Crop production on medium-and coarse-textured soils in the lower Miss. River Valley usually involves a subsoiling (deep tillage) operation to improve root and water penetration on these soils that often develop restriction layers beneath the soil surface. Also, these soils are generally low in organic matter (<1%), and this contributes to their development of these restrictive layers.
Subsoiling is an expensive tillage operation since it requires a high-horsepower tractor in addition to the specialized tillage implement that can be used only for this operation. However, using the proper implement for the operation minimally disturbs the soil surface. Thus, this operation can be used in a conservation tillage system since it does not bury crop residue–i.e., residues from a previous crop are left on the soil surface following properly conducted subsoiling.
Cover crops may become an integral part of any cropping system that seeks to become more sustainable and supportive of conservation agriculture. Cover crops are grown in most cropping systems to provide environmental and soil productivity benefits. The benefits arise from: 1) Providing soil cover to prevent erosion in the off-season; 2) Increasing water infiltration into the soil; 3) Providing plant residues to increase soil organic matter; 4) Reducing nutrient loss and leaching from the soil profile and/or lowering residual soil nitrogen (N); 5) Reducing herbicide runoff in a corn–soybean rotation; 6) Suppressing or reducing early-season weeds and weed biomass; and 7) In the case of legumes, increasing N supply for the following summer grain crop.
For row crop producers in the Midsouth, the major categories of winter cover crops to consider are either grasses (e.g. wheat, rye, oats), legumes (e.g. vetches, peas, clovers), brassicas (mustard, turnip, radish), or a mixture of the three. The grasses will generally require N fertilizer to produce the desired biomass. The legumes will not require any fertilization since they have the ability to “fix” N; however, they will require the appropriate N-fixing bacteria. Some of the N that is “fixed” by the legumes will be available to the following summer crop. Several of the brassica species are touted for their ability to penetrate into and minimize the negative effects of restrictive soil layers.
Results from a recently completed irrigated study conducted during the 2016 through 2018 growing seasons at the MSU Delta Research and Extension Center, Stoneville, Miss., are reported in a paper titled “Conservation Soybean Production Systems in the MidSouthern USA: Replacing Subsoiling with Cover Crops” (CFTM–https://doi.org/10.1002/cft2.20058). The objective of the research was to compare the effects of cover crops vs. subsoiling on soybean seed yield, net returns, and water use efficiency. Details about the conduct of and results from this research follow.
• Treatments were: 1) Reduced tillage, subsoiling 22 in. deep in the fall, natural winter vegetation killed prior to planting (stale seedbed system); 2) Reduced tillage, cereal rye cover crop planted in the fall and chemically desiccated prior to planting; and 3) Reduced tillage, tillage radish cover crop planted in the fall and chemically desiccated mid-winter. All plots were irrigated each year.
• Ground cover following cover crop desiccation prior to soybean planting was 57% and 64% greater in the treatment with cereal rye (treatment 2 above) than that in the other two treatments.
• Soybean seed yields from treatments 1 and 2 were similar, and yields from both were greater than that from treatment 3 (tillage radish cover crop). Tillage radish growth did not remediate restrictive soil layers.
• Net returns from cover crop systems (treatments 2 and 3 above) were significantly reduced below that from treatment 1 that had no cover crop costs.
• Averaged across years, the cost of subsoiling was $14.27/acre vs. costs of $39.20/acre and $26.33/acre for cereal rye and tillage radish seeding, respectively.
• These results indicate that fall subsoiling and natural winter vegetation vs. cover crops without subsoiling maximizes net returns from this irrigated soybean production system.
• Planting cereal rye and tillage radish cover crops in this system had no effect or resulted in a 12% reduction in WUE, respectively. The WUE reduction in treatment 3 was correlated with the reduction in soybean yield in that treatment.
• Overall, replacing subsoiling with either a cereal rye or tillage radish cover crop in this soybean system reduced net returns because of increased costs associated with cover crop seed and planting without a concurrent yield increase.
• Based on the results from this short-term study, widespread adoption of integrating either a cereal rye or tillage radish cover crop into a conservation soybean production system is highly unlikely in the Midsouthern U.S.
The integration of cover crops into a crop production system should be considered a long-term investment, and the results from the above study certainly confirm this since its short-term results do not indicate any benefit from their inclusion in lieu of subsoiling. This does not mean that an extended research period will yield different results. However, it is likely that an extended research period would allow more time for the perceived cover crop benefits to accrue in this production system. Click here and here for articles that support the requirement that both tillage research and cover crops research should be conducted long-term to properly assess their agronomic and economic value.
With the narrative in the above paragraph in mind, the short-term results from this study certainly do not support using a cover crop to replace deep tillage on these soils because it reduced profits in the years of the study. Since producers need to see a short-term advantage when replacing one practice with another, these results certainly pertain to the real world of farming where consistent positive returns are required annually to sustain the production of any crop or cropping system.
Click here for a Cover Crops White Paper and here for a Tillage White Paper on this website.
Composed by Larry G. Heatherly, Aug. 2020, firstname.lastname@example.org