Farm dairy effluent: A review of published data on chemical and physical characteristics in New Zealand

Abstract

Increased concern about environmental degradation and a move towards sustainable farming systems has lead to closer attention being paid to farm dairy effluents (FDE). Treatment of FDE in New Zealand is mainly through land application, or through oxidation ponds. Since the introduction of the Resource Management Act, 1991, regional councils require dairy farmers to be more accountable for the management of effluent from their dairy farms. Regulations have been imposed to limit the application of nitrogen (N) to land from FDE, and these limits range from 150 to 200 kg N ha -1 yr -1 . Farmers, consultants, and regional councils require information on the chemical composition, particularly N content, of effluents, so that land effluent application systems can be designed and managed within the guidelines or regulations imposed. Data gathered from previous investigations on effluents in New Zealand found an average solids content of 0.9% dry matter. Between 1977 and 1997 the mean N content of FDE doubled from approximately 200 to 400 mg N I -1 . The trend for higher N concentrations is likely to continue as dairy herd numbers increase. The most likely reason for the increase in N is that volume of washwater used per cow has proportionately decreased as herd size has increased, thus, FDE has become more concentrated with levels above 400 mg N I -1 increasingly common. Average values of phosphorus (P) and potassium (K) in FDE were 70 and 370 mg I -1 , respectively. Slurries obtained from anaerobic ponds, which require periodic desludging about every 5 years, had average nutrient concentrations of 1650, 290, and 510 mg 1 -1 for N, P, and K, respectively, representing an accumulation of minerals over the 5 years.

Land application of farm dairy effluent: Results from a case study, Wairarapa, New Zealand

“…We suggest that the soil at the two sites, prior to effluent irrigation, were similar because of their proximity to each other and to the Ruamahanga River, their age (Typic Fluvial Recent soils) and their similar physical characteristics (Table 1). As previously noted (Selvarajah 1996;Longhurst et al 2000), the calculation of annual loadings is problematic because the composition of FDE is temporally variable. Considerable spatial variability could also be expected as a result of the travel and application depth patterns of the spray irrigator.…”

“…Following Longhurst et al (2000), the application rate and properties of the FDE were assessed by collecting samples in "catchcans" placed under the spray irrigator throughout the whole irrigation. While this was only done in the summer, and so does not allow the temporal variability in FDE to be assessed, this time of year corresponds to the time of average N loading (Longhurst et al 2000).…”

“…While this was only done in the summer, and so does not allow the temporal variability in FDE to be assessed, this time of year corresponds to the time of average N loading (Longhurst et al 2000).…”

“…The majority of the nitrogen applied in the effluent is in a relatively immobile organic form due to the dung component (Di et al 1998;Silva et al 1999;Barkle et al 2000;Longhurst et al 2000). Hence, it is likely that the effluent application has resulted in increases in microbial biomass carbon and nitrogen which has, consequently, increased gross nitrogen mineralisation rates.…”

EAF Steel Slag Filters for Phosphorus Removal from Milk Parlor Effluent: The Effects of Solids Loading, Alternate Feeding Regimes and In-Series Design

“…This causes elevated levels of nutrients, suspended solids, oxygen demanding organisms and heavy metals in agricultural waste effluents, and poses a threat to surface and ground waters [3]. The pollution potential of CAFOs, however, depends on the number and type of animals, farm size, farm location, layout of facilities and fields, and practices used to collect and store wastes and choice of practices for waste management [3,4].…”