Nitrate leaching from a Sitka spruce plantation and the effect of fertilisation with phosphorus and potassium

Abstract

Mature Sitka spruce ( Picea sitchensis (Bong.) Carr.) plantations in the Beddgelert area of North Wales have comparatively large concentrations and leaching rates of soil water nitrate. To determine whether elimination of any phosphorus or potassium deficiency in the trees can result in increased demand for N and reduce nitrate leaching rates, P and K fertiliser was applied at two rates (P1K1 and P2K2) in a randomized block experiment. Soil water nitrate concentrations dropped significantly in the P2K2 treatment, compared with the Control, for two growing seasons following application of the fertiliser. There was no significant effect of the P1K1 treatment. Demand for N, P and K by the trees was estimated using root bioassay techniques. Three months after application of the fertiliser, uptake of all three nutrients from solution by excised roots was significantly lower in the P1K1 treatment, and very significantly lower in the P2K2 treatment, compared with the Control. These results imply that at least part of the demand for P and K in the trees had been satisfied by increased uptake of the applied fertiliser, resulting in an increased uptake of N. Foliar analysis confirmed that additional N was present in the trees in the P2K2 treatment. Fertiliser application is a technique which could reduce nitrate leaching rates. Only at sites where nitrate is a major component of the total inorganic anion concentration will reduction in nitrate concentration reduce acidification rates significantly.