Red Clay Soils of the Northern Piedmont by Jordan Hoffman
Typically, when someone hears the words clay and farming in the same sentence, a negative outcome is expected. Clay is associated with compaction and terrible drainage. This is because the clay soil most people have encountered has been compacted beyond repair. Clay soil has a lot of benefits for farming. The red clay soils in the Northern Piedmont are prime farming soils.
Soil is separated into three main particle size groups: sand, silt, and clay. Clay is the smallest with particles at less than .002 mm in diameter. These tiny particles interlock and form dense structures. This higher density makes clay soils more resistant to erosion than sandy soils. Clay is negatively charged and has a surface area more than a thousand times larger than sand or silt soils. Clay is able to attract and hold more positively charged nutrients like calcium, magnesium, potassium, than other soils. This ability is called Cation Exchange Capacity and the more clay the soil has then the higher the CEC and the more nutrients it can hold.
The smaller particles of clay also allow the soil to have a much higher water holding capacity because the smaller pores leach water out much slower than sandy soils. A higher water holding capacity allows the soil to hold nutrients like nitrogen that would normally be leached rapidly through other soils after a high rainfall event. Clay also enhances buffer holding capacity which is the soil’s ability to resist change in soil pH. This allows farmers to not have to make amendments to the soil as often to adjust soil pH.
The predominant soils in the Northern Piedmont are Davidson clay, Starr silt loam, and Dyke loam. All three have a deep, dark reddish- brown color and have significant clay layers and/or compositions. They are all well drained but not excessively so and are very deep. The Davidson clay soils consist of loam, clay loam, and clay layers. The upper layer has a fine, granular, friable structure which means that the soil is loose and easily manipulated by plant roots. It is used for growing small grains, corn, cotton, soybeans, grain sorghum, hay, and as pasture.
Starr loam soils consist of an upper friable, granular loam layer with friable clay loam layers beneath. The very friable layers of this soil allows for greater rooting depth. It is used for growing corn, cotton, small grains, soybeans and used as pasture.
Dyke loam soil has an upper layer of fine granular, friable loam with underlying clay layers. This soil is used for growing corn, small grains, hay, pasture, and orchards.
Clay is a very fertile soil because of its ability to attract and hold a lot of nutrients and provide them for plant uptake. The red clay soils of the Northern Piedmont are very beneficial to many different crops. As long as compaction is minimized and soil health and tilth maintained, there is no reason for clay not to be a fertile farming soil.
Written by Jordan Hoffman, a Culpeper County Virginia Cooperative Extension Intern. She is working closely with Carl Stafford on The George Washington Carver Agriculture and Research Institute project. A Crop and Soil Sciences major at Virginia Tech, Jordan is applying the skills learned in her studies to many aspects of the project and is able to assist on many occasions.