Bicultures of oat (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.) cover crops increase contents of carbon pools and activities of selected enzymes in a loam soil under warm temperate conditions

This study evaluated effects of oats (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.), bicultures, in rotation with summer maize (Zea mays), on soil organic matter fractions and activities of selected enzymes. The trial was initiated in April 2009. The treatments were 100% oat, 100% vetch, 90% oat + 10% vetch, 70% oat + 30% vetch, 50% oat + 50% vetch, and weedy fallow, in a randomized complete block design (RCBD) with three replications. Soil samples were collected in October 2011, from the 0-5 and 5-20 cm depths, and analyzed for total carbon (C), particulate organic matter (POM), water-soluble carbon (WSC), microbial biomass carbon (MBC) and activities of selected enzymes. Total C was higher in bicultures, particularly the 70% oat + 30% vetch, and 100% vetch than in 100% oats and the control. The greatest MBC, WSC, dehydrogenase, aryl-sulphatase and phosphomonoesterase activities were in the 70% oat + 30% vetch biculture, and declined where the proportion of oats or vetch was higher. Increasing proportions of vetch resulted in increases in urease and beta-glucosidase activity and decrease in POM. The findings suggested that, in addition to increased maize yields, bicultures of oats and vetch also have synergistic effects on soil carbon pools and enzyme activities, with potential benefits of improved soil physical condition and nutrient cycling compared with the individual crops, under warm temperate conditions.