Performance Story: Precision subsoiling of fields to improve soil physical conditions
Fall tillage on the Canadian prairies may involve subsurface tillage (subsoiling) tillage operations. These tillage practices alter soil physical properties such as aggregation, strength, bulk density, air and water permeability that can subsequently affect growth and yield of following crops. Reclaiming compacted Chernozemic and Solonetzic soils with hardpan B horizons may be possible through subsoiling operations to loosen the soil to depth e.g. ~30cm.
The objective of this study was to evaluate the effect of subsurface tillage on soil physical properties and subsequent crop yield. Subsoiling treatments with a minimum tillage subsoiler operated at ~30 cm depth were applied to wheel traffic compacted and non-compacted Chernozemic and Solonetzic soils at two annually cultivated field sites in south-central Saskatchewan, Canada in the fall of 2015, and effects on soil properties and crop growth monitored over the following three growing seasons. In the first season, subsoiling increased air permeability in the compacted Chernozemic soil from 4.5x10-7 m sec-1 to 2.9x10-6 m sec-1.
The subsoiler also significantly reduced soil bulk density and soil strength in both soil types. Subsoiling increased crop production on only one soil type; the long-term wheel traffic compacted Solonetzic soil, which had the highest soil strength (> 2000 kPa), where canola grain (first crop after subsoiling) yield was increased by 1,100 kg ha-1 from the subsoiling operation conducted the previous fall.
Effects of the subsoiling on soil physical properties and crop yield diminished greatly in the second year after subsoiling, and few significant effects were observed in the third year after. When considering fall tillage, subsoiling may be most effectively applied to only the long-term wheel traffic compacted areas of a field with identified high soil strength, such as in a wheel traffic compacted Solonetzic soil. These were the only conditions under which a significant positive economic benefit was realized.
Overall, subsoiling with a minimum till subsoiler to a 30 cm depth in the fall was generally effective in reducing soil density and strength to that depth in the first year in non-compacted and compacted Chernozemic and Solonetzic soils. The degree of reduction in density and increase in porosity achieved by the implement was greater in the Chernozem than in the Solonetzic soil.
Lesser effects of subsoiling were observed on aggregation and permeability in both soils, but it appears that air permeability at the surface is affected more by subsoiling than water permeability. For it to be worthwhile for growers to utilize subsoiling to address compaction, there must be a positive yield benefit.
The only subsoiling treatment that produced a significant positive yield benefit was subsoiling on the long-term wheel traffic compacted Solonetzic soil and this was only observed in the first year. These findings are consistent with this compacted soil having significant root penetration/exploration issues as evidenced by its very high soil strength values. Also, important to note is the evidence for natural reclamation through freeze-thaw and wet-dry cycles from short-term (1-year) wheel traffic compaction that was observed in the Chernozem soil. Water infiltration was overall greater in the Chernozem than the Solonetzic soil as expected. The Chernozemic soils, with more organic matter and better structure than the Solonetzic soil to begin with, appeared more resilient to compaction and tillage treatment.
Based on the responses to subsoiling tillage identified in this study, it is recommended that efforts be undertaken by growers to first identify the specific soil types and compaction conditions most likely to produce positive yield response by using maps of soil type (e.g., Solonetzic vs. Chernozemic), records of traffic history, and use of soil penetration resistance measurements to compare areas within the field. This may be followed by application of subsoiling only to these fields (e.g., Solonetz) or compacted areas of fields (e.g., field travel roads, seeder, combine load and unloading points at field entrances) identified as potentially responsive. This precision approach is recommended as an effective and economical approach to using subsoil tillage to significantly improve yield and provide economic benefit, rather than subsoiling entire farms or fields where a large majority of the land area may be unresponsive to the practice.