A summary of research results on pasture responses to fertiliser and lime in the South Island hill and high country

Abstract

The published results from trials used to determine nutrient and lime requirements of legume-based pastures in South Island hill and high country are summarised. Most of the research in the 1950’s and 1960’s found that sulphur (S) alone was required on the less weathered and leached Semi-arid and Pallic soils but both S and phosphorus (P) were required on the more weathered and leached Brown soils. The severe lack of S necessitated the application of rapidly plant-available S as gypsum. Research in the 1970’s and 1980’s determined the most effective particle size ranges in relation to frequency of application of elemental S to provide adequate S. This work highlighted a need for sufficient S for legume growth before a growth response to P was measured on most soils which has resulted in the manufacture of a range of suitable sulphur fortified superphosphate products. During this 40-year period a limited amount of work showed that nitrogen (N) fertiliser could enhance the growth of resident grasses and legumes and that added S could improve the response. Molybdenum (Mo) has been the only trace element that has been lacking for pasture growth and research has been reported that defines optimal rates, frequency of application and criteria for interpretation. In the last 20 years, the need lime to alleviate soil aluminium (Al) toxicity on these mainly acidic soils has been demonstrated to allow legumes to establish and persist. 
 Current gaps in available information indicate potential areas for more research. These gaps include identifying responses to rates of P and S on pasture with varying legume content on different hill slopes, differential application of elemental sulphur and lime on shady aspects of Semi-Arid and Pallic soils, definition of P and S requirements of pure legume swards, the role of fertiliser N to improve legume establishment, fertiliser and management options to break down thatch at the soil surface and improve legume establishment, determination of the soil and landscape factors that affect the spatial variability of soil Al concentrations, further confirmation of the role of lime injection into soil layers with high soil Al toxicity, the assessment of test strips of applied Mo to assist in the identification of deficiencies in legumes and the combination of information into a decision support system to aid farmers in their selection of legume species and fertiliser and lime requirements for different areas of their farms.

What are the best pasture improvement options for different South Island hill and high-country environments?

“…South Island hill and high country is defined as those areas that were in natural grassland at the time of early European settlement (Morton et al, 2021). This includes the major geographical regions of dry hill and high country in Marlborough, Canterbury and North and Central Otago, and the wet tussock grasslands of East and South Otago and Southland, most of it over 500 m altitude (Morton et al, 2021).…”

“…South Island hill and high country is defined as those areas that were in natural grassland at the time of early European settlement (Morton et al, 2021). This includes the major geographical regions of dry hill and high country in Marlborough, Canterbury and North and Central Otago, and the wet tussock grasslands of East and South Otago and Southland, most of it over 500 m altitude (Morton et al, 2021). It includes the flat and rolling inland intermontane regions, such as the McKenzie and Clutha Basins and Lees Valley. In this environment, average rainfall ranges from 400-500 mm/yr in Central Otago up to 2000/yr mm in the western fringes of the Southern Alps.…”

“…As a general pattern, rainfall increases with altitude and from east to west. Temperatures can drop to below zero in winter but can be over 30°C for short periods in summer, especially in areas with a Mediterranean-type climate, such as Central Otago (Morton et al, 2021).…”

“…There is still a large area of hill and high country in the South Island that could be improved sustainably by the establishment of legume-based pasture. Relatively high lamb and Merino wool prices, less suitable land to finish stock and a renewed research effort can support the opportunity to improve pastures (Morton et al, 2021). There is a reasonable amount of previously published research, together with farm monitoring data and user experience, which can be used to inform farmers of the best pasture improvement options.…”

“…Since the 1950's there has been much published research in South Island hill and high country to investigate these aspects, some included in the review by Morton et al (2021). In addition, for the last 10 years, the Dryland Pastures Research Group at Lincoln University have investigated the role of legumes in the improvement of hill and high-country land.…”