New Zealand Journal of Agricultural Research abstracts
Farm dairy effluent: A review of published data on chemical and physical
characteristics in New Zealand
R. D. LONGHURST
A. H. C. ROBERTS
M. B. O'CONNOR
AgResearch
Ruakura Agricultural Research Centre
Private Bag 3123
Hamilton, 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 l-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 l-1 increasingly common. Average values of phosphorus (P) and
potassium (K) in FDE were 70 and 370 mg l-1, respectively. Slurries
obtained from anaerobic ponds, which require periodic de-sludging about every 5
years, had average nutrient concentrations of 1650, 290, and 510 mg
l-1 for N, P, and K, respectively, representing an accumulation of
minerals over the 5 years.
Keywords farm dairy effluent; oxidation pond effluent;
nitrogen; land application
New Zealand Journal of Agricultural Research, 2000, Vol. 43: 7-14
0028-8233/00/4301-0007 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (563K); (scanned from paper original: notes about this process)
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