Cuarenta años de fertilización en prados de la montaña de León. I. Influencia sobre la producción

Zusammenfassung

The área devoted to meadows in the mountains is scarce, but they give a high yield that assures the livestock winter-feeding. Therefore, any improvement on their yield or grass quality contributes to an increase in the number of animáis per farm, that leads to a more efficient use of nearby rangelands and, consequently, to an improvement of mountain farms profitability and stability, and to a decrease in wood fires. This work deals with the results of nine different triáis (some published partially, others unpublished) in three different groups. In order to find out how to correct the deficiency of phosphorus in the soil, the first three experiments two different phosphate fertilisers were used (superphosphate of lime and basic slag) applied in different doses with and without addition of bovine organic manure. Thereafter another four experiments were performed with different nitrogen fertilisers (ammonium nitrate, urea, ammonium sulphate and sodium nitrate) applied at different doses which were fractionated or not. However the main limitation in all these experiments was their design as randomized blocks. That is the reason why in 1978 a new experiment, the most important, was established. It consists in a factorial design with 64 different treatments of fertilisation. However, only the results concerning 22 of them are showed in the present work. This trial can be divided in three periods of ten years each: in the first and second periods two and three cuts were given each year, respectively. Finally, during the third part (that has been programmed to end up in the 2007) three cuts are being done as well, being the only difference with the previous period the fractionation of the N applied. In relation to the results of the fertilisation triáis it could be suggested that P is an essential element for the mountain grasslands, so its application at doses of 160 kg P205 ha-1 leads to yields of more than 10 000 kg DM ha-1 year1 in management systems with two or three cuts per year. Its application together with the potassium allows to obtain a significant increase of the production, mainly in the second and third cuts. Moreover, the phosphoric and phosphate-potassium fertilisation allows to obtain a more homogeneous distribution of the biomass along the productive cycle, increasing yield in September (two cuts system) or in Jury and September (three cuts system) to the detriment the yield harvested in June. The nitrogen is located in a second level of importance, increasing the yields signifícantly, mainly in the first cut, and especially if it is applied together with a phosphate fertiliser. Anyway the production reached with the application of P+K fertilisation is only slightly overeóme when N+P or N+P+K fertilisation is used. However, it would require the application of high levéis of N, which means a high energetic cost. There were no signifícant differences in yield due to different forms (ammonium nitrate, ammonium sulphate amónico or sodium nitrate) of nitrogen fertilization. The main limitation of the N+P and the N+P+K fertilisation is an important seasonal variation, increasing first cut production to the detriment of September (two cuts system) or July and September (three cuts system) cuts. Regarding to K, this element is much more important as the frequeney of harvest is increased and the N applied dose is fractionated. There was no significant increase of the grassland production due to the frequeney of harvest (two vs. three cuts). However, it could be observed an increase in the yield when P+K fertilisation was applied in the intensive management system (three cuts). On the contrary, N and N+K fertilisation depressed the production in three cuts system.