Concentrations of nitrate in soil water following herbicide treatment of tree planting positions in an upland agroforestry system

Abstract

Concentrations of nitrate have been measured in soil water samples collected during the first year of an agroforestry trial at an upland site in Wales. Nitrate concentrations were higher in water samples collected from herbicide-treated areas around trees than from undisturbed pasture between the trees. These differences were statistically significant fo samples collected during the summer but not for those from the main winter leaching period. The enhanced nitrate concentrations that were measured beneath the tree planting positions may have implications for the nutrition of the trees but, at the planting densities included in the trial (100 and 400 trees/ha), are estimated to represent only a small increase in the nitrate content of water draining from the agroforestry area as a whole, relative to that from unplanted pasture. There was some evidence that preferential deposition of urine, but not of dung, contributed to the increased nitrate contents in the soil around the planting positions.