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This work studies the ecological impact to the environment (soil, vegetation) produced by the application of differenttreatments, such as phosphoric fertilization, superficial tillage on the pasture, or deep ploughing and sowing fodder, ontwo types of soil, slate and granite over the period 1994-1997. The evolution of the chemical and granulometric compositionof the soil and also the covering and floral composition of the vegetation was monitored. The duration of the residualeffect was also considered, in order to determine the best possible time to carry out these practices. The evolution ofthe pH and the levels of organic matter, carbon, nitrogen, calcium, phosphorus, potassium, clay, lime and humidity werethe main factors surveyed on the soil. For each type of treatment, the floral abundance and density of the vegetation wasrecorded and catalogued. One of the conclusions obtained was that both the content in organic matter of the soil and thefloral cover decreases with sowing of fodder. The recovery of the soil organic matter usually takes more than four years,whereas the vegetation cover reaches its initial levels after three years. By the end of the experimental period these coverlevels are even higher than the original ones. In three year old oat stubble, pastures that can be related to syntaxonomicunits (Koelerio Corynephoretea y Molinio-Arrhenateretea) were seen. The plots of fertilized pasture showed higher levelsof legumes whereas the plots that had been fertilized and ploughed showed increased values of both legumes and grasses.The oat stubble showed higher levels of Composites after the first year, but their presence decreased with time., Se estudió el impacto ecológico que produjo sobre el medio natural (suelo y vegetación) la aplicación de las variables fertilización fosfórica, laboreo superficial de pastos y laboreo profundo con siembra de forraje en dos suelos, uno desarrollado sobre pizarras y el otro sobre granitos, durante el período 1994-1997. En el suelo se controló la variación de diversas propiedades químicas (pH, materia orgánica, elementos asimilables) y físicas (humedad, granulometría). En la vegetación espontánea se controló la cobertura y composición florística, así como la duración del efecto residual, con el fin de estimar el período aconsejable para la repetición de estas prácticas. Los resultados indican una disminución del contenido de materia orgánica del suelo y de la cobertura vegetal en las siembras de forraje. Los contenidos de materia orgánica se recuperaron muy lentamente a lo largo de más de cuatro años. La cobertura y la vegetación se recuperaron a partir del tercer año (...)

In two «dehesa» grasslands with different soils, one over slate and the other over granite, studies were carried out toinvestigate the influence that phosphoric fertilization, surface tillage of pastures and oat sowing have on the primaryproduction and its nutritive value, on the index of utilization of raining water, and on the evolution of oat stubble withtime. Additionally, economic studies of the previous results have been carried out. Phosphoric fertilization and superficialtilling of pastures did not have a relevant influence on the primary production. Additionally, in the successive regrowthover oat stubble there was no response to phosphoric fertilization. The production increments with respect tocontrols are related to the preparatory tillage for sowing the oats, and the changes that the vegetation experimented.This effect decreased with time. The dry matter production in the oat treatments was higher than in the pastures, bothin slate and granite soils. In dehesa systems the use of raining water for the production of 1 kg dry matter ha-1 was verylow, and, on the average, 0.278 and 0.588 l m-2 were needed in pastures, but this amount decreased significantly in theoats: 0.059 and 0.110 l m-2 in slates and granites, respectively; with better use of the water in the more fertile soils. Theeconomic response to the oat sowing was about 252 and of 160 euros ha-1 year-1 in slates and granites, but there was noeconomic response to the fertilization and superficial tilling of pastures during the period of the experiment., En dos sistemas adehesados, uno con un suelo de pizarras y otro de granitos, se estudió la influencia de la fertilización fosfórica y del laboreo superficial de pastos, así como de la siembra de forraje de avena. Se analizaron la producción primaria y su valor nutritivo, el índice de utilización de agua de lluvia, la evolución del rastrojo de avena con el tiempo, y el estudio económico de los resultados. La fertilización fosfórica y el laboreo superficial de pastos en ambos suelos. Los incrementos de producción sobre el testigo están relacionados con el laboreo preparatorio para la siembra de avena y los cambios de vegetación experimentados, efecto que se debilita con el tiempo. En estos sistemas adehesados la utilización del agua de lluvia fue muy baja, necesitándose para producir 1 kg MS ha sup(-1) de pasto cantidades medias de 0,278 y 0,588 l sup(-2) (...)