The in situ ion exchange resin membrane allows a partial simulation of the behavior of plant roots regarding phosphorus absorption from soil solution. Soil sampling is rendered unnecessary since the technique is used directly in the soil where the plants are grown and may be a promising methodology in the determination of phosphorus availability for crops. To evaluate the technique, a greenhouse experiment was carried out with resin membranes buried in the soil when plants were sown (day zero) and removed after 2, 5, 10, 20 and 40 days, to evaluate the amount of phosphorus extracted in different soils maintained at a moisture content near the water-holding capacity, under corn (method resin-cc) and water-saturated, without cultivation and under rice (method resin-sat). Soil samples were collected to determine available P by the methods resin membrane (standard), Mehlich-1 and Mehlich-3 and the extracted amount was correlated with P absorbed by crops. On average, Mehlich-1 extracted 1.3 and 1.9 times less phosphorus than the resin standard and Mehlich-3 methods, respectively; resin-cc method extracted, on average, 2.2 times less phosphorus than the resin-sat. The correlation coefficients among phosphorus extracted by the different methods and phosphorus absorbed by corn and rice increased in the sequence resin-cc < resin standard < Mehlich-1 < Mehlich-3 < resin-sat. The correlation coefficient between phosphorus extracted with buried resin and phosphorus absorbed by corn and rice plants was highest after a period of 10 days. Results indicate that the resin-sat method is suitable to determine soil phosphorus availability to plants.
soil analysis methods; phosphorus availability; flooded soils
