Influence of land use change and tillage practice on soil organic matter in southern Brazil and eastern Paraguay

Abstract

Agricultural colonisation in eastern Paraguay and adjacent areas in Brazil results in major land use change. Semi-deciduous subtropical forest is replaced by agricultural land use, which along with the type of cultivation technique increases the potential for soil degradation. On a clayey Haplic Ferralsol, the predominant soil in the region, several land use types were selected to study the influence of different tillage techniques on topsoil (0–10 cm) organic matter content. In the winter of 1995 the organic matter content was determined for six situations: (Fo) a natural forest habitat, (CCl) a field that has been cultivated conventionally for 20 years, (CCs) conventionally cultivated for six years, (TC) a traditionally cultivated field, (NT3) a mechanical no-tillage field since three years, and (NT10) a field where mechanical no-tillage has been practised since 10 years. The six research sites are equal in size and have the same topographical position. It was found that the transition from forest to agricultural use leads to a significant decrease of organic matter in the topsoil. Prior to deforestation soil organic matter was 2.09% and 2.42%. Afterwards, it decreased to 1.59% when the soil was cultivated conventionally. Mechanically tilled fields appear to have a more rapid decline in organic matter than manually tilled fields (1.59% vs. 1.89%) suggesting more severe soil degradation. A transition from conventional tillage (using a heavy disk plough and harrow) to no-tillage leads initially to a lower organic matter content of 1.45%. After 10 years a transition like this appears to result in benefits in terms of an increase in soil organic matter content to 1.90%.