Management effects on herbage yield and botanical composition of rhizoma peanut-mixed grass associations

Broadleaf weeds invade rhizoma peanut (Arachis glabrata Benth,) (RP) stands as they age, possibly because of decline in associated grasses, particular ly bahiagrass (Paspalum notatum Flugge), Our objective was to assess the ef fect of spring N fertilization and summer stocking rate (1.5 vs. 2.5 animal s ha(-1); Exp, 1) or spring N fertilization and presence or absence (no gra zing until July) of spring grazing (Exp, 2) on the herbage yield and botani cal composition of mixed RP-grass swards. In both experiments, pastures wer e fertilized with either no N (N-0) or 35 kg ha(-1) of N (N-35) in March or early April for 3 yr. Sward herbage mass (Mg ha(-1)) and botanical composi tion were assessed in spring (April), summer (July), and fall (October) of 1995 and 1996 and spring of 1997. In Exp, 1, stocking rate did not affect h erbage mass or botanical composition, but N fertilization did. By spring 19 97, there was an eight percentage unit increase in grass contribution (0.30 Mg ha(-1) increase in dry matter) and a trend for greater decline in RP (f ive percentage units, but no change in RP dry matter) for N-35 vs. N-0. Oth er forbs, Mexican tea (Chenopodium ambrosoides L.), and cogongrass [Imperat a cylindrica (L.) Rausch.] were not affected by N rate. Similar changes in herbage mass and RP percentage were noted for Exp, 2, but there was a stock ing rate x N fertilization interaction for grasses because the percentage i ncrease in grass was greatest when N was applied and grazing deferred in th e spring. Forb content of the sward was not affected by N fertilization or spring grazing. Our results show that grass yield and content of RP-grass s wards ran be manipulated by N fertilization and deferral of spring grazing, but for the limited time period studied (3 yr), increased grass presence w as not sufficient to inhibit encroachment of weedy forbs.