INTERACTIVE EFFECTS OF TILLAGE AND CROP ROTATIONS ON YIELD AND CHEMICAL-PROPERTIES OF SOILS IN SEMIARID CENTRAL SPAIN

This study evaluates the potential of no-tillage practices in the mana gement of soils in semi-arid Mediterranean areas from central Spain, F ield experiments on the interactive effects of tillage and crop rotati ons on soil chemical properties and crop parameters were conducted on a Calcic Haploxeralf (non-calcic brown soil), The experimental design included the comparison of plots subjected simultaneously to (a) no-ti llage or conventional tillage and (b) barley (Hordeum vulgare L. cv. ' Aramir') monoculture or crop rotations, The latter consisted of barley -vetch (Vicia sativa L.) or barley-sunflower (Helianthus annus L.) rot ations, The results were analysed for 3 growing years. Irrespective of tillage systems, crop yield depended greatly on environmental conditi ons. Crop parameters in the no-tillage system were not significantly d ifferent from those under conventional tillage. When compared with con ventional tillage, no-tillage favoured the surface accumulation of soi l C as well as of available P and K. Crop rotations increased barley y ield in comparison with a barley monoculture. The barley-sunflower rot ation gave the greatest barley yield and improvement in soil fertility . Our results suggest that no-tillage can lead to a progressive improv ement in soil nutrient status, but have little or no effect on crop pa rameters; the latter may be successfully controlled through suitable c rop rotations. Of the factors examined, the environmental conditions o f temperature and rainfall in the Mediterranean climate showed the gre atest influence on the results between different cropping years.