| The chloropicrin has been widely applied in strawberries, vegetable and ginger to efficiently control soil-borne disease. However, parts of chloropicrin emit to atmosphere during use, which reduce the controlling effect and are harmful to human and environment. So, developing the technology for reducing fumigant emission is important to enhance the fumigating effects and protecting environment. The paper conducted two pathways to reduce emissions of chloropicrin, including adding biochar to surface soil and covering the films to soil. And the results are as following:Adding biochar to surface soil, the emission rate and total emission amounts significantly reduced. The maximum emission rate and total emission amounts were 80.9 μg/m2/s and 15.9% for non-biochar added soil and were 9.9 μg/m2/s and 0.4-2.3% for biochar amended soil. However, the residuals of chloropicrin were no significant increase and the concentrantions of chloropicrin in surface soil were lower in biochar amended soil.The characteristics of biochar were related to pyrolytic temperature. Increasing the pyrolytic temperature, the specific surface area(SSA) was increasing and biochar was highly carbonized, which showed a highly aromatic structure. However, the biochar yield rate showed a reduction as the temperature increased. The difference of biochars characteristics led to different adsorption behavior to chloropicrin(CP). The Lagergren model fit the adsorption kinetics of biochars, showed that adsorption rate constant for B300, B500 and B700 was 0.01, 0.07, and 0.24 min-1, respectively. The Freundlich equation provided a well fitting degree in adsorption isotherm of CP, indicating that adsorption capacity of biochars were B700 > B500 > B300. However, the maximum adsorption amounts were similar for the three biochars, indicated that biochar may degrade CP. Adding biochar to soil, the half-life of CP greatly shorten. The half-life of chloropicrin was 0.57 d in non-biochar added soil and was 0.30, 0.28, and 0.17 d in soil amended with B300, B500 and B700. The degradation rate accelerates with enhancing pyrolitic temperature and adding amounts of biochar.Generally, the fumigants were easy to penetrate the PE film, and then WSB and VIF, and it was hard to penetrate TIF film. The concentration of chloropicrin was 7.8 mg/L in TIF5 for 168 hours, which possessed best resistance to chloropicrin; and the concentration in PE was 28.65 mg/L for 3 hours. The relative humidity greatly affected permeability of WSB(water solution and biodegradation) film. The resistance of WSB was similar to TIF in low RH(RH=50%). However, increasing the humidity to saturation, the resistance of WSB sharply decreased to level of PE. The resistance of TIF films had a little difference due to producing technology and thichness. Many factors affected permeability of films, especially temperature. There existed a critical temperature in 30-40 ℃, the resistance significantly decreased under higher that temperature. Additionally, it was a positive correlation between substrate concentration and permeation rate, i.e. increasing the concentration, the permeation rate enhanced.The field experiment showed that compared to PE, TIF could decrease the emission amount of chloropicrin in field fumigation. The TIF was far superior to PE to control emission of chloropicrin. In a dose of 20 g/m2, the emission rate of chloropicrin was closed to zero for TIF and 3.45 ug/m2/ s for PE. The emission amounts increased with the increase of applied dose. Increased applied dose from 20 g/m2 to 30 g/m2, the maximum emission rate was 10.69 ug/m2/ s and 25.23 ug/m2/ s, respectively. The residuals of chloropicrin in soil were lower than 0.30 mg/kg after removed film, but those were significantly higher than that in PE treatments. The results indicated that TIF could effectively control the emission of fumigants. |
PDF Full Text Request