Quantifying phosphorus fertilizer distribution and the contribution of fertilizer and soil legacy phosphorus to phosphorus uptake by maize - A ³²P-labelling study

The availability of phosphorus (P) fertilizer applied to soil can diminish rapidly because of the complex soil P immobilization processes. However, the quantitative distribution of fertilizer P in the soil P fractions is not fully understood. Here, two experiments were conducted in a greenhouse using P-32-labelled KH2PO4 to (i) quantify the distribution of P fertilizer in soil fractions, microorganisms and maize shoots grown in contrasting soils; (ii) characterize the effect of planting maize on soil P fractions and (iii) determine the amount of plant P derived from fertilizer vs. soil. Depending on the soil type, 74.1%-84.1% of the labelled P was retained in the soil, 11.4%-14.5% was found in maize shoots and 0.7%-4.5% was present in microorganisms. Distribution of applied P in the soil P fractions was dependent on soil type, with most P present as NaOH-Pi and residual-P in the Red soil, and as HCl-P in the Fluvo-aquic soil. Root-mediated processes were involved in mobilisation of residual-P in all three soils, with significant depletion of NaOH-Pi in the Red soil, NaOH-Pi and HCl-P in the Black soil, and HCl-P in the Fluvo-aquic soil. The plant P derived from fertilizer and soil increased with increasing P addition rates in all three soils. In the soils with low-P availability, fertilizer contributed more P to plants than soil, whereas in the initially high-P soil, the opposite occurred. In conclusion, the partitioning of fertilizer P to various soil P fractions is dependent on the soil type, and the contribution of P derived from fertilizer to maize P uptake was related inversely to the soil legacy P.