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T.J. Vyn, Department of Crop Science, Ontario Agricultural College
Winter wheat is similar to most small grain crops in that it can be successfully established on fairly coarse seedbeds. Uniform plant establishment is not critical with winter wheat since wheat plants can compensate adequately for most gaps because of their ability to tiller. Decisions concerning the type and amount of tillage operations required prior to seeding should be based on the effects of various tillage systems on timeliness, cost, soil erosion potential and final grain yield.
Unfortunately, almost all of the research effort on tillage systems in Ontario has been for corn rather than cereal crops; very little research information is available to help assess various approaches for winter wheat. Also, because crop response to tillage varies so dramatically with climate and soil type, field research results from Europe, the United States or even western Canada are of very little value for Ontario. With corn we have found appreciable differences between our tillage results and those of the south-eastern United States or even Ohio. Therefore, while several research and extension personnel may be endorsing the concept of direct drilling (zero tillage) for winter cereals in England or the Western United States, there is little likelihood that their results would be transferable to Ontario conditions.
The success of zero tillage or other mulch-tillage systems for cereal production in the prairies of Canada and the United States can largely be attributed to increased conservation of soil moisture, a factor which is usually not as critical in Ontario. Although winter wheat production in the Canadian prairies is primarily restricted to south-western Alberta, where the winter is comparably mild, survival of this crop on the rest of the prairies may be improved if seeded directly (zero tillage) rather than conventionally. Standing stubble would tend to trap more snow which, in turn would help protect the crop from killing frosts.
Although there is no comparable information available for winter wheat in Ontario, Prof. G. Anderson (Crop Science Department) found that yields for spring grains were reduced at least 10% if zero tillage was used in place of conventional tillage (moldboard plow plus secondary). The major difficulty encountered with the zero tillage system was the increased presence of perennial weeds whether the spring grains where grown continuously or in rotation with alfalfa.
If wheat crops are grown consecutively on the same field, phytotoxic injury may also occur to young wheat seedlings if the straw residues of previous crop have not been incorporated. Recent evidence from the United States and England suggests reduced yields of wheat grown directly in wheat stubble compared with clean cultivation, in all likelihood due to the release of phytotoxic chemicals from decomposing straw. Phytotoxic injury only occurs if the wheat seed and/or seedling is in very close proximity to the straw. Pest problems may also arise if all straw residues are left on the surface. It is not known whether these same conditions are likely to occur under Ontario conditions. Nevertheless, in those situations where winter wheat does follow winter wheat, at least partial incorporation of the residue is advisable.
In Ontario, however, winter wheat most often follows a rowcrop (usually soybeans or whitebeans) in a rotation. In 1978, a survey of tillage and related crop management practices was conducted on 150 farms (46 of which grew winter wheat) in the Counties or Regional Municipalities of Elgin, Oxford, Haldimand, Wellington, Durham, Dufferin and Grey. Fully 90% of the winter wheat produced on the surveyed farms followed a row crop, while the remaining 10% of the winter wheat followed forage crops in a rotation. Furthermore, the majority (67%) of the winter wheat was sown on land which had been moldboard plowed, 2% of the wheat was sown on chisel plowed soil and 31% of the wheat acreage was on land which received no primary tillage other than tandem discing (usually twice) in the fall. However, there was considerable discrepancy among the survey regions. In Elgin County 77% of the winter wheat acreage was prepared only by tandem discing; this practice was also common in Oxford and Haldimand, but not in other areas. Where the land had been moldboard plowed, an average of 4 secondary tillage operations were completed prior to seeding. In the survey regions other than Elgin County, winter wheat received proportionately more secondary tillage than other field crops.
In our view, the tillage practice which is already prevalent in the south-western part of the province should be extended to the other winter wheat growing areas. Winter wheat can be successfully established on bean stubble following a single pass with a tandem disc. Such minimal tillage is possible, in part, because the soil has frequently been observed as being looser or more "mellow" after a crop of soybeans. The advantages for such a tillage system would include reduced energy consumption as well as earlier seeding, a factor which is very important to the successful production of winter wheat. Late harvesting of the previous crop only makes timeliness of tillage and seeding operations that much more critical. A few farmers who grow winter wheat after soybeans in Central Ontario have experimented with aircraft seeding of winter wheat just prior to leaf senescence of soybean fields. This practice has also met with considerable success.
If moldboard plowing is deemed necessary, we feel that there is little advantage in performing more than one secondary tillage.
Tillage depth is also important. Regardless of the soil type, there is no crop yield advantage to deep tillage. Increased depth merely increases draft requirements, energy consumption and tillage time. Excessive depth is particularly deleterious if the soil moisture content below the surface is fairly high. Tillage depth should be kept to the minimum required to create an acceptable seedbed. Tandem dishing need not be deeper than 5 to 8 cm.
Furthermore, unless winter wheat is already grown in rotation with hay crops, consideration should be given to the interseeding of red clover when the nitrogen is applied in the early spring. Winter wheat alone already results in improved aggregate stability of the surface soil when compared to other cereals or row crops. However, the inclusion of red clover as a plow-down crop would result in further improvements in soil structure, particularly in aspects such as soil drainage and aggregate stability, as well as soil fertility. This practice is already popular in the south-western part of the province. In the survey referred to earlier, 53% of the wheat acreage in Elgin was interseeded with forage legumes intended for autumn plow-down.
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