2019 ASHS Annual Conference

Nitrogen management is one of the most challenging aspects of nutrient management in strawberry (Fragaria × ananassa) production, particularly in the California northern district (Watsonville and Salinas). Excess of nitrogen application results in potential for leaching and possibly in low fruit quality; low nitrogen availability for crop uptake can result in reduced yield. Plant nitrogen uptake is low from planting to the beginning of harvest (about 30 lb/ac from November to March), and moderate and constant from spring until crop termination (1 lb/ac day from April to September). Pre-plant slow-release fertilizers consisting of a formula of nitrogen, phosphorous and potassium coated by a polymer layer are commonly used in strawberry production. However, there are concerns on the rate of release of the fertilizer, and some evidence that much of the fertilizer may be released during winter months, when crop uptake is low and leaching potential due to rains is high. Therefore, some growers rely mostly on fertigation during spring and summer rather than on pre-plant applications to increase crop nitrogen availability. We conducted an applied research and extension experiment in collaboration with four commercial strawberry growers with the goal of informing nitrogen management and evaluating different strategies. Growers applied different rates of pre-plant fertilizer and some ranches supplemented nitrogen with in-season fertigation. We monitored nitrate in the soil monthly with soil nitrogen quick tests (MQuant nitrate test strips). There was substantial evidence of nitrate leaching by winter rains and some evidence of leaching due to over irrigation. We also found some evidence that fertilizer beads were still in the soil as late as June. In all ranches, residual nitrogen from the previous crop and nitrate in the irrigation water provided substantial contributions to the crop total nitrogen balance, contributing to a seasonal nitrogen availability over 300 lb/ac while the generally recommended crop demand is below 250 lb/acre. In one ranch, nitrate in the irrigation water and estimated nitrogen release from soil mineralization appeared sufficient to satisfy the rate of 1 lb/acre day of crop uptake. In one ranch, we measured yields on a strip plot with three replicates; the yield was about 10% higher for the pre-plant treatment than in the fertigation treatment, despite the first received from fertilizer a total of 117 lb of nitrogen/acre and the second 158 lb of nitrogen/acre. In conclusion, this work provided insight into pre-plant fertilizer availability and suggested in-season nitrogen fertigation management strategies for strawberry growers in northern California.