Sustainable Alfalfa Production on Coastal Plain Soils of the United States

Abstract

Alfalfa (Medicago sativa L.) is rarely grown on the Coastal Plain of southern United States. Production problems include infertile acid soils, inadequate pest control, and high humidity with frequent rainfall events that preclude adequate alfalfa hay drying conditions in spring. Research to overcome soil fertility problems included evaluation of nitrogen (N) rates over alfalfa row spacings and limestone and boron rates in split plot studies; phosphorus (P) rates using a randomized complete block design on eight soil series; and potassium (K), magnesium (Mg), and sulfur (S) rates and zinc (Zn), copper (Cu), and molybdenum (Mo) rates in central composite, rotatable design studies. Field‐scale demonstrations were conducted to verify data from small plot research. Results indicate little need for N fertilization of alfalfa on Coastal Plain soils except possibly under cool or dry surface soil conditions. Increasing the between‐row planting distance from 23 to 69 cm lowered alfalfa dry matter yield by 2.1 Mg ha⁻¹ the seedling year. Alfalfa yielded 11 Mg ha⁻¹ at all row spacings in the drought‐affected third year. Dry matter yield was maximized at 49–73 kg applied P ha⁻¹ on soils testing below 19 mg P kg⁻¹ by the NH₄OAc‐EDTA extraction method. The alfalfa stand was lost after one season on plots not fertilized with K. Applied Mg, S, Zn, Mo, and Cu had no significant effect on alfalfa yield. Dry matter increased >5 Mg ha⁻¹ as pH was increased from 6.0 to 7.5. Boron applied at 3.4 kg ha⁻¹ increased alfalfa yields 3.9 Mg ha⁻¹. With improved methods for site selection and adequate fertility, sustainable economic production of alfalfa is possible with rain‐fed conditions on selected, limed Coastal Plain soils.