Soil Potassium Availability In Winter Wheat Rhizosphere Of Three Kinds Of Parent Materials Under Long-term Fertilization

We investigated the dynamics of soil potassium as affected by different fertilizers managements based on a long term fertilization experiment. The experiment, located in Experimental Station of Hunan Qiyang, Chinese Academy of Agricultural Sciences dealt with establishing and improving soil fertility of three kinds of parent materials. We also discussed the forms of potassium in rhizospheric and non-rhizospheric soils as well as the bioavailability of soil potassium in rhizospheric soil of winter wheat on the basis of an acidification and pH correction experiment. The soils tested are developed from granite,quaternary red clay and purple sand shale. The treatments of the long term experiment included: 1) No fertilizered control(CK-T); 2) Straw incorporation in situ(CK-R); 3)Synthetical fertilizers of nitrogen, phosphorus and potassium(NPK); 4) NPK plus in situ straw return(NPK-R); 5) Rice straw return(M-T); and 6) Rice straw return plus in situ straw return(M-R). In the acidification simulating experiment, two sets of quaternary red soil were adjusted to a pH gradient of 4.0, 4.5, 4.8 and 5.2(refer to acidifying), of which one set has been remediated by lime to a final pH value of 6(refer to liming). Then we conducted a pot experiment aided with nylon root bag, and compared exchangeable and non-exchangeable potassium of rhizosperic and bulk soils between these two sets of soils. The main results obtained are as follows::1. Fertilization management had significant impacts on potassium availability of soils developed from three investigated parent materials.. Both soil available potassium and slowly available potassium in soils developed from granite tended to be enhanced during 32 years of experimentation for all 6 treatments. For soils developed from quaternary red clay, soil available potassium of M-T and M-R, plots receiving rice straw return, remained constant,while it tended to be increased in other 4 treatments; as contrasted to soil available potassium,slowly available potassium of M-T and M-R increased as a function of time, while it remained constant in other 4 treatments. Soil available potassium in soils developed from purple sand shale showed no significant responses to fertilization management; soil slow available potassium decreased on plots of CK-T and CK-R, but increased on other 4 plots.Fertilization decreased soil pH value; the decrease rate of pH was faster in soils developed from granite and quaternary red clay than that from purple sand shale. Fresh straw incorporation could delay the decline of pH.2. Potassium bioavailability in soil developed from the purple sand shale was higher than that from granite; it was the smallest in soil developed from quaternary red soil parent material. Application of chemical fertilizers further decreased soil pH and potassium bioavailability in two investigated acidic soils, the straw return plus NPK could slow down the increase in soil acidity, and thus beneficial to improve the bioavailability of potassium,which reached to the highest value in Purple soil. The application of chemical fertilizers and organic materials can maintain or increase soil potassium balance.,.3. Within the pH range of our experiment, under the acidifying condition, the content of the rhizospheric soil available potassium decreased with the increasing soil pH value, but the amount of potassium uptake by winter wheat seedlings and its biomass increased with soil pH value. This suggested that the dominant factor governing potassium nutrient absorption by winter wheat on acidification red soil is soil acidity. Lime application could reduce the acidity of soil, therefore improve crop yield and the amount of the potassium absorbed. Liming should be carried out best before the pH value dropped down to 5.0.