The effect of organic amendments on mineral phosphate fractions in calcareous soils

Organic amendments considerably affect nutrient balance and interfraction mobility of nutrients by influencing the chemical, physical, and biological environment in soils. In this study, the effects of five amendments including: two composts, farmyard manure, packaging‐industry by‐product, and olive‐mill waste on time‐dependent interfraction mobility of P among mineral P fractions in two semiarid‐region soils differing in carbonate content and texture were investigated. Organic materials were applied at the rate of 0, 25, 50, and 100 g (kg soil)^–1 soil thoroughly mixed and incubated at 27°C ± 2°C for 110 d. Phosphorus fractions were sequentially extracted by 0.1 M NaOH + 1 M NaCl (NaOH‐P), citrate‐bicarbonate‐dithionite (CBD‐P), and 0.5 M HCl (Ca‐P). Results showed that organic amendments especially farmyard manure significantly influenced NaOH‐P, CBD‐P, and Ca‐P. In addition, higher application rates of organic residues increased NaOH‐P fraction. NaOH‐P and CBD‐P fractions were increased after addition of organic residues and then converted to Ca‐P fraction within the end of incubation period. Increasing application rate of organic residues allowed P to be retained in more labile fractions for a longer period. The amount of Ca‐P was found to be related with carbonate content of soils. It can be concluded that organic residues applied to calcareous soils may enhance P nutrition of agricultural plants.