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

Abstract

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 fertiliser (125 kg/ha/a superphosphate (9% 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./ha 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 spring‐early summer than set‐stocked sheep pastures, or about 12% more on an annual basis. Slope of measurement site, on a within‐hillside microtopo‐graphic basis, had a strong negative relationship with HAR. For the linear part (15–27 ° slope) of the cubic function used, annual herbage accumulation decreased about 370 kg DM/ha/a per degree slope increase. Aspect influences on HAR were less marked than those of slope. NW and E aspect classes showed similar annual accumulation and pattern of seasonal accumulation. SW aspects had higher HARs than NW aspects for 2–4 months in January‐April, and lower (20–40%) HARs 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 fertiliser treatment or slope.