Performance Story: Effects of Vertical Tillage on Soil Structure and Crop Yields in Southern Saskatchewan
Research questions: The accumulation of crop residue at the soil surface can interfere with field operations like seeding, negatively affecting germination and emergence and hence crop yield. Vertical tillage and tandem disc implements are used to manage residue and alter soil physical conditions, mainly at the soil surface. Also, raking and burning is used as an alternative for management of difficult crop residues such as flax straw. It is hypothesized that the approach to managing flax residue (tillage, raking and burning) will directly influence surface soil physical properties and yield of following crops.
The objective of this study was to evaluate and compare the effect of surface vertical tillage, conventional tillage utilizing a tandem disc, raking and burning, and no-till direct seeding into flax stubble on soil physical properties and crop yield in a Chernozemic soil in southern Saskatchewan, Canada over a three year period.
Treatments and measurements: Two different types of surface tillage implement were compared: 1) combination of disc and a rolling basket, called vertical tillage and 2) tandem disc consisting of sharp-edged convex discs that roll obliquely to the direction of movement. In addition, the two types of tillage implement were also compared with raking and burning as practices for residue management, in this case flax straw.
The examined soil physical properties include soil aggregation, air and water permeability. Also measured are yield of wheat, pea and canola grown the following three years after the tillage and raking and burning treatments.
The key results and achievements are:
· Vertical tillage and tandem disc tillage treatments did not significantly affect aggregate size (MWD) in the surface (0-10 cm) soil in the years following the treatment. Raking and burning also did not influence the aggregate size.
· Aggregate stability was affected by tillage system, with slightly lower aggregate stability in tandem disc treatments compared to vertical tillage treatment in both 2016 and 2017. This is attributed to a greater depth of incorporation of residue in the tandem disc treatment that would reduce organic matter available at the surface for binding particles together. There was a trend for raking and burning to decrease aggregate stability, but it was not significant.
· Vertical tillage tended to decrease air permeability and water infiltration rate compared to other treatments in the first year, which may be explained by an increase in the number of fine pores created by the pressure imposed by the rolling baskets attached to the vertical tillage implement. There were no crop stubble burning effects on water infiltration or air permeability in 2016 or 2017.
· Crop yields (2016 wheat, 2017 peas, 2018 canola) were not significantly affected by any of the residue management strategies, including tillage and raking and burning, and were similar among all treatments. Mean yields were highest in the vertical tillage treatment over the three years but were not statistically significantly different from other treatments. Direct seeding into the flax residue was successful because the flax crop was harvested when conditions were dry, and the residue was evenly distributed by the straw chopper on the combine. Tillage or raking and burning to reduce flax straw residue interference therefore was not needed to maximize yield under the conditions of this study. There were also no problems with equipment plugging identified in the field that would be considered an inconvenience or delay operations.
· In the first year after treatments were imposed, vertical tillage of the flax stubble appeared to reduce air permeability while tandem disking increased it. Tillage in general also resulted in reduced aggregate stability compared to no-till in the first year. However, these effects had largely disappeared in subsequent years. Tillage reduced density and strength at the soil surface, particularly the tandem disc treatment due to the greater working depth. The effect of tillage on reducing soil strength was still apparent in 2017, but effects had disappeared by 2018. Raking and burning treatment in spring of 2016 had relatively little influence on soil physical properties but burned stubble ash covering the soil surface appeared to cause some slight reduction in air and water penetration. In 2018 canola crop, nutrient concentrations measured in the plant were slightly higher in burned treatments. There were no large differences in water infiltration (hydraulic conductivity) observed among stubble tillage and burning treatments.
Recommendations: Reflecting relatively limited impact of the treatments on soil properties, yields among treatments were similar at the site in 2016, 2017 and 2018, with no significant difference (p = 0.10) among treatments. For this field scenario: flax combined on dry day with chopper functioning well, no large yield benefit to successive crops was realized through further stubble management (tilling, burning) apart from that conducted during harvest. Because of costs incurred from tillage and raking and burning operations without associated yield benefit, these operations were calculated to produce limited or negative economic return under the conditions of this study.
Next step: The relationship among soil management practices like tillage, raking and burning and crop yield can be complex and variable. Future research on soils of higher and lower organic matter content than those used in this study would be interesting to see if they are more or less impacted by these practices. The effects of tillage and burning on nutrient availability would also be interesting to investigate in more detail over both short and long time intervals as some interesting effects were observed in this study. A better understanding of relationships between alteration of soil conditions through tillage or other disturbance and root growth, morphology would be valuable in more reliably predicting the effects of tillage management on crop yield.