This is because, prior to 1990, these systems received only one preseeding tillage compared to an average of four tillage operations on the fallow-wheat. These results suggest that by curtailing the frequent soil stirring associated with tillage during the fallow period, we severely reduced the amount of N released from organic matter during this period. The resulting lower soil tests led to the greater requirement for fertilizer. The problem does not end with poorer grain yield and likely lower protein. Lower grain yields mean less crop residues.
Crop residues provide the raw materials for building soil organic matter.
It has not done this. It may be that any positive contributions due to increased crop residues are being counterbalanced by greater rates of organic matter decomposition in the more moist soil conditions. Dr. Campbell, Dr. Lafond, and Dr. Zentner are Research Scientists with Agriculture and Agri-Food Canada, located at Ottawa, ON, Indian Head, SK, and Swift Current, SK, respectively.