A grazing trial was conducted on 99 ha of moist, low-fertility hill country near Woodville, New Zealand, during 1975. Treatments were: low fertiliser (125 kg/ha/a superphosphate (9070 P, 10% S» and high fertiliser (average 630 kg/ha/a superphosphate, plus lime) application rates; and 3 grazing managements -rotational grazing by sheep and by cattle, and set stocking by sheep. Some replication was included in the design, 10 self-contained farmlets being used. Over a 6-year period stocking rate was increased from 6.5 to 12.0 and from 8.8 to 16.1 s.u.zha on low and high fertiliser farmlets respectively. Over this period, and also in the 3 previous years, herbage accumulation was measured, using grazing exclosures and a trim technique. November-April rainfall had a large effect on herbage accumulation rate (HAR) causing year-to-year variation of 23% about mean annual herbage accumulation. The high fertiliser treatment grew 9% more herbage than low fertiliser in the first year after differential application, and 21-50% more in the last 5 years. The main effect of the grazing management treatments was that annual herbage accumulation in the rotationally grazed cattle pastures was depressed by 12% compared with the sheep-grazed pastures, presumed to be a result of severe treading damage. Differences in HAR between rotationally grazed and set-stocked sheep pastures were not detected. The trim technique used probably overestimated HAR of set-stocked pastures during the reproductive phase of grass growth. Measurements of herbage mass suggested that rotationally grazed sheep pastures grew about 20% more herbage over springearly summer than set-stocked sheep pastures, or

DairyMod and EcoMod, which are biophysical pasture-simulation models for Australian and New Zealand grazing systems, are described. Each model has a common underlying biophysical structure, with the main differences being in their available management options. The third model in this group is the SGS Pasture Model, which has been previously described, and these models are referred to collectively as ‘the model’. The model includes modules for pasture growth and utilisation by grazing animals, water and nutrient dynamics, animal physiology and production and a range of options for pasture management, irrigation and fertiliser application. Up to 100 independent paddocks can be defined to represent spatial variation within a notional farm. Paddocks can have different soil types, nutrient status, pasture species, fertiliser and irrigation management, but are subject to the same weather. Management options include commonly used rotational grazing management strategies and continuous grazing with fixed or variable stock numbers. A cutting regime simulates calculation of seasonal pasture growth rates. The focus of the present paper is on recent developments to the management routines and nutrient dynamics, including organic matter, inorganic nutrients, leaching and gaseous nitrogen losses, and greenhouse gases. Some model applications are presented and the role of the model in research projects is discussed.

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Effects of two fertiliser treatments on soil characteristics were measured during 1972-87, within 10 grazed permanent-pasture "farmlets", on steep hill country in southern Hawke's Bay, New Zealand. The low fertiliser (LF) treatment received 125 kg ha-1 superphosphate p.a., and the high fertiliser (HF) an average 625 kg ha-1 p.a. for 5 years then 375 kg ha-1 p.a. subsequently. Ground limestone was applied to HF in 1975 and 1979. Grazing pressure was the same across treatments. Soil fertility decreased with increasing slope of measurement site, and aspect had a less marked effect. Phosphorus initially accumulated mainly in inorganic forms, with organic P accumulating at a slower rate similar to that for organic S. Olsen P status reflected P application regime, although the responsiveness was lower than anticipated. Soil pH in the non-limed LF treatment increased slightly over time, probably as a consequence of the decline in soil organic C. Soil total N (0-75 mm depth) A99035

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