Nitrogen fixation and productivity of winter annual legume cover crops in Upper Midwest organic cropping systems

Sharon Perrone,Jessica Gutknecht,Alex Liebman,Julie Grossman,Thanwalee Sooksa-Nguan

doi:10.1007/s10705-020-10055-z

Abstract

Legume cover crops can play a valuable role in maintaining and increasing soil quality and nitrogen availability, but are infrequently grown in the Upper Midwest due to short growing seasons with minimal management windows; cold, wet springs; and harsh winters. This study was performed to assess the viability of winter annual legume species in northern climates as a potential source of nitrogen (N) fertility to a 75-day sweet corn (Zea mays convar. saccharata var. rugosa) cash crop in Lamberton and Grand Rapids, MN in 2016 and 2017. Treatments included medium red clover (Trifolium pratense), two cold-hardy ecotypes of hairy vetch (Vicia villosa Roth), a cereal rye-hairy vetch biculture (Secale cereale L., Vicia villosa Roth), cereal rye as a non-legume control, and a fallow weed-free control. Legumes were split into rhizobia inoculated and non-inoculated treatments. Inoculation had no effect on nodulation, biomass production, or N fixation likely due to competition with endogenous rhizobia strains. The rye monoculture and biculture produced the most biomass at all site-years averaging 7.7 and 7.0 Mg ha−1 respectively while the two vetch ecotypes averaged 4.5 and 3.9 Mg ha−1. Both vetch ecotypes contributed among the most nitrogen in all site-years, contributing up to 211 kg N ha−1 from aboveground biomass. Data from natural abundance isotopic approaches indicate that 75% of vetch tissue N in Grand Rapids and 59% of vetch tissue N in Lamberton was derived from atmospheric N fixation, with equal or higher percent fixation of vetch in biculture at all site-years. More studies should be performed to better understand controls on N fixation of legume cover crops in cold climates.

Highlights

Nitrogen is often a limiting nutrient in organic cropping systems (Berry et al 2002)
Growing cool-season legumes such as winter annuals may deliver these benefits while enhancing soil N stocks, with evidence suggesting that winter annual legume cover crops can accumulate enough biomass nitrogen to maintain a warm-season cash crop in various environments (Fageria et al 2005; Parr et al 2011; Tonitto et al 2006)
While winter annual legumes have been successful in other more southern regions of the U.S, the Upper Midwest presents unique challenges, such as: (1) short growing seasons that limit establishment and biomass production; (2) extreme minimum temperatures and variable snow cover leading to winter kill; and (3) wet springs that limit field working conditions

Summary

Introduction

Nitrogen is often a limiting nutrient in organic cropping systems (Berry et al 2002). While winter annual legumes have been successful in other more southern regions of the U.S, the Upper Midwest presents unique challenges, such as: (1) short growing seasons that limit establishment and biomass production; (2) extreme minimum temperatures and variable snow cover leading to winter kill; and (3) wet springs that limit field working conditions Despite these challenges, legume cover crops have been successfully managed in more northern climates for nitrogen delivery to a cash crop (Griffin et al 2000; Lawson et al 2012), yet we lack information about the capacity of legumes to provide supplemental fixed N to cash crops in cold climates

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