Conservation tillage for Delta cotton
Mar 2, 2001 12:00 PM, J. Scott McConnell
Cotton production in the Delta region of the Mississippi River typically requires intensive tillage. Most conventional tillage of cotton fields is done during the early spring months when breaks in the weather permit.
Tillage operations are commonly used in bedding the soil, knocking down the beds, running drain furrows and ditches, and frequent cultivation for weed control during the growing season. These tillage practices have been linked to soil erosion, sediment loading of tail water, nutrient loss from fields, and enrichment of surface water with sediments and nutrients.
Field loss of nutrients and sediments to surface waters may have adverse environmental effects and result in algal blooms and fish kills. Additionally, agricultural activities that result in field loss of nutrients and sediments to surface waters have been reported by some to impact the hypoxic zone in the Gulf of Mexico.
Some cultivation, at least periodically, seems essential to cotton production in the Delta. Bedding the soil into raised crown beds allows the soil to warm rapidly and promote drainage of excess surface water.
In the predominately flat, almost zero-sloping soils of the Delta, unbedded crop land may be subject to localized zones of ponding within a field. Heavy rains or irrigation may leave areas in a field saturated. Undrained soils become oxygen depleted and cotton plants, especially seedlings, may not survive.
Cotton plants acquire air and oxygen through their roots. Without bedding operations and the draining furrows that conduct excess water from the field, cool and wet soils can severely impact seedling mortality.
To combat the loss of nutrients and sediments from fields, conservation tillage is gaining acceptance and is more frequently utilized by cotton producers. Many different methods and degrees of conservation tillage are employed in the Delta, however bedding frequently becomes the crux of the problem for successful conservation tillage.
The weather conditions in the Delta region vary widely from season to season, and early spring rains frequently leave excess water in the field. Bedding is sometimes necessary to conduct the water away from the field, allowing the soil to become oxygen rich and easily warmed.
The timing of the bedding operation then becomes critical to retaining soil in the field. After harvest, the soil is typically well-packed and sealed, winter weeds begin growing, and the shredded crop residue covers the soil. These conditions tend to protect the soil and hold it in place and reduce erosion.
Occasionally, after harvest, producers bed the soil in the fall on the previous year's beds. Although fall bedding eliminates the need to disk, the tillage incorporates the crop residue and weeds, and disrupts the well-packed soil. The loose soil surface is then extremely vulnerable to erosion. Heavy winter rain may then easily dislodge soil particles and carry them and attached plant nutrients away from the field. This process may continue for most of the winter and spring when heavy rainfall tends to occur.
Research from Mississippi indicates that more than 2 tons of soil per acre per year may be lost from almost-level Delta cotton fields under conventional tillage. Fall-bedded cotton fields could lose even more soil due to the exposure of unconsolidated soil to intense rainfall.
An alternative to fall bedding was investigated at the University of Arkansas at the Southeast Branch Experiment Station near Rohwer, Ark. Conventional spring tillage; disking, smoothing and bedding, were compared to a reduced-tillage system where beds were formed on the previous year's rows in the spring.
Because conventional tillage involves disking then smoothing the soil, spring rains may saturate the soil and cause delays in seedbed preparation. These delays in bedding may set back planting operations and, thereby, reduce the length of the growing season.
Elimination of spring disking, and beginning tillage by bedding on the old rows allows surface water from spring rainfall to be drained away and the cotton crop may be planted into warm beds.
By not tilling in the fall, shredded crop residue, winter weeds, and a packed and sealed soil surface better protect the soil and reduce the erosion associated with heavy winter rainfall.
Further, surface soil strength is decreased by the disking and bedding of conventional tillage compared to reduced tillage. Disking, in particular, tends to destroy the soil strength in the surface. The greater the surface soil strength, the heavier load the soil will bear without deforming.
Reducing soil strength may prohibit tractor traffic in conventionally tilled fields, particularly when spring rains saturate the soil. Practically, this means that producers may use heavy tractors and implements in reduced tillage fields earlier without cutting deep ruts in the soil and damaging the field.
Research from the University of Arkansas indicates that reduced tillage did not significantly affect yield. Reduced-tillage cotton was not lower yielding than conventionally tilled cotton. Since there was no yield loss using reduced tillage, this indicates that neither conventional spring tillage nor bedding in the fall has to be used by cotton producers.
The sealed soil surface, crop residue and growth from winter weeds maybe left intact to protect the soil from heavy winter rainfall, thereby minimizing soil erosion.
Soil strength may be preserved by omitting spring disking and bedding on the previous year's rows, thereby allowing tractor traffic back into the fields after rainfalls.
J. Scott McConnell is an associate professor at the University of Arkansas.
