Continuous No-Till Impacts on Soil Biophysical Carbon Sequestration

Increasing C sequestration through no-till (NT) can reduce agricultural CO emissions. However, for long-term NT, information is lacking on the effect of biophysical C pools and processes on C sequestration. Composite soil samples taken at 7.5-cm increments to a 30-cm depth from conventionally tilled (CT) and 2 (NT), 23 (NT), and 44 yr (NT) of NT corn (L.) plots in northwest Ohio were analyzed. The microbial biomass (SMB) was 13, 83, and 86% higher in NT, NT, and NT, respectively, than in CT. No-till had slightly higher basal respiration rates but significantly lower specific maintenance respiration rates and SMB loss than CT. Aggregate stability in NT was 35 to 45% higher than in CT. Macroaggregate-protected C (C) was 24, 80, and 92% higher in NT, NT, and NT, respectively, than in CT. For all tillage treatments, these properties decreased with depth. The C sequestration rates for SMB were 22, 13, 7, and 3 kg ha yr at the 0- to 7.5-, 7.5- to 15-, 15- to 22.5-, and 22.5- to 30-cm depths, respectively for the first 10 yr of NT. During the same time, the C sequestration rates were 92, 63, 47, and 37 kg ha yr at the four depths, and macroaggregate (MaA) formation rates were 3170, 350, 170, and 70 kg ha yr, respectively However, these rates decreased over the 44 yr of NT. By 20 yr of NT, at all depths the C sequestered in SMB reached a plateau. Similarly, C sequestration plateaued at the surface by 20 yr and MaA formation at the surface leveled out by 10 yr.