Nitrogen cycling with oilseed radish cover crop in Indiana crop rotations

Kaylissa A Horton, Purdue University

Abstract

Cover crop interest among Midwestern farmers has greatly increased over the past few years, with a focus on cover crops that can be successfully integrated into corn-soybean rotations. Oilseed radish (Raphanus sativus L.) is receiving attention due to its large fleshy taproot that winter-kills and is excellent at scavenging nitrogen (N) and penetrating deep into the subsoil. Although oilseed radish (OSR) can scavenge large quantities of N in the fall, its rapid decomposition in spring may release N too early for the succeeding cash crop to benefit, thereby allowing N to leach out of the root zone. It was hypothesized that planting OSR in combination with a higher C:N ratio cereal cover crop would tie up N longer in the spring and reduce premature N release. The objectives of this one year study in west-central Indiana were to determine the effects of OSR and OSR bicultures on soil ammonium (NH4-N) and nitrate (NO3-N) concentrations with time and distance from the OSR tuber, soil penetration resistance, and succeeding corn crop N uptake and yield compared to the no cover crop control. The cover crop treatments included OSR (var. Groundhog), OSR/oat (Avena sativa L.), OSR/cereal rye (Secale cereale L.), and a control (no cover crop), and were established on silt loam soils in the fall of 2011. The experimental design consisted of a randomized complete block design with four cover crop treatments and three replicates at each of four sites. Cover crop treatments were established into wheat ( Triticum aestivum L.) or soybean (Glycine max L. Merr.) stubble at a seeding rates of 13 (OSR), 7/31 (OSR/oat), and 7/36 (OSR/rye) kg ha-1. Cover crops that did not winterkill were chemically terminated in late March-early April 2012. Corn was planted after all cover crop treatments on 4 May 2012. Starter fertilizer (39 to 44 kg N ha -1) was the only fertilizer applied in order to look at cover crop N cycling and return to the succeeding corn crop under conditions of low N availability. Bulk soil samples were obtained in the fall and detailed sampling with depth and distance from the OSR tuber was performed in the spring, to observe the timing and pathways of N release. Above- and below-ground biomass was sampled in the fall to observe dry matter accumulation and N content. Soil penetration resistance and soil temperature were measured in the spring to determine the effects of the cover crop treatments on soil physical properties. Nitrogen concentration at two growth stages, V6 and VT, and yield was determined of the succeeding corn crop as affected by cover crop treatment. Cover crop treatment had more of an effect on soil NO3-N concentrations than on soil NH4-N concentrations. Oilseed radish, OSR/oat, and OSR/rye soil NO3-N concentrations were highest at the surface and decreased with depth, while control soil NO3-N concentrations increased with depth. Soil NO3-N concentrations increased with time at the 0-15 cm depth but stayed about the same with time at the lower depths over the March-April sampling period. Soil NO3-N concentrations were also higher closer to the OSR tuber than further away from the OSR tuber. Oilseed radish, OSR/oat, and OSR/rye tended to reduce maximum soil temperatures and increase minimum soil temperatures compared to the control. Cover crop treatment*depth had an effect on soil penetration resistance in the upper 20 cm with OSR generally having a higher penetration resistance than the other three treatments. Corn N concentration at V6 and corn yield was highest in previous OSR plots, with the lowest corn yield in previous OSR/rye plots, possibly due to N release in the OSR plots and N immobilization in the OSR/rye plots.

Degree

M.S.

Advisors

Kladivko, Purdue University.

Subject Area

Agronomy|Soil sciences

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