Extent, Distribution, and Causes of Soil Acidity under Subsistence Farming System and Lime Recommendation: The Case in Wolaita, Southern Ethiopia
Extent, Distribution, and Causes of Soil Acidity under Subsistence Farming System and Lime...
Laekemariam, Fanuel;Kibret, Kibebew
2021-09-26 00:00:00
Hindawi Applied and Environmental Soil Science Volume 2021, Article ID 5556563, 9 pages https://doi.org/10.1155/2021/5556563 Research Article Extent, Distribution, and Causes of Soil Acidity under Subsistence Farming System and Lime Recommendation: The Case in Wolaita, Southern Ethiopia 1 2 Fanuel Laekemariam and Kibebew Kibret Wolaita Sodo University, Department of Plant Science, P.O. Box 138, Wolaita Sodo, Ethiopia Haramaya University, School of Natural Resources Management and Environmental Sciences, P.O. Box 138, Dire Dawa, Ethiopia Correspondence should be addressed to Fanuel Laekemariam; laeke2005@yahoo.com Received 27 February 2021; Revised 23 July 2021; Accepted 2 September 2021; Published 26 September 2021 Academic Editor: Durgesh Jaiswal Copyright © 2021 Fanuel Laekemariam and Kibebew Kibret. +is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Soil acidity is one of the most important environmental threats to the Ethiopian highlands where the livelihood of the majority of people is reliant on agriculture. Yet, information regarding its extent, distribution, causes, and lime requirement at a scale relevant to subsistence farming systems is still lacking. +is study (1) investigates the extent and spatial distribution of soil acidity, (2) identifies factors attributing to soil acidification, and (3) predicts the lime requirement for major crops. A total of 789 soil samples were collected from arable lands in the Wolaita area which is mainly characterized by poor soil fertility and soil degradation in southern Ethiopia. Results revealed that the landscape is characterized by a gentle slope followed by strongly sloppy> flat> hilly topographies. Clay is the dominant soil textural class. A soil pH map, which is generated using geospatial analysis, demonstrates that 3.3, 78.0, and 18.7% of the total area were under strongly acidic, moderately acidic, and neutral soil reactions, respectively. +e exchangeable acidity (Cmol(+)/kg) varied from nil to 5.1, whereas exchangeable Al ranged from 1.4 to 19.9 Cmol(+)/kg. +e soil pH has shown a significantly (p < 0.001) negative association with clay content (r � − 0.33), exchangeable Al (r � − 61), exchangeable acidity (r � − 0.58), and inorganic fertilizer application (r � − 0.33). Increased 2 2 rates of diammonium phosphate (DAP) (r � 0.91) and urea (r � 0.88) markedly elevated soil acidity. Conversely, manuring showed a significant (p< 0.001) and positive relationship with pH (r � 0.37) in which the increasing rate of manure significantly reduced acid- ification (r � 0.98). DAP and urea applications above 75 kg/ha lowered soil pH units by 0.56 and 0.48, respectively,<25 kg/ha while at the same time farmyard manure (FYM) at 4 t/ha raised pH by 0.75 units over the unfertilized field. Residue management significantly (p< 0.001) influenced soil pH wherein it ranged from 6.09 (complete residue removal) to 6.61 (residue incorporation). Changes in land use, cropping intensity, and socioeconomic status were also significantly attributed to soil acidification. To curb the effects of soil acidity, the lime requirement for common bean growing fields varied from zero to 6.6 t/ha, while for maize it was between zero and 4.3 t/ha. It is concluded that soil management interventions such as maintaining and incorporating crop residues, integrated use of organic and inorganic fertilizers, liming, and enhancing farmers’ awareness should be advocated to overcome soil acidification and improve soil fertility. In addition, introducing crops with traits that tolerate acidity and Al toxicity is also suggested. acidity and soil calcareousness are thought to be the two 1. Introduction major crop production constraints considerably threatening Crop plants need 17 kinds of nutrients to complete the life the global food production system and afterward food se- cycle, of that 14 nutrients should be present in the soil in curity [2]. adequate quantity and proportion for healthy plant growth Agriculture plays the most important share in the [1]. However, the availability of nutrients is influenced by Ethiopian economy, and therefore, the sector heavily de- chemical reactions like acidity or alkalinity in the soil. Soil pends on soil. About 43% of cultivated lands in Ethiopia, 2 Applied and Environmental Soil Science where major staple food crops are grown, are affected by soil 2. Materials and Methods acidity [3]. +e realm might probably be larger because of 2.1. Study Area. +e study was conducted in three districts of the conversion of forest and grazing lands into arable lands the Wolaita zone in Southern Ethiopia. +e districts (Damot as a result of fast human population increment and asso- Gale, Damot Sore, and Sodo Zuria) cover 84,000 hectares ciated poor land management practices [4]. +is signifies the ° ° (ha) of land located between 037 35′30″-037 58′36″E and magnitude of how soil acidification is threatening crop ° ° 06 57′20″ - 07 04′31″N. +e ten-year mean annual rainfall production and thus reducing food security particularly in and temperature were 1355 mm and 19.7 C, respectively. the Ethiopian highlands where the area is conducive for soil +e elevation ranges from 1473 to 2873 meter above sea level acidification processes [2, 3]. (m.a.s.l). +e predominant soils are Nitisols [19]. Generally, Soil acidity resulted from a rise in the concentration of the soil has an acidic reaction with varying degrees [16]. hydrogen ions (H ). It should occur because of natural and Rain-fed-based agriculture is the major source of live- human-induced processes. Acid parent materials, leaching of 2+ 2+ lihood. +e major grain crops include tef (Eragrostis tef basic cations (calcium (Ca ), magnesium (Mg ), and po- (Zucc.) Trotter), maize (Zea mays L.), bread wheat (Triticum tassium (K )), hydrolysis reactions within the soil exchange aestivum L.), haricot bean (Phaseolus vulgaris L.), and field sites, rainfall containing sulphuric and nitric acids, cations pea (Pisum sativum L.). +e root and tuber crops such as uptake by the crop over the long run cultivation, crop residue sweet potato (Ipomoea batatas), taro (Colocasia esculenta), removal, and addition of soluble salts and fertilizers into the potato (Solanum tuberosum), and enset (Ensete ventricosum) soil (mineral and organic) would possibly cause soil acidifi- are also widely cultivated. +e surroundings of homestead cation [3, 5–7]. In Ethiopia, though the amount of inorganic areas are used for perennial crops. Continuous cultivation fertilizers applied was in small doses (e.g., [8, 9]), repeated use without fallowing is common in the area. Farmers com- of urea (46N-0-0) and diammonium phosphate (DAP) monly apply organic fertilizer sources for perennial crops (18N–46P O -0) over many years was reported as a favoring 2 5 while they used inorganic fertilizers for annual crops. +e factor for soil acidification in the Northwestern and South- inorganic fertilizers used at the time of study include urea western highlands of Ethiopia [10, 11]. In general, soil acidity 3+ (46N-0-0) and diammonium phosphate (DAP) elevates aluminum (Al ) concentration within the soil so- (18N–46P O -0). lution to a level of toxicity [5], limits the availability of es- 2 5 sential plant nutrients, and restricts crop performance [12]. +is would imply that soil acidity and associated low nutrient 2.2. Soil Sampling and Laboratory Analysis availability are among the major constraints toward attaining sustainable production and achieving food security. +ere- 2.2.1. Soil Sampling and Preparation Procedure. From the fore, investigating soil acidity, mapping its extent, and three districts, 789 surface soil samples were collected, air- planning applicable management techniques are fundamental dried, ground, and sieved through a 2 mm mesh. +e to realize sustainable levels of agricultural production. sampling points were geo-referenced using geographical In Ethiopia, agricultural production is irresistible of positioning system (GPS) (model Garmin GPSMAP 60Cx). subsistence nature. According to Gebissa [13], 97% of +e depth of sampling for grain crops was 0–20 cm while for Ethiopian agricultural activities are constituted by subsis- perennial crops it extended up to 50 cm. Depending on tence farmers. Subsistence farming is a form of farming in topography and observed heterogeneity, 10 to 15 subsamples which nearly all of the crops or livestock raised are used to were taken to form a kilogram of the composite sample. feed the family. Generally, land degradation including soil acidity is a great threat to future agricultural production in the country [2, 3, 13]. Varied soil management practices that 2.2.2. Soil Analysis. Soil samples were analyzed for pH, farmers apply into their field like the use of inorganic or exchangeable acidity (EA), exchangeable Al, exchangeable organic fertilizers [5, 14, 15], returning of crop residue into bases (Ca, Mg, K, and Na), and effective cation exchange the soil [3], and the practice of continues cropping over capacity (ECEC). Soil pH was measured using a pH meter mono-cropping or crop rotation 16, 10 influence soil acidity. with a ratio of 1 : 2.5 soil to water [20]. +e EA was de- Meanwhile, liming is the most widely used technique to termined by leaching with potassium chloride (KCl) fol- correct soil acidity, cut back phytotoxic levels of Al and Mn, lowed by titrating with 0.02 M HCl [21]. Exchangeable bases and lift soil pH to the amount that is appropriate for and Al were determined using the Mehlich-3 method [22], maximum nutrient availability, plant growth, and crop yield and the concentration of elements was measured using an [12, 15]. Yet, the amount of lime to mitigate soil acidity inductively coupled plasma (ICP) spectrometer. +en, depends on the acid tolerance level of the crop [10, 17], level ECEC was computed as a summation of exchangeable bases of soil pH, soil and the lime type, and the farming method (Ca, Mg, K, and Na) plus EA. [18]. However, empirical evidence on soil acidity and at- tributing factors and also the lime needed to reclaim acidity for subsistence farming system is lacking. +erefore, this 2.3. Estimation of Lime Requirement (LR). Haricot bean, study (1) assesses the extent and spatial distribution of soil wheat, and maize are major field crops grown in the study acidity, (2) identifies the factors attributing to soil acidifi- area. +e crops have different acid tolerance levels and were cation, and (3) suggests the lime needed for reclamation of purposively selected for lime requirement (LR) estimation. soil acidity. +eir LR was estimated based on Taye [17] as Applied and Environmental Soil Science 3 of soil pH, exchangeable acidity, and exchangeable Al could LR � 1600(EA − (ECEC ∗ PAS)), (1) demonstrate the presence of certain influences on nutrient availability [16] and crop productivity [3]. where LR is the lime rate (ton/ha), EA is the exchangeable − 1 acidity (cmolc kg ), ECEC is the effective cation exchange − 1 capacity (cmolc kg ), and PAS is the permissible acid 3.2. Factors in Relation to Soil Acidification saturation for a specific type of crop (%). Crop tolerance level indicates the PAS that can be tol- 3.2.1. Landscape Characteristics and Soil Texture. erated by different crops [6]. +e PAS used to calculate the Landscape, which is characterized by topographic position, lime requirement for major crops grown in Ethiopia was 5% elevation, slope, and aspect, did not show a significant in- for beans, 10% for most annual crops (e.g., wheat and fluence on the soil pH (Table 3). However, a declining trend barley), and 20% for maize [10, 17]. in soil pH from flat toward hilly topographic position was recorded. Elevation in the study area ranges between 1473 and 2873 m.a.s.l where the area is predominantly charac- 2.4. Digital Mapping of Soil Acidity and LR. Point data of soil terized by mid-highland (1500–2300 masl) agroecology [9]. pH, EA, and LR were interpolated for unsampled locations +us, its influence on microclimate and then soil reaction using Ordinary Kriging. +e semivariogram is represented may be limited. +e slope is related to soil erosion and in equation (24) [23]. deposition processes. Yet, the majority (68%) of the study 2 area is within flat to gentle slope conditions, and hence, c(h) � Z X − Z X + h , (2) i i significant variation in soil pH was less recorded. +e finding 2n n�1 agrees with Melku et al. [27] who reported a statistically where n is the number of pairs of sample points separated by nonsignificant difference in soil pH between slope classes the distance h and Z (x )’s are the value of the characteristic and landscape positions in Geshy subcatchment, Gojeb th under study at i location (i � 1, 2, 3, ..., n). River Catchment, Ethiopia. +e authors mentioned de- creasing trend of soil pH with increasing slope classes. Aspect is related to the amount of solar energy received by 2.5. Statistical Data Analysis. +e data were subjected to the slope and affects plant growth and soil water content analysis of variance (ANOVA) with a one-way approach [28]. +e area is predominantly characterized by flat-gentle using Statistix software version 8.0. Whenever significant topography, and its influence on soil pH was not found differences (p< 0.05) were detected, Tukey’s HSD (Tukey’s statistically significant (p> 0.05) (Table 3). Honestly Significant Difference) test was performed to Soil texture significantly (p< 0.001) influenced soil pH compare means. Furthermore, the data were evaluated using (Table 3). +e mean pH value ranged from 5.99 in clayey soils descriptive statistics and Pearson’s correlation analysis. +e to 6.46 in silt loam soils (Table 3). Clay particles are the most values of the coefficient of variation (CV) of soil properties active portions determining the soil’s chemical activity. +e were rated as low (<20%), moderate (20–50%), and highly reason for the lower soil pH could be attributed to the in- variable (>50%) [24]. Geospatial analysis, mapping, and lime fluences of higher clay content on active, exchangeable, and requirements were executed using GIS software (Arc Map reserve acidity. +is is also supported by a significant version 10.4.1). (p< 0.001) and negative relationship between soil pH with clay content (r � − 0.33), exchangeable Al (r � − 61), and ex- 3. Results and Discussion changeable acidity (r � − 0.59). In agreement, Chalsissa et al. [10] reported lower soil pH on clay soils due to a relatively 3.1. Extent and Distribution of Soil Acidity. Soil pH was higher concentration of exchangeable acidity. +e authors between 4.5 and 8.0 with a mean pH value of 6.13± 0.39 also associated the lower pH with low soil OM content. (Table 1) [25]. It showed low variability (CV< 20%). From the total sample size, 21% were strongly acidic (pH< 5.5), 53.3% moderately acidic (5.6–6.5), 22.7% neutral (6.6–7.3), 3.2.2. Soil Management Practices. Application of inorganic and 3.06% moderately alkaline (7.4–8.4) [25]. +e ex- fertilizers containing nitrogen (N) and phosphorus (P) in the form of urea (46N-0-) and diammonium phosphate (DAP) changeable acidity (Cmol (+)/kg) based on the sample observation ranges from nil to 5.1 whereas exchangeable Al (18N–46P O -0) application has long been started 50 years 2 5 varied from 1.4 to 19.9 with a mean value of 9.02 Cmol ago in Ethiopia. Fields continuously managed with inorganic (+)/kg (Table 1). Based on geospatial analysis, 3.3, 78, and fertilizer showed significantly (p< 0.001) lower soil pH than 18.7% of the total area were qualified under strongly acidic unfertilized fields (Table 4). Generally, the amount of in- (<5.5), moderately acidic (5.6–6.5), and neutral (6.6–7.3), organic fertilizers applied to soil was less than the blanket respectively (Figure 1 [25]; Figure 1(a)). Soil pH exhibited a dose [9]. Yet, pH decline was recorded at the increasing rate significantly (p≤ 0.001) negative correlation with ex- of DAP and urea fertilizers (Tables 2 and 4, Figures 2 and 3 ). changeable acidity (r � − 0.58) and exchangeable Al On average, application of DAP and urea above 75 kg/ha (r � − 0.67) (Table 2). decreased pH by 0.56 and 0.48 units, respectively, compared Crops have different abilities to tolerate acid soil con- to applications below 25 kg/ha. Similarly, research reports ditions [3]. Nonetheless, crop production is restrained at pH from western Ethiopia [10] and northwestern Ethiopia [11] values below 5.5–6.5 [26]. Consequently, the observed values indicated that the application of DAP and urea fertilizers in 4 Applied and Environmental Soil Science Table 1: Descriptive statistics of predicted values of soil properties for maps using geostatistical analysis (point sample � 789). Soil properties Unit Mean SD Min Max CV (%) pH_ point observation 6.11 0.63 4.5 8.0 10.4 pH_ after mapping — 6.13 0.39 5.02 7.28 6.0 Ex. Al_ point observation Cmol (+)/kg 9.02 2.01 1.4 19.9 22.4 Ex. Acidity_ point observation Cmol (+)/kg 0.32 0.83 0.00 5.12 257 333000 344000 355000 366000 377000 388000 399000 345000 354000 363000 372000 381000 0 4.25 8.5 17 Km 04 8 16 Km 333000 344000 355000 366000 377000 388000 399000 Soil pH 6.6-7.3 (Neutral) 345000 363000 372000 381000 4.1-5.5 (Strongly acidic) 354000 Sodo town 5.6-6.5 (Moderatly acidic) Exchangeable Acidity (Cmol(+)/kg) 0 - 0.5 1.1 - 1.6 0.51 - 1 Sodo town (a) (b) Figure 1: (a) Extent and spatial distribution of soil pH across the study site. (b) Extent and spatial distribution of exchangeable acidity (Cmol (+)/kg) across the study site. Table 2: Pearson’s correlation matrix between soil pH and different factors in crop lands (N � 674). pH Altitude (m.a.s.l) Slope (%) CI no. Al Cmol(+) (kg) Ex. Ac Cmol (+) (kg) FYM t (ha) DAP (kg/ha) ns Altitude 0.03 ns ∗∗ Slope 0.00 0.49 ns ∗∗ ∗∗ Crop intensity (CI) − 0.16 − 0.02 − 0.13 ∗∗ ns ∗∗ ∗ Al − 0.67 0.05 0.15 0.08 ns ns ∗∗ ∗ ∗∗ Ex. Ac − 0.58 − 0.10 − 0.06 0.05 0.63 ∗∗ ns ns ∗∗ ∗∗ ∗∗ FYM 0.37 0.03 − 0.05 − 0.23 − 0.25 − 0.15 ∗∗ ∗∗ ∗∗ ∗∗ ∗∗ ∗∗ DAP − 0.39 − 0.14 − 0.05 0.14 0.20 0.20 − 0.46 ∗ ∗∗ ns ns ns ns ∗∗ ∗∗ Urea − 0.10 − 0.14 − 0.06 − 0.06 − 0.01 0.01 − 0.17 0.42 CI � cropping intensity, Al � aluminum, Ex.Ac � exchangeable acidity, FYM � farmyard manure, DAP � Diammonium phosphate, ns � not significant, ∗ ∗∗ p< 0.05, p< 0.01. Table 3: Effects of topographic position and soil texture on the mean value of soil pH (n � 789). Topographic position and slope pH Textural class pH F (<4%) 6.13 (157) Silt loam 6.46a (148) GS (4–8%) 6.11 (382) Silt clay 6.14 b (98) SL (8–16%) 6.09 (162) Clay 5.99c (543) ∗∗∗ HI (>16%) 6.08 (88) p value p value NS — CV (%) 10.4 CV (%) 9.92 ∗∗∗ F � flat, GS � gentle slope, SL � strongly sloppy, HI � hilly. Note. Numbers in the bracket refer to sample size. p< 0.001. Means in a column followed by the same letters are not significantly different at 5% level of significance; CV � coefficient of variation, NS � not significant. 748000 760000 772000 784000 748000 760000 772000 784000 730000 740000 750000 760000 770000 780000 730000 740000 750000 760000 770000 780000 Applied and Environmental Soil Science 5 Table 4: Effects of fertilizer types and crop residue management on soil pH. Fertilizer types Field management Crop residue status pH DAP Urea FYM Unfertilized 6.24a (399) 6.11 (687) 5.96b (621) Removed 6.09b (758) Fertilized 5.97 b (390) 6.06 (102) 6.66a (168) Maintained 6.61a (31) ∗∗∗ ∗∗∗ ∗∗∗ p value NS p value CV (%) 10.18 10.42 9.3 CV (%) 10.3 ∗∗∗ Note. Numbers in the bracket refer to sample size. p< 0.001. Means in a column followed by the same letters are not significantly different at 5% level of significance; CV � coefficient of variation; NS � not significant. 6.30 6.20 P=0.09 6.12 6.24 P < 0.001 6.20 CV (%)=10.4 6.10 6.11 CV (%)=10.04 6.10 6.07 6.00 6.02 6.00 5.90 5.91 5.90 y = -0.164x + 6.355 5.80 y = -0.1728x + 6.4343 2 5.80 R = 0.88 R = 0.91 5.70 5.70 5.68 5.64 5.60 5.60 5.50 5.50 0-25 (407) 26-50 (155) 51-75 (141) > 75 (86) 0-25 (696) 26-50 (70) 51-75 (14) > 75 (9) DAP (kg/ha) (No. of samples) Urea (kg/ha) (No. of samples) pH pH Linear (pH) Linear (pH) Figure 2: pH level on crop fields with different rates of DAP Figure 3: pH level on crop fields with different rates of urea fertilizer. fertilizer. 6.71 cultivated fields resulted in soil acidification. Indeed, inor- 6.69 6.70 ganic fertilizers have a considerable role in yield increment. 6.58 Yet, in yield-making processes, plants uptake more cations 6.50 than anions to neutralize organic acid synthesized, and y = -0.15x + 0.986x + 5.145 R = 0.98 consequently, more cations than anions are removed by crop 6.30 with grain and residue [5]. +is induces acidification es- p<0.006 pecially when crop residues are removed from the cropland 6.10 CV (%)=9.3 like the study area [5, 29]. Additionally, ammonia-based 5.96 5.90 fertilizers or other conditions that produce ammonia in the soil liberate more protons than the amount consumed 5.70 during transformations processes within the soil and af- 0 (621) 0.1 -2.0 (58) 2.1-4.0 (78) > 4.0 (32) terward generate acidification [5]. FYM (t/ha) (No. of Samples) Alternatively, fields that have been continuously man- aged with farmyard manure (FYM) showed significantly pH Poly. (pH) (p< 0.001) higher soil pH than untreated fields (Tables 2 and 4, Figure 4). +e average pH unit increase due to farmyard Figure 4: pH level on crop fields that received different rates of manure application at 4 t/ha over the unfertilized field was farmyard manure. 0.75 units (Figure 4). +e result regarding the incorporation of crop residue also followed a similar pattern of FYM application (Table 4). +is explains that the addition of unit decline between the maximum (enset field) and the minimum (grassland) was 1.22 units followed by 0.91 units organic fertilizers/retaining crop residue renders phytotoxic levels of Al by forming organo-Al complexes and increases (main croplands) (Figure 5). +e impact of land use on soil acidification depends on how it affects proton fluxes [5]. the pH [3]. Manure application due to its high base cation concentrations alleviates acidification [14]. Comparing enset fields versus main field/grasslands, the latter is more acidified. +is was because of variable man- agement practices. Management practices, like organic 3.2.3. Land-Use Type, Cropping Intensity, and Continuous fertilization, are common on enset fields than cereal and Cropping. Statistically significant differences in soil pH were legume growing fields that were managed with inorganic recorded among land-use types (Table 5). +e average pH fertilizers and rotation. Additionally, legumes grown as sole Soil pH Soil pH Soil pH 6 Applied and Environmental Soil Science Table 5: Field position and cropping intensity effects on the mean Table 6: Soil pH level under farmers’ soil types and on fields owned value of soil pH (N � 789). by farmers with different wealth statuses. Field position pH Cropping intensity pH Soil type pH Wealth pH H 6.77a (104) One 6.31a (254) Arrada Bita 6.45a (261) Poor’s_ field 6.25a (143) M 6.37b (119) Two 6.06b (395) Talla Bita 6.24b (94) Medium_ field 6.11b (423) D 5.93c (566) — — Kereta Bita 6.17bc (27) Rich_ field 6.06b (161) p value 0.0005 p value 0.0001 Lada Bita 5.97cd (149) p value 0.0268 CV (%) 9.2 CV (%) 10.3 Gobo Bita 5.89de (118) CV (%) 10.5 Chere Bita 5.76ef (48) H � homestead field, M � middle field, D � distant field; Note: numbers in ∗∗∗ Zo’o Bita 5.60f (92) the bracket refer to sample size. p< 0.001. Means in a column followed p value 0.0006 by the same letters are not significantly different at 5% level of significance; CV � coefficient of variation. CV (%) 9.2 10.5 ‘Bita’ literally means soil. Numbers in parenthesis indicate the sample size. ∗∗∗ Note: numbers in the bracket refer to sample size. p< 0.001. Means in a y = -0.2349x + 7.1112 column followed by the same letters are not significantly different at 5% 7.50 R = 0.89 level of significance; CV � coefficient of variation. 6.98a (15) 7.00 P < 0.001 6.73a (55) CV (%) = 9.7 6.50 6.60 6.14b(134) 6.45 6.07b(470) 6.05bc (11) 6.40 6.00 6.24 6.20 6.17 5.76c (104) 5.50 6.00 5.89 5.97 5.80 5.76 5.00 5.60 5.60 Enset Coffee RTV CP Fallow Grass y = -0.1318x + 6.5399 5.40 LUT 2 R = 0.95 5.20 pH Linear (pH) 5.00 Areda Talla Kereta Gobo Lada Chere Zoo Figure 5: Soil pH along with different land-use types (note: Bita Bita Bita Bita Bita Bita Bita numbers in the bracket refer to sample size). RTV � root, tuber, and Farmers' Soil Type vegetable crop field; CP � crop field. pH Linear (pH) and intercrop in the main field uptake excess cation to Figure 6: Soil pH along farmer’s named soil types. neutralize the carboxylic groups of amino acids during synthesis [5]. +is together with the above-mentioned permeability, water retention capacity, workability, and soil management practices might acidify main fields more than fertility as assessed qualitatively. +e details of perceived soil enset/coffee fields. characteristics are found in Fanuel et al. [9]. Soil pH in view Cropping intensity refers to growing a number of crops in of farmers’ soil nomenclature varied from 5.6 (Zo’o bita) to the same field continuously during one agriculture year. +e 6.4 (Arrada bita) (Table 6, Figure 6). Zo’o bita literally is red result indicated that soil pH was significantly affected by colored and nonfertile soil. Subsequently, farmers relatively cropping intensity (Table 5). Growing two successive crops in apply higher amounts of inorganic fertilizer compared to a year in the same field decreased soil pH more than mono- Arrada bita (fertile soil) [9]. Zo’o bita has a higher clay cropping did. Plants uptake more cations than anions to neutralize organic acid synthesized. It implies that the uptake fraction (71%) than Arrada bita (45%) and its pH declined significantly p< 0.001) with an increase of clay proportion would become more under continuous cultivation [9]. +is may result in soil pH reduction. In agreement with this, (r � − 0.33). In most cases, farmers apply home left wastes particu- Tesfaye et al. [30] reported pH decline under continuous larly wood ash and animal wastes into Arrada bita as it is cultivation. In the study area, farmers grow two successive mostly situated close to homestead. +is might improve soil crops by rotation. Cereals are often rotated with legumes and organic matter and base cations and finally end with higher root crops [9]. According to Viera et al. [31], leguminous pH compared to soils located on distant fields (e.g., Zo’o bita, species increased soil acidification attributed to the increment Lada Bita, Chere Bita) which are mostly subjected to in the removal of alkaline plant material by grain yield. complete crop residue removal and inorganic fertilizer use. In agreement, Yihenew et al. [11] reported acidic soil re- 3.2.4. Farmers Perspective: Local Soil Types and Socioeco- action in cultivated fields due to depletion of basic cations nomic Status. Farmers in the study area have a tradition to through crop harvest and continuous use of urea and DAP classify soils and apply localized management accordingly. [(NH ) HPO ] fertilizers. In line with this, decreased soil pH 4 2 4 +ey used holistic approaches such as soil color, from home fields to remote fields mostly due to differences Soil pH Soil pH Applied and Environmental Soil Science 7 350000 360000 370000 380000 345000 354000 363000 372000 381000 0 3.5 7 14 Km 14 Km 0 3.5 7 350000 360000 370000 380000 345000 354000 363000 372000 381000 LR_Haricot bean (t/ha) LR_Malze (t/ha) No lime 1.1 - 1.5 2.1 - 6.6 No lime 1.1 - 1.5 2.1 - 4.3 0.01 - 0.5 1.6 - 2 Sodo town 0.01 - 0.5 1.6 - 2 Sodo town 0.51 - 1 0.51 - 1 Figure 7: Extent and spatial distribution of lime requirement (t/ha) Figure 8: Extent and spatial distribution of lime requirement (t/ha) for legume (Haricot bean) production across the study site. for maize production across the study site. in input levels was reported by Chikowo et al. [32]. +is finding implies that understanding farmers’ soil typology is widely considered a major option to manage soil acidity could be useful for site-specific soil pH and nutrient and sustaining food production. It is a quick and effective management strategies. way to neutralize acidity, especially in highly acidic soils Soil pH on the resource-poor farmers’ field was signifi- [29]. In addition, the growth of relatively acid-tolerant crop varieties on slightly acid soils is also suggested. +e cantly higher than the other wealthy groups (Table 6). Re- source-poor farmers own less land than wealthy farmers and remaining 15,708 ha of the study area does not require lime. use a range of other sources of nutrients, such as compost, crop +e amount of lime estimated based on permissible acid residues, and leaf litter compared to richer farmers who use saturation (PAS) level for the respective crops is presented in mineral fertilizer [33]. +e author also described that richer Figures 7–9 . It was noted that lime requirement (LR) across farmers produce more manure, mainly because they have landscapes varied depending on exchangeable acidity, ex- larger herds. However, in terms of the amount being applied changeable Al, and soil pH. +is was substantiated by the ∗∗∗ per unit of land, resource-poor farmers apply more manure highly significant correlation (r � 0.99, 0.96, 0.88 ) be- per hectare because they only cultivate very small areas. +is tween exchangeable acidity and LR at 5% PAS, 10% PAS, and might have caused higher soil pH on resource-poor fields. 20% PAS, respectively. +e correlation between exchange- Despite the fact that poor farmers have little access to able Al and LR was also significantly positive at 5% PAS ∗∗∗ ∗∗∗ organic and inorganic nutrient sources, their land is being (r � 0.62 ), 10% PAS (r � 0.59 ), and 20% PAS ∗∗∗ managed with better care to get more produce from it. On (r � 0.52 ). +e correlation matrix for soil pH also showed the contrary, wealthier farmers have a better land size and a highly significant but negative relation with LR at 5% PAS ∗∗∗ ∗∗∗ continuously cultivate under relatively higher application (r � − 0.54 ), 10% PAS (r � − 0.50 ), and 20% PAS ∗∗∗ rates of inorganic fertilizer. (r � − 0.43 ). +e strong spatial dependence of LR for semivariograms in all PAS computation also strengthens the earlier statements (Appendix Table 1). 3.3. Estimating Lime Requirement. From the total area, It was estimated that the amount of lime required to 2,772 ha was strongly acidic (<5.5) whereas 65,520 ha was neutralizing acidity on common bean fields varied from zero moderately acidic (5.6–6.5) suggesting the need for site- to 6.6 t/ha (Figure 7), while for maize, it was between zero specific management in order to correct soil acidity. Liming and 4.3 t/ha (Figure 8). Farmers under strongly acidic soils, 740000 750000 760000 770000 780000 790000 740000 750000 760000 770000 780000 790000 740000 750000 760000 770000 780000 790000 740000 750000 760000 770000 780000 790000 8 Applied and Environmental Soil Science 345000 354000 363000 372000 381000 390000 the acid sensitivity of the crops. Smallholder farmers have to be encouraged to return crop residue and integrate chemical fertilizer with manure in order to reduce the impacts of soil acidity. In addition, introducing crops with traits that tol- erate both acidity and Al toxicity is suggested. Finally, liming alone cannot be a complete solution to increase crop yield. +us, it has to be integrated with an adequate and balanced supply of crop limiting nutrients. Data Availability +e data used to support the findings of this study are available from the corresponding author upon request. Conflicts of Interest +e authors declare that there are no conflicts of interest. Authors’ Contributions All the authors collected, analyzed, interpreted, and pre- 0 4 8 16 Km pared the manuscript. 345000 354000 363000 372000 381000 390000 Acknowledgments LR_Most Crops (t/ha) No lime 1.1 - 1.5 2.1 - 6.4 +e authors are grateful to the Ministry of Education (MOE) 0.01 - 0.5 1.6 - 2 Sodo town and now the Ministry of Science and Higher Education 0.51 - 1 (MoSHE) and Ethiopian Soil Information System (EthioSIS) Figure 9: Extent and spatial distribution of lime requirement (t/ha) at the Agricultural Transformation Agency (ATA) for fi- for most annual crops production across the study site. nancial support. Supplementary Materials regardless of crop types, are advised to apply a maximum of 6.4 t lime/ha (Figure 9). Nevertheless, soil test-based ad- Appendix 1: model performance and semivariogram char- justment prior to a lime application every year is also rec- acteristics of soil properties of the study area. (Supplementary ommended. In addition, it should be stressed that liming Materials) cannot stand on its own to increase crop productivity; rather, it guarantees higher yield when used with an ade- References quate and balanced supply of crop limiting nutrients. Nonetheless, liming may not be practical for resource-poor [1] N. K. Fageria, M. P. B. Filho, A. Moreira, and farmers due to supply shortages or high labor and monetary C. M. Guimarães, “Foliar fertilization of crop plants,” Journal of Plant Nutrition, vol. 32, no. 6, pp. 1044–1064, 2009. costs. +us, integrating chemical fertilizer with manure and [2] M. B. Hossain, M. H. R. Khan, S. Khanom, and S. A. Shahid encouraging farmers to retain/incorporate residue to sig- Akhtar Hossain, “Amelioration of soil acidity by the appli- nificantly alleviate soil acidification are relevant [29]. cation of maize straw ash in mixed soil,” Dhaka University Journal of Biological Sciences, vol. 30, no. 2, pp. 207–219, 2021. 4. Conclusion [3] G. Agegnehu, C. Yirga, and andT. Erkossa, “(EIAR). Addis ababa, Ethiopia,” Soil Acidity Management, Ethiopian Insti- Soil acidity is identified as one of the most important tute of Agricultural Research, 2019. [4] B. Gurmessa, Soil Acidity Challenges and the Significance of constraints to crop production. However, the magnitude Liming and Organic Amendments in Tropical Agricultural and extent of acidity are location-specific which suggests the Lands with Reference to Ethiopia, Environment, Development need to have site-specific management. In the study area, and Sustainability, Addis ababa, Ethiopia, 2020. where environmental and landscape characteristic systems [5] R. Alvarez, A. Gimenez, F. Pagnanini et al., “Soil acidity in the are mostly similar, soil acidification is attributed to inherent Argentine Pampas: effects of land use and management,” Soil and human-induced factors. Amount of clay, fertilizer type, and Tillage Research, vol. 196, Article ID 104434, 2020. land use, management practices, and socioeconomic con- [6] B. Iticha and C. Takele, “Digital soil mapping for site-specific ditions contributed to soil acidity. Liming is suggested as an management of soils,” Geoderma, vol. 351, pp. 85–91, 2019. effective way to counteract soil acidification and improve [7] J. L. Havlin, S. L. Tisdale, W. L. Nelson, and J. D. Beaton, Soil crop yields. Accordingly, the digital mapping indicated site- Fertility and Fertilizers: An Introduction to Nutrient Man- crop-specific lime rates in which the amount varies based on agement, Pearson, Uper Sadle River: NJ, 2014. 730000 740000 750000 760000 770000 780000 740000 750000 760000 770000 780000 Applied and Environmental Soil Science 9 [8] E. Eyasu, P. F. Okoth, and E. M. A. Smaling, “Explaining bread [25] EthioSIS, Soil Fertility Status and Fertilizer Recommendation Atlas for Tigray Regional State, Ethiopia, EthioSIS, Addis wheat (Triticum aestivum) yield differences by soil properties and fertilizer rates in the highlands of Ethiopia,” Geoderma, ababa, Ethiopia, 2014. [26] J. Holland, P. White, M. Glendining, K. Goulding, and vol. 339, pp. 126–133, 2019. [9] F. Laekemariam, K. Kibret, T. Mamo, and E. Karltun, S. McGrath, “Yield responses of arable crops to liming-An evaluation of relationships between yields and soil pH from a “Physiographical characteristics of agricultural land and long-term liming experiment,” European Journal of Agron- farmers’ soil fertility management practice in Wolaita Zone, omy, vol. 105, pp. 176–188, 2019. Southern Ethiopia,” Environmental System Research, vol. 5, [27] M. Dagnachew, A. Moges, and A. Kebede, “Effects of soil and p. 24, 2016. water conservation measures on soil quality indicators: the [10] C. Takele, B. Iticha, and G. Sori, “Index,” =e Anabasis of case of Geshy subcatchment, Gojeb River catchment, Cyrus, vol. 18, no. 5, pp. 275–281, 2018. Ethiopia,” Applied and Environmental Soil Science, vol. 2020, [11] Y. Gebreselassie, F. Anemut, and A. Solomon, “+e effects of Article ID 1868792, 16 pages, 2020. land use types, management practices and slope classes on [28] H. Zhu, Y. Zhao, F. Nan, Y. Duan, and R. Bi, “Relative in- selected soil physico-chemical properties in Zikre watershed, fluence of soil chemistry and topography on soil available North-Western Ethiopia,” Springer Open Journal, Environ- micronutrients by structural equation modeling,” Journal of mental Systems Research, vol. 4, no. 3, pp. 1–7, 2015. Soil Science and Plant Nutrition, vol. 16, no. 4, 2016. [12] N. K. Fageria and V. C. Baligar, “Chapter 7 Ameliorating Soil [29] Q. Zhu, X. Liu, T. Hao et al., “Cropland acidification increases Acidity of Tropical Oxisols by Liming For Sustainable Crop risk of yield losses and food insecurity in China,” Environ- Production,” Advances in Agronomy, vol. 99, pp. 345–399, mental Pollution, vol. 256, Article ID 113145, 2020. [30] W. Tesfaye, K. Kibebew, B. Bobe, T. Melesse, and E. Teklu, [13] G. Y. Wendimu, “+e challenges and prospects of Ethiopian “Long term effects of cultivation on physicochemical prop- Agriculture,” Cogent Food and Agriculture, vol. 7, p. 1923619, erties of soils at metahara sugar estate,” American-eurasian Journal of Agricultural & Environmental Sciences, vol. 18, [14] A. P. Martins, S. E. V. G. Andrade Costa, I. Anghinoni et al., no. 5, pp. 246–257, 2018. “Soil acidification and basic cation use efficiency in an inte- [31] F. C. B. Viera, C. Bayer, J. Mielniczuk, J. Zanatta, and grated no-till crop-livestock system under different grazing C. A. Bissari, “Long-term acidification of a Brazilian Acrisol as intensities,” Agriculture, Ecosystems & Environment, vol. 195, affected by no till cropping systems and nitrogen fertilizer,” pp. 18–28, 2014. Australian Journal of Soil Research, vol. 46, pp. 17–26, 2008. [15] S. Getaneh and W. Kidanemariam, “Soil acidity and its [32] R. Chikowo, S. Zingore, S. Snapp, and A. Johnston, “Farm managements: a review,” International Journal of Advanced typologies, soil fertility variability and nutrient management Research in Biological Sciences, vol. 8, no. 3, pp. 70–79, 2021. in smallholder farming in Sub-Saharan Africa,” Nutrient [16] F. Laekemariam and K. Kibret, “Explaining soil fertility Cycling in Agroecosystems, vol. 100, no. 1, pp. 1–18, 2014. heterogeneity in smallholder farms of southern Ethiopia,” [33] E. Elias, “Soil enrichment and depletion in southern Ethio- Applied and Environmental Soil Science, 2020. pia,” in Nutrients on the Move–Soil Fertility Dynamics in [17] T. Bekele, “Estimation of lime requirement,” in Training African Farming Systems, T. Hilhorst and F. M. Muchena, Manual for Regional SoilTesting Laboratory Heads and Eds., pp. 65–82, International Institute for Environment and TechniciansNational soil Testing Center, Ministry of Agri- Development, London, 2000. culture and Rural Development, Addis Ababa, Ethiopia, 2008. [18] K. W. T. Goulding, “Soil acidification and the importance of liming agricultural soils with particular reference to the United Kingdom,” Soil Use and Management, vol. 32, no. 3, pp. 390–399, 2016. [19] B. Tesfaye, Understanding farmers: Explaining soil and water conservation in Konso, Wolaita, and Wollo, Ethiopia, PhD +esis, Wageningen University and Research Center, Wageningen, +e Netherlands, 2003. [20] R. Mylavarapu, UF/IFAS Extension Soil Testing Laboratory (ESTL) Analytical Procedures and Training Manual, 2009. [21] S. Sahlemedhin and B. Taye, “Procedures for soil and plant analysis,” National Soil Research Center, Ethiopian Agricul- tural Research Organization, Addis Abeba, Ethiopia, Tech- nical Paper 74, 2000. [22] A. Mehlich, “Mehlich III soil test extractant: a modification of Mehlich II extractant,” Communications in Soil Science and Plant Analysis, vol. 15, pp. 1409–1416, 1984. [23] C. Costa, E. M. Papatheodorou, N. Monokrousos, and G. P. Stamou, “Spatial variability of soil organic C, inorganic N and extractable P in a Mediterranean grazed area,” Land Degradation & Development, vol. 26, no. 2, pp. 103–109, 2015. [24] U. A. Amuyou, E. B. Eze, P. A. Essoka, J. Efiong, and O. O. Egbai, “Spatial variability of soil properties in the Obudu Mountain region of southeastern Nigeria,” International Journal of Humanities and Social Science, vol. 3, no. 15, pp. 145–149, 2013.
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