Radish and annual ryegrass alter corn yield response to nitrogen rate

Abstract

Fall‐planted cover crops are a strategy for scavenging residual reactive N. In the northern U.S. Corn Belt, the short growing season continues to limit adoption of cover crops. Planting cover crops following wheat (Triticum aestivum L.) in a three‐crop rotation (wheat [cover crop]–corn [Zea mays L]–soybean [Glycine max L. (Merr.)]) increases establishment time. Two cover crops noted for N scavenging, annual ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) and radish (Raphanus sativus L. ‘Tillage’), were selected. We hypothesized that corn yield could be maintained with less N fertilizer when following a cover crop compared with no cover crop as determined by direct comparison and regression analyses. The study was repeated 3 yr and had three cover crop treatments: annual ryegrass, radish, and the no‐cover‐crop control. A second treatment, factorially applied in corn years, was N application rates relative the recommended rate of 0× (0 kg N ha–1), 0.25× (39–48 kg N ha–1), 0.5× (78–95 kg N ha–1), and 1× (157–190 kg N ha–1). When cover crops were planted after wheat, about 60 kg N ha–1 yr–1 was measured in the roots and shoots of radish and annual ryegrass, representing 35 or >60% of the inorganic N in the soil. Corn yield averaged 5% higher following radish and 13% lower following annual ryegrass compared with the no‐cover control. Both cover crops scavenged residual N, but neither cover crop treatment supported the hypothesis that corn yield could be maintained with less N fertilizer compared with no cover crop.

Cover crop and nitrogen rate management practices influence corn NDVI and nitrogen content

“…Although root biomass was measured, rather than root length or root length density, increased root growth at 0.5× treatment suggests that other root function related to uptake of water or other nutrients might have been improved at this N rate relative to others. The shift in root biomass and related function might also contribute the observation that corn yields at the 0.5× N rate were similar to or higher than the 1× N rate (Johnson et al., 2021).…”

“…The average monthly precipitation from long‐term averages (1981–2000) and during the current experiment years from 1 Jan. 2012 to 12 Dec. 2016 (collected by an onsite weather station) are described in Johnson et al. (2021).…”

“…Several baseline soil measurements were made prior to cover crop planting for each study year, as previously reported by Johnson et al. (2021) (Supplemental Table S2). Total C stock in the surface 30‐cm soil was 131.8 Mg ha −1 , 123.3 Mg ha −1 , and 131.9 Mg ha −1 in fall 2012, 2013, and 2015, respectively, prior to cover crop planting.…”

“…Radish (Raphanus sativus L.) has been shown to effectively trap residual fall N and have mostly neutral effects on inseason plant-available N in Wisconsin, USA (Ruark et al, 2018). In contrast, our previous research in west central Minnesota, USA indicated that radish could increase corn yields (Johnson et al, 2021). However, corn nutritional status throughout the growing season has not been evaluated in the northern Corn Belt with cover crops.…”

“…One study in southern Ontario found that red clover ( Trifolium pratense L.) provided a yield benefit to subsequent corn, but oilseed radish, oat ( Avena sativa L.), and rye ( Secale cereale L.) did not (Vyn et al., 2000). Comparisons of corn yield following spring wheat among N rates and cover crop treatments have previously been reported (Johnson et al., 2021). Averaged over 3 yr, cover crop (estimated marginal mean [unadjusted pairwise comparisons of least squares means from diff in the LSmeans statement in SAS at P < .5]; no‐cover control = 7.8[b], annual ryegrass [ Lolium perenne L. ssp.…”