What Farmers Can Learn from Their Soil in the Off-Season
Using soil probe readings in the off-season or cool-season can reveal important information for farmers....Read More
Shawn Holladay, a cotton grower in Texas, hasn’t seen real rain since last November. “The only storms we’re getting are severe,” he says. “They don’t really produce much rainfall. They just make a big mess when they come through.”
Holladay has 10,000 acres in Dawson and Martin counties in west Texas, a semi-arid region that’s accustomed to very dry conditions. “This is cotton country,” he says. “It’s nearly all cotton out here because it’s very drought and heat-tolerant, to a point.”
But the conditions of recent years, including severe drought in 2011, are testing the limits of even experienced pros like Holladay, a fourth-generation farmer. The dryness has been “borderline ridiculous,” and he says he can only do so much to manage it.
One technique, he said, is paying special attention to the soil. For cotton, good soil encourages boll development, lint yield, and fiber quality, while soil lacking the right texture, pH, and nutrients can result in a lackluster crop.
Cotton is grown on every continent besides Antarctica—in temperate, subtropical, and tropical regions—but each environment brings a distinct set of challenges.
Within the United States, for example, Georgia produces more cotton than any state except for Texas. But in 2017, the average cotton yield per acre in Georgia dropped to 863 pounds due to Hurricane Irma and an influx of Silverleaf whiteflies. It was a big loss compared with the state record of 1,091 pounds-per-acre, set in 2012, and growers are still recovering.
Cotton plants tend to do well in deep, well-drained, and highly fertile sandy loam soils with a pH between 5.5 and 7.5—cotton plants are vulnerable to the aluminum concentration often found in soils with a pH below that range. The ideal range, according to Southeast Missouri State University, is between 6 and 6.5. Soil where cotton is grown typically requires a lot of lime, which should be applied several months before planting to allow time for it to dissolve into the soil, which increases pH.
Holladay’s soil is all sandy loam, with some clay and a fairly high sand content, which he says is typically “a very good combination to grow in.” He uses minimal inputs and is constantly on the lookout for new technologies that might help him to increase yields, including drought-tolerant seed and ways to increase organic matter in soil.
In determining when to plant seed, cotton farmers consider the amount of heat units in soil and tend to plant when ground temperatures stay higher than 60 degrees Fahrenheit throughout the night. In the southeastern and western U.S., growers typically plant toward the end of April or beginning of May, whereas in steamy south Texas, February is standard.
The reason for this is that cotton plants uptake soil nutrients, including nitrogen, phosphorus, and potassium, in direct proportion to temperature (heat units in soil) and growth. During the spring, cotton grows more slowly and takes up fewer nutrients, but nutrient needs increase during the peak growing months, when temperatures spike. To produce one 480-pound bale of lint, the National Cotton Council of America recommends 62 pounds of nitrogen, 22 pounds of phosphorus (P2O5), and 61 pounds of potassium (K2O).
Boron applications at flowering and boll development, as well as 10 to 20 pounds of sulfur per acre annually, will also keep cotton in good health—which will lead to higher yield for cotton farmers.
Soil plays a role in a few key cotton fiber properties: strength, length, and micronaire (air-permeability measurement). Lack of soil moisture and nutrients can lead to shorter fibers, while poor growing conditions during the boll-filling period can cause weak fiber with low micronaire, for example. Potassium deficiency hastens the processes of cellulose accumulation and dehydration in fiber, leading to a disorder called premature senescence, which causes reduced fiber strength and lower lint weight.
Harvest-aid chemicals must also be applied carefully and at the right time: too early, and they’ll prevent cellulose deposits, leading to weaker, less developed fibers and potentially lower yields. Defoliation when 60 percent of total crop has opened, and desiccant application when 80 percent or more of bolls have opened are good rules of thumb.
Even while keeping all of that in mind, Holladay says, “We’re very limited in what we can do for soil health in a dry situation like we are in right now.” Using a ridge-till system helps keep the soil rough enough so that it won’t blow away; no-till or minimum-till would require transitioning to a true rotation, which is particularly difficult under dry conditions and because cotton is not a high-residue crop.
Once there’s some good rain, Holladay has a pilot project in mind for a transition from his current 100-percent row crop to 50-percent, which can minimize the need for inputs even while optimizing yields.
Despite the challenges, Holladay does all that he can to keep his soil in shape, like testing soil samples and using the results to help increase fertility and produce healthier plants. This leads to higher yields, he says. He’s always watched nitrogen and phosphorus levels closely, but has recently started adding micronutrients like zinc and manganese, thanks to insights gleaned from knowing what’s going on in the soil.
“We live off of this soil and the healthier we can make it, the better off we’ll be,” he says.