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 revie w of the research on N fertilization management for no-till cereal producti on in the Canadian Great Plains, on mainly Chernozem and Gray soils, was do ne 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 environme ntal 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, cr op and fertilizer management practices. Overall efficiency of applied N has been < 70%. Reducing tillage intensity modifies both the demand of crops f br 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 fo r this by adjusting the fertilizer rate. Fertilizer use efficiency may also change with changes in tillage management, microclimate, microbial activit y and distribution of fertilizer relative to crop residue. Placing the fert ilizer in a band I educes contact with soil microorganisms, reducing immobi lization of both ammonium (NH4) and nitrate (NO3). Banding also slows the c onversion of urea to NH3 and NH4 to NO3, which can reduce losses by denitri fication and leaching. The use of the urease inhibitor n-(n-butyl) thiophos phoric triamide (NBPT) shows promise in improving the efficiency of surface -applied urea-containing fertilizers in no-till systems and reducing seedli ng damage from seed-placed fertilizers. Ultimately, any N fertilization pac kage has advantages and disadvantages. In selecting the optimum fertilizer management system for a farming operation, the balance between rate of appl ication, cost and availability of equipment, soil disturbance, seedbed qual ity, moisture conservation, time and labor constraints and fertilizer use e fficiency must be considered. The "best" management system is not fixed, bu t depends on the major limiting factors on each individual farm. (C), 2001 Elsevier Science B.V. All rights reserved.