Dynamics of Soil Nitrogen Availability Following Sunn Hemp Residue Incorporation in Organic Strawberry Production Systems

Abstract

Sunn hemp (Crotalaria juncea L.), as a summer leguminous cover crop, is often grown before fall planting of strawberries (Fragaria ×ananassa Duch.) in Florida. Although sunn hemp has been suggested as a green manure for supplying nitrogen (N) to subsequent crops, limited information is available regarding the contribution of sunn hemp biomass to soil N availability in Florida sandy soils with low levels of organic matter. This is especially true for organic strawberry production where nutrient management remains one of the major yield-limiting factors. This study was conducted in Citra, FL, and assessed the dynamics of N availability after soil incorporation of sunn hemp in organic strawberry production systems established on sandy soils in a subtropical environment. Sunn hemp was planted at a seeding rate of 44.9 kg·ha−1 on 19 July 2017 and 24 July 2018 and terminated 65 days after seeding; a summer weedy fallow was used as the control. Containerized strawberry seedlings of Sweet Sensation® ‘Florida127’ were transplanted on 13 Oct. 2017 (22 days after sunn hemp incorporation) and 4 Oct. 2018 (8 days after sunn hemp incorporation). Immediately after sunn hemp incorporation, anion exchange membranes (AEMs) were buried in the soil to monitor soil NO3-N fluxes, together with traditional soil testing to measure extractable soil NO3-N concentrations. In the 2018 season, soils incorporated with sunn hemp residues were also incubated in the laboratory at 24 °C over 8 weeks to determine the N release pattern by quantifying soil NO3-N and NH4-N. Overall, nitrate fluxes monitored by AEMs in the first 3 weeks after sunn hemp incorporation were significantly higher in the sunn hemp treatment than in the weedy fallow control (by 66% to 185%) in both years. Sunn hemp incorporation also led to a considerable increase in extractable soil NO3-N concentration (by 20% to 94%). The early and fast release of plant available N (PAN) from sunn hemp residues was confirmed by the 8-week laboratory incubation study, which demonstrated that the net N mineralization rate of sunn hemp remained highest over the first 2 weeks of the incubation period. Sunn hemp showed a positive impact on organic strawberry early-season fruit yield in both years, with significant increases in marketable (by 59%) and total (by 52%) fruit weight yields and marketable fruit number (by 46%) in 2017 and total fruit number (by 15%) and weight yield (by 14%) and marketable fruit number (by 13%) in 2018. Given the typical waiting period between sunn hemp residue soil incorporation and strawberry planting as well as the lag in nutrient uptake shortly after transplanting, a large fraction of N released from sunn hemp residues is likely not taken up by strawberry plants. Our findings highlight the challenges of using sunn hemp residues to improve N availability for meeting crop demand and enhance fruit yield in organic strawberry production while minimizing environmental N losses in Florida sandy soils.

Crotolaria juncea L., A NEW LEGUME CROP FOR CULTIVATION IN RUSSIA: CHARACTERIZATION AND PROSPECTS (review)

“…Показано, что выращивание кроталярии существенно увеличивает урожайность последующих культур -риса, пшеницы, ржи и кукурузы в севообороте: (56,76,(79)(80)(81). C. juncea также была предложена в качестве зеленого удобрения для производства органической клубники (82). Изучение культуры с позиции зеленого удобрения на разных культурах выявило значительную положительную корреляцию между высотой растения, зеленой и сухой биомассой и количеством корневых клубеньков (83).…”

Using High Tunnels to Enhance Organic Vegetable Production in Florida: an Overview

“…As the relatively warm conditions inside high tunnels help promote soil organic matter decomposition and organic nutrient mineralization, short-term and longterm management plans need to be developed to maintain and improve soil fertility and health for Florida sandy soils in high tunnel systems. For organic crop production, matching available nitrogen with crop demand remains challenging (Bi et al 2021;Gaskell and Smith 2007;Lei and McDonald 2019;Li et al 2021). Although more tools are becoming available for estimating the release of plant available nitrogen from cover crops, organic fertilizers, and other nutrient sources, the environmental differences between high tunnel and open field production need to be carefully considered.…”

Residue management and genotype effect on sunn hemp organic matter and nitrogen decomposition

“…Currently, it is used worldwide as a cover crop, green manure, or forage (Akbar & Ahmed, 2006; Bearden, 2018; Wanapat et al., 2021). The use of sunn hemp in crop rotation has been effective to increase the production of tomato ( Solanum lycopersicum L.) (Q. Wang et al., 2009), strawberry ( Fragaria × ananassa Duchesne) (Li et al., 2021), and sweet corn ( Zea mays L.) (Cherr et al., 2006b) in Florida.…”