INCREASE IN FORAGE YIELD IN NARROWLEAF BIRDSFOOT-TREFOIL (LOTUS-TENUIS WALDST AND KIT EX WILLD) IN A PERMANENT PASTURE WITH FOLIAR-APPLIED GIBBERELLIC-ACID (GA(3)), AND PHOSPHORUS

Lotus tenuis is a perennial legume with a good adaptation to infertile , heavy and waterlogging soils. It can replace alfalfa in these sites with a similar feeding value. An important constraint is its weak comp etitive capacity with other graminae and weed species in permanent pas tures, having consequently a poor forage yield. The objective of the p resent research is to overcome this disadvantage, enhancing its compet itive ability with foliar applications of GA(3) (GA) and phosphorus (P ), increasing L. tenuis forage yield. Field experiments were conducted during 1994 with foliar application of GA (50 mg.l(-1)) and during 19 95 with foliar application of GA (25 and 50 mg.l(-1)), phosphorus (8 k g.ha(-1), as P2O5) and their combinations, in permanent pastures with L. tenuis and other companion grasses. In 1994 GA 50 increased signifi cantly L. tenuis dry matter (DML) in 64.6% but not the dry matter of g raminae fraction (DMG) and in consequence the total dry matter of the pasture (TDMP) was increased. In 1995 all GA treatments and their comb inations with phosphorus enhanced DML, but not DMG. In this sense GA 2 5 + P was the most effective treatment with a 151 % increment of DML. Consequently TDMP was significantly increased due to a larger particip ation oft. tenuis in the forage yield. This increase was achieved due to a greater length and diameter of L. tenuis branches, with a logical modification in leaf:stem ratio. Moreover GA treatments reduced L. te nuis flower number. Phosphorus treatment, applied alone, showed an inc rease in the DML. GA treatments did not modify the feeding value of th e forage in L. tenuis and graminae fractions, except GA 50 and GA 50 P in acid detergent fiber (ADF), neutral detergent fiber (NDF) and cr ude protein (CP), respect to the control. The total crude protein (CP. m(-2)) was enhanced in all GA and GA + P treatments. Foliar GA(3) and phosphorus spray applications increased the competitiveness of trefoil for light, on account of morphological changes in the spatial disposi tion of L. tenuis stems reaching faster the top of the pasture canopy. This practice can be an adequate alternative to increase the forage y ield and total crude protein in permanent and cultivated pastures with a low cost-benefit ratio.