Comparacao de extratores químicos de fósforo en solos do sul da Bahia

Abstract

The available phosphorus in 10 soils samples taken from the Southern region of Bahia was measured by the sulfomolibdic colorimetric method using Mehlich (North Carolina), Egner-Riehm, Truog and modified Olsen and Olsen as extractors. At he same time the reactions of these soils to phosphorus fertilization was evaluated through pot experiments conducted under greenhouse conditions using cacao seedlings as the indicator plant. A complete randomized experiment with four replications was used and phosphorus was applied at the rate of 0, 75, 150 and 225 ppm. The dry weights of aerial parts and roots of cocoa seedlings were obtained and analyzed 105 days after emergence. The chemical extractants showed different capacities as follows: Truog major Olsen modified major Olsen major Egner-Riehm major Mehlich. In 6 of the 10 soils there was an increase in seedling dry weight in both roots and aerial parts due to the additon of phosphorus. The correlation coefficients between dry weights of the aerial parts without P treatments and P extracted by different extractants showed the following decreasing order: Truog (r=0.8252*) major Egner-Riehm (r=0.8200*) major Olsen modified (r=0.7900*) major Olsen (r=0.7760*) major Mehlich (r=0.7000 NS). There was low association between variables when root growth was considered.