Liquid Digestate Fertigation Demonstration Begins on Two Potato Varieties

Andrew Corbin, Director of Research, OFS

In collaboration with our partners at Vashon Bioenergy Farm, Organic Farm School began to experiment with liquid anaerobic digestate injected into our drip irrigation system (fertigation) on two varieties of potato this week. This side-by-side trial is happening on two 100-foot beds of newly planted seed potatoes. Each of the two beds is planted with 50 feet of the variety Russet and 50 feet of the variety Adirondack Blue. By splitting the beds with the two varieties, we can observe and measure the differences (if any) on both varieties with and without digestate in the drip irrigation. Liquid digestate is what remains along with captured methane gas (used for power) after the process of anaerobic digestion (bacterial decomposition under oxygen-free conditions) of a biodegradable feedstock. This locally produced feedstock is Okara (soy pulp) and whey generated during tofu production at Island Spring Organics and digested on-site with a custom, scale-appropriate digester by Impact Bioenergy.

From now through harvest, each of the two beds (with and without digestate) will receive the same volume of liquid (water, or water + digestate) for every irrigation event – this avoids any variability in the treatments due to over or under-watering. If you’re interested in seeing the details of the demonstration design, you can view it here.

Throughout the season, OFS will be monitoring any differences through observation (we’ll take pics!), then at harvest time – we’ll measure, via subsampling, total above-ground biomass (fresh weight of the tops), total tuber (potato) weight and marketability. Like many Whidbey farms, OFS has a history of poor marketability of potatoes due to blemishes caused by extensive wireworm damage. It will be interesting to see if the digestate treatment has any effect (positive or negative) on the activity of our resident wireworms. Stay tuned for updates on the progress of our demonstration and as always, feel free to come by the farm and observe for yourself – we’re always up for any questions or ideas from our community!