Long-term straw management and N fertilizer rate effects on crop yield, N uptake and N balance sheet in a Gray Luvisol
A field experiment with barley monoculture (1983-1996), and wheat/barley-canola-triticale-pea rotation (1997-2009) was conducted on a Gray Luvisol [Typic Haplocryalf] loam soil at Breton, Alberta, to assess the influence of straw management (straw removed [SRem] and straw retained [SRet]), N fertilizer rate (0, 25, 50 and 75 kg N ha-1) and N source (urea and polymer-coated urea [called ESN]) under conventional tillage on seed yield, straw yield, total N uptake in seed + straw and N balance sheet. On the average, SRet produced greater seed yield (by 102 kg ha-1), straw yield (by 196 kg ha-1) and total N uptake (by 3.7 kg N ha-1) in the 1997-2009 period for both N sources. There was a considerable increase in yield and total N uptake up to 75 kg N ha-1 rate. The ESN was superior to urea in increasing seed yield (by 109 kg ha-1), straw yield (by 80 kg ha-1) and total N uptake (by 2.4 kg N ha-1) in the 1983-1996 period (mainly at the 25 and 50 kg N ha-1 rates). The N balance sheets over the 1983-2009 study duration indicated large amounts of applied N unaccounted for, ranging from 740 to 1518 kg N ha-1, suggesting a great potential for N loss from the soil-plant system through denitrification and/or nitrate leaching, and from the soil mineral N pool by N immobilization. In conclusion, the findings suggest that longterm retention of crop residue may gradually improve soil productivity.
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