Influence of No-Till System on the Distribution of Organic Carbon and Nitrogen by Aggregate Size Fractions in Protocalcic, Endocalcic, and Pantocalcic Chernozems

— The specific features in accumulation and distribution of organic carbon and nitrogen in the aggregates of typical, ordinary, and southern chernozems (Protocalcic Chernozems, Endocalcic Chernozems, and Pantocalcic Chernozems, respectively) during the transition from conventional farming to a no-till system are evaluated. For this purpose, the contents of organic carbon and nitrogen were determined in different aggregate size fractions (>10, 10–2, 2–1, 1–0.25, and <0.25 mm). All three chernozem subtypes differ in the content of organic carbon in a statistically significant manner. The carbon content in all no-till chernozems is higher as compared with the control (conventionally tilled chernozems). The no-till and conventional variants display no statistically significant differences in the nitrogen content. However, the nitrogen content statistically significantly depends on the aggregate size in no-till variants in contrast to conventional farming. In Protocalcic Chernozems, the higher nitrogen content is observed in all agronomically valuable aggregate size fractions (10–0.25 mm); in Endocalcic Chernozems, in the fractions of 2–0.25 mm; and in Pantocalcic Chernozems, in the fractions of <0.25 mm and 2–1 mm. In addition, characteristic of no-till Endocalcic Chernozem is the dependence of carbon content on the aggregate size. The use of no-till system significantly changes the transformation patterns of soil organic matter and biological activity in chernozems.