Organic kale and cereal rye grain production following a sunn hemp cover crop

Authors: Kornecki, Ted; Balkcom, Kipling

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2020
Publication Date: 12/4/2020
Citation: Kornecki, T.S., Balkcom, K.S. 2020. Organic kale and cereal rye grain production following a sunn hemp cover crop. Agronomy. 10(12):1913. https://doi.org/10.3390/agronomy10121913.
DOI: https://doi.org/10.3390/agronomy10121913

Interpretive Summary: ARS scientists located in Auburn, AL conducted a field experiment in central Alabama between 2015 and 2017 to determine how three termination methods (rolling, mowing and mowing with incorporation) for sunn hemp affected organic kale production and cereal rye for grain. Greater kale yields were obtained for mowed and incorporated residue (15,054 kg/ha) compared with 55% lower yield for mowed and 63% lower for rolled sunn hemp. These lower yields were related to poor kale seed-to-soil contact (hair pinning) from large amounts of sunn hemp residue on the soil surface. Similarly, cereal rye grain yield was affected by sunn hemp termination method with higher yields observed for rolled and mowed residue averaging 1443 kg/ha, compared with 18% lower yields for mowed and incorporated sunn hemp residue. Better soil planting conditions due to rolling and mowing sunn hemp resulted in higher yield of cereal rye grain. Higher levels of nitrate and ammonium in the topsoil layer were measured at planting for each cash crop compared to levels at sunn hemp termination, indicating N release from sunn hemp residue. Overall, findings from this study indicate that selecting a suitable cover crop combined with proper management are important factors to optimize crops yields in vegetable organic systems.

Technical Abstract: A four-year field experiment was initiated in 2011 at the EV. Smith Research Station, in central Alabama to determine the effect of sunn hemp (Crotalaria juncea, L.) termination methods on organically grown kale (Brassica oleracea, var. acephala L.) for fresh market and cereal rye (Secale cereale, L.) for grain. Three different termination methods for the sunn hemp cover crop were chosen: (1) rolling/crimping with an experimental two-stage roller/crimper, (2) rotary mowing, (3) rotary mowing with incorporation (disking). Kale plots were harvested in the winter and rye plots were harvested in the following spring. Kale plots were fallow from January to June (kept mowed) until planting sunn hemp again across all plots in late spring of the next growing season. Over four growing seasons, average sunn hemp biomass (dry basis) was 10981 kg ha-1 with plant height of 2.4 meters. The average C/N ratio of sunn hemp was 23:1. Sunn hemp biomass amounts differed among growing seasons (from 5589 to 14720 kg ha-1) due to different weather conditions. Kale yield also varied across growing seasons with the highest yield of 17565 kg ha-1 measured in 2012 and the lowest (3915 kg ha-1) in 2014 due to massive weed pressure. Generally, sunn hemp residue management affected kale yield with greater yields measured for mowed and incorporated residue (15054 kg ha-1) compared with lower yields for mowed (6758 kg ha-1) and rolled sunn hemp (5559 kg ha-1). Lower yields were related to poor kale seed-to-soil contact (hair pinning) from large amounts of sunn hemp residue on the soil surface. Over four growing seasons, cereal rye grain yield varied among growing seasons with an average yield of 1358 kg ha-1. Moreover, sunn hemp residue treatments affected grain yield with greater yields for rolled (1419 kg ha-1) and mowed residue (1467 kg ha-1) compared with a lower yield (1187 kg ha-1) for mowed and incorporated sunn hemp residue. Over four growing seasons, average amounts of soil NO3, and NH4 were 25 kg ha-1 and 9 kg ha-1, respectively. Sunn hemp biomass averaged over the growing seasons was 10981 kg ha-1 producing an average total C percentage of 46.5% with an average total N percentage of 2.1%.