Soil Fertility and Phosphorus Leaching in Irrigated Calcareous Soils of the Mediterranean Region.

To ensure soil quality and soil health, it is necessary to improve fertilization practices while minimizing environmental impacts. The aim of this study was to record the state of the art on soil fertility related to fertilization management (organic and/or mineral) and to detect environmental challenges in highly productive fields. A soil survey was set up in a new irrigated area (c. 20 years old), in the north-eastern part of Spain, which is mainly devoted to double annual crop rotations of cereals and maize. The area also supports an important animal rearing activity. The survey covered 733 ha of calcareous soils, owned by 35 farmers. At each farm, fertilization management was recorded, and soil was analyzed for nutrients and heavy metals. Multivariate analyses were performed. Total N, P, Cu and Zn, and available P, Cu, Zn and Mn soil concentrations were associated to the use of organic amendments. Heavy metals concentrations were below established thresholds. Available P (Olsen-P) was identified as an indicator of the previously adopted fertilization management and of the potential of P leaching towards deeper soil layers. Regression analyses were performed. A displacement of available P from the uppermost layer (0-0.3 m) occurs in the breakpoint of 86 mg P kg-1 soil. Preventative actions might be established from 53 mg P kg-1 soil due to the slowdown in P immobilization. Our results reinforce the importance of setting up P threshold soil levels for best practices of fertilization, as a basis for sustainable agriculture intensification.

Oribatid mites in different Mediterranean crop rotations fertilized with animal droppings.

Unsustainable soil management is one of the drivers of soil degradation, but impact assessment requires the development of indicators. Oribatids might be considered as early indicators of disturbances due to the stability of their community. The aim of this study was to investigate the feasibility of oribatids as bioindicators of sustainable agricultural practices. Under a dry Mediterranean climate, three fertilization experiments - two under a two-crop rotation system and one under maize monoculture and established 12 years earlier - were sampled 3× for oribatid identification during the last annual cropping cycle. The hypothesis was that different nutrient and crop managements affect the number of oribatid species and individuals present, and these parameters could be used as indicators of soil degradation. In total, 18 oribatid species were identified, and 1974 adult individuals were recovered. Maximum abundance was found prior to sowing. Pig slurry (PS) vs. control, and dairy cattle manure (CM) vs. mineral fertilization increased oribatid abundance. This increase was evident when the average applied rates with PS were ca. 2 Mg of organic matter (OM) ha- 1 yr- 1, or higher than ca. 4 Mg OM ha- 1 yr- 1 for CM. When the preceding crop was wheat and PS or CM were used, Oribatula (Zygoribatula) excavata (which reproduces sexually) predominated. In maize monoculture fertilized with CM, Tectocepheus sarekensis and Acrotritia ardua americana (which can reproduce through parthenogenesis) prevailed vs. Oribatula, which indicated a heavily disturbed soil. Under this specific Mediterranean environment, the predominance of certain parthenogenic oribatid species and the number of individuals provide advanced warning on soil degradation.