Cuarenta años de fertilización en prados de la montaña de León. III influencia sobre la composición química y valor nutritivo

Abstract

As stated in previous papers (Rodríguez et al., 2003; García et al., 2004), mountain meadows herbage yield and their botanical composition are highly influenced by factors such as mineral fertilization, harvest season and cutting frequency. Consequently, all these factors have a marked effect on the nutritive valué of the grass harvested, because both botanical composition and the stage of maturity at harvest determine to a great extent the herbage quality. The present study summarizes the results obtained in 8 fertilization triáis performed in mountain meadows. The main objective is to analyze the effect of mineral fertilization -including the fractionated application of N- and the number of cuts per year on crude protein (CP), crude fiber (CF), neutral detergent ñbre (NDF), P, Ca and K contents, and on dry matter digestibility (DMD). The results show that CP, CF, NDF and DMD are more influenced by the harvest season (June, July or September) and by the number of cuts per year (1, 2 or 3) than by the mineral fertilization. It was observed that meadows improved with the application of phosphorus and phosphorus-potassium fertilizers. These elements were responsible of a significant increase on CP content and DMD, while NDF decreased. CP content and DMD are positively correlated, and both are negatively correlated to NDF. In addition, CP and DMD valúes are higher in the second cut performed during summer or at the beginning of autumn in comparison to the first harvest done in spring. The best forage quality was obtained with the three cuts per year harvest system. No differences were observed in herbage chemical composition between plots that received N as a unique application or fractionated in two It was the combination of P and K fertilizers the one that had the best effect on herbage chemical composition, independently of the number of cuts per year (2 or 3). Taking only into account the statistically signiñcant triáis, the following average results were obtained: 106 and 139 CP g /kg DM in June and September, respectively, in the two cuts system, and 121, 180 and 162 CP g/kg DM in June, July and September, respectively, for the three cuts system. Regarding DMD, the valúes were 670 and 732 g/kg, in June and September for the two cuts system, and 807, 865 and 874 g/kg in June, July and September, respectively, for the three cuts system. Corresponding NDF mean vales were 580 and 467 g/kg, and 551, 459 and 451 g/kg DM. With the P and K combination the following mean contents in herbage samples were found: P=2.3 g/kg in June and September, Ca=8.9 and 11.6 g/kg in June and September, respectively, and K=15.8 and 16.4 g/kg in June and September, respectively.