Effects And Mechanism Of Biochar On Methyl Isothiocyanate Of Degradation And Bioactivity

With increasing of the cμltivated area of protected and high-value crop, soil-borne pests and diseases were severer. Soil fumigation is the most effective way to solve the problem. Methyl isothiocyanate(MITC), the active ingredient of fumigant Dazomet and Metam Sodium, is efficacy on soil-borne pathogens, nematodes and weed. Studies have shown that MITC degradation increased with soil organic matter content increases. Biochar as a new organic fertilizer with rich microporous and adsorptive, was used to improve soil quality, increase crop yields, reduce the greenhouse effect, control soil pollution, reduce fumigant emission, in addition studies have shown that biochar itself can prevent and control soilborne diseases. However, the impact of biochar on MITC environmental behavior and its efficacy to control soil-borne pests and diseases in the soil is unclear. In this thesis through the dryer soil fumigation and vial cμlture to investigate the influence of biochar production from different raw materials on MITC degradation and biological activities. Resμlts are as follows:(1) Effect of biochar on methyl isothiocyanate degradationThree cases of MITC degradation in biochar amendment soil are as followings, one is suppressed, the second is accelerated, and the third is not affected. Biochar itself has the ability to degrade and adsorb MITC, and the degrade to MITC not only on biochar′s degradation and adsorption, but also on biochar physicochemical properties. For example biochar with larger surface area and smaller H/C, has a stronger ability to inhibit MITC degradation. On the contrary, biochar with smaller surface area, larger H/C value, has a stronger ability to accelerate MITC degradation. The biochar inhibiting MITC degradation can reduced 2.8-6.1 times MITC degradation rate, and the biochar accelerating MITC degradation can increase the degradation rate of 2.2-31 times.Biochar can be effect both biological and chemical degradation of MITC in varying degrees, the inhibit MITC degradation biochar can be increase the biodegradation and reduce the chemical degradation; the accelerate MITC degradation biochar can increase chemical degradation and reduce biodegradation. In addition, environmental factors such as soil temperature, humidity, soil texture and soil microbial will affect the degradation of MITC in biochar amendment soil. For the inhibit degradation biochar, as the soil temperature, humidity, amount of biochar increased, the inhibition of MITC degradation increases. For the accelerate degradation biochar, with soil temperature, biochar adding amount increasing, the acceleration MITC degradation increases. MITC degradation varies in different soil types, soil physical and chemical properties such as p H, organic matter can affect MITC degradation in different levels. Regardless of the kinds of biochar, the inhibit or accelerate action to MITC degradation are difference in different soil.(2) Effect of biochar on methyl isothiocyanate biological activityNot reducing bioactivity of MITC on major pathogens in biochar low dosages, but with the amounts increased can be produce negative effects. However, it can eliminate the negative impacts under higher dazomet dosages.For the biochar adsorption of MITC, when the dosage of dazomet was equal or greater than 125 mg/kg, has no negative effects of MITC on root-knot nematode(Meloidogyne spp.), Fusarium spp. Phytophthora spp., Abutilon theophrasti and Digitaria sanguinalis under 1% biochar amendment. For the biochar degradation of MITC, when the dosage of dazomet was equal or greater than 100 mg/kg, there is no negative effects of MITC on various soil pathogens with an amount of 0.5% biochar amendment.