Soil and Water

Most Delta soils are derived from alluvium of the present Mississippi River and tributaries and ancient rivers. Delta soils in SE Missouri, NW Tennessee, and NE Arkansas are generally high in phosphous and low in potassium. Without proper liming, they tend to become strongly acid. Soil organic matter content is usually below 2 percent. Climate is normally favorable for crop production with 3 to 4 inches of precipitation monthly during the growing season. However, summer droughts are common. With proper surface drainage, corn and soybean can be planted on most soils in the region. Because rice is flooded, it is usually planted on poorly-drained soils which will retain water with clay either in the surface or subsoil horizons. On the west side of Crowley's Ridge rice is often grown on soils with silt loam top soil and clay subsoil. On the east side of Crowley's Ridge, rice is often planted on Sharkey clay soil. The highest cotton yields are usually produced on well-drained silt loam and sandy loam soils.

Compaction. Many Delta fields have a compacted layer called a traffic or plow pan located 6 to 18 inches below the surface. Sometimes deep tillage is used to penetrate the pan and allow roots to grow into the subsoil horizons. Typically, the greatest yield response occurs on sandy soils. A soybean field experiment was conducted from 1999 through 2001 to evaluate the effects of compaction on soil physical properties and evaluate tillage equipment on Malden fine sand, Tiptonville silt loam and Sharkey clay soils.  Experiments were conducted at Portageville and Clarkton, Missouri. In a test comparing types of tillage equipment, treatments included no-till, paraplow, chisel, and parabolic sub-soiling systems.  On the Malden fine sand soil, soybean yields were increased by deep tillage on average 8 bushels per acre by parabolic sub-soiling followed by disking and do-alling. When sub-soiling was done without disking afterwards, the seedbed was often very rough and caused problems getting a good stand of soybeans.

Cone pentrometer used
to measure subsurface
compaction.

In 2000 and 2001, a corn deep tillage experiment was conducted at Portageville on a Reelfoot fine sandy loam. Artificial compaction was applied with a heavy roller when the field was wet to simulate the effects of large farm equipment. A parabolic sub-soiler was used with and without chicken manure to remediate the effects of compaction. On average subsoiling increased corn yields 30 bushels in 2000 and 52 bushels in 2001.  This research was publish in Soil and Tillage Research 71:121-131  REQUEST REPRINT

Soil Variability. The effects of the 1811-12 earthquakes along the New Madrid Fault can still be observed in crop fields today. The most significant soil features for farmers are sand vents shown in the photo on the right. These occurred as downward pressure from shaking caused the wet sand deep in the soil to spew up in small sand volcanoes. Furrow irrigation is inhibited because water flows into a vent and does not continue down the row middles. For rice and catfish farmers the sand vents make it difficult to flood because the fields often leak water through the vents. Variable rate nitrogen was evaluated in 1999 through 2001 on a cotton field with numerous sand vents. Cotton yields were significantly reduced in sandy zones. These areas also had lower optimum nitrogen rates. READ MORE.

Three-year cotton yields at Portageville in variable rate cotton test.

Light colored areas in aerial photo are sandy zones resulting from earthquake vents. Narrow horizontal lines were alleys mowed through the cotton before harvesting to divide the field into a matrix of cells. Yellow curvey lines are soil type bonderies.

Cover Crop Management in Ridge-till Cotton. Cover crops help provide wind protection to cotton seedlings and minimize injury from blowing sand. In the 1990's a field study at the Delta Center showed the yield benefits of planting winter wheat in the cotton row (READ MORE). Currently three ridge-till cotton cover crop experiments are being conducted at Clarkton, Missouri. Experiment 1 has eight wheat glyphosate burndown date treatments (April 19, April 26, May 3, May 10, May 17, May 24, May 31, and June 7). Experiment 2 has two burndown dates (April 19 and May 17) with three nitrogen rates (0, 30, 60, and 90 lb N/acre). Experiment 3 has three cover crops (wheat, Robin crimson clover, and spring oats) in combination with four nitrogen rates (0, 40, 80, and 120 lb N/acre). Wheat in cotton row middles killed in early April was less effective in reducing wind damage to cotton seedlings than wheat killed after boot stage. Water stress was significant in cotton seedlings from wheat cover crop terminated after May 9. Wheat straw contained 25 to 45 lb N, 7 to 30 lb P2O5, and 15 to 46 lb K2O per acre. The highest yielding cotton treatment produced 995 lb lint per acre with wheat cover crop terminated on May 9. Cotton yields declined when killing wheat was delayed after cotton planting (May 16- 870 lb lint, May23- 583 lb lint, May 30- 697 lb lint, and June 6- 485 lb lint per acre). READ MORE.