2019 ASHS Annual Conference

Strawberries are among the top selling organic commodity in the U.S. and are undergoing an increase in organic acreage recently. In Florida, the second leading state in organic strawberry production, organic nutrient management is complex due to sandy soils with poor water and nutrient retention capacity and a warm and moist subtropical climate. The objective of this study was to assess the influence of integrated nutrient management practices and their synergistic effects on N availability and uptake, plant growth, and yield in organic strawberry production systems. The field trial was conducted on certified organic land at the University of Florida Plant Science Research and Education Unit in Citra, FL, using Sweet Sensation^® ‘Florida127’. A split plot design with 4 replications was used, and the main plots consisted of combinations of cover crop (sunn hemp or fallow) and compost (no compost, 22.4 t ha^-1 or 44.8 t ha^-1) treatments. The compost was a mixture of 50% food waste compost and 50% yard waste compost based on volume. The subplots consisted of organic fertilization treatments: no fertilizer control, preplant fertilizer (84.1 kg N ha^-1), in-season fertigation (328.7 kg N ha^-1), and a combination of both. Sunn hemp (Crotalaria juncea L.) was seeded at 44.9 kg/ha in July 2017 then flail-chopped and incorporated into the soil 64 days after seeding. The strawberry was transplanted in Oct. 2017 and the final harvest occurred in Apr. 2018. Sunn hemp residue incorporation increased soil NO₃-N availability before strawberry bed formation and marketable fruit yield during the early season. Compost increased soil pH and CEC, at the end of strawberry season but did not significantly affect fruit yield. Marketable fruit yield did not differ significantly between preplant fertilization and in-season fertigation during the early and mid season, while the combined fertilization treatment consistently produced the highest yield from Dec. to Feb. Total marketable yield was significantly higher in the fertigation and combined fertilization treatments compared with preplant fertilization. The combined fertilization treatments resulted in the highest total fruit yield for the whole season; in addition, the total fruit yield was significantly higher in the fertigation treatment versus the preplant fertilization treatment. Overall, the early release of N from sunn hemp residues, lack of response to compost and benefits of fertigation highlight the challenges of optimizing N availability in organic strawberry production to maximize yields while minimizing N losses.

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