Production improvement through phosphorus fertilization and legume introduction in grazed native pastures of Uruguay

Abstract

SUMMARYThe objective of the current study was to quantify the response of pasture to phosphorus (P) fertilizer application and legume introduction, by measuring herbage yield, nitrogen (N) and P content, and weight gain of calves in native pastures of Uruguay. Quantitative relationships between pasture characteristics and post-weaning daily live weight gain (DLWG) were also examined. The treatments studied were native grassland (NG) and improved pasture, oversown withLotus corniculatusL. andTrifolium repensL. with annual applications of either 13 and 26 kg P/ha. From 1996 to 2001 the treatments were evaluated each year with a new group of calves. Total herbage yields of the oversown pastures were not always higher than NG in the initial years, but legume production increased, although without significant differences between P rates on legume or total yield. This was also reflected in the N and P status of the swards. In the last 2 years legume proportion had declined to <0·1, but total herbage yield was significantly higher in the improved pastures. The average DLWG over the 6 years of measurements were 0·319, 0·478 and 0·586 kg/day for NG, P1 and P2, respectively, with average total live weight gain increased 1·8- and 2·5-fold by the legume introduction and annual addition of 13 and 26 kg P/ha, respectively. The study demonstrated that the evaluation of pasture response to P application should not be limited to assessing forage yield increase. Phosphorus availability in the herbage was a better predictor of animal performance than pasture yield. The study highlights that the benefits of oversowing and fertilizer inputs are short-lived, as withholding of fertilizer in the last 2 years resulted in a loss of sown legumes and decline in animal production.