Cropping rotations: Effect on aggregate stability and biological activity

Abstract

Growing crops and crop sequences over a period of 14 years leads to changes in soil properties. The effect of nine cropping rotations (wheat/soybean‐maize, wheat/soybean‐soybean, wheat/soybean, wheat‐wheat soybean‐soybean, maize‐maize, sunflower‐soybean, sunflower‐sunflower and soybean‐maize) on bulk density, structural stability, biological activity, and organic carbon (C) was investigated in experimental plots subject to conventional tillage. Type of soil used was a well‐drained Typic Argiudoll, with a silty loam texture and an easily alterable structure by cultivation and rainfall. Bulk density, structural stability and biological activity showed statistically significant differences between treatments, a high correlation between biological activity and stable aggregates was also found. Four of the crop sequences (wheat/ soybean‐maize, soybean‐maize, sunflower‐soybean, soybean‐soybean) were chosen because they represented extreme behaviour patterns as regards the effects of water. For these soil samples, the following fractions of organic C: fulvic acids, humic acids, humins, and light C and water soluble C were determined. The results indicated that maintenance of structure was stable in those sequences which included maize and wheat as opposed to soybean monoculture or soybean‐sunflower combinations.