Soil Uses During Two Sugarcane Growth Interval Periods.

The use of different crops between two sugarcane growth periods can improve soil aggregation, increasing the potential yield of the following growth period. The objective of the present work was to evaluate the aggregate stability index (ASI) at the 0 - 0.10, 0.10 - 0.20, 0.20 - 0.40 and 0.40 - 0.60 m depth and mean weight diameter (MWD) at the 0 - 0.10, 0.10 - 0.20 m depth of a clayey Red Oxisol (clay content = 450 g kg^-1). The soil was submitted to two soybean (Sb) growing seasons, with different crops (sunnhemp (Sh) and millet (Mi)) between them, during two sugarcane (Sc) growth interval periods. The experiment took place in Brazil (21°14’05” S, 48°17’09” W). The randomized block design was used with three treatments (Sc/Sb/Sh/Sb/Sc, Sc/Sb/Mi/Sb/Sc and Sc/Sb/fallow/Sb/Sc) and five replications. Soil samples were taken at three different times: before the first soybean growing season (October/2008), after the second soybean growing season and before planting sugarcane (February/2010) and after the first sugarcane harvest (June/2011). Comparing the effects of crops, there were not differences of ASI values over time. However, MWD values obtained on February/2010 were higher after millet than those observed after fallow. Besides, fallow between two soybean growing seasons promoted decreasing of the MWD. The soil management adopted between two sugarcane growth periods increased ASI in all layers. ASI values on June/2011 were lower on all layers, probably due to the intensive pre-planting tillage before sugarcane was planted. The results showed that: 1) leaving land uncropped during two sugarcane growth interval periods causes decreasing on soil aggregation; 2) although crops between two sugarcane growth periods can improve soil aggregation, the tillage operations for sugarcane planting reduce soil aggregate stability.