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Title: Water and Methyl-Isothiocyanate Distribution in Soil Following Drip Fumigation

item NELSON, S - Texas A&M University
item AJWA, H - University Of California
item Trout, Thomas
item STROMBERGER, M - Colorado State University
item Yates, Scott
item SHANKAR, SHARMA - University Of California

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2013
Publication Date: 10/3/2013
Citation: Nelson, S.D., Ajwa, H.A., Trout, T.J., Stromberger, M.E., Sharma, S. 2013. Water and Methyl-Isothiocyanate Distribution in Soil Following Drip Fumigation. Journal of Environmental Quality.DOI: 10.2134/jeq2013.03.0072.

Interpretive Summary: Due to the ban on Methyl Bromide use as a soil fumigant, growers and researchers are seeking and testing alternative soil fumigants that can provide crop protection required for consistent high yields of high-value crops. Metam Sodium is a soil fumigant that has been used for many years but sometimes has not provided the desired crop protection. Many believe that inconsistent efficacy is the result of inadequate distribution of the active ingredient, methyl isothiocyanate (MITC), through the soil. In this research, we studied the distribution and dissipation of MITC in the soil when applied through drip irrigation systems. The distribution of MITC in the soil was best when applied with a moderate amount of irrigation water – 50 mm in a sandy loam soil. Dissipation of MITC followed first order kinetics with a half-life of 27 hours. Although a popular soil water model, Hydrus-2D could predict water distribution in the soil, it failed to simulate MITC distribution.

Technical Abstract: Methyl isothiocyanate (MITC) generators, such as metam sodium (Met-Na), are used for soil fumigation of agricultural land. The ban on the fumigant methyl bromide (MBr) has resulted in greater use of MITC generators. In order to understand the efficacy of MITC, it is necessary to assess its generation and disappearance kinetics when Met-Na is applied to soil. This study evaluated the movement of water and distribution and dissipation of MITC in soil after application of Met-Na through surface drip irrigation systems. The effects of varying water application volume (25, 50 and 75 mm) and rate (1.9, 5.0, and 7.5 L h-1 m-1) were evaluated in a sandy loam soil. Good fumigant distribution within the sandy loam soil was observed under medium water application amount (50 mm) with slow to intermediate drip application rates (1.9-5.0 L h-1 m-1). Low water application amount (25 mm) or high application rate (7.5 L h-1 m-1) did not provide adequate MITC distribution throughout the soil bed width and rooting depth. Dissipation patterns of MITC in soil in all water application amounts and rates followed first order kinetics with a rate constant of 0.025±0.004 h-1 and a half-life of 27±3 h. Simulated water distribution through the soil profile using HYDRUS-2D fitted measured field data well, but the model failed to simulate MITC fumigant distribution in the soil.