Nitrogen leaching from soils in the Kopais area of Greece

Abstract. The contribution of agriculture to the nitrogen pollution of surface and ground waters of calcareous lake soils in the Kopais area (190 km²) of Greece was studied over three cropping seasons. Sample fields were chosen from seven representative soil units under different crop rotations. The distribution of mineral N (NO₃-N + NH₄-N) throughout the soil profile and the concentration of NO₃-N in the ground water and drainage water were measured and allocated to 6-month winter or spring periods. For all fields N was leached to the deeper soil layers and to the saturated zones by both excess winter rainfall and spring irrigation of different crops The amount of nitrogen leached depended on the amount of nitrogen fertilizer applied; the depth of leaching varied with the physical properties of the soils. Losses in individual fields accounted for the equivalent of 17.6–80.8% of the nitrogen applied to maize and 70.5–94.1% of that applied to wheat. For the whole region estimated minimum N losses ranged from 175, 912 to 783, 564 kg for the 6-month period. Nitrate concentrations in the ground and surface waters were often more than the EC target level of 25 mg/1.