Short-term effects of cover crop incorporation on soil carbon pools and nitrogen availability

Winter cover crops are increasingly used to maintain water quality and agoecosystem productivity. Cover crop incorporation influences transient soil microbial dynamics and nutrient availability at an early growth stage of subsequent crops. Short-term (less than or equal to 35 d) effects of cover crop incorporation on soil C pools and N availability were evaluated using sandy loam soils from organically and conventionally managed fields. Field and incubation experimeuts were designed to investigate whether cover crop incorporation had differential effects on C pools and how they were related to N mineralization. Labile C pools (soil carbohydrates and soil microbial biomass C [SMBC]) and coarse organic debris (GOD) increased two- to threefold, whereas total organic C increased by only 20% by Day 7 after incorporation, The COD decreased faster than other C pools and best predicted SMBC (P < 0.0001), A rapid decrease in SMBC after Day 21 was accompanied by an increase in available N. Discriminant analyses revealed that organic soils were distinct from conventional soils by their higher total C, N, and SMBC, and lower available N, but cover crop incorporation obscured the distinction in the first 14 d. Residue decomposition was Slightly faster in organic soils than in conventional soils at the early stage (3-4,vk), but >30% of N in cover crop residues was mineralized in both soils by Day 35 after incorporation, suggesting that manipulations of soil microbial dynamics and N mineralization in the short term can be of particular significance in synchronizing N release with the need of subsequent crops.