Short-term changes in soil carbon and nitrogen pools during tillage management transition

It is well established that distribution of organic C and N within a soil profile is substantially influenced be long-term conversion of soil from plow-tillage to no-tillage management, but little is known about the short-term changes in the character of soil organic matter during transition between these two soil management systems. To characterize the changes in composition of organic C and N pools in soil during tillage transition, we measured total N, organic C, active N, biomass N, and biomass C at depth intervals of 0 to 2.5, 2.5 to 5, 5 to 12.5, and 12.5 to 20 cm within the profile of soil during the first 3 yr in the transition from plow tillage to no tillage. The results obtained showed that transformation of a soil profile from that typical of plow tillage management to one characteristic of no tillage occurred rapidly within a 3-yr period of transition. In this time period, stratification of organic matter in the profile progressed significantly toward that which occurs after 20 yr of no-tillage treatment. For example, substantial increases in total N (30%), organic C (38%), biomass N (87%), and biomass C (33%) were detected in the top layer of no-tillage soil along with corresponding decreases of 6%, 7%, 35%, and 15% of those respective components in the bottom layer. With transition, the biomass C, biomass N, and active N pools increased more rapidly in the upper soil profile than did the total pools of C and N. Although the characteristic profile of no-tillage soil developed quickly during tillage transition, evidence was equivocal for any significant increase in organic matter content within the first 3 yr after conversion to no-tillage management