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

Abstract 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 32P‐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.