Crimson clover growing as a winter cover crop at the LSU AgCenter's Red River Research Station.

Figure 1: Influence of winter cover crops / cotton rotation on seed cotton yield (lbs./A) after 50 years.

Figure 2: Influence of winter cover crops / cotton rotation on soil organic matter (%) after 50 years.

The fertile soils of the Red River valley in northwest Louisiana have supported cotton production for decades. This continuous cultivation has resulted in a decline of soil fertility, especially in organic matter. While organic matter makes up only a small portion of the soil, it has significant influence on soil quality. Organic matter is a major source of nitrogen, phosphorus and sulfur in the soil. It also contributes to the water-holding capacity and water-infiltration rates of the soil. Concerned with the decline in soil fertility, David Melville initiated a project in 1959 at the LSU AgCenter’s Red River Research Station in Bossier City, La., to study the effects of winter cover crops on soil fertility and cotton production.

This project has been ongoing for the last 50 years with few changes. Eight treatments are studied with four replications. Cover crops are planted each fall after cotton is harvested and the remaining stalks are shredded. In mid-April of each year, cover crops are clipped using a flail cutter, then disked under. All nitrogen fertilizer is applied either pre-plant to cotton or as a sidedressing after planting. Cotton is planted approximately 10 days after incorporating the cover crops. The use of herbicides, cultivation and insecticides are the same for all plots.

The treatments studied are:

1. Wheat, 60 lbs. N per acre
2. Crimson Clover, no N
3. Hairy Vetch, no N
4. No Winter Cover Crop, no N
5. Berseem Clover, no N
6. Hairy Vetch, 40 lbs. N per acre
7. No Winter Cover Crop, 40 lbs. N per acre
8. No Winter Cover Crop, 60 lbs. N per acre

This long-term study continues to show the benefits of using a winter cover crop in rotation with a summer cotton crop. The winter cover crops resulted in higher cotton yields (Figure 1) and increased organic matter (Figure 2).