Productivity and environmental sustainability of grasslands receiving liquid hog manure

A two-year (2004 to 2005) experiment was conducted to determine the effect of liquid hog manure as a fertilizer on grasslands composed primarily of Kentucky bluegrass (Poa pratensis) and quackgrass (Agropyron repens), its effect on forage yield and quality, as well as pasture and animal performance. Environmental sustainability in terms of nutrient removal and enteric methane (CH4) emissions were also examined. Forage production data was collected from replicated grass hayfields and pastures receiving no liquid hog manure or liquid hog manure as a single application (Full) of 155 kg ha1 of available nitrogen (N) in the spring or as a split application (Split) of 74 kg ha-1 of available N in both the spring and the autumn. Multiple 0.25m2 quadrats of standing forage were clipped in hayfields immediately prior to haying to determine DM yield and forage nutrient composition. Quadrat samples were collected in pastures every 28 days to determine DM yield, and hand-plucked forage samples were collected to determine nutrient composition of forage consumed by cattle. As well, pasture productivity, animal production, and enteric CH4 emissions data were collected. Enteric CH4 emissions were quantified using the sulphur hexafluoride (SF6) tracer gas technique. Animal weight, blood samples and 24-h CH4 expiration were measured once in each of three 28-day periods. Nutrient balance of hayfields and pastures was determined by comparing nutrient removal in the form of animal gain or baled hay to nutrients applied in the form of liquid hog manure.;Nitrogen and phosphorus (P) removal efficiencies based on nutrients applied were up to 7- and 4-fold greater in the hayed system compared to the pastoral system, in which only 4.7% of applied N and 6.1% of the applied P were recovered. The low nutrient utilization efficiencies in each system indicate a need to monitor the rate or frequency of liquid hog manure application to reduce nutrient build-up in the grassland system.;Hog manure application on hayfields increased forage yield and nutrient profiles relative to hayfields receiving no fertility. Average standing forage biomass generated in Control, Split and Full hayfields were 3.7, 8.8 and 8.4 +/- 0.31 t ha-1, respectively (P=0.0001). Mean standing forage CP was lowest in unmanured standing forage (7.1 +/- 0.24% CP, P=0.0004), while Split and Full hayfields had CP concentrations of 9.4 and 10.5%, respectively. Neutral detergent fibre was higher in Split hayfields (61.9 +/- 1.05%, P=0.0545) than in Control or Full hayfields (57.1 and 58.9%) due to its advanced state of maturity at cutting. Gross energy was highest in manured hayfields (18.3, 18.6 and 18.5 +/- 0.06 kJ g -1 DM, in Control, Split and Full hayfields, respectively, P=0.0443). Application of hog manure increased nutrient profile of pasture forages relative to those receiving no fertility. Mean forage CP was more than doubled with manure application (P=0.0492). Steers grazing unmanured pastures had lower serum urea N (2.56 +/- 0.61 mmol L-1 P=0.0225) values compared to steers grazing manured pastures (Split = 6.06, Full = 6.09 mmol L-1). Animal DMI and enteric CH4 emissions (% GEI) were unaltered by the changes in forage quality as a result of manure application. The addition of hog manure increased pasture carrying capacity over the grazing season by more than three-fold compared to unmanured pastures, which averaged 101 grazing days ha-1 yr-1. Animal productivity increased from 104 kg gain ha-1 for unfertilized to 325 and 344 kg gain ha-1 for Split and Full pasture treatments, respectively (P=0.0019).