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Optimizing Legume Based Nitrogen Fertility for Organic Small Grain Systems

Pickoff, M. A.. 2019.


Legume green manures (LGMs) are a vital source of nitrogen (N) for many organic grain systems. A common practice a mong organic growers in the Northeast and other parts of the U.S. is to undersow a LGM into a small grain, harvest the grain crop, and terminate the LGM stand in late fall by moldboard plowing. While fall plowing offers excellent LGM kill, growers increasingly seek an alternative termination method that reduces tillage intensity and bare winter soil. This study, performed at three sites in Maine and Vermont, evaluates three LGM termination methods for kill efficacy, winter soil cover, spring soil conditions, and N uptake and yield of a subsequent test crop of hard red spring wheat (Triticum aestivum L., var. Glenn). The experiment was a split-plot randomized complete block design, with green manure treatment as a split-plot factor and termination treatment as a main plot factor. A no-clover check treatment and a red clover (Trifolium pratense L., var. Freedom) treatment were established as an intercrop with spring barley (Hordeum vulgare L., var. Newdale) and terminated in late fall by moldboard plowing (PL), skim plowing (SK), or undercutting (UC). An additional termination treatment, winterkill (WK), was evaluated at one site. SK, UC, and WK increased soil cover relative to PL, though UC resulted in low red clover kill efficacy, and is in need of improved design. Early and mid- season plant N uptake in the wheat test crop was higher following PL and SK than UC in Maine, though yield was unaffected by termination method. Grain crude protein following PL was higher than UC in two of three sites, indicating a more favorable delivery of N