Phosphate extractability and mobility in leached soil columns as affected by polymer amendments

Abstract

Little information is available concerning the beneficial effects of polyacrylamide (PAM) polymer on plant nutrient availability. To obtain a better understanding on this subject, a laboratory column leaching study was conducted to investigate the effect of water‐soluble synthetic polymers on the availability and mobility of fertilizer P added to the surface of two agricultural soils collected from the central and southern regions of Saudi Arabia. Air‐dried soil samples were uniformly treated with three PAM polymers (one nonionic and two anionic) at rates of 0 and 200 mg kg−1, and packed into 50 cm columns. The top 5 cm of soil from each column was removed, mixed thoroughly with fertilizer P (KH2PO4) at rate of 400 mg kg−1, and then replaced in the column. All columns were subjected to an intermittent leaching and incubation for 63 days. Extraction and analysis of each 5 cm layer of the soil columns at the end of the experiment showed that extractability and movement of added P in soils were drastically reduced in the presence of synthetic polymers compared to fertilizer P only. The extractability and movement of P decreased with increasing anionic charge of the polymer. Thus the reactivity of P fertilizer with the polymers was the dominant and overriding determinate of the extraction and movement of surface‐applied P. The transformation of added P showed a decrease in NH4Cl‐P, Al‐P, and Ca‐P fractions in all samples amended with polymers, whereas the Fe‐P fraction increased with polymer addition. In general, evidence is provided for synthetic polymers playing a major role in reducing downward movement, and available inorganic fractions of added P in both calcareous and noncalcareous soils. The actual mechanisms involving fertilizer P reactions with polymers merit further investigation.