Assessing nitrogen uptake and the impact of fertilizer amounts and sources on strawberry production in California
A study was conducted in Oxnard, CA, from 2014 to 2015 to assess seasonal nitrogen (N) uptake, and 2018–2019 to assess the effect of fertilizer rates and types (calcium nitrate [CN9] and ammonium nitrate [AN20]) on yield of two strawberry (Fragaria × ananassa Duch.) cultivars (Fronteras and a proprietary cultivar). The 2014–2015 study identified mainly two seasonal uptake rates: 0.59 and 1.30 kg ha–1 d–1 for early (October–February) and late season (March–June), respectively. The N fertilizer rates for the 2018–2019 study, derived from the 2014–2015 study, were defined as low (CN9‐L and AN20‐L; 132 kg ha–1 total applied), optimum (CN9‐O and AN20‐O; 233 kg ha–1 total applied), and high (CN9‐H and AN20‐H; 334 kg ha–1 total applied). Marketable yield for Fronteras plateaued at the optimum fertilizer rate, suggesting the average rate determined from the 2014–2015 study (equivalent to the optimum rate in the 2018–2019 study) achieved the highest yield for that cultivar. Marketable yield of the AN20 treatments for the proprietary cultivar was significantly greater than the CN9 treatments. Increasing N fertilizer rates resulted in greater aboveground vegetative biomass and consequent increased yield for both cultivars. The AN20 treatments resulted in 193–264% less nitrate found in the 30.5‐to‐61.0‐cm depth of soil than the CN9 treatments at crop termination, indicating significantly less nitrate‐leaching potential for fertilizers with greater proportion of N as ammonium. Assessing N uptake and tailoring fertilizer amounts and sources accordingly can maximize strawberry yield and minimize nitrate leaching.