Effects of different management practices on soil conservation and soil water in a rainfed olive orchard

A field experiment was conducted in an olive orchard of impoverished sandy soil to evaluate the efficacy of different management systems involving the use of plant covers, with respect to the tillage systems generally used in semiarid, continental environments. The results obtained were used to establish the most appropriate herbaceous cover in terms of reduced competition for water and erosion control, and to assess the efficacy of different strategies aimed at increasing soil N and OM contents. Experimental plots were subjected to the following treatments: (1) non-tillage plus a natural vegetation cover; (2) non-tillage plus a subterranean clover (and natural vegetation) cover; (3) tillage plus a vetch cover; (4) non-tillage and weeds control by herbicides; and (5) tillage, leaving the soil free of weeds all year-round. Water contents were determined for soil samples collected at depths of 0–20, 20–40 and 40–60 cm in the plots subjected to the different management systems to identify the effects of rainfall and management on soil water balance in periods of normal, high or low rainfall. The impact of the different management systems on chemical (OM, N, K, P2O5, anions) and biochemical (ATP, CO2/ATP, urease, phosphatase) fertility was also examined. During years of normal or high rainfall, these covers showed no significant, or scarce, competition with the tree. The management strategy used favored the presence and abundance of spontaneous legumes in the covers including natural vegetation. Soil C and N contents were higher in the plant cover systems. Effects on biochemical soil fertility are starting to emerge, with clear indications of microbial regeneration. This was of greatest intensity in plots with substantial proportions of legumes in the covers. The control of soil erosion achieved by covers comprised of herbaceous species was especially satisfactory.