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Anionic resin-extractable phosphorus as an index of phosphorus availability in calcareous soils of Crete amended or not amended with pig manure compost

Mohamed, M.A., A. Stamatakis and V. Keramidas. 2012. Communications in Soil Science and Plant Analysis 44:50-61


The objectives of this study were (a) to evaluate whether the phosphorus (P)-supplying power of soils, as assessed by Plant Root Simulator (PRS)™ probes, constitutes a reliable index of bioavailable P in calcareous soils and (b) to examine whether pig compost addition to calcareous soils increases their P-supplying power, P uptake by the crop, and yield. The study was conducted in a pot experiment with 14 calcareous soils and involved control soils, test soils, and soils treated with compost in which ryegrass was grown and harvested every month. Three biomass cuts were obtained, and P uptake, P concentration in the biomass, and biomass yields were determined. Correlations of total P uptake or P concentration in the biomass versus P-supplying power gave statistically significant coefficients of determination (P ≤ 0.01), which explained 82% and 87-92% of the variability of P uptake and P concentration, respectively. The relation between biomass yields and P-supplying power of soils satisfactorily obeyed the Mitscherlich-Bray growth function, permitting the establishment of a "critical point" of P-supplying power, which was about 5 μg P/resin surface area/15 days. These results provide strong evidence that the P-supplying power of soils, as assessed by PRS™ probes, is a reliable index of bioavailable P in calcareous soils and even more reliable than the one determined by the conventional method of Olsen. Compost addition to soils had a beneficial effect because it increased their P-supplying power, P uptake by the crop, and biomass yields but the P-supplying power of the treated soils did not correlate with P uptake and P concentration in the biomass. Although this discrepancy could not be explained by the data at hand, it remains certain that pig manure compost increased yields and it might not only complement but also substitute for P fertilization.

Key Words

Mitscherlich-Bray function, PRS™ probes, ryegrass