by Paige Burns Clark, N.C. Cooperative Extension Richmond County Director

For people interested in gardening in the Sandhills, one of the most important practices is adding organic matter to your soil by using compost and cover crops. Organic matter is created with decomposed plant and animal manure residues. Compost is made of decomposed plant and/or animal manures. Cover crops are plants grown just to build soil, and include plants like crimson clover, annual rye, and sorghum Sudangrass. Why is adding organic matter to soil important? Organic matter holds onto vital water and nutrients rather than letting them leach out or wash away. It improves soil structure and encourages types of soil microbes that enhance plant growth. Organic matter levels in the soil can make all the difference in the ability to grow healthy plants. It is not uncommon for native soil in the Sandhills area to be less than 2% organic matter (a soil sample sent to NCDA will provide this information). In contrast, prairie soils of the Mid West, which are some of the most productive agricultural soils in the world, have organic matter levels as high as 10%.

Organic matter provides numerous benefits. Without organic matter, sandy soils have little ability to “hold” the plant nutrients in fertilizer, which may easily wash down through the soil particles with rain or irrigation. Plant nutrients from fertilizer adhere to organic matter in soil, and remain available to plants as they grow. Compost and cover crops not only supply organic matter; they are both good sources of plant nutrients as well. Their use has the added benefit of reducing the amount of fertilizer that must be purchased for the garden. Sandy soils also have little ability to capture and hold water from rain or irrigation. Organic matter allows soils to retain water so plants do not require as much supplemental water, making plants more drought tolerant. In contrast, in heavier, clay soils, organic matter has an important role to play by improving drainage. By improving soil porosity, water can drain through the soil profile away from plant roots. This is important, as water- logged soils can be an even more challenging problem than drought for plants.

As organic matter is being added, it is also being constantly lost. Soil inhabitants consume organic matter as it is added to the soil. One of the primary benefits of soil organic matter is the habitat it provides for a host of soil flora and fauna. Earthworms are a macro (large) organism that thrives in soil rich in organic matter, improving it further by tunneling and creating castings that increase soil fertility. Other soil inhabitants are soil microbes, nematodes, and fungi. You may think these soil critters are ones that cause problems in the garden, like plant diseases, but the majority of these microorganisms are beneficial. Beneficial nematodes prey on soil dwelling plant pests; beneficial fungi live symbiotically with plant roots, extending the plant’s ability to capture water and nutrients. Soil bacteria, the most numerous of all with up to a million in each teaspoon of soil, convert organic matter to plant-available nutrients and secrete plant growth hormones that stimulate root development.

Whether you are gardening organically or conventionally, adding organic matter on a regular basis with compost and cover crops has multiple benefits for plant health and improved resource management. Contact the North Carolina Cooperative Extension Richmond County Center Office at 910.997.8255 for more information on composting or cover crops.