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. Th e 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%). Th e barley N uptake derived from digestate was 41%, which was signifi cantly greater than manure (22%), separated solids (17%), and pellets (2%). Digestate increased P uptake, while signifi cantly reducing soil-test P accumulation compared with the other coproducts and cattle manure when applied at N-based rates. Our results confi rmed that management practices for solid beef cattle feedlot manure may be used for separated solids, but not digestate. Pelletized separated solids may be an eff ective slow release fertilizer, while also supplying C, but determination of its nutrient release patterns is required.
As biogas production expands, digestates from that industry are increasingly available as potential nutrient sources for crop production, but their agronomic value is poorly understood. Thus, a 5-yr field experiment was conducted to determine the agronomic values of anaerobically digested solid beef cattle feedlot manure (ADM) and the separated solids (SS) from ADM under a semiarid reduced-tillage dryland barley (Hordeum vulgare L.) forage cropping system. Three organic amendments, ADM, SS, and undigested solid beef cattle feedlot manure (CM), were applied annually at 200 or 400 kg total N ha −1 for 4 yr, while the residual effect was examined in the fifth year. The higher N and P availability in ADM translated into greater barley forage yields, total N uptake, amendment-derived N uptake, and apparent N recovery (ANR) from ADM-amended soil than SS-and CM-amended soils, while there were no significant differences between soils receiving SS or CM. The ANR was 22% for ADM but only 12% for CM and 9% for SS. In contrast, P uptake, the fraction of amendment-derived P uptake, and apparent P recovery were similar among all amendments. Similar yields, ANR, post-harvest soil NH 4 , NO 3 , and Olsen-P concentrations between SS-and CM-amended soils suggest that they have a comparable agronomic value. Less residual Olsen-P in soil receiving ADM than SS or CM suggests that ADM is a lower risk for P accumulation when applied at N-based rates. We recommend that current agronomic values for cattle feedlot manure could be applied to SS but not ADM.
Abstract.With increasing production of bio-gas and availability of anaerobically digested cattle feedlot manure (ADM), we need a better understanding of the impact of its application on crop production and the environment. The objective of this study was to investigate nutrient and heavy metal uptake by barley forage from soil amended with ADM. A four-year field study was conducted in southern Alberta to compare annual application of ADM liquid (ADML), and the solid fraction separated from the ADM (ADMS) to raw undigested cattle feedlot manure (CFMR). An unamended control (CK) was also included for comparison. Treatments were replicated four times using a split plot experimental design. All amendments were applied in spring each year prior to seeding and barley was grown and harvested at the soft dough stage for making cattle silage feed. All amendments were applied at rates supplying 100 or 200 kg N ha-1 yr-1, assuming 100% mineral N and 50% organic N was available to crops in the year of application. Averaged over four years, the highest yields were found from ADML (9.55 and 9.6 Mg ha-1 yr-1), and lowest from CK (6.93 Mg ha-1 yr-1), with ADMS and CFMR (7.80 to 8.66 Mg ha-1) in between. Contents and total uptake of nutrients and heavy metals (N, P, Cu and Zn) by barley forage from ADML were higher than ADMS and CFMR. and higher at 200 kg N ha-1 yr-1 than 100 kg N ha-1yr-1. Our data suggest that anaerobic digestion increases nutrients and heavy metal availability in cattle feedlot manure, but most increases occurred in the liquid fraction. Our data also suggest that the impact of organic amendment application on forage barley production is not only affected by the types of amendment used, but also by agronomic practices (e.g., seeding date) as well as growing conditions.
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