Research Background

     Because we are dependent upon the soil to yield forth plants that supply much of our food, we are directly affected by attributes of soils in which those crops are planted. Lack of water, high traffic, amount of organic matter, composition of the soil (amount of sand, silt, and clay), and use of the land all affect the outcome of plant growth. Roots in the soil need to be able to penetrate the soil in order to grow. However, when the roots of a plant cannot find conditions in which to grow, the entire plant suffers.

     The southeastern Coastal Plains are flat lands and gently rolling hills with climate favorable to the growing of crops. However, hardpan soils (rock-like layers usually below the surface layer) make it difficult for roots to grow freely. In order for roots to grow uninhibited, it is often necessary to reduce soil strength. Soil strength refers to the hardness of the soil. The stronger the soil, generally, the more difficult it is for roots to penetrate. Tillage reduces soil strength by breaking up the soil; rainfall and/or irrigation reduce soil strength by moistening it (Note: most, but not all, soils will reduce strength by moistening).

     Soil strength can be measured with a penetrometer. It is a tool that has a probe with a scale on the opposite end. Soil strength measured above 20 atmospheres will not allow healthy root growth. Strength below 10 atmospheres is ideal for crops to grow adequately. The Agricultural Research Service and other research entities constantly experiment with ways to develop methods for preparing soils that propagate healthy plant growth. Plots are constantly monitored to record plant growth responses to treatments. Some plots have been tilled at the surface while others have been tilled to a deeper level. Still other sections have been tilled with a combination of surface and deep tillage. Some sections are irrigated above ground while others are not irrigated at all. Still other sections have been irrigated with subsurface irrigation.

     Traffic tends to make the soil stronger. Methods of disruption (tillage) that reduce soil strength can encourage root growth. Cover crops are used to penetrate hardpans during seasons of non-growth between crops. Hardpans are layers of soil that are very hard, so hard in fact that clumps of hardpan may appear to be rocks.

     The more a soil is compacted the stronger it is and the harder it is for roots to penetrate. So soil compaction is a major problem for crops. When soil is highly compacted, roots are not physically able to penetrate the soil. If roots cannot penetrate the soil, then they cannot go deep enough to get the water and nutrients that will sustain plant survival.

     Many techniques and technologies are employed in this research. A computerized irrigation system (site specific center pivot irrigation litigatioii) is one of the tools used. It is an irrigation system that can be programmed to spray specific plots with water, pesticides, and fertilizers. This system allows conservation of water and reduction of droughts. Improvements are being developed to allow this system to accommodate irregular-shaped areas.

     The different kinds of scientists at the USDA-ARS work together to investigate the best plan for encouraging the healthiest plant growth possible in this sandy soil found in the Coastal Plain. Constant research is being done to make the best possible use of the soil. Some of the testing going on involves surface and/or deep tillage, above-ground irrigation, subsurface drip irrigation, crop rotation, pesticide use, and mulching techniques. Soil Scientists, Physicists, Chemists, Agronomists, Microbiologists, Geneticists, Agricultural and Environmental Engineers, and Plant Physiologists are all involved with this research to improve agricultural practices.