Role of Soil Total Nitrogen and Organic Carbon Accrual in Affecting 15n Fate to Grain Corn Comparing Long-Term vs. First-Time vs. No Cover Cropping

Abstract

Long-term use of cover crops (LTCC) increases soil organic matter (SOM); however, the effect of CC duration on nitrogen (N) uptake by subsequent crops remains unclear. We hypothesized greater N uptake by grain corn (Zea mays L.) with LTCC, due to both CC decomposition and LTCC-induced greater mineralization of particulate- and mineral-associated OM (POM and MAOM). Cover crops were grown for the first time on a sub-set of no-CC control (NOCC) plots to facilitate comparisons among LTCC, first-time CC (FTCC), and NOCC. We applied 15N (12 kg N ha–1) in microplots after CC emergence and traced into CC, corn, and soil (0–90 cm depth). During CC season (late fall and spring before corn planting), LTCC and FTCC had about 1.5 to 2 times greater total 15N recovery in CC biomass and soil, compared to NOCC where only 30% of 15N applied was accounted for, indicating both LTCC and FTCC are equally effective at reducing potential overwinter N losses. At corn harvest, LTCC and FTCC had approximately ten times greater 15N recovered in soil than in corn biomass, indicating CC-scavenged N likely contributed more to soil organic N retention than soil inorganic N supply to subsequent crops. Moreover, structural equation modeling found that POM was positively related to soil mineral N content and corn yield, while MAOM was not, in this sand-dominated soil. Overall, our study demonstrated cover cropping improved N availability to subsequent crops by taking up residual N (reducing N losses) and building SOM in the long-term.

Keywords: catch crops, service crops, nutrient cycling, isotope labeling, best management practices, climate-smart agriculture