Measuring In Situ Changes in Labile Soil Phosphorus with Anion‐Exchange Membranes

Abstract

Conventional chemical extraction methods to measure labile soil P are often inadequate for detecting fine temporal‐ and spatial‐scale soil P dynamics in situ. We refined and calibrated methodology for anion‐exchange resin‐impregnated membranes (AEM), related AEM‐P to soil solution P for a high‐P‐retaining soil, and evaluated the method's viability under humid tropical field conditions. We determined: (i) AEM recyclability, (ii) AEM P sorption kinetics, (iii) the correlation between soil solution P and AEM‐P for an Andic Humitropept, and (iv) potential interference from other anions (NO−3 and SO2−4) on AEM P extraction. We used AEMs in a field decomposition study to evaluate plant residue and manure P release characteristics and concurrent fluxes in labile soil P. The AEM P sorption capacity was not altered significantly by repeated use. Nitrate solution concentrations in an aqueous medium of 50 and 100 mg NO3‐N/L reduced AEM P sorption by 50 and 75%, respectively, regardless of P solution concentration; SO4‐S at 500 and 1000 mg/L reduced AEM P sorption by ≈98%. The relationship between AEM‐P and soil solution P was curvilinear at both nonequilibrium and equilibrium soil solution P concentrations; it was essentially linear at soil solution concentrations ranging from 0 to 2 mg P/L. The AEM behaved as a dynamic exchanger rather than an infinite sink for P, particularly in the context of a low‐pH, high‐P‐retaining soil. The AEMs detected biologically relevant soil P pulses in the field decomposition study. The technique holds promise as an easy method for measuring soil P fluxes with minimal soil disturbance.

Practical applications of ion exchange resins in agricultural and environmental soil research

“…When resin capacity is large enough to easily sorb all the ions released throughout the exposure period, the resin functions as a sink. Otherwise, the resin-soil system will change its function from sink to a dynamic exchanger (Cooperband and Logan 1994). One should always bear in mind that ion adsorption by resin never acts as a sink indefinitely.…”

Sampling spatial and temporal variation in soil nitrogen availability

“…In a laboratory study using homogeneous soils, variability in nitrate uptake among individual membranes was generally found to be low (CV<10%) (reanalysis of data presented in Subler et al 1995). Previous work also indicates that storage of air-dried membranes for up to several months does not signi®cantly aect the retention of nutrients on the membranes, and that membranes may be reused several times in the ®eld without appreciable loss of ion exchange capacity (Cooperband and Logan 1994;S. Subler, unpublished data).…”

Efeito da moagem do solo no teor de fósforo disponivel por Mehlich-1, resina em esferas e em lâmina

“…A resina em lâmina foi utilizada com êxito para medir o "P disponível" por outros autores (Parfitt et al, 1994;Myers et al, 2005). Para análise de P, Cooperband & Logan (1994) testaram a resina em lâmina, considerando-a eficiente na avaliação do P em soluções puras de laboratório e do P-lábil em solos. Bissani et al (2002) testaram o Mehlich-1, a resina em esferas e em lâmina em 20 solos do Rio Grande do Sul e encontraram resultados semelhantes entre estes três métodos e a resposta das plantas.…”