This study examined changes in soil enzymatic activity caused by constant nitrogen fertilisation and varied potassium fertilisation in soil abundant with available phosphorus. Pea (Pisum sativum L.) was used as the test plant. A field experiment was carried out in 2010-2012, in a field located at a greenhouse facility owned by the University of Natural Sciences and Humanities in Siedlce. The experiment was completely randomized and carried out in four replications with the following mineral fertilisation: control object, N, NK1, NK2, NK3, NK4 and NK5. Mineral fertilisation was applied in kg ha-1: N-20, K1-41.5, K2-83, K3-124, K4-166, K5-207.5. Nitrogen was applied as ammonium nitrate in early spring, potassium – as 60% potassium salt split into two doses: I (to 124 kg ha-1) – in early spring, II (above 124 kg ha-1) – after the first date of soil sampling. The soil samples were collected from the Ap horizon (0-30cm) of the rhizosphere in four times. The activity of urease decreased significantly with the increasing doses of potassium. The highest activity of dehydrogenases was found in soil fertilised with nitrogen at 20 kg ha-1 and potassium at 166 kg ha-1. Varied potassium fertilisation did not significantly affect the level of acidic or alkaline phosphatase. The biochemical index of potential soil fertility, as affected by nitrogen fertilisation, was the highest with nitrogen supplied at 20 kg ha-1 and with potassium at 166 kg ha-1.

23.1.2018