Does potentially mineralizable nitrogen predict maize yield in newly cropped soil?

Abstract

Fallow soils converted to crop use have unpredictable soil organic nitrogen (SON) availability during the growing season, which incentivizes over‐applying fertilizer N by way of compensation. Potentially mineralizable nitrogen (PMN) is a soil health indicator, and its increase is a management strategy to meet crop N demands. How well does PMN predict yield in transition, periods from fallow to crop, especially when conservation practices are imposed simultaneously? In a short‐term study, conducted in Madison County, Kentucky (37.85 N, 84.29 W) from 2015 to 2017, we tested the hypothesis that implementing conservation practices (use of cover crops and manure) during the transition period would mitigate adverse effects on N availability by increasing PMN and significantly benefit maize (Zea mays L.) grain yield. Six treatments were used: (a) an unamended control; (b) cover crops; (c) horse manure; (d) cover crops and horse manure; (e) chemical fertilizer; and (f) cover crops and chemical fertilizer. Soils were sampled after cover crop termination, before manure or fertilizer application in spring, and at fall harvest each year and analyzed for PMN. The seasonal PMN and maize grain yield were influenced by cover crops and manure (p < .05). Maize grain yield had a positive response to cover crops but not manure. The correlation between PMN and grain yield, though positive, was very weak (R2 = .03). We conclude that conservation practices, particularly cover crops, in the transition period can benefit PMN and crop yield, but PMN is not a good predictor of yield during transition stages.

How Much Margin Is Left for Degrading Agricultural Soils? The Coming Soil Crises

“…Cover cropping entails using vegetative crops (e.g., mixes of legumes and grasses) to prevent soil erosion, suppress weeds, and provide nitrogen to subsequent cash crops [84]. Cover crops have the potential to sequester carbon below ground, but the amount and type of residues produced by plants place a strong control on SOC storage [85]. Studies have shown higher rates of soil carbon sequestration on former croplands when planted with diverse mixtures of grass and legume [86,87].…”

“…Over the past two decades, advances in soil conservation practices, cover cropping, and other improved soil amendments have demonstrated the potential to improve degraded soils, especially of marginal lands. However, as recent reports have noted, these exciting advances in knowledge have not widely penetrated farmers' practices [82,84,85]. While there are some exemplary programs (e.g., NRCS cover crop initiatives in the United States), the wide-scale changes needed to bolster wider adoption have yet to be materialized [107].…”