Larry Cihacek, NDSU Department of Soil Science
Recent issues with availability of rail capacity for transportation of distillers grains (DGs) away from regional ethanol plants has resulted in individual plants, at times, stockpiling the DGs. In addition, stockpile storage of dried distillers grains (DDGs) requires additional costs for drying the material as well as accommodating for long term storage (>30 days). Wet distillers grains (WDGs) have a short storage life due to excess moisture promoting spoilage and during warmer weather, storage is limited to only a few days before disposal is necessary. Disposal of large volumes of WDGs becomes another significant cost in ethanol production.
Condensed distillers soluble (CDS), WDGs and DDGs from three ethanol plants within a 60 mile radius of Fargo, ND were analyzed for their plant nutrient contents. The materials included two samples each of CDS, WDG, and DDG collected weekly for 8 weeks and then monthly for 4 more months and represent the nutrient quantities contained in the materials over a 24 week sampling period.
The CDS materials contained 25.3-29.1 % dry matter (D.M.), 0.95-1.24 % nitrogen (N), 0.39-0.43 % phosphorus (P), 0.59-0.62 % potassium (K), and 0.32-0.45 % sulfur (S) and smaller quantities of other plant nutrients. The WDG materials contained 31.4-52.0 % D.M., 1.45-2.39 % N, 0.25-0.41 % P, 0.33-0.55 % K, and 0.31-0.34 % S. The DDG materials contained 84.6-85.3 % D.M., 3.78-3.81 % N, 0.72-0.77 % P, 0.97-1.04 % K, and 0.61-0.89 % S. The differences within each material appear to be primarily due to the water (or D.M.) content. The nutrient contents of the CDS products showed the most variation over the time of sampling. However, the WDG and DDG products were relatively uniform in nutrient content over the sampling period.
Evaluation of the three by-products of ethanol manufacture showed that each of them was somewhat different in nutrient content. The differences appear to be mainly influenced by the water (dry matter) content of the material. All materials had amounts of N, P, K and S as well as other nutrients that can make them useful as plant nutrient sources. Sampling over a 24 week period showed that WDG’s and DDG’s were relatively uniform over time. However, the CDS products showed some variability which may be due to differences in feedstock composition and quality and changes in composition of the water sources used in the production of ethanol. When utilizing these materials as a nutrient source for crops, each lot or batch of material should be analyzed for nutrient content in much the same way that animal manures or other biosolids should be handled. The availability of the nutrients in these materials to crops is currently being evaluated in separate field trials.