Assessing the impact of crop diversification on nitrate leaching losses in irrigated maize under Mediterranean conditions

Including leguminous cover crops or double cropping in intensive maize-based systems under irrigated Mediterranean conditions are strategies with potential to increase yields and reduce nitrate leaching, but their interaction with specific crop management and soil conditions needs to be ascertained. Four maize-based systems were assessed in 24 lysimeters filled with two soils common in the region differing mostly in depth: deep (0–1.20 m depth, 243 mm maximum available water) and shallow (0–0.50 m depth, 78 mm maximum available water). The systems tested were: a long-season maize with winter fallow (F-LSM), the reference system, or after a legume cover crop (CC-LSM), and a short-season maize after barley (B-SSM) or after pea (P-SSM). Irrigation was scheduled according to crops water needs resulting in annual average of 701 mm (F-LSM), 717 mm (CC-LSM), 821 mm (B-SSM) and 826 mm (P-SSM). Drainage volume was influenced by soil depth. In deep soil, grain yield and crop water productivity were + 26 % and + 13 % higher than in shallow soil. Compared to the F-LSM system, the B-SSM system increased grain yield in deep (+36 %) and shallow (+ 44 %) soils but required more irrigation water (+17 %) and N fertilizer (shallow: +40 %; deep: +71 %) but reduced nitrate leaching by about 70 % in both soils, with nitrate concentrations below 10 N-NO3 mg L−1. Introduction of leguminous species in the rotation (CC-LSM and P-SSM systems), allowed to reduce N fertilization and increased the partial factor productivity of N, but did not decrease nitrate leaching. The P-SSM increased grain yield by 17 % and 34 % in deep and shallow soils.