Long-term tillage, straw management and N fertilizer rate effects on crop yield, N uptake and N balance sheet in a Black Chernozem
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A field experiment (established in autumn 1979, with monoculture barley [1980-1990] and barley/wheat-canola-triticale-pea rotation [1991-2008]) was conducted on a Black Chernozem [Albic Agricryoll] silty clay loam soil at Ellerslie, Alberta, to determine the influence of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [SRem] and straw retained [SRet]) and N fertilizer rate (0, 50 and 100 kg N ha-1 in SRet, and only 0 kg N ha-1 in SRem plots) on seed yield, straw yield, total N uptake in seed + straw (1991-2008), and N balance sheet (1980-2008). The N fertilizer urea was midrow-banded under both tillage systems in the 1991-2008 period. There was a considerable increase in yield and total N uptake up to 100 kg N ha-1 under both tillage systems. On the average, CT produced greater seed yield (by 332 kg ha-1), straw yield (by 323 kg ha-1) and total N uptake (by 6.3 kg N ha-1) than ZT. Compared to SRem treatment, seed yield, straw yield and total N uptake tended to be greater with SRet at the zero-N rate used in the study. The amounts of applied N unaccounted for over the 1980-2008 period ranged from 845 to 1665 kg N ha-1, suggesting a great potential for N loss from the soil-plant system through denitrification, and N immobilization from the soil mineral N pool. In conclusion, crop yield and N uptake were lower under ZT than CT, and long-term retention of straw suggests some gradual improvement in soil productivity.
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