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

No abstract

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

Pastures with a 6-year history of grazing by cattle (cattle pasture) and sheep (sheep pasture) were used to measure the effects on soil disturbance of a single severe grazing/treading event by sheep (S), one by cattle (C1), or 2 events within 3 weeks by cattle (C2). Treatments were stocked at 35 500 kg LW 0·9 /ha (≡ 200 cattle/ha) for 48 h when the soil was wetter than the plastic limit. A control plot (untrodden, U) was grazed only lightly by sheep to control pasture cover while causing minimal observable surface damage. Change in surface contour, random roughness, soil surface damage, and pasture cover were determined with a ‘contometer’. The construction and use of the contometer to measure change in microtopography and to describe the soil surface and vegetative state by grazing is described. Disturbance was calculated as the change in height (mm) of soil level at fixed positions along transects within treatment plots. Both sheep and cattle pastures were affected similarly (P > 0·05) in relation to absolute and net disturbance of soils. Averaged across both pasture types, very little absolute surfacesoil disturbance was measured on S, whereas cattle-treading caused significant upward and downward movement of soil. Mean ( s.d.) absolute surface disturbance (sum of upward and downward movement on a transect) was greater by cattle (C1, 11·2 8·1; C2, 9·9 5·0 mm) than by sheep (5·1 1·8 mm) (P < 0·01) after the single treading and 9·0 4·1 mm for C2 after the second treading. Net disturbance (average of upward and downward movement on atransect) was 1·9 4·0, 1·8 4·0, and 3·0 1·8 mm for C1, C2, and S (P > 0·05), respectively, after the first treading and 4·1 3·7 mm for C2 after the second treading. Cumulative net disturbance resulting from C2 on sheep pasture was greater than on cattle pasture (P <0·05), especially after the first treading, suggesting sheep pasture was more susceptible to compaction than the previously damaged cattle pasture. Random roughness and percentage of surface soil penetrated by hooves, based on observation, was greater following cattle than sheep treading. Random roughness tended to increase more (P < 0·07) following treading of sheep than of cattle pastures, which were already rougher. It was concluded that the effect on soil surface configuration of severe short-term treading events on wet soils was greater by cattle than by sheep stocked at the same metabolic liveweight per hectare and that this occurred irrespective of the previous grazing history. Although absolute disturbance in each of the 2 cattle treadings in C2 was similar, net disturbance (compaction) on sheep pasture was more than twice that on cattle pasture (P < 0· 05).

Total nitrogen (N) concentration in the urine of 12-to 18-month old female sheep, cattle and deer grazing a common pasture was measured in the morning, noon and evening for three consecutive days on two separate occasions in spring, and on a single occasion sampling in autumn. Mean (and range) of urine N concentrations for single urinations were 7.9 (1.4Á17.8), 4.4 (0.9Á13.2) and 4.1 (0.5Á16.6) g N kg(1 fresh urine for sheep, cattle and deer, respectively. Wide ranges in urine N concentration were found within days, between days and between animals within the same species. Differences in urine N concentration between the three different species in any one measurement occasion were significant but inconsistent between measurement occasions. The results presented in this study may have implications for the development of process-based models capable of accounting for the spatially heterogeneous return of excretal N in grazed systems.