Effect Of Long-term Fertilization On Supply Of Soil Potassium And Availability

This study based on a long-term fertilizer location experiment of brown soils inShenyang Agricultural University concentrates on the research of effect of differentfertilization on potassium supply capacity, spatial-temporal variation characteristics of Kadsorbed by minerals, transformation between potassium mineral, features of fixation,adsorption and desorption dynamics, Q/I value of potassium in brown soils. The objectives ofthis study are providing theoretical foundation of rational application of potassic fertilizeralong with improving fertilizer availability ratio. Some results as follows:1. Long-term different fertilization affects potassium supplying power and effectivenessof potassium. The results show that long-term no-potassic fertilizer, single potassic fertilizer,and single low level of organic fertilizer treatments reduce the soil K deliverability andeffectiveness. Long-term single high level of organic fertilizer treatment （M2） could improvesoil K effectiveness, but it is unable to maintain long-term supply capacity of soil K.Combined application of high level of organic fertilizer and potassic fertilizer can improvesupply capacity and effectiveness of soil K.2. Study of temporal and spatial variation of potassium mineral fixation in different soilpotassium adsorption points（p, e and i sites） in the condition of long-term differentfertilization shows that （1） both long-term single high level of organic fertilizer and combinedapplication of organic fertilizer and potassic fertilizer could maintain the soil absorbedpotassium content of p, e and i sites;（2） spatial variability of the soil absorbed potassiumcontent of p, e and i sites displays that0²0cm＞20⁴0cm.3. The result of X-ray diffraction identification shows that （1） there is no change inrespect of species of clay mineral （＜2μm） and mineral composition （hydromica, chlorite,kaolinite, montmorillonite, vermiculite and small amounts of quartz） under long-termdifferent fertilization;（2） application of both potassic fertilizer and organic fertilizer affect thecontent of hydromica in clay mineral, and single high level of organic fertilizer or combinedwith potassic fertilizer could increase the content of hydromica. However no-potassicfertilizer application makes the content of hydromica decline significantly. There is mutualtransformation between hydromica and vermiculite-chlorite. The correlation analysis shows that there is a significant negative correlation between the content of hydromica andvermiculite-chlorite （r=0.859, P=0.028）, and S-avail K and R-avail K have close relationswith the change of clay mineral: there are positive correlations between the content ofhydromica and S-avail K and R-avail K （0.908*and0.947**）. Nevertheless there arenegative correlations between the content of vermiculite-chlorite and S-avail K and R-avail K（-0.958**and-0.921**）.4. Analysis of potassium fixation capacity of brown soils in the condition of32consecutive years fertilization shows that （1） when the concentration of exogenous potassiumis in range of400⁴000mg·kg^-1, potassium fixation capacity increases along with the rise ofconcentration of exogenous potassium, whereas K fixation rate reduces;（2） compared withno-potassic fertilizer, application of potassic fertilizer and organic fertilizer reduces soilpotassium fixation capacity;（3） there are close relations between physio-chemical propertiesand potassium fixation capacity of soil. The correlation analysis shows that （1） there issignificantly negative correlation between R-avail K and potassium fixation capacity;（2）there are significant negative correlations between potassium fixation capacity, R-avail K,S-avail K and clay particle （＜2μm）;（3） there is negative correlation between CEC andpotassium fixation capacity.5. Samples of arable layer were flowed through with deionized water as pretreatment toinvestigate the kinetics characteristics of K+adsorption and desorption of brown soil underlong-term （32years） fertilization. Result shows that （1） the equilibrium time and amount ofadsorption and desorption were different, and the time of desorption is longer than adsorption,amount is inverse. The changes of the velocity of potassium adsorbing and desorbing with theincreasing time can be described by the model of V=A+Blnt. There were correlation betweenparameters of adsorption and desorption were related with CEC、Clay、OM and R-avail K indifferent degree. First-order, Elovich, parabolic diffusion and dual constant were used todescribe the kinetics of K adsorption and desorption of experimental soils. The result showedthat first-order was the best of the various kinetic equations.The effect of long-termfertilization on K+adsorption and desorption kinetics of brown soil is up to the changes ofphysic-chemical properties of soil. Under this experiment condition, the K+adsorption and desorption kinetics is mainly controlled by surface diffusion6. Potassium Q/I curve shape of brown soils is basically the same after32years ofdifferent fertilization.Characteristic parameters of Q/I of different treatments（-ΔK⁰、AR_e^K、PBC^K�'�K_X） have large differences. Long-term application of potassic fertilizer and organicfertilizer could improve-ΔK⁰value and K content of specific adsorption sites（K_X）,andorganic fertilizer affects K_Xmore than-ΔK⁰.Long-term application of potassic fertilizer andorganic fertilizer makes the effectiveness of soil K higher. Absorbed potassium of M₂NPKand M₂mainly stay in the lattice edge, however that of other treatments mainly keeps in theinterlayer of crystal lattice of clay minerals. Long-term application of potassic fertilizer andorganic fertilizer makes the value of soil PBC^Klower. The physicochemical properties of soilaffect potassium Q/I curve parameters. Path analysis shows that （1） the content of clay affects-ΔK⁰indirectly, and organic matter affects PBC^Kindirectly;（2） rapidly available potassiumaffects AR_e^Kand K_Xdirectly,which is through the organic matter, clay content and cationexchange capacity of soil that affect rapidly available potassium indirectly.To sum up, long-term different fertilization affects potassium supplying capacity andeffectiveness of potassium of brown soils, in which combined application of high level oforganic fertilizer and potassic fertilizer is the optimum fertilization model of maintain soilpotassium supplying capacity and effectiveness of potassium. Therefore more attentionshould be payed to using potassic fertilizer combined with organic fertilizer in agriculturalproduction. Chemical behavior of potassium is complex in soils, and is restricted by manykinds of factors. This study shows that the effect of long-term different fertilization on soilpotassium supplying capacity and effectiveness is by way of changing physio-chemicalproperties of soil.