The impact of crop residue management in irrigated wheat- row crop rotation on crop yield, soil organic matter and aggregate (case study in Isfahan province)

Stubble burning has been a conventional method for wheat residue management for last four decades and caused environmental damages such as air pollution, soil depletion from organic matters and aggregate degradation. This study was aimed to evaluate alternative methods of crop residue management in a rotation of wheat with sunflower and forage corn in Esfahan area. Four treatments for wheat residue management and two treatments for second crop residues were compared in terms of their effects on crop yield and some soil physical parameters in an split plot experiment based on randomized compelet block design for four years. Four treatments of wheat residue management as the main factor were included: 1. Chopping stubble and burring them to a depth of 25 cm by a moaldboard plow and disking (burying method) 2. Chopping stubble followed by a chisel plow to a depth of 20 cm and incorporating the remaining residues to a depth of 10 cm by a rotivator (incorporating method) 3. Leaving residues on the surface as an stubble mulch in a no-tillage system (leaving on the surface) 4. Burning stubble followed by a moldboard plow to a depth of 25 cm and disking (Burning). The two treatments applied for the second crop residues were 1.Collecting and taking the residues out of plot and 2. Leaving the residues on the surface. The results of comparing different methods of wheat residue management showed that the incorporating method has the fastest effect on increasing soil organic matter. This method caused soil organic carbon (O.C.) to have a 20% increase after two years and made a significant difference in soil bulk density after three years. This increase in O.C was due to decomposition of residues and brought about nitrogen immobilization which in turn caused a reduction in yield for first two years of experiment. This method however had no effect on improvement of aggregate stability. Leaving residues on the surface increased the O.C slower and its increase in three years was equal to the increase achieved in two years in corporation method. In this method simptome of nitrogen deficiency was lessened more rapidly and wheat yield reduction occurred for only one year. The most important advantages of this method were its ability in maintaining soil moisture content and moderating soil temperature. This method also showed significant improvement in aggregate stability to other methods. Burying residues to a depth of 25 cm did not cause any reduction in crop yield compared to burning. However, no significant increase in O.C. and mean weight diameter of aggregates were perceived after three years. The two treatments applied in residue management of second crop had no significant difference in crop yield and soil physical parameters. Smallness of amount of second crop residues compared to wheat stubble was the reason that its presence had no significant effect.