Options to reduce N loss from maize in intensive cropping systems in Northern Italy

Maize (Zea mays, L.) is not only the main crop in the intensively cultivated Po Plain (Northern Italy), but also the one that produces the largest N Surplus. This study is based on experimental data from the Tetto Frati long-term trial (Turin, NW Italy) to demonstrate that the impact on soil and water quality of high-yielding, maize-based cropping systems can be reduced through proper management. Nitrogen use efficiency and loss indicators were calculated and compared among various management options: (i) maize monoculture at high N fertilizer rates for grain production (most widespread management), (ii) entire plant (with straw) harvest, (iii) double-cropping system with a winter crop, (iv) maize–grass ley rotation, and (v) change in fertilizer type. The entire maize plant removal reduced N leaching by 10–20%; however, carbon sequestration was also reduced. A maize–Italian ryegrass double cropping system improved the efficiency of organic fertilizers, and reduced leaching by 25–40% relative to monoculture. A rotation with grass ley reduced N impact only when fertilized with urea, and not when organic fertilizers were used. Urea, slurry, and farmyard manure were equally utilized by the crop; if distributed and incorporated just before sowing, both organic fertilizers built up the soil organic matter content and reduced N leaching by 20–50% with respect to urea. This study has shown that farmers in NW Italy have several opportunities to continue cultivate maize thus accomplishing agri-environmental legislation.