Crop Rotation and Tillage Effects on Soil Organic Carbon and Nitrogen

Abstract Sustaining or increasing soil productivity depends in part on soil and crop management practices that maintain or increase soil organic matter. This study was conducted to determine the effects of tillage, crop rotation, and fertilizer N on soil organic C and N. Two long‐term tillage/rotation studies and one long‐term rotation/N‐rate study were conducted on eastern Kansas soils. Soils were sampled from conventional (CT) and no‐tillage (NT) treatments applied to continuous sorghum [ Sorghum bicolor (L.) Moench] (S/S), continuous soybean [ Glycine max (L.) Merr.] (B/B), and sorghum‐soybean (S/B) rotations in the tillage/rotation studies and from the 0 and 252 kg N ha −1 treatments on continuous corn ( Zea mays L.) (C/C), B/B, and corn‐soybean (C/B) rotations in the rotation/N‐rate study. Organic C and N were determined on soils sampled at depths of 0 to 2.5, 2.5 to 7.5, 7.5 to 15, and 15 to 30 cm. Compared with CT, NT had greater organic C and N contents. Compared with B/B, S/B and S/S increased orgnaic C and N under NT and, to a lesser extent, under CT (at 0‐2.5‐cm depth). Increases in organic C and N with NT compared with CT and with sorghum rotations compared with B/B were directly related to the quantity of residue produced and left on the soil surface (S/S > S/B / > B/B). Fertilizer N increased soil organic C and N only slightly. Crop management systems that include rotations with high residue‐producing crops and maintenance of surface residue cover with reduced tillage result in greater soil organic C and N, which may improve soil productivity.