Forages resources in "dehesa" system: fertilization, tillage and forage sowing. I. Influence to the environment (soil and vegetation)

Abstract

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.