Pasture management under hardwood plantations: legume implantation vs. mineral fertilization

PresentationEurope, and particulartly Spain, have a shortage of quality wood. Indeed, there is a growing interest from many owners into these species with intensive management, which are compatible with the implantation of silvopastoral systems. The fertilization is one of the most controversial management practices that is used for reducing rotation length. The implantation of legumes, which are able to fix atmospheric nitrogen, could allow reducing the economic costs of these plantations, improve the pasture production and quality and optimize their environmental functions. The objective of this project is to study the response of trees and pasture in a silvopastoral system established in an intensive hardwood plantation, to the implantation of legumes as nitrogen fertilizer, and its environmental implications. This study was developed in various plantations of 15-s year old walnut in Extremadura (Spain). Three treatments were tested: mineral fertilization (NPK), sowing of legumes (complemented by PK mineral fertilizers) and control treatment, combined with three levels of irrigation. The nutritional and physiological status of trees were analyzed, as well as their growth. In addition, pasture production, available nutrients (N,P,K) in soil and nitrate leaching were studied. The implantation of legumes, which improved the available nutrients in soil, and the mineral fertilization treatments, both produced similar pasture production, tree growth and nitrogen content in tree leaf, and higher than the control treatment. However, there was no differences in physiological status of trees and organic matter content in soil. Respect to nitrate leaching, the highest values was observed in the uppermost soil layer (0-30 cm), especially in legume treatment, but there was no difference among treatment under this deep, that reduces groundwater pollution. In conclusion, the sowing of legumes, as the substitution of N mineral fertilizers, can improve the profitability of silvopastoral systems developed in quality timber tree plantations