ChileanJAR

Subterranean clover (Trifolium brachycalicinum, Trifolium yanninicum)-phalaris (Phalaris aquatica)annual rye grass (Lolium rigidum), pasture production was evaluated during 15 years (1973 to 1987). At interior dryland of the Mediterranean subhumid zone (annual rainfall = 695 mm), of Chile, in a granftic soil. Annual evaluations were in exclusions by monthly cuttings of 2 x 6m plots. The pasture was sown in 1970. The mean of annual yield (TP), forthe evaluated years, was 3,609 kg D.M./ha. with a standard deviation of 1,253 kg D.M./ha and a variation coefficient of 35%. Spring rainlall and water balance (August to November) explained 84 and 78%, respeetively, of the TP variation, only lorthe years with annual fertilization (P and N). The effect of the annual fertilization. P(20-22 u) and N (12-32 u), in the accumulated yield of the pasture was more important in years of humid springs than in dry ones. According to fitted values to a fourth order polynomial model, the estimated maximum in years with humid springs was 4.1 and 2.2 ton D.M./ha, with and without annual fertilization. respeetively. On the contrary in years with dry springs it was 2.8 and 1.7 ton D.M./ha, respectively. Up to the tenth year the sown species contribution was about 90 %. The weeds increased since the year fourteenth coinciding with the interruption of the fertilization. However, after 18 years there is still 75% contribution of the sown species.