Phosphorus in the soil and in the herbage of the Karst pasture

Abstract

The results of P fertilization on karst pasture in a 7-year study are discussed. The changes of P availability for plants, the content of P in herbage and the yield increase at different rates of applied fertilizer (0, 90, 270 and 540 kg P2O5 ha-1 - total in 3 years) were measured. In treatment with low rate of P (30 kg P2O5 ha-1 year-1), the concentration of available P in soil was increased for 40 %. At three times higher rate of applied P, the content in soil was increased for 4,4 fold. The most of available P was found in top layer of soil as show the results of soil sampling at two depths (0 - 3 cm and 3 - 6 cm). The contentration of P in soil decreased during five growing seasons for 0.4 mg to 3.6 mg P2O5 100 g-1 of soil, depending on rate of applied fertiliser. Because the soils of karst pasture are very poor on P, the concentration of P in herbage is very low too. Only one half of the animal's need for P can be covered this way. The increase of P concentration in herbage as a result of applied P is more important than the increase of the yield. At annual rate of 90 kg P2O5 ha-1 the average concentration of P in herbage was 2.1 g P kg-1 of DM. The effect of applied P on the yield of available and used herbage by grazing animals was small, due to low soil pH and slow improvement in floristic composition of the sward.