Spotlight on Beltwide Cotton Growers

Soil Variability Multiplies the Lessons Learned Each Year

September 2015
Hartsville, South Carolina
Name of Cotton Grower: Gill Rogers

Soil Variability Multiplies the Lessons
Learned Each Year

Cotton farmers understand that yields reflect all the good and bad things during the season. A math wiz would say that yield integrates the daily interaction between variety and environment over the time period that seed is placed in the ground till harvest. Gill Rogers, of Hartsville, South Carolina, clarifies this by saying that the size of the local church reflects the soil quality in the surrounding community. The church size integrates the local soil quality and management skills over many decades. This long view of cotton farming is essential in regions like West Texas and South Carolina where crop adversity and weather uncertainty are frequent unwanted visitors. After 45 years of fixing tires and chasing money to farm, Gill has learned a key trick to financial survival that he puts to work on his diverse cotton-corn-soy-wheat-peanut 7,000 acre irrigated and dryland farm.

Utilize Variability in Soil Texture to Improve Management.

Gill’s key trick to financial survival relates to those small and large churches. Over the long term, the most important soil parameter for crop production is the soil physical composition – the size and distribution of soil particles. Over many years farmers can change the other soil parameters impacting yield, but not soil texture. Considering that each acre-foot of soil weighs approximately 2,000 tons, no one can afford to swap-out bad soil texture for good. Instead, Gill adjusts his inputs (herbicides, water, tillage, nematicides) and most importantly, his yield expectations to the gravel-sand-silt-clay present in the soil.

The table below shows how soil texture (or the relative amount of sand-silt-clay) impacts many management decisions for cotton farmers.

Management Impact Sand Silt Clay
Water holding capacity low medium to high high
Aeration when moist good medium medium to poor
Drainage high slow to medium slow to very slow
Warming in spring rapid medium slow
Compactability low medium high
Susceptible to wind erosion moderate (high if fine sand) high low
Susceptible to water erosion low (unless fine sand) high low if aggregated, otherwise high
Nutrient retention low medium high
pH stability low medium high
soil herbicide activity high (unless high organic, then low) medium low

Rainfall and organic matter interact with soil texture on many of these management decisions. Although a clay soil can be high yielding in the dry Far West, clay soils are usually lower yielding where rainfall exceeds crop water use. Herbicide and fungicide crop injury is usually higher in sandy soils, especially if rainfall occurs shortly after planting, but high organic matter suppresses herbicide activity in all soil textures. While clay generally holds nutrients best, if rainfall reduces soil aeration (low oxygen) then nitrogen retention can be low in clay soil due to denitrification.

Since crop production adjustments interact with weather, the learning curve is long and painful unless you accelerate your learning using inherent soil variability. Gill gains 3 to 5 years of experience from every growing season by scrutinizing his yield maps with the recent weather pattern still fresh in his mind. With a hydraulic soil sampler, Veris data, soils maps, and footprints, he has learned the soil textures in his many fields. Each combination of soil texture and weather is only one year of experience to a grower with highly uniform soil, but it’s 3 to 5 years of soil-weather combinations for Gill. From this year-multiplier, Gill has learned the 2 to 3 key production practices for each crop on his farm. For corn it is getting the stand density correct for each soil texture, avoiding water stress during tasseling, and not overspending on fertilizer for each patch of soil. For cotton it is frequent rotation, frequent field visits, and adjusting inputs to yield expectations.

Following these guidelines, Gill tweaks his irrigation, fertilization, seeding rate, and rotation for his soil types. Of these production inputs, rotation has the greatest impact on cotton and the soil. Borrowing knowledge from the medical community, he knows that it’s more than just the amount of organic matter one eats – it is the types of foods we consume and how well our gut microbes process them. Although rotation does not alter the soil texture, the crop residues alter the food that soil microbes eat and thus provide a multi-season impact on soil performance.

With this management approach, Gill is able to turn what most growers would see as a detriment (soil texture variability) into a learning opportunity that helps him better adjust inputs to the crop needs.


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