Part I. Production and Management Practices that Affect Sustainability
Growing soybeans in Mississippi and the Midsouth (generally below 37 deg. latitude and west of Alabama) is affected by production environments that include:
- Both alluvial and upland soils,
- Planting dates from late March through mid-June,
- Both dryland and irrigated systems,
- A doublecropping system with wheat,
- Rotation systems with cotton, corn, or grain sorghum,
- Summer drought with high temperatures,
- Infrequent inundating rainfall events from late-summer tropical storms, and
- Maturity dates from late July through mid-October
Average 4-year yields (2007-2010) for Arkansas, Louisiana, and Mississippi were 36.6, 38.6, and 39.1 bu/acre, respectively. These yields are below the 42.3 bu/acre national average over the same period.
Sustainable production and management practices for growing soybeans in the Midsouth should be directed toward raising the regional yield average to a level that exceeds the above values. The following management categories are discussed in this context.
Tillage. Increased yields coupled with decreases in erosion, water runoff, and fuel use support the premise that growing soybeans in Mississippi with conservation tillage is more economically and environmentally sustainable than with any other tillage system. In fact, conservation tillage is the only tillage approach that realistically supports environmentally sustainable soybean production in the Midsouth.
Research is needed to determine the need for and how to integrate periodic operations such as deep tillage and row-crop cultivation into a conservation tillage system.
Cover Crops. Cover crops are rarely used in soybean production systems in the Midsouth. However, cover crops provide positive environmental benefits, especially in the winter months between successive soybean crops on upland soils.
The drawback to their use is the lack of income to offset the cost of establishment and destruction. This can be offset somewhat by developing technologies that lower costs associated with their use, by instituting a program of government incentive payments to encourage their incorporation into a production system, and by using a cover crop such as wheat that provides income in a doublecrop system.
Crop Rotation. The perception in the Midsouth is that crop rotation provides positive production and environmental benefits to both soybeans and the rotated crop for the following reasons.
- Rotation of a grain crop with soybeans decreases erosion potential because of the grain crop residue.
- Energy output:input ratios favor rotating soybeans and a grain crop.
Long-term soybean:corn rotation research conducted in the Midwest has determined the allowable reduction in nitrogen fertilizer requirement for a grain crop following soybeans. However, the amount of this reduction is unknown in a Midsouth soybean:grain crop rotation. Thus, it is unreasonable to assume that results from Midwest research will directly transfer to the Midsouth. The reasons are:
- Midsouth soil properties present a much different environment for off-season maintenance of soil nitrogen levels because of higher soil temperatures and frequent long-term soil saturation that results in anaerobic conditions. This results in greater losses of soil nitrogen during the winter months.
- Higher temperatures in the Midsouth during the winter months will result in greater decomposition of crop residues between harvest and next season’s planting. This also will affect residual soil nitrogen levels.
- Lower dryland yields in the Midsouth will presumably result in different nitrogen use patterns by corn, and subsequently, less crop residues.
Midsouth corn and soybean researchers should make a concerted and cooperative effort to initiate and conduct research that will ascertain the perceived benefits/effects of a soybean:grain crop rotation system of production.
Soil Fertility. The tenets of soil fertility management for sustainably growing soybeans in Mississippi are unchanged.
- Sustainable and environmentally sound soil nutrient management continues to rely on the tried and true process of accurate soil sampling and soil tests. A systematic process of sampling over time and space should be used to ensure accurate fertilizer additions based on crop yields and the different soil properties within and among production fields.
- Some fertilizers should be applied using variable rate technology to prevent overfertilization.
- Application of nitrogen fertilizer to soybean is unjustified and incurs unnecessary expense with no benefit.
- Maintaining soil pH in the range of 6.0 to 7.0 will enhance availability of fertilizer nutrients, decrease availability of toxic elements, and improve microbial activity.
Agronomic research in collaboration with Agricultural Economists is needed to verify current soil test recommendations to ensure that fertilizer elements are applied only in an amount that will ensure maximum economic yield from growing soybeans in Mississippi production systems.
Planting Date. Early planting (late March through mid-April) of soybeans in the Midsouth is now commonplace and has been associated with a higher yield plateau for the last decade. It is used as a mechanism to avoid drought, avoid or reduce susceptibility to late-season pest infestations, reduce amount of irrigation water applied, and ensure early harvest.
Current and future research results should soon provide resistant soybean varieties and more effective preventative and curative control guidelines for managing the late-season seed decay problem that plagues the early-planted system that is widely used for growing soybeans in Mississippi.
Irrigation. Irrigation results in consistent, profitable, and sustainable soybean yields in the Midsouth.
Continued use of water from the Mississippi River alluvial aquifer to irrigate crops in the Lower Mississippi River Valley is causing depletion of the resource, and this may result in less water being available for future irrigation needs. This is being addressed by exploring alternative sources such as impounded surface water that can be used to replace some of the groundwater used for soybean irrigation. This approach is important because even a small reduction in groundwater withdrawal will stabilize the aquifer’s water level.
Reduced water available for irrigation may require that less irrigation water be applied during the growing season. Research is needed to determine how irrigating soybeans with less water over the usual irrigation period will affect yields and net returns.
The next installment will look at how soybean breeding and variety development will impact sustainable soybean production and enhance the opportunities from growing soybeans in the Midsouth.