Interseeded Cover Crop Effects on Dynamic Indicators of Soil Health.

Interseeding cover crops into corn provides an opportunity to increase soil organic matter and improve soil health. Soil health indicators were measured in 2015-17 on three field sites in southern Ontario, Canada, after grain corn was interseeded at V5 with annual ryegrass (ARG), red clover (RC) and an ARG/RC blend (MIX). Cover crop treatments and a no-cover control were arranged in a RCBD and replicated four times at each field site. Soil samples (0 – 15 cm) were collected at grain corn harvest and in the spring following cover crop termination. Cover crop biomass yields at grain harvest and before winter (mid-late Nov) varied among sites and ranged from 4.2 to 395 kg ha^-1 for ARG, 21 to 626 kg ha^-1 for RC, and 11 to 245 kg ha^-1 for MIX. There were no statistically significant changes in soil microbial biomass (SMB), basal respiration (BRESP), β-Glucosidase and dehydrogenase enzyme activities, particulate organic matter, and potentially mineralizable N due to cover crop treatments in the fall or subsequent spring. However, there were moderately weak correlations between fall cover crop biomass and spring BRESP (r = 0.40), and between SMB-C and cover crop C/N ratio (r = 0.48) or N content (r = 0.43). Overall, soil health indicator measurements were more dependent on the site year; thus, other factors (e.g. soil type, precipitation, or temperature) were potentially more influential than cover crop treatments in this study. These findings suggest the need for more frequent sampling to capture temporal changes when investigating cover crop effects on dynamic soil properties. Also, cover cropping may require longer periods to produce detectable effects even on sensitive parameters under field conditions. Detailed results for four site years and additional indicators such as the flush of CO₂ on rewetting and microbial community C utilization profiles will also be presented.