Nitrogen fertilization management for no-till cereal production in the Canadian Great Plains: a review

Nitrogen (N) is the nutrient most limiting crop production in all areas of the world and is generally applied to soil in the largest quantity. A review of the research on N fertilization management for no-till cereal production in the Canadian Great Plains, on mainly Chernozem and Gray soils, was done to illustrate the management practices which can be used to optimize the N use efficiency so as to minimize the N loss from root zone and environmental damage. Applied N is subject to loss by volatilization, immobilization, denitrification and leaching in soil and its efficiency of use by plants is governed by soil and climatic factors, fertilizer material, and soil, crop and fertilizer management practices. Overall efficiency of applied N has been < 70%. Reducing tillage intensity modifies both the demand of crops fbr N due to changes in yield potential, and the supply of N due to changes in N cycling and losses. Consequently, it may be necessary to compensate for this by adjusting the fertilizer rate. Fertilizer use efficiency may also change with changes in tillage management, microclimate, microbial activity and distribution of fertilizer relative to crop residue. Placing the fertilizer in a band I educes contact with soil microorganisms, reducing immobilization of both ammonium (NH(4)) and nitrate (NO(3)). Banding also slows the conversion of urea to NH(3) and NH(4) to NO(3), which can reduce losses by denitrification and leaching. The use of the urease inhibitor n-(n-butyl) thiophosphoric triamide (NBPT) shows promise in improving the efficiency of surface-applied urea-containing fertilizers in no-till systems and reducing seedling damage from seed-placed fertilizers. Ultimately, any N fertilization package has advantages and disadvantages. In selecting the optimum fertilizer management system for a farming operation, the balance between rate of application, cost and availability of equipment, soil disturbance, seedbed quality, moisture conservation, time and labor constraints and fertilizer use efficiency must be considered. The best management system is not fixed, but depends on the major limiting factors on each individual farm. (C), 2001 Elsevier Science B.V. All rights reserved.