Soil Tillage and N Fertilization: Key Practices for the Sustainability of Mediterranean Agroecosystems.

Soil tillage and N fertilization play an important role on the agronomic and environmental sustainability of Mediterranean agriculture. A series of long-term field experiments were established in NE Spain to compare different tillage systems and N fertilization strategies under rainfed and irrigated cropping systems. Soil water, mineral N and organic carbon dynamics as well as annual crop productivity have been continuously measured. Soil greenhouse gas emissions (N₂O, CO₂ and CH₄) were measured under dryland and irrigated conditions with the static chamber method. At specific points in time, other soil quality attributes such as aggregation and organic C protection in aggregates were also measured. Tillage and N fertilization had a significant impact on most of the variables measured. Under dryland winter cereal production, no-tillage (NT) led to greater crop productivity and C sequestration than conventional intensive (CT) or reduced tillage (RT) given its positive impact on soil water storage. Crop biomass, grain yield and soil organic C sequestration response to mineral N fertilizer only occurred when using NT. Soil N₂O emissions were similar between tillage systems and increased at increasing N rates under dryland barley production. Nevertheless, greater soil N₂O emissions occurred when using NT at high N rates compared to CT or RT under irrigated maize. However, the use of RT and NT guaranteed a proper establishment of corn plantlets and increased corn yield when compared to CT, given the susceptibility of the soil to crusting when applying irrigation. Tillage and N fertilization had a minor impact on CH₄ uptake by soil. The synthesis of long-term experimental and modelling results we present highlights the adequacy of NT and medium rates of N to maintain crop production and environmental sustainability in semiarid Mediterranean agroecosystems.