Research news New UC ANR working group to address residual material from anaerobic digesters A naerobic digestion is an increasingly popular waste management strategy in California, with over 200 facilities operating and more under construction. Anaerobic digesters use microbes to break down organic wastes, including biosolids in treated wastewater, lawn trimmings, food wastes and manure. The digestion process produces methane-rich biogas, which can then be captured and used to generate electricity or power vehicles. The residual solids and liquids left over after di- gestion is complete are known as digestates. As the anaerobic digestion sector has grown, so has the need for a coordinated strategy to manage these digestates. Since they are rich in nutrients and organic matter, digestates are potentially valuable as soil amend- ments. But their composition can vary considerably and their performance has not been well documented. Better information about digestates and their poten- tial uses could promote the development of markets for the materials, which would in turn help make digester facilities more financially sustainable by replacing digestate disposal costs with revenue opportunities. To facilitate the beneficial use of digester residuals, Stephen Kaffka, a UC ANR Cooperative Extension Letters RSVP Re: O’Geen et al., “Soil suitability index identifies potential areas for groundwater banking on agricultural lands,” California Agriculture 69:75-84: I believe we should also con- sider old approaches that at the time weren’t considered aquifer recharge, but water wasted to the ground. Being raised in the Central Valley, I remember many a hot day spent swimming in cool canals carved into the soil. April–June 2015 Then I observed the conver- sion of nearly all dirt-lined canals to concrete-lined canals, mostly in the name of water conservation. While probably reducing maintenance needs, this also eliminated miles (and acres) of recharge surfaces. If we could return lined canals back to earthen canals, this “old” approach could expand recharge across many portions of the state crisscrossed with canal systems. Furthermore, if the purpose of canal man- agement could be expanded from water delivery con- veyances to include water storage (i.e., kept watered year-round except during periods of maintenance), there might be enough water stored in them to obviate the need for new a reservoir or two. Brad Valentine Santa Rosa 138 CALIFORNIA AGRICULTURE • VOLUME 69 , NUMBER 3 I found the concept behind the article — artificial in- filtration and accelerated recharge — fascinating. Resource management looks at stormwater as an economic resource. In the climate upheavals to come, the predictions are for sudden, massive storms that shorten the infiltration intervals. The kind of flood infiltration talked about in the article tends to this direction. I think we do need to design farms for recharge rather than drainage. Sustainable design aims at preserving the structure and function of the natural water cycle, including groundwater recharge, de- spite an unstable climate. Ecology tends to look at the structure and function of the natural world, and how best to preserve natural cycles is a high priority of sustainability. But this is a difficult, if not impos- sible, task that challenges the best of us. We need to know the natural recharge capacity of the land, and derive a realistic threshold value for recharge — what nature would do had the land remained wild and un- converted to farmland. “Ecological farming” strains my imagination, because I am not an ecologist — but I wonder if we couldn’t model natural thresholds in the same manner as this article models artificial recharge. Bud Hoekstra Glencoe WHAT DO YOU THINK? The editorial staff of California Agriculture welcomes your letters, comments and sugges- tions. Please write to us at: 2801 Second Street, Room 184, Davis, CA 95618, or calag@ucanr. edu. Include your full name and address. Let- ters may be edited for length and clarity.