Soil Aggregates and their Associated Carbon and Nitrogen Content in Winter Annual Pastures

Winter annual pastures are traditionally established using traditional tillage (TT) on grazing areas that are steeply sloping and not suitable for row-crop production. This leads to increased erosion and rapid soil degradation. The objectives of this study were to determine the effects of tillage intensity on water-stable soil aggregates (WSA), their C and N content, and soil bulk density (BD). The study consisted of three tillage treatments; TT, disk tillage (DT), and no-tillage (NT). Total WSA was greater in the 0- to 5-cm soil layer than the 5- to 10-cm layer for the DT and NT treatments, but was similar in the IT treatment. Mean WSA in the four largest aggregate size classes was greatest in the 0- to 5-cm soil layer but similar for both sample depths in the smallest size class. As aggregate size decreased, relative aggregate content at the toeslope position increased. For all tillage treatments and soil depths, mean WSA decreased from the largest size class (>4 mm) to the next size class (4-2 mm), and increased thereafter as aggregate size decreased. Soil BD was unaffected by tillage treatment. Water-stable aggregate C and N content and weights were equivalent in the DT and NT treatments and greater than the IT treatment. Winter annual grass production using DT or NT practices is a viable means of maintaining or enhancing soil quality.