Managing an annual legume green manure crop for fallow replacement in southwestern Saskatchewan
Date
2003-02-18
Authors
Zentner, R.P.
Campbell, C.A.
Biederbeck, V.O.
Selles, F.
Lemke, R.
Jefferson, P.G.
Gan, Y.
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Abstract
Some scientists have suggested that in the Brown soil zone an annual legume green manure crop
(GM) could be used as a partial-fallow replacement to protect the soil against erosion and
increase its N fertility, particularly when combined with a snow trapping technique to replenish
soil water used by the legume. We assessed this possibility by comparing yields, N economy,
water use efficiency, and economic returns of hard red spring wheat (W) grown in rotation with
Indianhead black lentil (i.e., GM-W-W) vs. that obtained in a F-W-W system. Further, we
assessed whether a change in management of the GM crop (i.e., moving to earlier seeding and
earlier turn-down) was advantageous to the overall performance of this practice. The study was
conducted over 12 years (1988-99) on a loam soil at Swift Current, SK. (wheat stubble was left
tall to trap snow, tillage was kept to a minimum, and the wheat was fertilized based on soil tests).
When examined after 6 years, the results suggested that by waiting for full bloom of the legume
(usually late July or early August) to maximize N2 fixation, soil water was being depleted to the
detriment of yields of the following wheat crop. However, the change in management of the GM
crop since 1994 has resulted in wheat yields following GM equalling those after fallow. It also
produced a significant increase (after one rotation cycle) in grain protein and N yields of aboveground
parts of wheat in the GM-W-W compared to the F-W-W system, and lead to a gradual
decrease in fertilizer N requirements of wheat in the GM system in the last 6 years. These
savings in N fertilizer, together with savings in tillage and herbicide costs for weed control on
partial-fallow vs conventional-fallow areas, and higher revenues from the enhanced grain
protein, more than offset the added costs for seed and management of the GM crop. Thus, our
results imply that, with proper management and given sufficient time, an annual legume GMcereal
rotation is a viable option for area producers.
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Part Of
Soils and Crops Workshop