Anaerobically Digested Cattle Manure Supplied More Nitrogen with Less Phosphorus Accumulation than Undigested Manure

Abstract

Core Ideas Barley recovered 19% of N applied by anaerobically digested cattle manure over 4 yr. Barley recovered 10% of N applied by undigested cattle manure over 4 yr. Separated solids and cattle manure supplied similar amounts of N and P to barley. Pelletized separated solids released N too slowly for a barley yield benefit. Separated solids posed a greater risk of P accumulation than cattle manure. Solid beef cattle manure is a good anaerobic digestion feedstock for methane production, but more research is needed to determine how co‐products of the anaerobically digested manure may be used in crop production, while limiting the risk of nutrient loss to the environment. Over four growing seasons, we measured the N and P supplied to barley (Hordeum vulgare L.) forage test crops from (i) anaerobically digested solid beef cattle manure (digestate), (ii) separated solids from the digestate (separated solids), (iii) pelletized separated solids (pellets), and (iv) undigested solid beef cattle manure (manure) that were applied to target 1× (260 kg N ha−1) and 2× (520 kg N ha−1) the recommended N rates. Non‐amended soil was the control. Digestate led to 31 to 50% greater barley forage yield than the other amendments. The apparent N recovery from digestate (19%) was much greater than pellets (2%) and about double that of the separated solids (9%) and cattle manure (10%). The barley N uptake derived from digestate was 41%, which was significantly greater than manure (22%), separated solids (17%), and pellets (2%). Digestate increased P uptake, while significantly reducing soil‐test P accumulation compared with the other co‐products and cattle manure when applied at N‐based rates. Our results confirmed that management practices for solid beef cattle feedlot manure may be used for separated solids, but not digestate. Pelletized separated solids may be an effective slow release fertilizer, while also supplying C, but determination of its nutrient release patterns is required.