Yield trends of wheat – impact of fertilization and legume
A long-term (34-yr) crop rotation experiment being conducted at Indian Head, Saskatchewan, on a thin Black Chernozem with heavy clay texture, was used to assess the influence of fertilizer (N and P), sweetclover green manure, and alfalfa-bromegrass hay on yield trends of hard red spring wheat grown on wheat stubble in rotations of varying cropping intensity. When no fertilizer was applied, yields of wheat grown on wheat stubble trended downwards for fallowwheat- wheat, presumably due to increased soil erosion and declining fertility. Yield trends remained generally constant for unfertilized continuous wheat, perhaps because of less soil erosion. The inclusion of green manure in an unfertilized green manure-wheat-wheat rotation increased the yields of wheat grown on stubble compared to unfertilized fallow-wheat-wheat, but the yield trends were still negative. We speculated that this was because legumes do not provide any P to the system. The unfertilized fallow-wheat-wheat-hay-hay-hay system maintained stubble wheat yields at a generally constant level due to low soil erosion and because the hay-containing system markedly increased N-supplying power of the soil. The addition of N and P fertilizer at rates based on soil tests resulted in a positive divergence in yield trends of fallow-wheat-wheat and continuous wheat systems. We suggest that legumes require added P if they are to sustain crop production in a manner similar to that provided by responsible use of fertilizers.
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