All photos courtesy of Caroline Eberlein. Do Liquid Digestates, By-Products of Bioenergy Production, have Nematode-Suppressive Potential? BY CAROLINE EBERLEIN | Department of Nematology, UC Riverside, Parlier, California RUIHONG ZHANG | Department of Agricultural and Biological Engineering, UC Davis ABDELHOSSEIN ADELATI | Department of Agricultural and Biological Engineering, UC Davis ANDREAS WESTPHAL | Department of Nematology, UC Riverside, Parlier, California Experimental tank wagon for band application of liquid digestate in a walnut orchard. The digestate is pumped via a custom nozzle underneath the tree row. Food hygiene guidelines need to be observed. Large amounts of organic wastes of food or animal origin accrue in cropping systems and in the food industry. Traditionally, many of these byproducts could remain in the agricultural production chain. For example, almond hulls may be used as dairy feed. Others ended up in landfills. With the continually increasing amounts, and for other market changes, alternative uses are urgently needed. When converting these energy-rich materials to biogas, organic matter from food waste or animal manure are processed through anaerobic digestion by microorganisms in specialized biodigesters. The resulting biogas is then used as fuel for electricity and heat generation or put into cars and other vehicles as transportation fuel. The anaerobic digestion process has been favored to reduce the emissions of methane and other gases from organic waste materials during natural decomposition. Although animal manure is probably the most widely used substrate for anaerobic digestion worldwide, food waste is another organic substrate due to its high methane production potential. Besides biogas, a liquid effluent called anaerobic digestate is also produced from digestion processes. The disposal of such residues represents an environmental and economic challenge. A meaningful use of this material would favorably impact environmental stewardship by reducing waste disposal issues, and could benefit agriculture by recycling the nutrients in the digestate for plant growth benefits. Plant-parasitic Nematodes Plant-parasitic nematodes are a constraint in crop production, especially in perennial crops in California. Long cropping cycles, soils that favor high nematode densities, and favorable climate conditions, increase nematode reproduction. In the past, nematodeinfested fields have been effectively treated with soil fumigants before planting or with various post-plant nematicides. The use of fumigants and non-fumigant nematicides is challenged by human and environmental health concerns. For example, regulation limits the use of 1,3-dichloropropene materials under so-called township cap. The quantity that may be used per year is restricted per 36 square miles (=Township). Clearly, more environmentally friendly alternatives to the use of these chemicals are urgently needed. Environmentally Friendly Alternatives A number of studies have investigated the potential of these digestates as bio-fertilizers. Because these wastes originate from plant material they are nutrient rich and their use fits into a cyclic production of returning byproducts to the primary field production. Such cycling has positive environmental effects. In some studies, the potential of these digestate for managing pests and diseases in different crops were explored. In a study in Germany, anaerobically digested maize silage suppressed the sugar beet cyst nematode, a major pest of sugar beet production in Central Europe. Using organic materials as nematode management tool is challenging because such materials can vary greatly in their physico-chemical composition. This composition likely will impact the nematode-suppressive potential of digestates. It probably depends not only on the substrate but also on the conditions during anaerobic digestion. In a project supported by the Department of Pesticide Regulation (DPR), digestates from different sources of different processing conditions and substrate base as well as varying chemical constitution showed differences in nematode suppressive potential. This illustrated the challenge of working with organic materials, Continued on Page 18 16 <strong>Progressive</strong> <strong>Crop</strong> <strong>Consultant</strong> <strong>July</strong> /<strong>August</strong> <strong>2019</strong>
Experiment with pepper in microplots. Microplots are contained areas of two foot diameter and five feet long culvers perpendicularly inserted in the ground, and filled with test soils. Each of these plots allow for precise application amounts of digestates or other treatments. <strong>July</strong> /<strong>August</strong> <strong>2019</strong> www.progressivecrop.com 17
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