Effects Of Long-time Fertilization On The Potassium Supplying Characteristics Of Greenhouse Vegetable Soils

The research took samples from greenhouse vegetable fields under long-term experiment of fertilization. With the technique of isothermal incubation, miscible displacement, cation exchange resin adsorbing, continuous extracting, the character of K fixing and releasing, the kinetics of K adsorbing and desorbing, the releasing of non-exchangeable k, the quantity- intensity relation of K, and the kinetics of K adsorbing and desorbing affected by the organic matter had been investigated and got the following results:1. The treatments with inorganic fertilizer had strong capacities in K fixation, while the treatments with organic fertilizer had strong capacities in K release. The difference in the amount of interlayer site fixed K maybe the main reason of the difference in the K fixation capacities between treatments with organic and inorganic fertilizer.The amount of fixed K was significantly correlated with the CEC/(exchangeable & non-exchangeable K),and the amount of released K was significantly correlated with the CEC* exchangeable K/(exchangeable & non- exchangeable K).2.The equilibrium times and capacities of K adsorption and desorption were different in each treatmen. Main effect factors were soil cation exchange capacity(CEC),the contents of clay,organic matter and readily-available potassium.Elovich equation was the best model adopted to simulate K adsorption and desorption for all treatments, however some made the first order diffusion equation the best .Long time located fertilizations had casused changes between soil surface and characteristics of potassium3. The amount of non-exchangeable K released were highly correlated with their slowly-exchangeable K contents. The amount of non-exchangeable K released of the treatments with organic fertilizer were distinctly bigger than that of the treatments with inorganic fertilizer. The amounts of non-exchangeable K released from the treatments with K was much high, while that released from the treatment with N was relatively low.Release rates in the beginning stage (0-1h) were far beyond that in later stages. Release rates of the treatments with organic fertilizer in the beginning stage were higher than that of the treatments with inorganic fertilizer, and this maybe the main reason of the differences on the release rate and the amount of the non-exchangeable K between the treatments of organic and inorganic fertilizer. Parabolic equation was the best way to simulate the release of non-exchangeable K, which indicated the release of non-exchangeable K was diffusing controlled proceeding.4. Both of the treatments fertilized with organic fertilizer or with potassuim had much higher value of -ΔK⁰. There was a markedly or even more positive correlation between -ΔK⁰ with CEC, readily available K and clay contents.The ARe^K value was high in the treatments of organic fertilizer,potassuim and higher nitrition fertilizer(AN2,BN2). The soil organic matter,CEC, readily available potassium,clay contents and saturation of K⁺ had a markedly positive correlation with ARe^K.The ARe^K value in the treatments with organic fertilizer is 1³ times higher than that of the treatment with inorganic fertilizer. The PBC^K value in the treatments with organic fertilizer were decreased with long-time fertilized of greenhouse vegetable soils. The PBC^K value in the treatments with potassuim and higher nitrition fertilizer(AN2,BN2) were low. The CEC, organic matter, readily available potassuim contents all had a markedly negative correlation with the PBC^K value. The value of edge sites exchangeable potassium devided by plan sites exchangeable potassium(e/p) had a markedly positive correlation with PBC^K, and was the main reason to affect the PBC^K value.The best equation to simulate the K release with H₂O and CaCl₂ extracting was both the first order equation, and that was power diffusing equation when extracted with NaCl, while that was two constants equation when extracted with NH₄Cl. Both in the treatments of with or without organic fertilizer , the treatments with only potassium(K)and the treatments with potassium and phosphorus (PK) both had higher quantities of potassium extraced by 0.1molL^-1NaCl, NH₄Cl,CaCl₂ and H₂O,but the treatments with only nitrition (N1)or the treatments with nitrition and phosphorus both had lower quantities of potassium extracted.5. About 30%-50% of the fixed K in the treatments with inorganic fertilizer could be extracted, while in the treatments with organic fertilizer, not only the newly fixed K could be extracted but also the elder fixed K. The rate of the amount of potassium released by countinous extracting to the amount of interlayer sites potassium was similar to that of readily available potassium /slowly available potassium in the soil,and had a markedly positive correlation between them. The release of fixed K when extracted with NaCl in each treatments were diffusing controlled proceeding6. The best equation to simulate the adsorbing and desorbing K after organic matter removed still was the Elovich equation. The simulations of equations to the treatments after organic matter removed were not as well as that of original treatments. Plan sites, edge sites and interlayer sites took part in the proceedings of adsorbing and desorbing simuitaneously. Which site was dominat in the proceeding would be the essence that impact the fitting degree of kinetic equations.The research had got a preliminary understanding that the capacities of K supplying in the different fertilized treatments in thegreenhouse vegetable soil had its own characteristics and were different in each. The differences in CEC, organic matter, clay (the role of Potassium sites), readily and slowly available K contents (Potassium effective forms) were the main reason to affect the distinction of K supplying capacity in each treatment.