Cuarenta años de fertilización en prados de la montaña de León. II. Influencia sobre la composición botánica

Résumé

Mineral fertilization increases herbage production in mountain meadows. In addition, rapid and significant changes in botanical composition are observed depending on the fertilizers and doses applied. The flora of these áreas can also be modified by harvesting frequency and N rate fractionation. Therefore, all these management practices must be combined properly in order to get a suitable balance among the plants (grasses, legumes and weeds) influencing not only the quantity and the quality of the forage, but also the stability of the meadow. The present study summarizes nine experiments dealing with different management practices (doses and type of mineral fertilizer, number of harvests and fractionation of the N dose) and their effects on the botanical composition of mountain meadows. According to these triáis, one of the main factors influencing the botanical composition is the nitrogen fertilization; this element favours the grasses to the detriment of legumes, which can even disappear with the highest doses regardless of the source of this mineral. In relation to the fractionation of the N dose, only the weeds seem to be affected by this factor; thus, a significant increase of this botanical component can be observed. On the other hand, phosphorus favours the production of both, grasses and legumes, but especially the last ones. Therefore, this fertilizer improves the botanical composition in mountain meadows, this effect being the same regardless of the different sources (type of fertilizer) studied. Phosphorous is needed to keep a balanced and lasting production. Potassium fertilization has a less evident effect on the botanical composition, its effect was only significant when combined with an intensive harvesting system. With regards to the harvest system, three cuts per year favour legumes and weeds, whereas grasses production decreased dramatically. To summarize it can be said that the most balanced effect on the botanical composition of these mountain meadows can be achieved using PK fertilizers. Thus, doses of 80-60 kg ha-' of PK fertilizers can give rise to 62.2% of grasses, 20.3% of legumes and 17.5% of weeds (total production in a two harvest system), or up to 58.4% of grasses, 22.1% of legumes and 19.5% of weeds (total production in a three harvest system).