the effects of crop residue management and tillage depth on wheat yield and soil organic matter in corn-wheat rotation

a four - year field experiment (1999-2002) was conducted on a silty clay loam soil at laklak research field of hamedan to determine the effects of crop residue management and plowing depth on soil fertility and wheat yield in a maize-wheat rotation. in this investigation, four corn residue managements were used consisting of 1) stalk shredding by maize stalk shredder 2) stalk shredding by disk  3) stalk shredding by rotivator  4) removal of corn residue and two levels of plowing depth (20 and 30cm). corn residue managements and plowing depths were combined in eight treatments. a factorial experiment based on randomized complete block design was used with three replications. wheat residue were incorporated in soil by plowing to the depth of 20-25 cm in all plots. to evaluate the efficiency of shredding implement, percentage of chopped stalks were calculated. to study the c organic changes, this index was measured in three stages (1-13 apr 1999, 2-17 aug 2000 and 3-12 jul 2002). wheat yield and its components (spike/m2, number of grain per spike and kernel weight) and corn grain yield were determined. the results showed that machine type had significant effect on precentage of chopped stalks. maize stalk shredder had higher shredding content than the other two machines (disk and rotivator). also after four years, incorporation of corn - wheat residue increased c organic about 25% and incorporation of wheat residue and removal of corn residue increased c organic about 16%. it was also found, wheat yield and corn grain yield were not affected by residue management or plowing depth, but wheat yield in 2002 increased about 40% compared to 1999.