CROP RESIDUE MANAGEMENT FOR IRRIGATED CEREALS ON THE SEMIARID CANADIAN PRAIRIES

Cereals grown under irrigated conditions in the Canadian prairies produce large amounts of residues and proper management of these residues is required to produce good crop yields and maintain soil quality. Field studies from 1986 to 1990 assessed the effect of straw-tillage treatments on plant growth of irrigated cereals on a Dark Brown Chernozemic Lethbridge (Typic Boroll) loam in southern Alberta. The crop sequence was wheat (Triticum aestivum L.)-wheat-oats (Avena sativa L.) wheat. Straw was retained on the plots or removed by baling. Tillage treatments were autumn mouldboard ploughing, spring mouldboard ploughing or direct seeding. Grain yield was greater in the autumn plough compared with the spring plough treatments (4336 kg ha-1 vs. 3763 kg ha-1, respectively) in 1 year (1989) out of 4. Grain yield was greater in the no straw-spring plough than the straw-spring plough treatment (4242 kg ha-1 vs. 3791 kg ha-1, respectively) in 2 years out of 4. Spring plough treatments had the advantage of ground cover over winter compared with autumn plough treatments. The problems associated with straw incorporation in the spring could be alleviated by removing the straw by baling but this practice removed 16.0 kg N ha-1 year-1 and 1600 kg C ha-1 year-1 from the soil system. Grain N concentration was decreased by 10% if straw was incorporated in the spring compared with autumn incorporation. Straw N concentration was decreased with spring ploughing compared with autumn ploughing when straw was incorporated and also when straw was removed by bailing. Total plant N was decreased by spring ploughing compared with autumn ploughing if straw was incorporated. Incorporation of straw also decreased total plant N compared with removing the straw with spring but not with autumn ploughing. Under a no straw-direct seeding treatment, grain yield and plant N uptake were generally less than in the no straw-tillage systems. Straw-tillage treatment effects on grain yield and plant N uptake were attributed to differences in seedbed quality and mineral N levels. Lower spring and autumn soil NO3-N levels in the straw-spring plough and direct seeding treatments throughout the 4 crop years were attributed to great N immobilisation compared with the autumn plough and no straw-spring plough treatments. This field study showed that although spring incorporation of straw and direct seeding treatments encountered seedbed problems and lower N availability, these treatments with added N could be as productive and be more sustainable systems than other treatments as they enjoy advantages in terms of better soil conservation and less harmful environmental impact.