The influence of organic fertilizers application on phosphorus and potassium bioavailability

A prerequisite to use organic fertilizers in a sustainable way is to quantify the amount of phosphorus and potassium available for plants that could be taken up by a crop. The objective of this study was to evaluate direct and subsequent influence of organic fertilizers addition (poultry manure and two types of composts) on the changes of bioavailability of phosphorus and potassium in soil and their accumulation in the aboveground oat biomass (Avena sativa L.) during three years. The available phosphorus and potassium contents in soil had a degressive trend during the years of experiment. The lowest contents of these elements in soil were found in all treatments in the last year of the experiment. The plants took up the least P and K after application of compost derived from predominant sewage sludge portion. A stronger correlation (R = 0.88; P < 0.05) was found between available content of K in soil treated with organic fertilizers and K content in the aboveground biomass of oat than in the case of P (R = 0.45; P < 0.05).