Crop-Pasture Rotation and Tillage Effects on Physical Properties of Mollisols at Balcarce, Argentina.

Sustainability of agriculture depends on how management practices affect soil properties. The aim of this work was to evaluate the effect of different combinations of crop-pasture rotations (100% cropping; 50% cropping-50% pasture; 75% cropping-25% pasture) and tillage systems (no tillage (NT); conventional tillage (CT)) and a continuous pasture control on aggregate stability, bulk density (BD), and mechanical resistance (MR) of the arable layer at Balcarce, Argentina (37º45’S; 58º18’W). Soil was sampled in 2000, 2003 and 2006 in a long term experiment started in 1976 on a complex of Typic Argiudoll and Petrocalcic Paleudoll. Bulk density was lower under crop-pasture than under continuous cropping systems, independently of the tillage system (1.06-1.33 Mg m^-3 for 0-5 cm and 1.14-1.33 Mg m^-3 for 0-20 cm). On the other hand, MR was higher either under NT or pasture than under CT (0.11-1.28 for CT and 0.11-1.97 Mpa for NT for 0-20 cm). There has not been evidence of effect of higher BD and MR values on grain crop (wheat, soybeans, corn) growth and/or yield. Aggregate stability index (ASI) fell with cropping after pasture, but at a lower rate under NT than under CT. Three years under CT-cropping reduced ASI from about 100 to approximately 35-40 and remaining constant afterwards. Twelve years under NT after 18 yr of continuous CT-cropping did not lead to a recovery of the ASI showing values not differing of those under continuous CT-cropping for 30 yr. A 3-year pasture in the rotation after either NT- or CT-cropping increased ASI up to values similar to the control (≈90). A short pasture was an effective strategy to recover soil surface physical condition after cropping but NT was not. No tillage after pasture showed effectiveness only to reduce ASI decrease rate. However, cropping system effect on soil physical properties was not yield limiting.