ASSESSMENT OF PHOSPHATE-BUFFERING CAPACITY

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Abstract
We assessed phosphate-buffering capacity directly using six croppings in a greenhouse study. The quantity of available soil P (Q) and the concentration of water-soluble P (I) were determined on five soils after zero, one, four, and six crops were grown and harvested (tops and roots). Thus, a plant desorption isotherm was established in which the P buffering capacity (.DELTA.Q/.DELTA.I) could be evaluated. We then compared the P-buffering capacity from the plant desorption isotherm with an adsorption isotherm and with a resin desorption isotherm, both obtained in the laboratory. The adsorption isotherm showed greater similarity to the plant desorption isotherm than did the chemical (resin) desorption isotherm, which was more difficult to reproduce. We discuss the field implications for buffering capacity values.