Effect of dilution ratio on the amount of metam sodium-produced methyl isothiocyanate and its dissipation
Pre-plant soil fumigation with metam sodium can effectively control soil-borne pathogens,which is attributed to methyl isothiocyanate(MITC),a degradation product of metam sodium.It is convenient and safe to apply metam sodium by drip irrigation.However,in dilution process before drip irrigation metam sodium may produce MITC through hydrolysis,which will continue to degrade or volatilize,resulting in a decrease of effective components in the soil.Therefore,it is necessary to select a suitable dilution multiple of metam sodium,which can ensure uniform distribution of MITC and reduce its loss by volatilisation or disintegration before being applied in the soil.In this study,the effect of dilution ratio on the amount of metam sodium-produced methyl isothiocyanate and its dissipation in aqueous solution were investigated under different pH conditions.The results showed that the amount of MITC and its dissipation rate increased with the increase of dilution ratio under neutral conditions.Under acidic conditions,the amount of MITC and its dissipation rate was maximum when diluted 100 times,the minimum amount of MITC occurred at 50 times of dilution,and the slowest dissipation rate was found at 400 times dilution.Under alkaline conditions,the produced MITC increased with the increase of the metam sodium dilution ratio,and the dissipation rate was the fastest when diluted 1 000 times,and was the lowest when diluted 100 times.The results have a guiding significance on how to formulate field water consumption,and application dosage when applying metam sodium by drip irrigation.
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