YIELD TRENDS ON LONG-TERM DRYLAND WHEAT ROTATIONS AT LETHBRIDGE

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Abstract
Yield trends on fields of dryland wheat rotations established in 1912 at Lethbridge, Alberta were examined to assess the impact on productivity of climatic, genetic, edaphic, and technological changes. Yields and moisture use efficiency have increased since 1963. This increase was more pronounced for crops grown on fallow than on stubble and occurred without the use of fertilizer. Applied N and P enhanced the upward trend particularly when applied to the crop grown on stubble. Yields varied widely from year to year, mainly due to large fluctuations in precipitation; however, no climatic changes were detected that could account for the increase in productivity. Improved cultivars accounted for a small portion of the yield increases. Soil N declined while pH increased over the years. The organic carbon has, after an initial loss, increased steadily. Broadleaf weeds were a serious problem until 1950, but, with the advent of 2,4-D, there was a shift to an increasing problem with wild oat for which there was no effective control until 1961 when triallate became available. This coincided roughly with the beginning of the upward trend in yield. Therefore, we suggest that chemical weed control was the main contributing factor to the yield increases. This control has resulted not only in reduced competition from weeds, but also in better seedbed moisture because fewer cultivations are needed in the spring.

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