Soil Biochemical Responses of Cover Crops in a Winter Wheat-Summer Fallow System.

Cover crops (CC) influence soil water and biogeochemical cycling of soil organic carbon (SOC) and nutrients in agroecosystems. A study was initiated in spring 2016 at the Agricultural Science Center, Clovis, NM to assess the effect of CC on seasonal dynamics of available Nitrogen (N) and Phosphorus (P), soil water content (SWC) and potentially mineralizable carbon (PMC) under no tillage winter wheat – summer fallow system. Eight CC treatments including fallow (no CC), pea, oat, canola, pea + oat, pea + canola, pea + oat + canola and a six-species (pea, oat, canola, radish, barley, hairy vetch) mixture of cover crops were established. Soil samples were collected from 0-15 cm depth before and different times after cover crop termination. All the samples were analyzed for available N and P, SWC and PMC. There was significant (p<0.05) effect of time on seasonal dynamics of SMC and available N while there was significant time × treatment interaction effects on PMC. The SWC (11.54 % ±0.19) and N (4.24 kg ha^-1±0.46) were significantly lower before CC planting and during CC termination than SWC (16.89 %±0.45) and available (N (25.27 kg ha^-1±0.97) during wheat planting time. The PMC, however was significantly lower during wheat planting. PMC (217.67±8.76, 415.33±5.25) was consistently greater in pea + canola after CC termination and wheat harvesting respectively, followed by its least value (75.05±22.04) during wheat planting. The CC used soil water and available N during their growth period but might have been retained by their residues during wheat planting. Increased PMC might be due to contribution from CC and wheat above and belowground residues while decreased PMC might be due to its utilization for N and P mineralization.