Influence of fertiliser and grazing management on North Island moist hill country

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Abstract
A grazing trial was conducted on 99 ha of moist, low-fertility hill country near Woodville, New Zealand, during 1975-1981. Treatments were low fertilizer (125 kg/ha per annum superphosphate (9% P, 10% S)) and high fertilizer (average 630 kg/ha per annum 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-yr period stocking rate was increased from 6.5-12.0 and from 8.8-16.1 s.u. [stocking unit]/ha on low and high fertilizer farmlets, respectively. Over this period, and also in the 3 previous yr, herbage accumulation was measured, using grazing exclosures and a trim technique. Nov.-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 fertilizer treatment grew 9% more herbage than low fertilizer in the 1st yr after differential application, and 21-50% more in the last 5 yr. The main effect of the grazing management treatments was that annual herbage accumulation in the rotationally grazed cattle pastures was depressed 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 spring-early summer than set-stocked sheep pastures, or about 12% more on an annual basis. Slope of measurement site, on a within-hillside microtopographic basis, had a strong negative relationship with HAR. For the linear part (15-27.degree. slope) of the cubic function used, annual herbage accumulation decreased about 370 kg DM [dry matter]/ha per annum per degree slope increase. Aspect influences on HAR were less marked than those of slope. Northwest and east aspect classes showed similar annual accumulation and pattern of seasonal accumulation. Southwest aspects had higher HAR than northwest aspects for 2-4 mo. in Jan.-April and lower (20-40%) HAR for most of the remainder of the year. Seasonal spread of annual herbage accumulation was also influenced by grazing management, but was not influenced by fertilizer treatment or slope.

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