Straw removal and fertilization on grain yields and soil organic matter in a fallow-wheat-wheat rotation
There is considerable interest being shown in the harvest and use of straw for industrial purposes in Manitoba and Alberta. In 1987 we measured soil C and N in a 30-year crop rotation experiment at Indian Head. Results at that time suggested that harvesting straw two in three years from a properly fertilized fallow-wheat-wheat system did not deleteriously influence soil organic matter. Our calculations in 1987 were based on a “volume basis”. Recently, some scientists have suggested that such calculations can sometimes lead to inaccurate interpretations. They suggested that calculations based on an equivalent mass basis would be more accurate. Consequently, we re-sampled this experiment in 1996 and made calculations using both volume and mass basis. We concluded that the latter may indeed provide more meaningful results. In contrast to the results with the volume analysis the equivalent mass analysis suggested that the harvesting of straw has resulted in a strong tendency for soil C and N to decrease over the years. This implies that the practice of harvesting and using straw for industrial purposes will have negative consequences for soil conservation in the long run. To date, soil degradation due to straw removal has not been reflected in grain yields. This study also showed that soil organic N was increased by fertilizer, and organic C tended to be increased. There was a close association between organic C and N and estimated crop residue (straw and roots) input into soil when the calculations were made on mass basis, but not when calculated on a volume basis. Grain yields of the unfertilized system is gradually decreasing, reflecting the gradual soil quality degradation of this system.
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