Fertilizer costs and increased awareness of point-source pollution are amplifying the pressures on farming, economics along with public demand for sustainable production methods and organically grown produce. Our research focuses on using effluent from thermophilic anaerobic digestion of poultry litter as an alternative fertilizer. Cucumbers (Cucumis sativus L.) were grown hydroponically using a bato bucket system to evaluate the effects of liquid effluent as a nutrient solution versus a commercial nutrient solution. Seeds of the beit alpha cultivar `Manar' were started in Horticubes and transplanted into buckets containing a perlite/coir media. The effluent fertilizer consisted of effluent diluted to the same ppm nitrogen found in the commercial fertilizer based on ammonium measured in the effluent. Hydroponic solutions were monitored twice a day to maintain a pH of 5.6-6.0. Fruit was harvested three times a week and graded on size and shape. Fruit of each grade were counted, weighed, and recorded. Average fruit weight and fruit number produced was statistically significant between the two fertilizer regimes with the commercial fruit, averaging 84 g compared to 75 g for effluent fruit. The effluent treatment produced a greater percentage of grade 1 fruit (33%) compared to the commercial treatment (26% grade 1 fruit). Thus, 74% of the commercial harvest was grade 2 or cull fruit compared to only 66% of the effluent harvest. Correlating grade with average fruit weight analysis identified statistical differences between treatments for the grade 1 fruit, but not the grade 2 or the culls. While effluent from thermophilic anaerobic digestion shows promise as an alternative hydroponic fertilizer, it is not better than the commercial fertilizer regime.
Barbara E. Liedl, Kristen Wilfong, Christina Taylor and Kari Mazzaferro
Barbara E. Liedl, John Bombardiere, Amanda Stowers, Kari Mazzaferro and J. Mark Chatfield
Increasing production of agricultural waste impacts health, economic, and environmental welfare. Thermophilic anaerobic digestion is a technology developed to treat these waste streams whereby the organic material is converted to biogas and effluent. The effluent, available in solid and liquid form, holds promise as a fertilizer. Digested (broiler litter) liquid effluent was compared to chemical and certified organic fertilizers with application rates based on soil analyses and crop recommendations. An unfertilized control and an effluent treatment at twice the recommended amount were also included. Beds treated with liquid effluent maintained higher levels of available phosphorus established from treatment in prior years with solid effluent. Beds treated with liquid effluent showed a significant increase in K, Mg, Cu, and Mn. Potato fresh weight and tuber number for 2× effluent beds were significantly better than the other treatments. Average tuber weight was also statistically significant, but organic, 2×, and 1× effluent were best. For tomato, the 2× effluent treatment was statistically better for fruit number, average weight, and total weight. In fact, the total weight per plant for the 2× effluent treatment was more than three times higher than the other fertilizer treatments. The chemical and effluent treatments were statistically better for broccoli than the organic or unfertilized control. Blueberry yields were not significantly different between treatments. As this is a perennial crop, it may be several years before a significant difference is observed. While not a total solution, our research shows the effectiveness of digested poultry litter as part of a nutrient management program, thereby making a safer, less-polluting alternative to raw livestock residuals.