The soils used to grow irrigated rice in the State of Santa Catarina have different mineralogical and chemical characteristics from the soils used for calibration studies of the Mehlich-1 extractant, for estimating soil phosphorus availability to plants. Thus, the aim of this study was to evaluate the effectiveness of Mehlich-1, Mehlich-3, Resin, Olsen and EDTA extractants in predicting P availability to flood irrigated rice in soils of State of Santa Catarina. The experiment was carried out in a greenhouse in 2014 with five soils collected from croplands previously planted to rice. Four rates of P were applied to the soils, corresponding to 0, ¼, ½, and 1.0 times the amount of P needed to reach 0.2 mg L-1 P in the soil solution (based on the maximum P adsorption capacity of each soil). Experimental units consisted of 8.0 L pots containing 3.5 kg of soil (dry base). Triplicates of each treatment were arranged in a completely randomized experimental design. Five days after mixing P with the soils, soil samples were collected to quantify P by five chemical methods (Mehlich-1, Mehlich-3, Resin, Olsen, and EDTA). The pots were then flooded and cultivated with six rice seedlings for 46 days. Shoot dry matter and P uptake were quantified. Linear correlations between P extracted from the soils and P taken up by the plants were used to evaluate the effectiveness of the chemical methods in predicting P availability. The amount of P taken up by rice plants varied according to soil type and increased with increases in the P rate. The EDTA method recovered the highest amount of P from the soils relative to the amount applied, followed by Olsen. Soil P extracted by EDTA and Mehlich-3 best correlated with the amount of P uptake by rice plants. Arranging soils according to their characteristics related to P adsorption improves the effectiveness of all methods in predicting P availability to rice cultivated in flood irrigated soils.
Oryza sativa; soil P extractants; flooded soils
