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POTENTIAL MOBILITY OF ACCUMULATED PHOSPHORUS IN SOIL AS ESTIMATED BY THE INDICES OF Q/I PLOTS AND BY EXTRACTANT

1991; Lippincott Williams & Wilkins; Volume: 152; Issue: 3 Linguagem: Inglês

10.1097/00010694-199109000-00007

1538-9243

Helinä Hartikainen,

Phosphorus and nutrient management

Phosphorus desorption indices determined from Q/I plots, their relation to the inorganic P fractions of Chang and Jackson, and water and acid NH4OAc test values were investigated using samples of soils cultivated for 7 years without P fertilization or amended annually with 30 or 60 kg of P ha-1. Fertilization markedly increased fractionable inorganic P, and it decreased the equilibrium P buffering capacity in three of five soils, though the decrease was statistically significant in only one soil. As would have been expected, fertilization considerably raised the equilibrium P concentration, i.e., the zero point of P exchange at which no net desorption from or adsorption to soil occurs and the quantity of water soluble P that could be desorbed under experimental conditions. In most soils, previous P additions increased the quantity of P available for desorption, determined from the Q/I plot at a given reference equilibrium P solution, more than the P extractable by water or acidic NH4OAc. A desorption-sorption procedure was proposed as a method for quantifying the effect of P fertilization in terms of the amount of P required to be removed from the fertilized samples in order to reduce their equilibrium P concentration to that prevailing in the unfertilized samples.