APPLICATION OF THE MEHLICH EXTRACTOR AND OF THE ANION EXCHANGE RESIN TO EVALUATE PHOSPHORUS IN THE LATOSOL IN GOIÁS ON SOYBEAN

Abstract

The Mehlich extractor has been used at the School of Agronomy of the U.F.G., in the State of Goiás since 1966. Therefore, some laboratories which operate in the “Cerrado” regions are beginning to use the Anion Exchange Resin Method. This experiment compared the two extractors, using three different sources of phosphorus; natural powdered phosphate (FN), hyperphosphate (H), and triple superphosphate (ST) in doses of 0, 200, 400 and 600 Kg of P₂O₅, per hectare. The two extractors showed a correlation for these sources of phosphate. However the results differed because of the two responses. Between the zero dose of P₂O₅, per hectare, of natural phosphate, the Mehlich extractor extracted 685.2% more for a production increase of soybeans of only 20.6%. At the same time, the resin method extracted only 81.26% more for the same phosphate variation. Changing the quantity of P₂O₅, from 0 to 600 kg per hectare of triple superphosphate, production increase in soybeans was 40.3% which corresponded to an increase of 316.6% in extraction using the amin exchange resin method and 241.9% using the Mehlich Method. It was concluded that the resin method was more efficient because it manifested a better correlation in superphosphate, but costly because it extracted less natural phosphate.