RESPONSE OF RYEGRASS TO LIMESTONE AND PHOSPHORUS

Annual or Italian ryegrass (Lolium multiflorum Lam.) is an important cool-season grass grown in the southeastern USA to provide high-quality winter forage. Other than N, limestone and P are the major inputs needed for ryegrass production. This field study was conducted on a Pomona fine sand (sandy, siliceous, hyperthermic Ultic Haplaquod) to determine the response of ryegrass to limestone and P additions and to determine if P and lime application levels can be reduced below the current agronomic recommendations without substantially affecting ryegrass production. Treatments consisted of four rates of calcitic limestone (0, 1, 2, and 3 tons/acre) and four rates of P (11, 22, and 44 lb P/acre) and all combinations in a factorial design with four replications. Limestone addition increased yields in all 3 yr of the study but had no effect on crude protein content of ryegrass. Addition of P increased yields and crude protein content of ryegrass. Root weights in the Ap horizon were increased by limestone and by P addition. Soil pH in the Ap horizon ranged from 4.8 to 5.8 for the 0 and 3 tons limestone/acre treatments, respectively. Soil exchangeable Al ranged from 4.1 to 7.5 in the Ap, 2.9 to 9.4 in the E, and 77.5 to 87.3 ppm in the Bh horizons. Soil-extractable P ranged from 7.8 to 10.6, 1.7 to 1.9, and 28.6 to 39.2 ppm for the Ap, E, and Bh horizons, respectively. This study demonstrates the importance of calcitic limestone and P for ryegrass and suggests that P and limestone application to ryegrass grown on spodosols in southern Florida may be able to be reduced. More studies are needed, however, on different soil types to reevaluate the current lime and P requirements for ryegrass.