CROP UTILIZATION OF PLACED AND BROADCAST 15N-UREA FERTILIZER UNDER ZERO AND CONVENTIONAL TILLAGE

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Abstract
Growth chamber and field studies were conducted to assess the relative utilization of placed and broadcast 15N-urea by spring wheat. The field studies were conducted on zero and conventional (shallow) tillage systems, of 4-yr duration, located on Chernozemic soils at two locations in Saskatchewan. Placement below the seeding depth in comparison to broadcast application, generally reduced fertilizer N immobilization and increased fertilizer N uptake, recovery, and efficiency. Under moisture stress, placed applications were effective in enhancing dry matter yield and total N uptake. It is concluded that fertilizer N placement for these two contrasting tillage systems should be identical, thus some soil disturbance under zero tillage may be necessary to achieve optimum crop use of applied fertilizer N. The dominant N transformation processes and possible tillage induced differences, in regard to methods of N application, are discussed. Key words: Placed and broadcast N application, N efficiency, N utilization, 15N-urea, zero tillage, soil moisture