EFFECTS OF WATER AND NUTRIENT APPLICATIONS IN A SCOTS PINE STAND TO TREE GROWTH AND NUTRIENT CYCLING

In a Scots pine forest stand, demineralized water and a complete set o f nutrients with water were applied to the soil by means of frequent i rrigation for four years in order to eliminate water and nutrient shor tage of the trees. Apart from this optimization, dissolved (NH4)(2)SO4 was irrigated at a rate of 120 kg N ha(-1) y(-1) to create a situatio n of N excess. Effect of treatments on tree growth and chemical compos ition of soil water and vegetation were monitored. From the first trea tment year onwards basal area growth increased by ca. 35% as a result of the increased water supply. Nutrient applications increased K and P concentrations in pine needles immediately, but growth was enhanced o nly in the fourth treatment year and coincided with an improved K supp ly. Most of the applied P and K was retained in the soil, and only 6% was recovered in the vegetarian. Tree nutrient status did not respond on Ca and Mg applications, whereas Ca and Mg seepage losses were incre ased with ca. 5 kg ha(-1) y(-1). The applied NH4 was mostly retained i n the 0 - 20 cm surface soil and caused a drastic increase of Al in so il solution. Tree growth was stimulated initially by extra NH4, but wa s hampered after three years obviously because of a decreased P nutrit ion. The applied base cations were absorped to the soil and the accomp anying anions were leached, thus temporarily increasing the acidificat ion of the soil solution.