P Pools After Seven-Year P Fertiliser Application Are Influenced by Wheat Straw Addition and Wheat Growth

Little is known about the effect of long-term P fertilisation on soil P pools and how they are influenced by straw addition and plant growth. Two experiments were carried out with soil which had been amended with 0, 10 and 20 kg P ha−1 for 7 years (referred to 0P, 10P, 20P). In experiment 1, soil was incubated moist for 4 months without or with 5 g kg−1 barley straw (C/P 255). Then wheat was grown for 4 weeks. In experiment 2, wheat was grown for 5, 10 and 15 weeks. HCl P, citrate P, resin P and microbial biomass P (MBP) were two-fold higher with 20P and 10P than 0P. After 4 months compared to 10 days, HCl P and citrate P were 25% lower with straw, but unchanged without straw. Resin P and MBP were two-fold higher. With 10P and 20P after 4-week wheat growth, citrate P was 25% higher and HCl P 25% lower. Plant P uptake was higher with straw, In experiment 2 after 10 and 15 weeks compared to the start at 10P and 20P, HCl P and citrate P were reduced by 20%. Plant P uptake was smaller than the decrease in HCl and citrate P. The greater P uptake by wheat in soil with straw indicates that microbial biomass P is an important P source for plants. In P amended soil, wheat mobilised HCl and citrate P, but only took up a fraction of the mobilised P.