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.

Nitrogen (N) was applied at 0, 25, 50, and 100 kg/ha in consecutive months from March to August 1980 and 1981 to pastures at No.2 Dairy, Ruakura. Pasture production was measured in 5 harvests and the botanical and chemical compositions of the pastures were determined in harvests I and 4. N usually increased pasture growth in harvests I and 2 but reduced it in harvests 4 and 5 because of reduced clover content. N concentration in pasture followed a similar pattern. Responses increased but efficiency of N decreased with increasing rates of application. Efficiency of N applied in winter-early spring was twice that applied in autumn. Responses in early spring depended upon the rate of pasture growth at the time. In additional trials, 0, 25, and 50 kg Nzha was applied either 2 or 3 times to the same areas. Efficiency of N from repeated and from single applications was similar.

Forty-six data-sets from a series of 17 long-term field trials measuring the effects of rates and forms of phosphate (P) fertiliser on pasture production and soil fertility in New Zealand were used to characterise the relationship between pasture dry matter (DM) yield in any year (expressed as relative yield, RY) and soil Olsen P test at the end of the annual DM measurement period. Average coefficients of variation in the measurement of these parameters were 7% and 17% for DM yield and Olsen P, respectively. The results failed to demonstrate that the RY at any site in any year could be reliably assessed from a common relationship between RY and the Olsen P test. However, the mean relationship did take the general "diminishing returns" form as expressed by the Mitscherlich equation, and as Olsen P levels *Dr A. G. Sinclair died on 2 December 1996 while this paper was in preparation. A97018 Received 6 March 1997; accepted 28 July 1997increased the probability of low RY decreased. There was no evidence that RY increased with increase in Olsen P test values above 20, with the exception of the one yellow-brown pumice soil in the series. The largest component of variability in the RY v. Olsen P relationship occurred within years within individual sites, reflecting inherent within site variability and treatment and measurement errors. Variability was also large between years within sites; this appeared to arise from erratic patterns of response within sites over time, possibly because of climatic, botanical, and edaphic fluctuations. The least variability in the RY v. Olsen P relationship arose from differences between sites. Soil pH, P retention, and rainfall did not significantly affect the relationship, but the yellowbrown pumice site and sites with high DM production gave lower RY for any given Olsen P than other sites.

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A farmlet grazing trial at the Te Kuiti Research Area (20 km south of Te Kuiti) began in April 1983 to study the effects on production of reducing or withholding fertiliser over a 6-year period. The effects of withholding fertiliser are considered in this paper. The soils on which the trial was conducted are Mahoenui or Mangatea silt loams typical of 1.3 million ha of North Island hill country. Applications of 250 kg/ha/annum of superphosphate had been applied for 10 years before the trial began, leading to Olsen P tests of 14. In spite of moderate soil test levels, declines in both animal and pasture production where fertiliser was withheld were evident from year 2. By years 3-4 onwards, production declines of some 20-30% were evident. Effects on pasture composition where fertiliser was withheld were evident, with less white clover and more moss and weeds. No noticeable increase in scrub weeds or brush weeds occurred. Maintaining a high stocking rate (or stock pressure) was considered a dominant factor in this regard. Keywords grazing trial, fertiliser, hill country, phosphate, animal production, pasture production