Potentially Mineralizable Carbon Under Cover Crops: Results of a Field and Laboratory Incubation Study.

Cover crops (CC) may benefit cropping systems by increasing soil organic carbon (SOC) and improving nutrient cycling. A study was initiated in January, 2016 at the Agricultural Science Center, Clovis, NM to assess the effect of CC in improving active soil carbon (C) pools 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-way mix of cover crops were established. Soil samples were collected from 0-15 cm depth after termination of cover crops and analyzed for potentially mineralizable C (PMC). Laboratory study was established with, the addition of 0, 5 and 10 Mg ha^-1 pea, canola, and oat residues. The PMC content was 10-41% greater in CC treatments than in fallow. The PMC content was highest (121 mg kg^-1) under canola and lowest (71.2 mg kg^-1) under fallow. The PMC content was greater with the addition of pea (731 mg kg^-1) and canola (754 mg kg^-1) than with the addition of oat (622 mg kg^-1) residue. The PMC content was significantly greater (1315 mg kg^-1) with 10 Mg ha^-1 cover crop residue addition compared to 695.4 mg kg^-1 with 5 Mg ha^-1 and 96.7658 mg kg^-1 with 0 Mg ha^-1 residue addition. Increased PMC may have been a result of greater C input from CC treatments. The greater input of CC biomass during the fallow period can increase SOC and improve soil fertility status of winter wheat – summer fallow system.