Nitrogen and phosphorus runoff losses from orchard soils in South China as affected by fertilization depths and rates

Fertilizers are heavily applied in orchards of the hilly and mountainous topography of South China and may increase nutrient loadings to receiving waters. A simple runoff collecting system was used to measure the effects of different fertilization treatments on total N and P concentrations of surface runoff in a Chinese chestnut (Castanea mollissima Blume) orchard in Dongyuan County, Guangdong Province, China. In such orchards, fertilizer was typically applied in two short furrows or pits on either side of each tree. Treatments included three application depths (surface, 10 cm and 20 cm), and three application rates (low, median and high). Results showed that 90.5% of the runoff water samples had a total N concentration higher than 0.35 mg L-1 and 54.2% had a total P concentration higher than 0.1 mg L-1. Fertilizer application at all depths and at all but the lowest rate significantly increased total N and P concentrations in runoff water. Fertilization with chemical compound fertilizer at a soil depth of 20 cm produced significantly lower (P < 0.05) total N concentration in runoff than both surface and 10-cm depth fertilization, and significantly lower (P < 0.05) total P concentration in runoff than surface fertilization. Total N and P concentrations in runoff significantly increased with the application rate of organic fertilizers. With the exception of total P concentrations, which were not significantly different between the control and fertilization at a rate of 119 kg P ha(-1) in organic form, all the other fertilization treatments produced significantly higher total N and total P concentrations in runoff than the control. A fertilization depth > 20 cm and an application rate < 72 kg N ha(-1) or 119 kg P ha(-1) for compound organic fertilizer was suggested to substantially reduce N and P runoff losses from hillslope orchards and to protect receiving waters in South China.