Abstract
Application of exogenous N fertilizers provides agronomic benefits but carries environmental liabilities. Managing benefits and liabilities of N-based fertilizers in conventional (CNV) and organic (ORG) cropping systems might be improved with better knowledge of nutrient dynamics, the generation of intrinsic N, and maintenance of soil organic matter. This study evaluated mineral N dynamics, yields, residue inputs, and change in soil organic C (SOC) and total N (TN) in strip-tilled, four-year crop rotations [corn (Zea mays L.)-soybean (Glycine max [L.] Merr.)-wheat under-seeded with alfalfa (Triticum aestivum L./Medicago sativa L.)-alfalfa] over eight years of production under CNV management using mineral-N (NO3NH4) and chemical pesticides or ORG management using organic-N (animal manure) and no chemical treatments. In ORG, N availability increased over time, but did not benefit ORG yields due to poor control of insects and weeds. Corn, soybean, and wheat grain yields were 1.9 to 2.7 times greater in CNV. In general, SOC was lost in CNV but did not change in ORG. Cumulative yield N removals exceeded cumulative fertilizer-N inputs by an average of 78% in CNV and 64% in ORG. These results indicated ORG management supported N availability by generating intrinsic N.
Highlights
Availability and use of N fertilizers, which has increased since the 1960s [1,2], carries environmental liabilities including off-site movement of reactive N that contributes to eutrophication [3]
The primary goal of this study was to build greater understanding of how management, including fertilizer-N source and application rate, impacts C and N dynamics quantified by N availability and mineralization as relative indicators of intrinsic N sources, and soil organic C (SOC) and total N (TN)
Better understanding was achieved by assessing yields, residue production, N mineralization, and soil organic matter (SOM) dynamics
Summary
Availability and use of N fertilizers, which has increased since the 1960s [1,2], carries environmental liabilities including off-site movement of reactive N that contributes to eutrophication [3]. Additional evidence of excess fertilizer use was gleaned from national survey data [5] that indicated fertilizer application rates often exceeded yield removal rates (Appendix A). Management strategies that can sustain crop yields while reducing excess fertilizer application are needed if negative environmental outcomes are to be avoided or mitigated. A viable strategy to reduce fertilizer inputs without compromising yields is to increase intrinsic (i.e., internal) soil N sources by increasing soil organic matter (SOM) [6,7]. Kahn et al [11] and Mulvaney et al [12]
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