A Growth Room Bioassay of Nitrogen and Phosphorus Availability in Soils Amended with Anaerobically Digested Beef Cattle Feedlot Manure.

Digestate or anaerobically digested manure (ADM) is a nutrient-rich byproduct of biogas generation from anaerobic digestion of animal manure. The ADM is separated into solid (separated solids, SS) and liquid fractions that are applied to cropland as a source of nutrients for crops.  Currently, little is known about nutrient release and availability in ADM-amended soils. We speculate that physicochemical changes resulting from anaerobic digestion may result in a product (ADM) with different nutrient release patterns compared to raw manure. We tested this hypothesis using a growth chamber bioassay in which five growth cycles (6 wk in duration) of barley (Hordeum vulgare) were raised in pots containing 1.5 kg of soil [a Dark Brown Chernozemic clay loam soil (fine-loamy, mixed, Typic Haploboroll) and a Black Chernozemic silty clay (Typic Haplocryoll)] mixed with enough amendment [beef cattle manure, ADM (from beef cattle manure), SS, and urea plus monoammonium phosphate] to supply 0, 100, and 200 kg N ha^-1. The plants were watered every 2 d to maintain moisture at approximately field capacity. At the end of each cycle, roots and shoots were harvested separately and analyzed for N, P and C concentrations, while a 20-g (dry wt.) soil sample was taken from each pot and air-dried for pH, available N and available P analysis. In this poster, we present results on the temporal and cumulative treatment effects on N and P availability and uptake during the 9 mo bioassay. This information will help formulate sound recommendations for ADM application which seek to optimize nutrient use efficiency while minimizing losses.