Soybean South

 - PRODUCTION -

Boost Bean Yields
On Heavy Clay


Following a three-year side-by-side comparison of flat plantings and raised-bed
plantings on heavy clay soil, MSU-DREC researchers report their findings.

By Brewer Blessitt

In Mississippi each year, an average of about 1.75 million acres of soybeans are planted. The majority of the crop is planted on clay soils (with poor internal drainage), which are found in naturally low-lying areas.

However, many possibilities are available for dodging the negative impacts of the poor drainage. Large scale practices include maintaining obstruction-free drainage ditches and land forming fields to a specific grade.

Also, less invasive and smaller-scale measures can be taken. One of the simplest considerations is bedding systems. In addition, growers have available certain varieties with better tolerance to “wet feet” than other varieties, and this information is can be obtained through the Extension service.

Background on research
Researchers at the Delta Research and Extension Center located in Stoneville have evaluated bedding systems for soybean production on clays soils over the past three years (2006-2008).

The research was a side-by-side comparison of flat plantings and raised-bed plantings of irrigated, 40-inch twin-row maturity group IV soybeans. A relatively flood-susceptible variety (Asgrow 4403) and a relatively flood-tolerant variety (Pioneer 94B73) were used within each planting system.

The large-plot research was conducted on-farm at Livingston Farms in Washington County, Miss., on heavy clay soil. The 32-acre field was land formed at 0.2 percent slope and had an average yield of 45 bushels per acre.

Leaf Area Index values
Soybean varietal response to a raised-bed system was similar. The yield of the flood-susceptible variety tended to improve to a greater extent, but that difference was only significant in one of the three years. Varietal tolerance to clay soils and improving drainage are therefore not mutually exclusive, meaning both practices should be utilized for maximum performance on these soils.

Soybean plants on raised beds tended to attain more vegetative growth and be healthier. Leaf Area Index (LAI) values are an indirect measure of canopy density. These values reflect the amount of light a soybean canopy can capture. An LAI value of three corresponds to 97 percent of the light being captured and used in photosynthesis.

LAI values for soybean grown on raised beds not only were higher than flat-planted soybeans, but also surpassed that critical value of three each of the three years of the study. It is also important to mention that flat-planted soybeans only reached that value in 2008.

Canopy density and closure have a major impact on weed pressure. Marked differences were noticed in grass pressure between flat plantings and raised beds. Canopy closure was around one week earlier, and in some cases flat-planting canopies never closed.

Yields over three years
Yield response to raised beds was different in different years. In 2006, yield in plots planted on raised beds was nine bushels higher than the flat plantings. In 2007, the bedded plots yielded 77 bushels per acre, compared to 59 bushels for flat plantings, a whopping 18-bushel difference.

Interestingly, in 2008, no differences in yield were noticed between flat plantings and raised beds. Averaged across years, raised beds increased yields nine bushels over flat plantings.

Of great importance in these findings are the differences in variability from year to year. Flat plantings yielded 70, 59 and 81 bushels in 2006, 2007 and 2008, respectively. On the other hand, raised beds seemed to stabilize year-to-year variability in yield. These plots averaged 80, 77 and 78 bushels in 2006, 2007 and 2008, respectively.

The 22-bushel swing from high yield to low yield for flat plantings is much larger than the three-bushel swing in high yield to low yield in raised beds. Improved drainage seems to remove a large part of the yearly inconsistency.

Influence of weather and water
So, why the differential re-sponse across years if the systems were managed the same?

Luckily, a weather station documents the weather just a mile or so away. Looking back on rainfall patterns, 2006 saw some early season rainfall. Just over eight inches of rain fell in the first two to three weeks after emergence. Remember that yield response between the two systems was nine bushels that year.

In 2007, late June and early July saw a similar eight inches of rainfall, corresponding to a very vulnerable pod-filling stage of the soybean. The yield difference was 18 bushels that year.

Looking back on the 2008 growing season, there was one moderate rainfall event in late May; however, it was only about six inches in a three-week period. That year, there was no difference between flat plantings and raised beds.

Taking this one step further, eight of the last 12 years held clusters of rainfall, around eight inches in a two-week period, which would likely stress soybeans on a clay soil. If you factor in irrigation, the likelihood of this stress would probably increase.

Soil saturation is not only caused by rainfall but can be caused by inefficient irrigation and irrigation followed by untimely rainfall.

Summary of net returns
Last but not least, how would these systems affect the bottom line?

We also kept up with costs of inputs and values for the crop for each system each year to get a relative sense of net returns. Fuel costs, chemical costs, as well as commodity prices fluctuated each of those years.

However, in both 2006 and 2007, raised beds increased net returns by $56 and $139 per acre, respectively. In 2008, although the raised beds didn’t increase net returns, they didn’t decrease them either. That point is critical.

Based on this research, a raised-bed system improved yields and made money in two out of three years and in the third year didn’t cost anything. That, worst case, can be viewed as good insurance. The raised-bed system also minimized yearly differences in yield, offering a bit more security.

I would encourage any growers who have clay acres to try the raised-bed system on some of them. The practice is not restricted to wide rows either, as some wider 80-inch beds can support narrow-row soybean production.

Brewer Blessitt is a research associate II with Mississippi State University-Delta Research and Extension Center in Stoneville. Contact him at (662) 686-3229 or jbb@drec.msstate.edu.



Negative Impacts Of Poor Drainage On Clay Soils

Clay soils are composed of finer particles, many with shrinking-swelling cycles. The fine clay particles bind water tightly, resulting in a high water-holding capacity.

When moisture levels increase, the soil swells and prevents water movement into the profile and through the profile as well.

This poor internal drainage is compounded by the native areas of clays, i.e. the depression areas generally with little slope.

Consequently, crops – predominantly soybeans – grown on clay soils may be compromised by waterlog stress.

Poor drainage can have various results limiting yield. First, timeliness in the spring, regarding field entry and planting temperatures, is delayed where drainage is insufficient.

Secondly, germination is an aerobic process, and saturated soil often is oxygen-deficient. This places germinating seed and seedlings in a more vulnerable position for soil pathogen attack.

Soil saturation also impedes root growth and function as well as nodulation and nitrogen fixation.

Also, flooded soils trigger an immediate ethylene-based stress response in plants closing stomata and slowing photosynthesis.

It is well known that yield is directly related to total photosynthesis.

Another important factor to mention is the increased efficiency of irrigation when drainage is adequate on
the farm.