Boron release kinetics was studied in six agricultural soils of three provinces in Iran by using 0.1M mannitol solution. In all samples, the rate of initial boron release was rapid followed by a slower reaction rate and at longer durations, however after 24 hours, the rate of release was very slow. Five mathematical models (Elovich, power function, parabolic diffusion, first and zero order) were used to describe and evaluate boron release kinetics. Comparison of the models, by means of the coefficient of determination (r2) as well as the standard error of estimate (SE) of equations, indicated that the Elovich equation bore the highest mean r2 along with the lowest mean SE. The power function model was the next best model, which also described boron release kinetics properly. Assuming three independent sources of boron release in soils, the analysis of the data indicated that a pseudo-first order equation could adequately describe the boron release from sources 1 and 2. It was estimated that about 67 to 94% of the desorbable boron from these two sources could be ascribed to source 1, which is the most rapidly desorbable fraction, the rest released being from source 2. Boron released from source3 with a very slow rate of release was very low in amount in all soils studied.
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