Using IRIS films to inform alternate wetting and drying (AWD) water management in rice paddies
Date
2020
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Publisher
University of Delaware
Abstract
Rice is a crucial part of the world’s food supply as over half of the world’s population eats it daily. Many rice farmers depend on rice production for their livelihoods; however, they face a difficult task of how to minimize contaminant uptake while maintaining yield. Rice is generally grown in flooded soil conditions, under which arsenic becomes more plant available. Arsenic is naturally found in the soil and when taken up by the rice plant it can decrease yield and grain quality. Arsenic’s impact on rice can be alleviated by increasing the soil redox potential, but this could increase cadmium plant-availability. Careful control of soil redox by implementing alternate wetting and drying (AWD) of the soil can decrease concentrations of plant-available arsenic and cadmium in the soil, but farmers in developing countries need a way to easily monitor soil redox. Indicator of Reduction in Soil (IRIS) tubes and films have been studied in recent years as a method of measuring soil redox potential in wetland environments. My work explores the use of the IRIS film technology as indicators of soil redox in rice fields as a low-tech means to indicate when farmers should drain their fields to minimize contaminant uptake. This study took advantage of an ongoing rice mesocosm study at the University of Delaware, where 30 rice paddies under different management have been instrumented with porewater samplers and continuous redox probes. Indicator of Redox in Soil (IRIS) films coated with Fe or Mn oxides were prepared and deployed in 6 different rice paddies initially after rice paddies were allowed to dry to > 30 cm below the soil surface (severe AWD) and again when paddies were only allowed to dry to 15 cm below the soil surface (safe AWD). The goal of this study was to test the response time of IRIS films to various conditions of soil redox and to establish the IRIS films as a tool for monitoring AWD in rice paddies. I explore quantification methods of paint loss from films, optimal residence time of films in situ, IRIS film paint removal as it relates to porewater chemistry and redox measurements, and highlight important considerations for the use of IRIS films to monitor AWD worldwide.
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Keywords
Agricultural Development, Alternate Wetting and Drying (AWD), Arsenic, Arsenic in rice, Indicator of Redox in Soils, Rice