Orchard groundcover management effects on nitrate leaching in an irrigated heavy-clay soil

The purpose of this paper is to monitor the penetration depth of the nitrate front within a heavy-clay soil in a plum orchard and to estimate nitrate leaching losses from the topsoil to the surface waters and/or groundwater from April to October. These effects were investigated under both rainfall conditions (experiment 1) and irrigation and rainfall conditions (experiment 2). For both experiments the influence of two groundcover management systems: cultivated and mowed sod strips, as well as three (0; 150 and 300 Kg N/ha) levels of N-fertilizer application were studied. Nitrate leaching from plum orchards on heavy-clay soils usually occurred in wet periods, when rainfall or irrigation depth was higher than evaporation, and downward and lateral flux of the soil solute was intensive. Mowed sod induced a better hydraulic conductivity of topsoil that enhanced a more homogeneous penetration of nitrate solution in the soil matrix, while the cultivated treatments rather showed a preferential character. The higher the N fertilizer application the larger the nitrate leaching losses below 1 m soil depth.