The phosphate desorption rate in soil limits phosphorus bioavailability to crops

Erik Smolders, Sophie Nawara, Evelien De Cooman, Roel Merckx, Stijn Martens, Annemie Elsen, Wendy Odeurs, Hilde Vandendriessche, Jakob Santner, Fien Amery

Research output: Contribution to journalA1: Web of Science-articlepeer-review

Abstract

This study was set up to identify the role of the phosphorus (P) desorption rate in P diffusion and in P bioavailability in soil. The P desorption kinetics were measured with a zero-sink method in soil suspensions (0–77 days) for a set of soils that either had or had not been mined for P in a glasshouse study. The desorption kinetics was fitted by a serial two-pool model, discriminating a fast desorbing P pool (Q1) with desorption half-lives of 3–8 days, and a slowly desorbing P pool (Q2), which replenishes the fast P pool with 100-fold larger half-lives than the fast pool. Phosphate desorption was smaller and slower after soil P mining compared to that in the original soil samples and mining reduced the Q1/Q2 ratio. This kinetic model was embedded in a 1D planar diffusion model predicting that the diffusive flux of P to a zero sink in 5 days varies by a factor of 1.4 among the observed Q1 desorption rate constants, keeping other parameters constant, and that the reduced Q1/Q2 ratio upon P mining sharply reduces the diffusible P in soil. The P uptake model of Barber-Cushman was extended with P desorption kinetics and was successfully calibrated to the P uptake data of the glasshouse P mining study. The model correctly predicted that reduced nitrogen (N) fertilization enhances the soil P-use efficiency because of lower critical P demand rates at slower growth. Finally, that new model predicted that maize requires >3-fold more available P in soil than wheat because of a higher P demand rate per unit root area of maize than that of wheat. This confirms a similar factor difference in critical soil P concentrations observed in P-response trials in Belgium between 1973 and 2018. This study shows that the P desorption rate limits P bioavailability for fast growing plants with a small effective root area, especially under negative soil P balances that slow down the desorption rate of P in soil. Highlights: The diffusion coefficient of P in soil is reduced by soil P mining Faster growing plants require more available P in soil because they rely on high diffusive P fluxes P desorption rate can limit the P bioavailability.
Original languageEnglish
JournalEuropean Journal of Soil Science
ISSN1365-2389
DOIs
Publication statusPublished - 1-Jan-2020

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