Effects Of Biochar On Soil Potassium Availability And Crop Growth

Biochar is the carbon-rich organic matter derived from biomass by high temperature pyrolysis in low or zero oxygen environments and it has many excellent characteristics including high carbon contents, large surface area and large amounts of mineral elements. Biochar has been found that it can improve the contents of soil exchangeable K and promotes the uptake of soil potassium, but there are few researches that focus on effects of biochar on the change of soil potassium availability. Besides, the effects of biochar on crop yield and biomass depends on the experimental conditions. Therefore, we conducted pot experiment to research effects of different biochar rates on soil potassium forms conversion as well as crop potassium uptake, and field experiment was also carried out to study biochar and its combined application with chemical fertilizers on soil physical and chemical properties, microbial quantity and crop yield. The main results were as follows:1.In the pot experiment, as the biochar application rates increased, the soil water soluble K and exchangeable K contents were also increased in both yellow brown soil and fluvo-aquic soil after the harvest of wheat. However, the difference of soil water soluble K contents between biochar application treatments and CK were non-significant after the second growing season, but the exchangeable K contents in biochar application treatments were still higher than that of CK, especially the difference reached the significant level at the 2.5% biochar application treatment. As for the non-exchangeable K contents, biochar at 1% and 2.5% of biochar application rates significantly improved the non-exchangeable K contents in fluvo-aquic soil, but effects of biochar on non-exchangeable K contents were not significant in two growing seasons in yellow brown soil.2. In the pot experiment, K+ contents in crop roots and stalks increased with the increase of biochar application rates, but the change of K+ contents in wheat grain was not significant. Biochar significantly increased the wheat yield and maize biomass in fluvo-aquic soil in two growing seasons. But in yellow brown soil, only the treatment at 0.5% biochar application rates enhanced wheat yield and biomass by 5.2% and 1.6%, respectively; the rest of the biochar treatments failed to improved crop yield and biomass. However, the potassium uptake of two crops also increased with the increase of biochar application rates in the yellow brown soil.3. In the field experiment, if the only biochar treatment compared with control treatment, and biochar with chemical fertilizers treatment compared with only chemical fertilizers treatment, both of the biochar application treatments significantly increased soil organic carbon and available K contents, but had no significant effect on soil pH, available P, bulk density and available N contents. The microbial quantity of bacteria and actinomycetes increased after biochar application and this increase was significant in the overwintering stage, while the fungi number showed a decreased trend after biochar application. Compared to the control treatment, only biochar treatment improved the straw and grain dry weight by 6.8% and 4.2%, respectively. Compared to only chemical fertilizers treatment, biochar with chemical fertilizers treatment also increased the straw and grain dry weight by 4.4% and 16.5%, respectively. The analysis results of wheat yield components reflected that the increased yield may derive from the increase of the number of grain per ear as well as the thousand seed weight.