S13 - Session O1 - Nitrogen management strategies for strawberry production in California
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Authors: Andre Biscaro *, Patrick Brown
California accounts for approximately 90% of the strawberries produced in the US, with practically all the production concentrated in the Central Coast region. Environmental regulations, variable nitrogen (N) uptake rate, and growers' concerns with potential adverse effects of N fertilization on yield and shelf life have made N fertilization challenging for strawberry growers in California. Three studies were conducted in Ventura County from 2015 to 2021 to optimize yield and quality while minimizing off-site movement of N. These projects consisted of 1) quantifying N uptake of Fall- and Summer-planted strawberries, 2) assessing the impact of N fertilizer amounts and sources on strawberry yield and quality, and 3) assessing the effectiveness of biostimulants to overcome N deficiency. Eight commercial fields of the four most popular cultivars were assessed for N uptake from 2015 to 2020. Nitrogen uptake curves identified two distinct N uptake patterns in each growing season: 0.59 and 1.30 kg N/ha/day for early and late seasons, respectively (Fall-planted), and 1.34 and 0.67 kg N/ha/day for early and late season, respectively (Summer-planted). A follow up randomized complete block study conducted in 2018-2019 assessed the impact of three N fertilizer rates (132, 233 and 334 kg N/ha total) and two N fertilizer sources (CN9 and AN20) on strawberry yield and shelf life. The N rate of 233 kg/ha (0.59 and 1.30 kg N/ha/day) applied as AN20 resulted in maximum yield and one of the lowest nitrate leaching among all treatments. Shelf life was not affected by the N rates and sources used in this study. Another randomized complete block study was conducted in 2020-2021 to assess how six biostimulant products applied in combination with optimal and reduced N rates (16 treatments) affected yield. Overall, the only product that showed evidence of recovering N shortage was a N fixing bacteria, which overcame approximately 40% of N.