Soil health responses to cover crop functional group and richness in semiarid Montana

Despite a plethora of studies on the effects of cover crops on soil health, few published papers have reported the effects of plant functional group and richness on soil health, especially in semiarid regions. We initiated a no-till study in semiarid Montana in 2012 that consisted of Pea (Pisum sativum L.), four two-spp single functional groups (Brassica, Fibrous-rooted, Legumes, and Tap-rooted), four three-functional group mixes, a four-functional group mix (Full), and a summer fallow control (Fallow). Cover crops were terminated with herbicide when pea was at first flower stage, and wheat (Triticum aestivum L.) was grown after each cover crop at three nitrogen (N) rates. After four cover crop cycles, soil in both Pea and Full had greater soil organic carbon (SOC), soil total nitrogen (STN), and potentially mineralizable nitrogen (PMN) than Fallow, but Pea, Full, and Fallow treatments did not differ in infiltration rate, penetration resistance, or soil enzyme activity. There were few differences in soil health parameters between Pea and Full, and among functional groups. Soil in the three-functional group treatments had 20%–35% greater PMN than in the one-functional group treatments (p < 0.05), yet SOC and STN were not affected by functional richness. Nitrogen rate did not affect SOC, STN, or PMN. Concentrations of SOC were weakly related (R² = 0.05–0.14, p < 0.05) with 7-year aboveground biomass returned, suggesting practices that increase residue amounts might be more important to SOC and other soil health parameters than functional group or richness.