Forages resources in "dehesa" systems: fertilization, tillage, and forage sowing. 2. Productivity and use of rain water

Abstract

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.