Effects of crop residue in conservation tillage systems on soil quality and crop productivity
No-tillage systems have not worked very well for corn which is a problem as corn is commonly used in a rotation with wheat and soybean. Furthermore, when corn follows winter wheat there may be an additional problem associated with residue management during the early stages of corn growth. The objectives were to determine the effects of no-tillage systems on soil physical, biological and chemical properties and to identify the problems associated with planting corn into wheat stubble. Treatments included conventional versus no tillage both with and without red clover in a wheat-corn-soybean rotation in a clay loam soil. Results have been reported for the corn year of the rotation. No-tillage treatments improved soil structure and when red clover was included further improvements occurred. No-tillage treatments increased soil water content and reduced soil temperatures by 2-3 degrees Celsuis in June. Soil drying occurred along the planting slot of the no-tillage treatments which enabled the soil seed furrow to open and the corn seedling to become water stressed, even though the no-tillage treatments were wetter in the spring. The net result was that the corn in the no-tillage treatment (without red clover) was significantly delayed (emergence and early vegetative growth) and was never able to catch up to the corn in the conventional tillage treatments. The soil respiration rates were 30% greater in conventional tillage than no-tillage treatments. Hence, residue decomposition was considerably greater with the conventional tillage treatments. The no-tillage treatment (without red clover) had lower corn grain yields than the conventional tillage treatment in all three years of the study. However, in both 1994 and 1996, when red clover was included in the crop rotation, corn grain yields in the no-tillage treatment were similar to conventional tillage treatments. Red clover improved soil structure and accelerated the decomposition of the crop residue which contributed to the yield improvement in the no-tillage treatments. A weed species shift from predominantly summer annuals to winter annuals and perennials was evident in the early stages of the switch to no-tillage on this clay loam soil. The presence or absence of red clover in rotation did not have a substantial impact on the number and types of weeds found. In summary, the combination of no-tillage and under-seeding red clover in a winter wheat -corn-soybean rotation worked very well for improvements in soil structural and microbial biomass C which resulted in increased corn grain yields and profitability. The no-tillage treatments with red clover had lower amounts of straw residue on the surface which also improved corn germination and emergence compared to the no-tillage treatment without red clover. When red clover was not included, the wheat straw residues insulated the soil surface which led to wetter and cooler soil conditions and reduced grain yields. No-tillage practices have to be modified by using techniques such as cover crops to ensure long-term soil quality and improved crop productivity on these poorly drained soils in southern Ontario. Additional research to enhance cover crop establishment, growth and management in a wheat crop would also ensure an improvement in soil quality under no-tillage conditions. Further, zone tillage systems should be investigated as they may improve seed bed conditions in the seed row while maintaining the benefits of no-tillage between corn rows.