) density and the soil hydraulic conductivity, which can be assumed as an appropriate indicator for root growth distribution. Conclusions At the time of root observations at silking, a deeper allocation of the maize root density was observed down the soil profiles in the meliorated than in the non-meliorated plot. On the vertical planes, root densities, expressed as dry mass and proportion of "full" squares consisting at least one visible root were similar in the topsoil, but significantly higher in the subsoil of the meliorated plot. At the same time, the control plot showed frequent root grouping in areas with lower penetration resistance like pores and cracks at the top- subsoil boundary. The horizontal planes in the meliorated plot had more homogeneous root distribution with more "full" squares at all tested soil depths. In opposite, the control-planes generally had less "full" squares and large areas without roots and great distances for water and nutrient transmission in the 172 soil. The spatial VMR test at 2 cm scale pointed to lack of root clustering only on the horizontal planes of the meliorated topsoil. At all other positions and scales examined, the VMR's were higher than 1.0 indicating different levels of clustering. Due to the root clustering and inter-roots competition, an inhibited water extraction from the subsoil was established in the control during the observed period, although the overall high plant available water estimated. The water reserves in the meliorated subsoil depleted more rapidly than those in the control. This was attributed to the faster plant growth and the more extensive root uptake there. At the same time, a delay in crop ontogenesis and a less biomass production was established in the non-meliorated plot. The strongest positive correlation was found between the root (mass and index) density and the soil hydraulic conductivity, which was assumed as a major root growth controlling factor in this case study. It can be further used as an appropriate indicator for root density distribution. Acknowledgement. The authors thank the ÖFG, MOEL-Plus-Förderungsprogramm (Project 316) for the fellowship of Dr. M. Himmelbauer spent at "N. Poushkarov" Institute of Soil Science and Agroecology, Sofia, Bulgaria. Spatial root distribution and water uptake of maize grown on field with subsoil compaction REFERENCES ALLEN R.G., PEREIRA L.S., RAES D., and SMITH M., 1998: Crop evapotranspiration- Guidelines for computing crop water requirements. FAO irrigation and drainage. Pap. No. 56, Rome. AMATO M. and RITCHIE J.T., 2002: Spatial Distribution of Roots and Water Uptake of Maize (Zea mays L.) as Affected by Soil Structure. Crop Science, 42, 773­780. 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Soil Science, Agrochemistry and Ecology, 4-6, 52­56. CHOPART J.L. and SIBAND P., 1999: Development and validation of a model to describe root length density of maize from root counts on soil profiles. Plant and Soil, 214, 61­74, DILKOVA R., FILCHEVA E., KERCHEV G., KERCHEVA M., 1998: Humus peculiarities of the virgin surface waterlogged soils. In Congres Mondial de Sci. du sol, 16e, Montpellier, France, 20­26 aout 1998. Resumes. Vol. 1, Symp. N 18, p. 378. DROOGERS P., VAN der MEER F.B.W and BOUMA J., 1997: Water accessibility to plant roots in different soil structures occurring in the same soil type. Plant and Soil, 188, 83­91. GEORGIEVA V., MOTEVA M., KAZANDJIEV V., 2007: Impact of Climate Change on Water Supply of Winter Wheat in Bulgaria. Agriculturae Conspectus Scientifi cus, Vol. 72, No. 1, 39­44. GRIEG SMITH P., 1983: Quantitative Plant Ecology. Univ. of Calif. Press, Berkeley, p. 347. HAKANSSON I. and LIPIEC J., 2000: A review of the usefulness of relative bulk density values in studies of soil structure and compaction. Soil & Tillage Research, 53, 71­85. HIMMELBAUER M.L., NOVÁK V., MAJERCÁK J., 2008: Sensitivity of soil water content profiles in the root zone to extraction functions based on different root morphological parameters. J. Hydrol. Hydromech., 56, 1, 34­44. HORN R., AKKER VAN den J.J.H., ARVIDSSON J. (Eds.), 2000: Subsoil compaction. Distribution, Processes and Consequences, Adv. Geoecology, 32, 462 pp. KOEDJIKOV H.A., 1975: The Root System of Cereal Plants. Publishing House of the Bulgarian Academy of Science, 581 pp. KOLEVA E. and ALEXANDROV V., 2008: Drought in the Bulgarian low regions during the 20th century. Theoretical and Applied Climatology, Vol. 92, No.1-2, 113­120. LABOSKI C.A.M., DOWDY R.H., ALLMARAS A.A. and LAMB J.A., 1998: Soil strength and water content influences on corn distribution in a sandy soil. Plant and Soil, 203, 239­247. 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TARDIEU F., 1988a: Analysis of the spatial variability of maize root density I. Effect of wheel compaction on the spatial arrangement of roots. Plant and Soil, 107, 259­266. TARDIEU F., 1988b: Analysis of the spatial variability of maize root density II. Distances between roots. Plant and Soil, 107, 267­272. TARDIEU F., BRUCKLER L., and LAFOLIE F., 1992: Root clumping may affect the root water potential and the resistance to soil-root water on the uptake of ions by roots: I. Soil water content near a plane transport. Plant and Soil, 140, 291­301. VOMOCIL J.A., 1965: Porosity. In: C.A. BLACK (Ed.): Methods of soil analyses. Part 1: Physical and Mineralogical Properties including Statistics of Measurement and Sampling. Agron. Monogr. 9, ASA and SSSA, Madison, WI, USA, pp. 299­314. WULFSOHN D., GU Y., WULFSOHN A., MOJLAJ E.G., 1996: Statistical analysis of wheat root growth patterns under conventional and no-tillage systems. Soil & Tillage Research, 38, 1­16. Received 26 February 2010 Accepted 23 June 2010 PRIESTOROVÉ ROZDELENIE KOREOV A ODBER VODY KOREMI KUKURICE V PÔDE SO ZHUTNENOU PODORNICNOU VRSTVOU Margarita L. Himmelbauer, Willibald Loiskandl, Svetla Rousseva Pocas rastovej fázy metania v porovnaní s nemeliorovaným variantom bolo pre meliorovanú pôdu pozorované hlbsie rozlozenie koreov. Vo vertikálnej rovine, hustota koreov vyjadrená hmotnosou suchých koreov a podielom ,,plných" stvorcov ­ co znamená výskyt aspo jedného korea ­ bolo podobné v hornej vrstve pôdy pre oba varianty, ale koreov bolo významne viac v podornicnej vrstve meliorovaného variantu. Súcasne, v ,,kontrolnom" variante sa vyskytovali zoskupenia koreov na hranici medzi ornicnou a podornicnou vrstvou, predovsetkým v póroch a puklinách. V horizontálnej rovine rezu meliorovaného variantu bolo pozorované relatívne homogénne rozdelenie koreov s viacerými ,,plnými" stvorcami vo vsetkých testovaných hbkach. V protiklade s uvedeným, kontrolné varianty obsahovali menej ,,plných" stvorcov a veké plochy bez koreov, teda veké vzdialenosti pre prenos vody a zivín v pôde. Priestorový test VMR v mierke 2 cm zdôraznil nedostatocné zhluky koreov len v horizontálnych rovinách rezov meliorovanou ornicnou vrstvou pôdy. V iných mierkach, ktoré boli aplikované, VMR boli vyssie ako 1,0, co naznacuje rozdielne úrovne zhlukov. Pre tvorbu zhlukov koreov a konkurenciu medzi ko- remi bol v kontrolnom variante znízený odber vody koremi z podornicnej vrstvy, hoci bol v nej zistený dostatok vody dostupnej rastlinám. Zásoby vody v meliorovanej pôde sa vycerpali rýchlejsie, ako tie v kontrolnom variante. Je to zrejme dôsledok rýchlejsieho rastu rastlín a teda vyssích intenzít odberu vody. Súcasne, v porovnaní s meliorovanou pôdou, v kontrolnom variante bola pozorovaná pomalsia ontogenéza a nizsia produkcia biomasy. Najvýraznejsia pozitívna korelácia bola zistená medzi hustotou koreov (hmotnos a index) a hydraulickou vodivosou pôdy, ktorá bola povazovaná v tejto stúdii za hlavný faktor regulujúci rast koreov. Bude sa aj naalej pouzíva ako vhodný indikátor rozdelenia hustoty koreov. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Hydrology and Hydromechanics de Gruyter

Spatial root distribution and water uptake of maize grown on field with subsoil compaction

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J. Hydrol. Hydromech., 58, 2010, 3, 163­174 DOI: 10.2478/v10098-010-0015-z MARGARITA L. HIMMELBAUER1), WILLIBALD LOISKANDL1), SVETLA ROUSSEVA2) 1) University of Natural Resources and Applied Life Sciences, Institute of Hydraulics and Rural Water Management, Muthgasse 18, A-1190 Vienna, Austria; Mailto: ml.himmelbauer@boku.ac.at 2) "N. Poushkarov" Institute of Soil Science and Agroecology, Shosse Bankya Street 7, Sofia 1080, Bulgaria. Soil compaction in agricultural areas inhibits plant root growth through increased mechanical resistance, altered water and nutrient supply. The main objective of this study was to evaluate spatial distribution of roots and its effect on water uptake of maize grown on field with subsoil compaction. Two treatments were examined: complex melioration consisting of deep loosening in combination with drainage and control without applied meliorations. Root observations were conducted on vertical and superposed horizontal planes covered with a 2 cm grid short after silking. Root distributions expressed as index of density and/or dry mass density were estimated down to 1 m soil depth and with a distance to a plant base. For analysis of root distribution pattern on the horizontal planes, a Variance to Mean Ratio (VMR) test was applied. Soil water monitoring were conducted during the vegetation period. On the vertical planes, root densities were similar in the topsoil of both treatments, but the results were significantly higher in the subsoil of the meliorated one showing deeper allocation of root density. In contrast, the control had more squares with lots of roots (i.e. higher indexes) just at the top- subsoil boundary owing to bunching of roots in macropores. The horizontal planes in the control generally consisted larger areas without visible roots and thus great distances for water and nutrient transmission, especially in the subsoil. The estimated VMR also pointed toward different levels of root clustering. Consequently, an inhibited water extraction from the subsoil in the control, a delay in crop ontogenesis and a less biomass production was established during the observed period. KEY WORDS: Maize, Soil Compaction, Soil Amelioration, Root Spatial Distribution, Water Uptake. Margarita L. Himmelbauer, Willibald Loiskandl, Svetla Rousseva: PRIESTOROVÉ ROZDELENIE KOREOV A ODBER VODY KOREMI KUKURICE V PÔDE SO ZHUTNENOU PODORNICNOU VRSTVOU. J. Hydrol. Hydromech., 58, 2010, 3; 29 lit., 5 obr. 4 tab. Zhutnenie ponohospodárskej pôdy bráni rastu koreov; je to spôsobené zvýseným mechanickým odporom pôdy, a znízeným prítokom vody a zivín. Cieom tejto stúdie je zhodnotenie priestorovej variability koreov, ich vplyvu na odber vody koremi kukurice na poli so zhutnenou podornicnou vrstvou. Boli hodnotené dva spôsoby obrábania: komplexná meliorácia pozostávajúca z hlbokého podrývania v kombinácii s drenázou a obrábanie (kontrol bez melioracných zásahov. Identifikácia rozdelenia koreov bola vykonaná vo vertikálnych a horizontálnych rovinách s 2-cm sieou, krátko po metaní. Rozdelenie koreov bolo vyjadrené ako index hustoty alebo ako hustota suchej biomasy koreov do hbky 1 m; v horizontálnom smere az k susedným rastlinám. Bol pouzitý test ,,Variance to Mean Ratio" (VMR) na urcenie rozdelenia koreov v horizontálnom smere pocas vegetacného obdobia. Hustota koreov vrchnej vrstvy pôdy vo vertikálnej rovine bola podobná pre obidve varianty, ale pre meliorovanú pôdu boli hodnoty hustoty koreov v podlozí podstatne vyssie a korene zasahovali hlbsie. Ako protiklad, na kontrolnom pozemku bolo viac stvorcov s mnohými koremi (t.j. vyssie indexy) práve na hranici ornicnej a podornicnej vrstvy, pre enormný rast koreov v makropóroch. V horizontálnej rovine tento kontrolný pozemok obsahoval veké oblasti bez viditených koreov, a to znamená veké vzdialenosti pre prenos vody a zivín v podornicnej vrstve. Výsledky aplikácie VMR naznacujú tiez rozdielne úrovne zhlukov koreov. Z toho vyplýva znízený odber vody koremi rastlín na kontrolnom pozemku, ako aj pomalsia ontogenéza a nizsia produkcia biomasy, ktorá bola identifikovaná pocas sledovaného obdobia. KÚCOVÉ SLOVÁ: kukurica, meliorácia pôdy, priestorové rozdelenie koreov, odber vody koremi. Introduction Soil compaction, occurring naturally or a consequence of inappropriate land management, is a problem often established in agricultural areas. It can deteriorate structure, porosity and pore-size distribution, and decrease water permeability in soil (Horn et al., 2000). Many cultivated soils in Bulgaria are compacted, characterized by poor structure, and about 5 % of them are prone to waterlogging (Dilkova et al., 1998). In such soils, roots suffer due to increased mechanical resistance against root penetration, inhibited water, nutrient and oxygen supply. The negative impact depends on climate conditions as well as on particular root system characteristics. For efficient uptake of water by plants, the water "availability "as well as its "accessibility" to the roots is critical (Droogers et al., 1997). Water "availability" refers to soil ability to supply roots with water at a sufficient rate and is mainly a function of soil hydraulic characteristics. The water "accessibility", however, highly depends on root system extension and spatial distribution of roots. Root elongation is influenced by penetration resistance of the soil and thus by its bulk density, structure and pore system. In compacted soils, roots are often confined into large pores and are less efficient in uptake due to high intra-root completion. In addition, an insufficient supply of water and nutrients occurs owing to low hydraulic conductivity and diffusion rate in compacted soil spots. As a result of root clustering, water cannot be taken up at a rate useful for plants compared to soils with equivalent but uniformly distributed roots (Baldwin et al., 1972; Tardieu at al., 1992; Amato and Ritchie, 2002). Droogers et al. (1997) extended this approach, showing that not only extreme compaction but also different aggregates structure of soil, formed by various land management practices, leads to root grouping and influenced the uptake of water. Besides the root density parameter widely used for modeling and simulation of root uptake at a field scale (e.g. Novak, 2003), the root spatial distribution (rooting pattern) appears to be also important for water and nutrient acquisition by plants. This concept provides a basis for novel modeling of root uptake, however fitting data for validation is really still scarce (Lipiec et al., 2003; Pardo et al., 2000). The main objective of this study was to assess root spatial distribution and water uptake of maize 164 grown on field with subsoil compaction. A specific task was to examine the effect of amelioration practices against subsoil compaction on soil characteristics and thus on root development and crop productivity. Hydro-technical and ameliorative measures against soil compaction have been seldom applied, since they are costly and their long-term positive effects are arguable. Material and methods Climate and soil conditions The experiments were conducted on a research field of the "N. Pushkarov" Institute of Soil Science and Agro-ecology in Thracian lowland, semi-arid area of South Bulgaria. The climate is continentalMediterranean with a mean annual temperature of 12°C and a long-term annual precipitation of about 600 mm. A major rainfall maximum has been observed at the end of autumn -beginning of winter, a minimum precipitation- in late summer along with long periods of drought (Georgieva et al., 2007). The precipitation sums during the winter are often insufficient to complete even the lower limit of the readily available water for plants (Koleva and Alexandrov, 2008). The soil is fine textured Dystric Planosol (PLd, FAO soil classification) having elluvial-illuvial deep profile with high degree of textural differentiation (Boyadgiev, 1994; Dilkova et al., 1998). This textural differentiation, derived from the difference in clay content between two soil horizons, leads to compaction and low permeability for water of the subsoil. As a result, the soil is prone to surface waterlogging in early springs. Experimental setup, soil and root observations Soil meliorations using different hydro-technical and ameliorative methods to increase water permeability of the waterlogged soil were applied a few years ago following Shopski et al. (1998). In this study two main treatments were examined: deep loosening in combination with mole drainage and a control without ameliorations applied. The combined soil amelioration consisted of loosened soil zones to a depth of 60 cm and mole channels with a distance between furrows of 11 m. A durability of the channels depends on the soil, the climate and the local land management, but the positive effect on soil water permeability generally disappears in a course of ten years after the treatment. Experimental plots of 90 m2 were planted in the beginning of May with maize (Zea mays L. var. "Kneza"). Herbicides were applied shortly after planting, rest weeds were removed mechanically or hand pulled. Else, the both plots were managed according to the common local farming using mouldboard ploughing to about 30 cm depth. A series of soil physical and chemical characteristics were measured in advance to the experiment taking disturbed and undisturbed soil samples down to 1 m depth in both plots, i.e. particle size distribution, particle and bulk density, porosity, hydraulic conductivity at saturation, plant available water, pH, humus content, carbonates. For evaluation of the gravimetric soil water content, soil samples down to 1 m depth were taken continuously throughout observation period. Plant growth and development stages of maize were monitored, biomass production was measured at harvest. Root spatial distribution was examined using soil profile method shortly after silking maize stage (female flowering) when root systems are fully developed reaching their largest extension. First, representative areas completely free of weeds, having a regular crop spacing and development were selected. A trench was dug perpendicular to the crop rows to about 1 m soil depth. A profile (100 x 72 cm) covering one maize row and two half "between rows" distances left and right to the row was carefully smoothed. A few millimeters of roots was made visible from the adjacent soil using air and water under pressure in addition to hand tools. Next the profile was covered with a fine grid mesh of 2 x 2 cm. Root contacts were counted and indexes of density were introduced, accounting for a presence and an absence of fine and coarse roots in each square following Tardieu (1988. The indexes of root density equaled to 0 ­ absence of roots, 2 ­ one thin root visible, 4 ­ many thin roots visible, 8 ­ two and more thick roots > 2mm and thin branches visible. The indexes were related to root mass density per volume of soil taking small soil monoliths (cubes) with a face one mesh square from different depths and positions. The roots were washed out, their dry mass was measured, and thus the root mass density distribution down the soil profile was estimated indirectly. Two profiles (replications) were prepared in the same trench dug a few cm apart resembling a distance between single plants. Three horizontal planes (40 x 72 cm), covering the same row and the two half "between rows" distances, were dug on superposed depths intersecting the rooting volume in the middle of the topsoil (A1A2 horizon) at 13 cm, at the bottom of the topsoil at about 25 cm, and in the middle of the compacted subsoil (B horizon) at about 50 cm depth. The horizontal planes were prepared in a similar way as the vertical ones. The root density index here equaled the number of roots counts in each square. Data analyses Root density distributions expressed as indexes of density per square, percentage of squares consisting roots and root mass per volume of soil were calculated and plotted over the soil depth and with a distance to the crop row. Estimated results were compared with the measured soil parameters. Summary statistics, analysis of variance, and correlation analyses were conducted to find out the relations between different root, and soil parameters. For analysis of root distribution (pattern) on the horizontal planes, an additional Variance to Mean Ratio (VMR) test, called also index of dispersion, was used. The VMR test is proposed to characterize spatial distribution of points (Grieg Smith, 1983). The point distribution in a certain neighborhood may represent some interactions in-between, i.e. the points may occur in clusters, or there is a lack of interactions and the point distribution is completely random, or following deterministic pattern, thus the points are regularly distributed within the definite area. If the point distribution is random, it can be described by a Poisson process, where the variance and the mean values are equal and the approximated Variance to Mean Ratio is close to 1. VMR values larger than 1 point to existence of clusters, i.e. grouped or cluster distribution pattern which is mainly associated with a Negative binomial or Neyman type A theoretical distributions. VMR values below 1 suggest more uniform (regular) point distribution (Wulfsohn et al., 1996). In this study, the VMR was estimated for the root counts observed on the all horizontal planes in both treatments. Results and discussions Soil properties Essential soil characteristics are presented in Tab. 1. The soil is classified as clay loam in the topsoil and clay in the subsoil. The topsoil is acidified due to carbonate leaching down the soil profile. 165 Bulk density (BD) is a commonly used indicator for soil compaction (Bennie, 1996; Hakansson and Lipiec, 2000). BD values optimal for plant growth vary for different soils, but roots rarely enter soil if BD exceeds 1.6­1.7 g cm-3 (Russel, 1980). In this study, all BD measurements at field capacity were relatively high, but below the cited threshold value approximating 1.45 g cm-3 for the a good portion of the rooting depth in both plots (Tab. 1). However, the BD rose rapidly with the soil getting drier in the course of time. At the time of root sampling, the BD's reached a maximum of 1.64 g cm-3 at 30 cm depth (the topsoil- subsoil boundary) in the control plot. The BD's down to 50 cm depth in the meliorated plot did not change greatly compared to the values measured in spring and lay between 1.36 and 1.54 g cm-3 (data not shown). This seemingly was a subsequent effect of the hydrotechnical ameliorations against soil compaction. T a b l e 1. Major physical and chemical properties of the soil in the experimental field. T a b u k a 1. Najdôlezitejsie fyzikálne a chemické vlastnosti pôdy na experimentálnom poli. Field capacity (FC) Total porosity Wilting point (WP) Particle size distribution* Bulk density at FC Hydraulic conductivity saturation Dystric planosol Air filled porosity ** Plant available water Particle density Humus [%] 1.88 1.50 1.32 0.74 1.74 1.00 0.90 0.65 Depth [cm] Non-meliorated plot A1A2(0­22) 10­15 B1(t)(22­42) 35­40 B2(t) (42­72) 50­55 B3(t)(72­95) 80­85 Meliorated plot A1A2(0­28) 10­15 B1(t)(28­55) 40­45 B2(t) (55­78) 65­70 B3(t)(78­100) 85­90 Horizon Clay Silt Sand [%] [%] [%] [g cm-3] [g cm-3] [vol. %] [vol. %] [vol. %] 27.1 40.2 48.0 44.9 32.8 53.8 53.1 51.8 42.7 32.3 30.5 31.2 44.9 29.9 26.7 33.9 30.2 27.5 21.5 23.9 22.3 16.3 20.2 14.3 2.63 2.68 2.68 2.70 2.56 2.73 2.74 2.79 1.46 1.46 1.45 1.47 1.35 1.47 1.45 1.53 42.08 40.57 39.59 39.23 34.48 42.14 42.64 41.46 13.80 20.54 17.41 19.37 13.57 30.30 31.40 29.27 28.28 20.03 22.17 19.86 20.91 14.76 16.31 15.87 [%] 44.49 45.52 45.90 45.56 47.27 46.15 47.08 45.16 [%] 2.41 4.95 6.31 6.32 12.79 4.01 4.44 3.70 [cm d-1] 105.5 0.00 0.00 0.36 42.03 5.04 2.01 10.05 [­] 4.00 4.05 4.80 6.00 3.50 3.80 4.60 5.60 *Texture fractions: Clay (< 0.002 mm), Silt (0.002­0.05 mm), Sand (0.05­2 mm). *Klasifikácia textúry: íl (< 0.002 mm), prach (0.002­0.05 mm), piesok (0.05­2 mm). **Air filled porosity at field capacity is calculated after Vomocil (1965) as a difference between the total porosity and the volumetric water content at FC **Podiel pórov zaplnených vzduchom pri ponej vodnej kapacite pôdy, bol vypocítaný poda Vomocila (1965), ako rozdiel medzi pórovitosou a vlhkosou pri FC. Surprisingly, the water content assessed at FC level was higher in the topsoil of the nonmeliorated than in the meliorated one, and the WPwater contents were lower. Correspondingly, more plant available water (Allen et al., 1998) was estimated for the entire rooting depth in the control. The estimated total porosity was a bit higher in the meliorated plot, but the differences to the control were insignificant. Air-filled porosity represents the pore space filled with air after the soil has been drained and includes pores mainly larger than 0.05 mm. As critical limits for air-filled porosity, below which root growth and uptake are inhibited, are accepted values of 10 % (volumetric) for clay and 15 % for sandy soils (Arvidsson, 1999; Hakansson and Lipiec, 2000). In this study, the air-filled porosity at field capacity (FC) was calculated after 166 Vomocil (1965). The estimates were below the critical limits except of the meliorated topsoil, suggesting insufficient amount of (macro-)pores in the large part of the rooting zone (Tab. 1). The minimum of 2.4 % was found in the topsoil of the nonmeliorated plot (control). Therefore, even at optimal soil water conditions the plant roots here will be at a risk of suffering for aeration. In addition, only minor differences between the air-filled porosity measurements in the subsoil of the two plots were established. At the same time, the hydraulic conductivity measured at saturation was higher in the subsoil of the meliorated than the nonmeliorated plot, but the variation between single measurements was high. No significant differences in the rest of the evaluated soil parameters between non-meliorated and meliorated plots were found. Carbonates [%] 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 pH KCl Root density distribution At the time of root observation, the maize root systems already reached a soil depth of 1 m (Fig. 1). A high variability in root density (indexes) was observed between the single profiles (replications) in both treatments. Between the treatments, however, the measured indexes and the shape of distribution curves down the soil profile did not differ significantly (P < 0.05, ANOV. The highest den0,0 2 6 10 14 18 22 26 30 34 38 42 depth, cm sity index for the both plots was measured in the top 30 cm depth (topsoil). Below this depth, the root density in the control decreased gradually resembling an exponential curve typically observed for field grown crops (Himmelbauer et al., 2008). In the meliorated plot, however, the density index values were comparable between 30 and 60 cm soil depth (i.e. the melioration depth), and downwards decreased. 20,0 40,0 60,0 80,0 p 0,0 2 6 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 20,0 40,0 ) 60,0 80,0 46 50 54 58 62 66 70 74 78 82 86 90 94 98 Index > 4 Index > 0 Index > 0 Index > 4 Fig. 1. Percent distribution of squares consisting at least one root (index > 0) and with lots of roots (index > 4) averaged for the two profiles in the non-meliorated and meliorated plots. Obr. 1. Percentuálne rozdelenie stvorcekov obsahujúcich aspo jeden kore (index > 0) a stvorcekov s viacerými koremi (index > 4) spriemerované pre dva profily; nemeliorovaný variant, meliorovaný variant. As can be seen on the Fig. 1, between 60 and 90 % of the squares in the topsoil consisted at least one visible root (i.e. proportion of squares with index > 0), with small differences between the treatments. Close to the top-subsoil boundary, the proportion of squares with index > 0 was considerably higher in the meliorated than in the nonmeliorated plot, showing more homogeneous distribution of roots there. In the subsoil of the meliorated plot 50 % "full" squares were found in the upper 30 cm and 20 % underneath at 60 cm depth, against 30 % and 10 % in the control, respectively. Hence, the effect of the former meliorations with deep loosening to 60 cm depth on the root distribution was obvious. On the other site, the nonmeliorated plot had more squares consisting plenty of roots (index > 4), especially close to the topsubsoil boundary. Root growth in compacted soil is not completely restricted when macrospores or cracks are present, and a preferential root growth occurs in these pores (Laboski et al., 1998; Bingham and Bengough, 2003). In this study, the observed high root density indexes were a clear indication of root grouping into macropores crossing the top- and compacted subsoil. The results of the root mass density averaged for the two profiles (replications) are shown in Fig. 2. Values between 0.10 and 0.70 mg cm-3 were estimated for the topsoil with no considerable difference between the treatments (P < 0.05, ANOV. Between 30cm (topsoil) and 60 cm (subsoil), the values in the meliorated plot were close to 0.20 mg cm-3, and ap167 proximated the half of the root density in the nonmeliorated one. Below this depth, the root density in both plots decreased gradually to about 0.03 mg cm-3. Spatial variations in the soil bulk density along with the soil water content changes allowed roots to find paths to cross the compacted layer. In the control, about 28 % of the total root mass was found within the subsoil and 72 % in top. In contrast, the corresponding values in the meliorated plot were 36 % against 64 % showing apparently deeper allocation of the maize root mass at the time of observation. 0,00 2 6 10 14 18 22 26 30 34 38 depth, cm 0,20 0,40 0,60 0,80 mg cm -3 0,00 2 6 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 0,20 0,40 0,60 0,80 mg cm -3 1,00 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 mean dry mass mean dry mass Fig. 2. Root density distribution down the soil profile expressed as root dry mass density [mg cm-3] for non-meliorated and meliorated plots. Horizontal bars represent standard deviations. Obr. 2. Rozdelenie hustoty koreov vo vertikálnom smere, vyjadrené ako hustota suchej masy koreov [mg cm-3] pre: nemeliorovaný variant, meliorovaný variant. Horizontálne bodkované ciary reprezentujú standardné odchýlky. Concerning the horizontal allocation of root density, a concentration of roots near the maize row was observed in the topsoil, more evident in the meliorated plot than in the non-melioration one. In the subsoil, more homogeneous distribution with respect to the plant base was observed in both treatments: the density distribution shifted to the inter-rows, the differences to the row position were smaller and variability got higher. On the horizontal planes (Fig. 3), the proportions of the squares where at least one root contact was observed (index > 0) were between 60 to 90 % at 13 cm depth in the meliorated plot, demonstrating more homogeneous distribution with close distances between single root axes. The average value for the 25 cm plane was 56.4 % and 39.3 % for the lowest one at 50 cm depth. The corresponding val- ues for the three superposed planes in the control were 63.3 %, 31.1 % and 15.6 %, respectively. Some discrepancies in the root density results between the vertical and the horizontal maps were observed. They most probably resulted from the preferentially horizontal direction of the seminal roots in the topsoil and vertical in the subsoil as well as due to root branching pattern of maize (Koedjikov, 1975). Thus, the results of the vertical mapping seemed to be underestimated for the areas with more horizontal root growth and lack of branching in the topsoil, and just the opposite phenomenon happened underneath. Similar phenomenon was reported also by Chopart and Siband (1999). Different tests have been proposed for analysis of spatial root distribution (pattern), i.e. theoretical distributions such as Poisson, Negative binomial or 80,0 % 60,0 40,0 20,0 0,0 36cm R 36cm R 0 8 6 4 2 4 6 34 32 28 26 24 22 18 16 14 12 8 12 14 16 18 22 24 26 28 32 32 36cm-L 30cm 20cm 10cm 10cm 20cm 30cm 34 34 row 2 0 2 4 80,0 60,0 40,0 20,0 0,0 8 6 4 0 6 34 32 28 26 24 22 18 16 14 12 8 12 14 16 18 22 24 26 36cm-L 30cm 20cm 10cm 10cm 20cm 28 30cm row 2 0 13cm 25cm 50cm interrow L interrow R Fig. 3. Percent distribution of squares consisting at least one root (index > 0) observed on the three superposed horizontal planes at 13 cm, 25 cm and 50 cm in non-meliorated and meliorated plots. Obr. 3. Percentuálne rozdelenie stvorcekov obsahujúcich aspo jeden kore (index > 0), pozorované v troch superponovaných horizontálnych rovinách v hbke 13, 25 a 50 cm; nemeliorovaný variant, meliorovaný variant. the Neyman type A (Baldwin et al., 1972; Wulfsohn et al., 1996), a nearest neighbor test, a spatial autocorrelation test (Tardieu, 1988, a skewness test (Rogers, 1974), etc. The Variance to Mean Ratio (VMR) test has been proposed for ecological studies (Grieg Smith, 1983). Reported scales of the application of the VMR test (the chosen size of the tested unit are vary between different studies. According to Baddeley (2008), the power of the VMR test depends on the size and falls to zero for squares which are either very large or very small. Nevertheless, it gives an clear indication of important clustering processes occurred in soil. Baldwin et al. (1972) coupled it to diffusion coefficients of certain nutrients in soil and applied the test at a centimeter scale. Enlarging the quadrates to a decimeter scale, Tardieu (1988 came to the conclusion that their size will not significantly affect the VM Ratios in soils with relatively small structural impediments. This statement was confirmed by Wulfsonh et al. (1996). In this study, the VMR test was applied for the three superposed horizontal planes starting with the squares size of 2 cm (the mesh grid size) and increasing it to 10 cm in both trials. The square sizes corresponded to the dimension of soil aggregation and compacted clods observed in situ. The mean number of the root counts observed in each square (the root index on the horizontal planes) and the corresponding variances were calculated. Then the ratios between them, the VMR values were estimated for each depth position and treatment. T-test was used to compare the calculated VMR with the theoretical value of 1. The results are presented in Fig. 4 and Tab. 2. 8,0 7,0 6,0 5,0 VMR 4,0 3,0 2,0 1,0 0,0 0 2 4 6 quadrate size (cm) 8 10 12 13cm mel 25cm no mel 25cm mel 50cm no mel 50cm mel 13cm no mel Fig. 4. Results of the Variance to Mean Ratio (VMR) test applied for the root counts per square of 2, 4, 8 and 10 cm size for the three superposed horizontal planes in non-meliorated (no mel) and meliorated (mel) plots. Obr. 4. Výsledky testu ,,Variance to Mean Ratio" (VMR), aplikované na pocty koreov vo stvorceku s vekosou strany 2, 4, 8 a 10 cm pre tri superponované horizontálne roviny v hbke 13, 25 a 50 cm; nemeliorovaný variant, meliorovaný variant. The obtained results showed that the spatial patterns of roots did not follow a regular spatial distribution (assumed in the majority models of water uptake) either in the meliorated or in the nonmeliorated plot. Just the VMR value at 2 cm scale (square size) at the 13 cm depth in the meliorated plot equaled 1.0, suggesting a non cluster but random type of root distribution (Tab. 2). In addition, only at this depth statistically significant differences in the root counts number were established between the meliorated and non-meliorated plot. With increasing the square size to 8 cm, the VMR values rose rapidly larger than 1, stronger in the ploughed topsoil layer than below it. These scales of the testing most probably coincidence with the size of the soil aggregates and clods in the field. At a decimeter scale (10 cm), the VMR values dropped at all positions except of the topsoil in the control. In this case, the quadrates probably oversized the dimension of the soil clods. Surprisingly, in most cases the subsoil had lower VMR values compared to the topsoil, although that the visual examination in situ showed large structural barriers and root clustering at a transit to and within the compacted subsoil. Soil water monitoring Changes of the soil water content down the soil profile measured gravimetrically during the vegetation period are shown in Fig. 5. The values varied more rapidly and higher in the topsoil (0 ­ 30 cm) than in the subsoil, due to fluctuations in precipita170 tion, temperature and evaporation as well as due to the foremost root uptake, especially in the beginning of the growing period. End of June, when maize approached the end of the vegetative stage in the meliorated plot, an apparent decrease in the water content occurred also in the subsoil. In the control, the subsoil- water content values were still high. The maize plants just came to the 9 to 12 leaf stage and obviously did not extract lots of water from the subsoil. Until end of July matching the crop stage of silking in the meliorated plot, the soil in the 0­50 cm depth rapidly dried due to the enhanced root water uptake. There were two dry periods observed: in the middle of July and in August. Coming to harvest, the soil water content further decreased in all soil layers in both plots. In the control, the topsoil-water was almost depleted, while the subsoil remained much wetter than in the meliorated plot. The water uptake by root was obviously still restricted to the topsoil with low activity down the soil profile, although the high amount of plant available water estimated. This suggested some limitations for water uptake by the maize roots. In the meliorated plot, the subsoil water content depleted further and greater than in the control. This was attributed to the faster growth and the more extensive root water uptake there. In spring, the estimated soil water storage in mm was close to the field capacity level and after that it decreased more or less steadily(data not shown). As the plants come to silking, the water storage approached the wilting point in both treatments and at harvest it fell below the WP level, first in the meliorated plot and thereafter in the control. In general, the available water reserves in the meliorated depleted more rapidly than those in the control. Maize in the meliorated and non-meliorated plots developed differently. As it was also reported by Bingham and Bengough (2003), the growth of crop shoots was reduced when part of the root system was in compacted soil, although some compensatory adjustments in root growth. The plants in the meliorated plot were observed to grow more rapidly reaching the next growth stage one to two weeks earlier than those in the control. Accordingly, higher above-ground biomass production was found there. Crop parameters measured at root sampling and at harvest are presented in Tab. 3. The maize plants in the meliorated plots were much higher and developed twice as spasing before leaf area and biomass. Spatial root distribution and water uptake of maize grown on field with subsoil compaction T a b l e 2. Analyses of spatial arrangement of the root counts (indexes) on the tree superposed horizontal planes in the nonmeliorated and meliorated plots. T a b u k a 2. Analýza priestorového usporiadania poctu koreov (indexy) v troch superponovaných horizontálnych rovinách meliorovanej a nemeliorovanej pôdy. Root counts per square VMR 1.535*** 1.271*** 1.223*** 2.429*** 1.803*** 1.769*** 4.108*** 2.04*** 2.00*** 7.057*** 1.491* 1.397 Mean 1.93 B 1.06 A 0.58 A 7.71 B 4.23 A 2.32 A 30.78 A 16.96 A 9.27 A 50.42 A 25.96 A 14.21 A Melioration median Variance 2 1 0 7 4 2 27 17 9 49 27 13 2.12 b 1.37 a 0.72 a 16.54 b 9.93 a 3.81 a 142.60 a 70.63 a 21.65 a 177.80 a 74.91 a 26.52 a VMR 1.101 1.298*** 1.235*** 2.147*** 2.347*** 1.639*** 4.634*** 4.166*** 2.337*** 3.527*** 2.886*** 1.867** Depth 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm 13 cm 26 cm 50 cm Nr squares Square size 720 720 720 Square size 180 180 180 Square size 45 45 45 Square size 24 24 24 Mean 1.33 A 0.43 A 0.19 A 5.06 A 1.73 A 0.76 A 20.13 A 6.89 A 3.00 A 35.33 A 10.50 A 4.88 A No melioration median Variance 2 x 2 cm 1 2.05 a 0 0.55 a 0 0.23 a 4 x 4 cm 5 12.29 a 1 3.12 a 0 1.34 a 8 x 8 cm 17 82.71 a 7 14.06 a 3 6.00 a 10 x 10 cm 31 249.4 a 10 15.65 a 5 6.81 a VMR-Variance: Mean Ratio, *** statistically significant differences from the theoretical value of 1 at 95%, 99% and 99.9% confidence level, respectively (T-test) ***Statisticky významné rozdiely od teoretických hodnôt 1 pre 95%, 99% a 99.9% intervaly spoahlivosti (T-test) Comparison between non-meliorated and meliorated plot: T-test for mean comparison: values followed by the same capital letter are not significantly different (P < 0.05); F-test for variance comparison, variances followed by the same small letter are not significantly different (P < 0.05) Porovnanir meliorovaných a nemeliorovaných variantov: T-test pre porovnanie priemerných hodnôt: Hodnoty nasledované tým istým vekým písmenom nie sú významne rozdielne (P < 0.05); F-test pre porovnanie variancií; Hodnoty variancií nasledované tým istým malým písmenom nie sú významne rozdielne (P < 0.05). 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 9.07. 12 leaf 15.07. 23.07. 31.07. 2.08. 8.08. 12.08. 19.08. milk rape 0-10cm 10-20cm 20-30cm 30-40cm 40-50cm 50-60cm 70-80cm 90-100cm g g-1 21.05. 27.05. 12.06. 14.06. 23.06. 26.06. 4.07. 10.07. 15.07. 23.07. 31.07. 2.08. 3-5 leaf 12 leaf dates silking root profiles 7.08. 12.8. milk rape 22.8. harvesting silking, root profiles dates Fig. 5. Soil water content measured at different soil depths during the vegetation period of maize in non-meliorated and meliorated plots. Obr. 5. Vlhkos pôdy meraná v rozdielnych hbkach pocas vegetacného obdobia kukurice; nemeliorovaný variant, meliorovaný variant. Correlation analyses Regarding the correlations between different root and soil parameters, dissimilar results were obtained for the two treatments. In the meliorated plot, the root density significantly correlated with the available soil water and the porosity (total and air-filled), and significantly but negative with the bulk density. In contrast, in the non-meliorated plot the root parameters correlated positively with the bulk density at sampling, but negatively with the porosity data. Looking at the correlation matrix (Tab. 4) one can recognize, that root density expressed as dry mass and percentage of squares consisting roots highly correlated with the hydraulic 171 T a b l e 3. Crop characteristics and biomass production of maize on meliorated and non-meliorated plots. T a b u k a 3. Charakteristiky porastov a produkcia biomasy kukurice na meliorovaných a nemeliorovaných variantoch. Occasion (Stage) Plant density Plot 1000 [pl. ha-1] 91.3 92.3 Height [cm] 141.9 230.9 At root observations (silking) Leaf area green [cm2] per plant 2247 4056 Biomass fresh [t ha-1] 19.9 44.5 Harvest (milk-dough stage) Biomass fresh [t ha-1] 25.6 48.0 No melioration Melioration T a b l e 4. Coefficients of correlation estimated between root density and different soil parameters. T a b u k a 4. Koeficienty korelácie medzi hustotou koreov a rôznymi pôdnymi parametrami. Depth [cm] RMD, mg cm-3 ­0.910 Index > 0, [%] Sq ­0.947 Index > 4, [%] Sq ­0.779 Porosity Bulk Available Hydraulic density* water conductivity Total Air-filled* [g cm-3] [vol. %] [cm d-1] [vol. %] [vol. %] ­0.590 ­0.624 ­0.484 0.557 0.414 0.644 0.785 0.682 0.811 0.061 0.184 ­0.079 0.300 0.323 0.235 pH Clay [%] Index RMD > 0 Index > 4 [mg cm-3] [% ]Sq [% ]Sq 1 0.961 0.954 1 0.837 1 ­0.755 ­0.744 ­0.873 ­0.750 ­0.558 ­0.655 *Parameters measured at filed capacity level, RMD ­ root dry mass density, percentage of squares (Sq) consisting at least one root (Index > 0) and a lot of roots (Index > 4). *Parametre merané pri vlhkosti pôdy na úrovni ponej vodnej kapacity; RMD ­ hustota suchej hmotnosti koreov, percentuálne vyjadrenie ,,stvorcov" (Sq) obsahujúcich aspo jeden kore (index > 0) a viac koreov (index > 4). conductivity, significant but negative with the clay content and the pH values at a certain soil depth. The strongest positive correlation (R = 0.7 to 0.8) was estimated between the root (index and mass) density and the soil hydraulic conductivity, which can be assumed as an appropriate indicator for root growth distribution. Conclusions At the time of root observations at silking, a deeper allocation of the maize root density was observed down the soil profiles in the meliorated than in the non-meliorated plot. On the vertical planes, root densities, expressed as dry mass and proportion of "full" squares consisting at least one visible root were similar in the topsoil, but significantly higher in the subsoil of the meliorated plot. At the same time, the control plot showed frequent root grouping in areas with lower penetration resistance like pores and cracks at the top- subsoil boundary. The horizontal planes in the meliorated plot had more homogeneous root distribution with more "full" squares at all tested soil depths. In opposite, the control-planes generally had less "full" squares and large areas without roots and great distances for water and nutrient transmission in the 172 soil. The spatial VMR test at 2 cm scale pointed to lack of root clustering only on the horizontal planes of the meliorated topsoil. At all other positions and scales examined, the VMR's were higher than 1.0 indicating different levels of clustering. Due to the root clustering and inter-roots competition, an inhibited water extraction from the subsoil was established in the control during the observed period, although the overall high plant available water estimated. The water reserves in the meliorated subsoil depleted more rapidly than those in the control. This was attributed to the faster plant growth and the more extensive root uptake there. At the same time, a delay in crop ontogenesis and a less biomass production was established in the non-meliorated plot. 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Received 26 February 2010 Accepted 23 June 2010 PRIESTOROVÉ ROZDELENIE KOREOV A ODBER VODY KOREMI KUKURICE V PÔDE SO ZHUTNENOU PODORNICNOU VRSTVOU Margarita L. Himmelbauer, Willibald Loiskandl, Svetla Rousseva Pocas rastovej fázy metania v porovnaní s nemeliorovaným variantom bolo pre meliorovanú pôdu pozorované hlbsie rozlozenie koreov. Vo vertikálnej rovine, hustota koreov vyjadrená hmotnosou suchých koreov a podielom ,,plných" stvorcov ­ co znamená výskyt aspo jedného korea ­ bolo podobné v hornej vrstve pôdy pre oba varianty, ale koreov bolo významne viac v podornicnej vrstve meliorovaného variantu. Súcasne, v ,,kontrolnom" variante sa vyskytovali zoskupenia koreov na hranici medzi ornicnou a podornicnou vrstvou, predovsetkým v póroch a puklinách. V horizontálnej rovine rezu meliorovaného variantu bolo pozorované relatívne homogénne rozdelenie koreov s viacerými ,,plnými" stvorcami vo vsetkých testovaných hbkach. V protiklade s uvedeným, kontrolné varianty obsahovali menej ,,plných" stvorcov a veké plochy bez koreov, teda veké vzdialenosti pre prenos vody a zivín v pôde. Priestorový test VMR v mierke 2 cm zdôraznil nedostatocné zhluky koreov len v horizontálnych rovinách rezov meliorovanou ornicnou vrstvou pôdy. V iných mierkach, ktoré boli aplikované, VMR boli vyssie ako 1,0, co naznacuje rozdielne úrovne zhlukov. Pre tvorbu zhlukov koreov a konkurenciu medzi ko- remi bol v kontrolnom variante znízený odber vody koremi z podornicnej vrstvy, hoci bol v nej zistený dostatok vody dostupnej rastlinám. Zásoby vody v meliorovanej pôde sa vycerpali rýchlejsie, ako tie v kontrolnom variante. Je to zrejme dôsledok rýchlejsieho rastu rastlín a teda vyssích intenzít odberu vody. Súcasne, v porovnaní s meliorovanou pôdou, v kontrolnom variante bola pozorovaná pomalsia ontogenéza a nizsia produkcia biomasy. Najvýraznejsia pozitívna korelácia bola zistená medzi hustotou koreov (hmotnos a index) a hydraulickou vodivosou pôdy, ktorá bola povazovaná v tejto stúdii za hlavný faktor regulujúci rast koreov. Bude sa aj naalej pouzíva ako vhodný indikátor rozdelenia hustoty koreov.

Journal

Journal of Hydrology and Hydromechanicsde Gruyter

Published: Sep 1, 2010

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