The landscape and overall soybean production system in Mississippi has changed dramatically in the past 20 years. Statewide yields have nearly doubled in that period of time.

Overall, we have more information and better tools at our disposal to produce higher yielding crops than we ever had in the past. However, the information part of this situation is often a doubleedged sword. In today’s world, we sometimes have more information than we can handle in a timely manner in order to grow a big crop.

Today’s farmers are still striving to grow a big crop but also working more with bankers, accountants, FSA and NRCS offices, consultants, GPS and guidance system contacts, distributors and seed salesmen and checking on the Farm Bill situation. Producers are doing all of these things and many more to get to the end goal – grow a big and profitable crop – and they all require management.

Optimize row spacing
Some of the specific areas that we have been focusing on in our Mississippi soybean production system include optimizing row spacings and seeding rates and managing glyphosate resistance and weed shifts. Row spacings, and more importantly identifying the optimal row spacing, has been an especially hot topic in recent years with increased interest in twin-row systems and raised beds.

Row spacing really can be broken down into two scenarios. The first is our soybean/rice grower farming heavy clay soils. The second is the producer anywhere in the state growing a combination of soybean, corn and/or cotton on light, mixed, to heavy ground.

For the first scenario, most of our soybean growers in the soybean/rice rotation on heavy clay are already using a soybean row pattern that is 20 inches wide or less. In these situations, row spacing is oftentimes not the issue. Drainage, in particular surface drainage, on these heavy clay soils is usually the biggest yield-limiting issue.

As far as row spacing goes, 30 inches seems to be the breaking point for us in the Mid-South. We rarely see a yield difference among row spacings of 30 inches or less. If drainage is equal, and that is a big if, we also have never seen an advantage for twin-row systems compared to row patterns from 7.5 to 30 inches wide.

In the research we have conducted where soybeans have been planted on an elevated bed, yields on heavy clay soils for row spacings from 7.5 to 20 inches wide have averaged 80 bushels/acre and yielded the same as twin-row patterns. Where we see the yield difference is between twin-row and conventional 38- or 40-inch row patterns.

Advantages of twin-row pattern
The twin-row pattern (twin rows spaced 10 inches apart on a 40-inch center) has consistently outyielded the conventional single rows by eight to 12 percent. We have seen this yield advantage for the twin-row system across the years, short and tall stature Group 4 varieties and seeding rates, which are discussed later.

The great thing about a twin-row pattern is that you really get the best of both worlds – optimal yields that are comparable to a narrow-row pattern and the advantage of planting on an elevated “hipped” row using conventional hipper equipment or the new hip-and-roll technology.

The twin-row system is good for the producer who has been planting on a “hipped up” 38- or 40- inch row. That grower already has the tillage equipment in place and is achieving good surface drainage with elevated rows.

The twin-row system can further improve yields in this situation compared to conventional 38- or 40-inch rows, and the twin-row planter can be used to plant soybean, corn or cotton. We have several growers planting twin-row cotton and harvesting it with conventional pickers. Some farmers are also using an offset hitch to plant single-row cotton with a twin-row planter.

Elevated beds do well
For our soybean/rice growers on heavy clay soils who are already on a narrow-row pattern and planting on flat ground, incorporating raised wide beds into their production system to facilitate better surface drainage and furrow irrigation will go a long way to improve and sustain yields. Most of our heavy clay soils in this soybean/rice rotation system are graded on less than 0.15 percent slope.

This shallow slope is excellent for rice, but we can get into serious surface drainage issues in this situation. We oftentimes can’t get water on and off quickly. This problem is compounded when we get a big rain after an irrigation event. We have seen tremendous benefits from planting soybeans on elevated wide beds in our soybean/rice rotation system on heavy clay soils. We have seen this same yield advantage from elevated beds on heavy clay soils having a shallow slope that are in a continuous soybean system.

In the soybean/rice rotation system, we have seen consistent yield advantages of four to eight bushels/acre for elevated beds compared to flat planting. In large-plot continuous soybean research, we have seen a 10-bushel/acre increase by planting on raised beds compared to flat planting in a graduate student’s research at the Delta Research and Extension Center in Stoneville (Brewer Blessitt, MSU student with Dr. Dan Poston). Coupling tillage equipment like the hip-and-roll system with our existing narrow-row planters in the soybean/rice rotation system can be used to develop elevated wide beds that will facilitate drainage and provide an optimal narrow-row pattern that we are already using.

Seeding rate suggestions
Seeding rates were not as big an issue when we bought seed by the ton relatively cheap. Today, as we buy it by the bag for upwards of $38 per 50-lb. bag, seeding rates required to attain optimal yields both from a production and an economic standpoint is critical.

The recommendations we have been using for our early planting system are based on planting maturity Group 6s and 7s in the old late planting system. We have focused on updating our seeding rate recommendations for early planted (early-to mid-April) Group 4s and 5s. We looked at seeding rates that would give us plant populations ranging from 75,000 to 155,000 plants/acre.

We found that our current recommendations from the late planting system weren’t far off for our early planting system. Planting to get plant populations of 100,000 to 120,000 plants/acre (plants, not seed/acre) for Group 4s and 5s resulted in optimal yield and net returns over seed costs.

This is not to say we don’t see slight yield increases by increasing the seeding rates to get upwards of 140,000 plants/acre. Our most consistent yields and net returns were attained when we planted to get plant populations of 120,000 plants/acre for Group 4s and 100,000 plants/acre for Group 5s. Our Group 5s often put on more leaf vegetation than group 4s and because of this often don’t require quite as thick of a stand.

Increasing the seeding rate
Situations where you may want to increase the seeding rates to attain plant populations greater than 120,000 plants/acre are planting earlier maturing Group 4 varieties and planting any maturity group in late March to very early in April (prior to April 5th). Plants often don’t reach the height and overall size when planting in this extremely early window for us in Mississippi as compared to planting in mid- to late April.

We often need to plant dryland acres first, and in cases where we plant in late March to very early in April, it will likely help to increase the seeding rate to attain plant populations of 130,000 to 140,000 plants/acre. In the past, we have made assumptions to determine how many seed to plant per acre. We have assumed 80 percent germination and that 90 percent of the seed capable of germinating will actually come up.

This percent emergence level is affected by the type of planter (air planter vs. drill), smoothness of the field, planting depth, seed vigor and potential for crusting in sandier soils. The percent emergence number is something we have to decide on a field-byfield basis, depending on the type of planter or drill we are operating.

Percent germination, however, is provided with each bag of seed purchased in Mississippi. The number of seed we plant in order to attain the desired plant population can be determined for each variety when we know the percent germination and estimate the number of seed capable of germinating that we feel will actually come up.

Managing glyphosate resistance
Increasing concern with glyphosate-resistant weeds is the weed management issue that deserves the most attention.

Currently, three weed species have been confirmed as being resistant to glyphosate. Populations of glyphosate-resistant horseweed (marestail), Italian ryegrass and Palmer amaranth (Palmer pigweed) have all been confirmed in Mississippi fields within the past five years.

Glyphosate-resistant Palmer pigweed was just confirmed this past fall in Mississippi cotton production systems in the north Delta. The glyphosate-based weed control program has revolutionized weed management in soybean, corn and cotton. Broad spectrum weed control, flexibility, lack of plant-back restrictions, ability to apply as needed depending on weed presence and pressure,economics and the ability to apply all Roundup Ready acreage regardless of specific crop are some of the reasons that this technology has been so widely adopted.

However, overusing a glyphosate-alone weed control program and reducing other weed control measures, such as tillage, have led to the development of glyphosate-resistant weed populations in virtually every state east of the Mississippi River.

Fortunately, we have several good residual options in soybeans that can be coupled with glyphosate or are already mixed with glyphosate that can be applied at-planting or over the top of glyphosate-resistant crops. Some of the residual herbicides that can be applied as a true preemergence residual herbicide behind the planter prior to crop emergence include Valor, Prefix, Canopy, Synchrony XP, Dual or Prowl H2O.

However, we often don’t get the full benefit of using preemergence residual herbicides applied behind the planter in our early planting system because we don’t have a lot of weed pressure in early April, especially on heavy clay soils where the majority of our soybean acreage has been concentrated.

Where residuals fit
By the time we begin to see weed pressure in our early soybean planting system, our crop is up, and we are into early May. Another concern with some residual herbicides applied behind the planter in our early planting system is that we can see significant soybean injury. This is especially true in cool, wet springs, which can be common in our early soybean planting system.

However, it is important to note that yield reductions rarely occur.

In our experience, there is often a much better fit for residual herbicides in the early postemergence window where residual products can be applied in conjunction with glyphosate over the top of small (two- to three-trifoliate plants) soybeans.

The most commonly used residual herbicide applied over the top of small (up to three-leaf plant) soybeans is Sequence or some type of glyphosate + metolachlor product. Sequence herbicide is a premixture of metolachlor (Dual) and glyphosate. Metolachlor provides residual activity of smallseeded broadleaves, such as pigweeds and annual grasses (barnyardgrass, browntop millet and crabgrass).

In the end, all of this discussion regarding crop inputs, technology, agronomics, etc., really centers on two things – management and stewardship.

Trey Koger is the Mississippi Extension soybean specialist. Contact him at (662) 686-3238 or tkoger@drec.msstate.edu.

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