High Soybean Yields--Definition and Components

The 2014 soybean harvest is about 20% complete, and will soon be reaching its halfway point. Even though harvest is just now in full swing, it is not too early to start preparing for the 2015 crop.

According to the latest Mississippi NASS report, soybean yield in Mississippi is forecast to average 48 bu/acre in 2014. This follows record yields of 45 bu/acre in 2012 and 2013, and leads to the apparent conclusion that we have entered a new era in soybean production in the state; i.e., a period of high yields.

The remainder of this article will discuss production components that likely contribute to these high yields, which are arbitrarily defined by me as 45 bu/acre or greater and 80 bu/acre or greater from nonirrigated and irrigated sites, respectively.

The following is a list of those components that are thought to contribute to sustained high yields such as those above. This list is a combination of agronomic and cultural practices that can be managed to ensure the highest yield potential.

Major Components

Variety selection. This is probably the most written-about component for achieving high yields. That is because current and forthcoming varieties include genetic components that are included to aid in stress tolerance and provide resistance to disease and nematode pests, all of which will contribute to maximizing yields. Also, this component arguably has the most information resources available for decision-making.

A soybean variety has a maximum yield potential that is genetically determined; however, its genetic yield potential is also supplemented with traits that allow it to avoid stresses from environmental extremes and pests. The genetic potential of all varieties is realized only when environmental conditions are optimum or near perfect. Thus, the actual yield potential of a variety may never be reached.

There are several keys to selecting varieties that will perform best in your fields.

• Match to soil. For example, choose a variety with a high level of Phytophthora root rot resistance if you are planting on clay soil, and choose a variety with resistance to soybean cyst nematode (SCN) if you are planting on a coarse-textured site that will support or has an SCN presence.


• Match to planting date. Choose the appropriate maturity group (MG) for your latitude and planting date to maximize yield potential. Click here and here for the latest information about this.


• Match to nematode presence or potential, especially SCN. Know the race(s) of SCN in your field, and select a variety that has resistance to that particular race. Click here for details on which nematode species to expect and where.


• Select a variety with the disease resistance combination that matches the known disease history of your field and environment. Be especially mindful to select a variety with resistance to both stem canker and frogeye leaf spot. In East Mississippi, select a variety with known tolerance to IDC.


• Use results from variety trials conducted in surrounding states to help with your decision. Click here for this information.


 

Soil Sampling. Sampling soil for SCN and fertility is important for both nonirrigated and irrigated production sites. Click here for detailed guidelines and references for soil sampling protocol. This is possibly the most neglected management component in soybean production in Mississippi.

Remember these important points.

• SCN. SCN will reduce yield even where no visible injury symptoms appear, so this makes sampling to determine nematode presence especially important. Once SCN is in a field, it cannot be eliminated.


• Match added fertilizer nutrients to expected yield potential. This is especially important for sites that have a history of and are anticipated to continue to produce yields at the above levels. For example, a 45 bu/acre soybean yield will remove about 36 lb/acre P₂O₅ (16 lb/acre P) and about 63 lb/acre K₂O (52 lb/acre K). An 80 bu/acre soybean yield will remove about 64 lb/acre P₂O₅ (30 lb/acre P) and about 112 lb/acre K₂O (93 lb/acre K). Thus, replacing K is especially important for sustained high soybean yields.


 

Fall-Winter Weed Management. This can enhance early planting and reduce pressure on early-season postemergence weed control.

Row Spacing. The simple fact is that narrow rows (30 in. or less) should be used wherever and whenever possible. This will ensure that canopy closure occurs as quickly as possible to reduce competition from weeds, and in time to ensure maximum light interception during the R3 to R6 period when pods are forming and seeds are filling. Click here for detailed guidelines about selecting the appropriate row spacing.

Early Planting. This is the surest way to avoid severe drought stress, late-season foliage feeding insects, and soybean rust occurrences. Click here for an objective analysis of how early planting vs. later planting can affect yield and pest avoidance.

Early Season Weed Management. This is the surest way to avoid yield-reducing competition from weeds during the early growing season, which in turn reduces the likelihood of weed escapes competing with soybeans later. Using preemergence residual herbicides can minimize the likelihood of early-season competition from weeds.

Irrigation. Irrigation of soybeans in the Midsouth is a proven input that will both increase yields and sustain high yields from year to year. Proper irrigation management will both maximize yield and conserve water. Click here for complete details about soybean irrigation and sustainable irrigation practices.

Scouting. Scouting for assessment of insect and disease infestations will ensure that timely control measures are applied when warranted. This, in combination with using insect thresholds for insecticide applications, will minimize yield-limiting damage from insect pests.

Minor or Supplemental Components

Seed Treatments. Seed treatments (fungicide and/or insecticide and/or nematicide) will increase soybean yield only minimally if at all. However, their value arises from ensuring a stand from a first planting (fungicide treatment–most important of the three), reducing injury from early-season insects (insecticide), and providing some protection against SCN (nematicide) when susceptible varieties are grown. The reduced risk of a failed stand resulting from use of a fungicide seed treatment is especially important (especially on clay soils where Pythium is prevalent) since replanting will necessarily mean a later planting date. Click here for a complete discussion concerning soybean seed treatments.

Tillage. When, where, and why tillage is used will affect many of the above components, but tillage is not necessarily a component that is associated with yield potential. Click here for a complete discussion of how tillage systems can be used to advantage in soybean production systems.

Future research efforts should and will be dedicated toward refining aspects of all of the above management components that will contribute to sustainable high soybean yields in the Midsouth.

Composed by Larry G. Heatherly, Sept. 2014, larryheatherly@bellsouth.net