Kinetics of K Desorption from Soils in a Constant Electric Field (Electro-Ultrafiltration) and Its Application

Kdesorption from soils in a constant electric field(field strength:44.5Vcm-1) by means of electro-ultrafil-tration (EUF) followed second-order kinetics and could be described by the equation dd/dt = k(D-d)2. From theequation, such kinetic parameters relating to K desorption from soils as the maximum desorbable quantity D, quantity of K desorbed within 40 minutes d40, initial desorption rate Vo, desorption rate constant k and half-time t1/2 could be calculated. An expression which describes the relationships between the kinetic parameters on the one hand and the responses of barley to fertilizer-K in the field experiments in different sites and the potassium-supplying power of soils on the other was established. Vo, D and d40 were significantly correlated with barley relative yield, K uptake by barley and the content of soil available potassium. The rate constants of K desorption varied between 4.42 × 10-4-1.80 × 10-3kg mg-1 min-1 and highly correlated with the relative yield of barley. The kinetic parameters including Vo, D, d40 and k were successfully used to estimate the K-supplying power of soils.

Electrical Characteristics and Desorption Kinetics of Soil Boron

The status and activities of boron in soils were studied by the approach of electro-ultrafiltration (EUF). The samples of soils, including brown-red soil and calcareous alluvial soil, were collected from Hubei Province of China. The soil samples were incubated in saturated water and then their nutrients were ultrafiltrated with EUF equipment. Filtration and extraction were conducted in accordance with routine process, but fractions in anode and cathode were all collected. Analyses of B, K+, Mg2+, Ca2+, Cl- and pH in fractions supposed that boron existed not only in a simple form of borate but also in ion-pair with canons partly in acidic soil, and borate was the primary form existing in the calcareous soil. In studying desorption kinetics with EUF, the boron content of Fractions 2-6 was accumulated, and the accumulative quantities were fit to time factors in three kinetic equations: the zero-order, first-order, and parabolic diffusion equations. Fit degree of the parabolic diffusion equation was the best, followed by the zero-order equation, and the first-order equation was the worst.

Kinetic Equations of Potassium Desorption and the Ap－plication of Equation Constants

Elovich, parabolic diffusion, power function and exponential equations were used to describe K desorptionkinetics of 12 soils in a constant electric field of electro-ultrafiltration (EUF). Results showed that the Elovich,parabolic diffusion and power function equations could describe K desorption kinetics well owing to their highcorrelatfon coefficients and low standard errors; but the exponential equation was not suitable to be usedin this study due to its relatively low correlation coefficients and relatively high standard errors. This workestablished successfully the relationships between the constants (slope or intercept) of kinetic equations andthe barley responses to K fertilizer in the multiple-site field experiments and K-supplying status of soils, theconstants of Elovich, parabolic diffusion and power function equations were very significantly or significantlycorrelated to the soil available K, relative yield of barley and K uptake of barley in NP plot. It was suggestedthat the kinetic equation constants could be used to estimate K-supplying power of soils.