Soil Carbon, Nitrogen, and Aggregation in Response to Type and Frequency of Tillage

Little information exists on the biogeochemical effects of combining no‐tillage planting with paraplowing (to improve deep water penetration) or with secondary tillage (to control weeds). We determined surface residue and soil C and N pools (total, particulate, microbial biomass, and mineralizable) and water‐stable aggregation at depths of 0 to 25, 25 to 75, and 75 to 150 mm from a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) in Georgia. Soil tillage treatments were a factorial arrangement of tillage type [(i) minimal disturbance with in‐row chisel at planting, (ii) no‐tillage planting with autumn paraplow, and (iii) no‐tillage planting with secondary tillage during the summer] and tillage frequency [(i) every year, (ii) every second year, and (iii) every fourth year]. No‐tillage planting without further disturbance occurred in remaining years. At a depth of 0 to 25 mm, basal soil respiration averaged 9 mg kg ‐1 d ‐1 with conventional tillage, 27 mg kg ‐1 d ‐1 with no‐tillage planting and soil disturbance every year, and 36 mg kg ‐1 d ‐1 with no‐tillage planting and soil disturbance every fourth year. At a depth of 0 to 150 mm, mean‐weight diameter averaged 1.03 mm with conventional tillage, 1.12 mm with paraplow, 1.17 mm with secondary tillage, and 1.23 mm with in‐row chisel. No‐tillage planting with alternative tillage types and frequencies not only improved surface soil properties compared with conventional tillage, but also improved seed cotton yield an average of 19%. Biophysical improvement of surface soil structure would presumably lead to greater water infiltration and improved water use efficiency in the long term.