Application of Phosphorus and Sulfur on Irrigated Alfalfa1

Abstract

AbstractLow nutrient supplies often limit crop production on irrigated sandy soils. Soils in the Sandhills region of Nebraska have a limited capacity to supply P and S to crops. This study was conducted to determine optimum application rates of P and S for intensive alfalfa (Medicago sativa L.) production and to determine the relationship between nutrient application rate and concentration of these nutrients in plant tissue. Seven rates of P were combined with seven rates of S in a central composite factorial design with three replications. Treatments were broadcast and incorporated into a Typic Ustipsamment prior to seeding in August 1978. Applications were repeated on the established stand in the early spring of 1980, 1981, and 1982. Dry matter yields were recorded in four cuttings each year. Whole plant samples were taken from each harvest and analyzed for P and S. Except for 1982, alfalfa yield increased curvilinearly with the application of both P and S, but there was no significant interaction between these nutrients. In 1982, there was no response to applied S, but the response to P was curvilinear. Rates of 44 kg P ha−1 and 56 kg S ha−1 were needed for maximum production. The P concentration in the tissue increased with the rate of applied P, while fertilizer S had no consistent effect. The S concentration in the tissue increased with the rate of applied S. Sulfur concentration decreased as the P rate increased. This reduction was attributed to plant dilution effects. Concentrations of both P and S were near reported critical values when rates of P and S needed for highest yield were applied.