Short‐term responses of soil carbon, nitrogen, and microbial biomass to cover crop mixtures and monocultures

Abstract

AbstractIncreasingly, cover crops are being adopted for the purpose of improving soil health, yet the timescale and magnitude by which living annual cover crops might modify soil chemical and biological aspects of soil health is not well understood. At the same time, there is growing interest among farmers in cover crop mixtures due to perceptions that species‐rich cover crop communities will enhance soil health relative to monocultures. In a field experiment in southeast New Hampshire, we investigated how groups of cover crops grown as monocultures and mixtures for specific seasonal niches (winter/spring, summer, and fall) influenced levels of soil nitrogen (N) and carbon (C), microbial biomass carbon (MBC), and nitrogen (MBN). Soils were sampled at cover crop maturity (winter/spring group), and at seeding, mid‐season, and maturity (summer and fall groups). In the winter/spring group, average total soil N ranged from 0.192 to 0.215 mg g−1 dry soil; highest total soil C content was 2.66 mg g−1 dry soil; and average MBC ranged from 304.8 to 387.3 μg C g−1 dry soil. In the summer group soil MBC decreased from 909.5 μg C g−1 dry soil at mid‐season to 644.9 μg C g−1 dry soil at the end of the growth cycle. In the fall group MBC fell and rose over the season in the range of 236.0–808.3 μg C g−1 dry soil. We found little evidence that cover crops influenced soil C and N parameters during the cover crop growth period relative to a weedy control or that mixtures differed from monocultures. MBC and MBN were more influenced by seasonality than the composition or diversity of the cover crop stand.