Explanation of Scientific and Technical Concepts
- Terminology and Definitions
- New Zealand Land Resource Inventory (NZLRI)
- Land Use Capability (LUC)
- General Soils Overview
- Rock Outcrops and Surface Boulders
- Particle Size
- Potential Rooting Depth
- Measure of Acidity (pH)
- Cation Exchange Capacity
- Phosphate Retention
The Land Use Capability (LUC) system of mapping and land classification can be used to map and classify land at any scale. It has therefore been used to map and classify all land in New Zealand at 1:50 000 as part of the NZLRI, and a large number of farm plans and catchment plans in most NZ regions at scales greater than 1:25 000. The classification and assessment is based on key physical resource information and knowledge of landform, rock type, soils, slope, erosion characteristics, vegetation, climate (e.g., rainfall, wind exposure), elevation or altitude, and land-use history. The LUC assessment for each parcel of land mapped (at a given scale) provides information on the land’s capacity for sustained productive use, physical limitations, and management requirements for soil conservation. LUC is used extensively in the New Zealand Land Resource Inventory (NZLRI) database and provides the basis for national and regional sustainable land management planning in New Zealand. It provides a standardised assessment of land capability (what the land is capable of sustaining or producing) and determines the resource base or capacity that can be used to achieve the land’s potential.
The New Zealand Land Resource Inventory (NWASCO 1975–1979; NZLRI GIS database (accessed June 2008 – February 2010) is a national spatial land resource database at a uniform scale of 1:50 000 (Harmsworth 1996; Lynn et al. 2009) with over 100 000 land management map units (GIS polygons) for New Zealand delineated primarily on the basis of landform and a physical inventory. The NZLRI has become an integral part of regional and district sustainable land planning and policy in New Zealand. It comprises three core sets of information:
- A land management unit (map unit) based on landform (minimum size of 15 ha);
- An inventory of classified data (inside each LUC map unit) describing five physical factors (rock type, soil unit, slope angle, erosion type and degree, and vegetative cover);
- A Land Use Capability (LUC) assessment (classification) for each LUC map unit.
The NZLRI comprises 11 main regions, 10 in the North Island with the South Island mapped as a whole region. Aohanga land resource data is derived from NZLRI region 8, Southern Hawke’s Bay–Wairarapa. Most field mapping and office compilation was carried out between 1976 and 1978. In the NZLRI, rock type, landforms, and soils are primary information that is highly relevant and seldom changes in situ. However, secondary factors such as erosion and land cover/vegetation do change year to year. In this case study we used the latest land cover database (LCDB version 2) to map vegetation and land cover at 2002, and an EcoSat version woody vegetation layer to map land cover from 2000.
NZLRI Reliability and use
The New Zealand Land Resource Inventory (NZLRI) was initially prepared for the National Water and Soil Conservation Organisation (NWASCO), later the National Water and Soil Conservation Authority (NWASCA), by the Water and Soil Division, Ministry of Works and Development, and later by DSIR Land Resources, Palmerston North and Christchurch. NZLRI information was collected and interpreted for the whole of New Zealand from approximately 1970 to 1982 with limited regional updates in the late 1980s and 1990s.
Land resource data was first published as a series of first-edition Land Resource Inventory hard copy worksheets at a scale of 1: 63 360 (1 inch to 1 mile) (NWASCO 1975-79), together with supporting extended legends and reports. All this national land resource data was entered into a Geographic Information System (GIS) from 1980. In the 1980s and 1990s many first-edition NZLRI worksheets were updated or remapped as second-edition worksheets at 1:50 000 scale, which correspond to the New Zealand Mapping Series (NZMS) 260 series topographic maps. Where the 1: 50 000 base was not available, the second-edition worksheets were prepared at 1: 63 360 scale. At 1:63 360 scale, an inventory map unit can be delineated to about 100 ha in size; at the 1:50 000 scale, an inventory map unit can be delineated to about 60 ha. When mapping at the scale of 1:50 000, the smallest practical area size determined in the NZLRI for a hooked (that is, joined by a vinculum) inventory map unit equates to approximately 15 hectares. The New Zealand Land Reource Invenory information is now all used at a scale of 1:50 000 (e.g. regional and national scale).
Visit the LRIS portal to access this data.
The LUC system of land classification assesses land in terms of its capacity for long-term, sustained productive use and indicates its degree of versatility. A physical inventory must be carried out before the land is classified for LUC. It is a national standardised classification for New Zealand that classifies land into one of eight main classes, Class I to Class VIII. The LUC classifies land management units based on a detailed inventory: rocktype, soil, slope, erosion, vegetation, climate, and land use practices (e.g. information from past and present land use). It also incorporates erosion history, and present and potential erosion severity for the assessment. The LUC classification therefore takes into account physical limitations, climate, land management requirements, past land-use history (e.g. flood history and risk), and soil conservation needs. It assesses land under the assumption of best practice.
The LUC system is hierarchical and has three main levels: class, subclass and unit. The classification has three key hierarchical components:
- LUC class (the most general level)
- LUC subclass (subdivides the LUC class), and
- LUC unit (the most detailed level).
Each LUC class is further classified into four main types of LUC subclass (showing the dominant physical limitation), and then subdivided for each region into LUC units – the most detailed description of land – which are ranked according to each NZLRI region.
The LUC class is the broadest category in the Land Use Capability (LUC) system of land classification. It is an assessment of the versatility of land for sustained agricultural production, taking into account its physical limitations. The NZ LUC system has eight land-use capability classes with limitations to land use increasing from Classes 1 to 8. Classes 1–4 are arable and LUC Classes 5–8 are non-arable, and versatility to land use decreases from Classes 1 to 8. LUC Classes 1–4 are suitable for arable use; LUC classes 5–8 are unsuitable for arable or cropping use and are more suited to pastoral or forestry use. While Class 6 (VI) land is typically stable productive hill country, some areas may be unsustainable for pastoral farming. Class 7 (VII) land has severe limitations for pastoral use and is usually very steep and erosion prone. The limitations reach a maximum with LUC Class 8 land, which is unsuitable for agriculture or production forestry and should be managed accordingly for catchment protection or under some type of continued protective vegetation cover. Typical Class 8 land includes very steep mountainous terrain, cliffs, and gravel floodplains.
|Land Use Capability class||Description of land versatility|
|1 (I)||Arable. Most versatile multiple-use land, few limitations for arable use.|
|2 (II)||Arable. Good land with slight limitations for arable use.|
|3 (III)||Arable. Moderate limitations for arable use restricting crops able to be grown.|
|4 (IV)||Arable. Severe limitations for arable use or cultivation. Requires care; more suited to permanent pasture and forestry.|
|5 (V)||Non-arable. Unsuitable for cropping. Negligible erosion under pasture and forestry.|
|6 (VI)||Non-arable. Productive pastoral hill country, slight to severe limitations and hazards.|
|7 (VII)||Non-arable. Moderate to very severe limitations.|
|8 (VIII)||Non-arable. Very severe to extreme limitations, requiring permanent vegetative cover and protection.|
Soils are the weathered skin of the earth that’s sustains life. Generally the top 30-60cm of the earth. The main factors that influence soil formation and development, and soil variation and pattern, are:
- Soil parent materials (e.g., greywacke, mudstone, volcanic ash, alluvium, loess)
- Topographic position (e.g., landform, ridge crest, hill slope, elevation, aspect)
- Climate (e.g., climatic zone, regional and microclimate, exposure to wind, coastal, inland, high altitude)
- Biological (e.g., previous vegetation, ecosystems, and land use over thousands of years)
- Human (e.g., anthropogenic, alteration and/or modification of soils, urban areas)
- Time (e.g., development and change through time, soil formation over thousands of years)
Essential elements are required for the normal life cycle and nutrition of all plants. Common nutrients are essential for higher plants and these elements are divided in macro-nutrients and micro-nutrients (trace elements).
This layer is an expression of the percentage of the area of the map units covered by rock outcrops or surface boulders. The classes originate from and are described more fully in Webb and Wilson's Manual of Land Characteristics for Evaluation of Rural Land.
Particle size class describes in broad terms the proportions of sand, silt and clay in the fine earth fraction of the soil except in the case of skeletal soils ( > 35% coarse fraction ) where it applies to the whole soil.
Potential rooting depth describes the minimum and maximum depths (in metres) to a layer that may impede root extension. Such a layer may be defined by penetration resistance, poor aeration or very low available water capacity.
Soil pH is one of the most indicative measurements of the chemical status and plant growing capability of the soil.
- Many plants and soil life forms have a preference for either alkaline or acidic conditions, affecting the choice of crop or plant that can be grown without intervention to adjust the pH.
- Diseases affecting plants also tend to thrive in soil with a particular pH range.
- The pH can affect the availability of nutrients in the soil.
Knowing the pH of a soil will help answer the following questions:
- Is the pH suitable for growing a range of plants or crops?
- Is the soil more acid, neutral, or alkaline?
- Do I need to add mineral supplements such as phosphate, lime or sulphur to my soil?
- Do I need to add fertilisers to raise or lower the pH?
- What mineral or nutrient problems could I expect and how do I correct these?
The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic. Therefore soils range in pH from acid to basic. Soil pH has a profound effect on the availability of soil nutrients. The soil pH influences nutrient adsorption and plant growth and affects the way essential elements (e.g., iron, manganese, and zinc) are incorporated. Plants have difficulty using elements (e.g. phosphorus) if the pH is too high or too low. Extreme pH can be toxic.
Soil particles and organic matter have negative charges on their surfaces called anions (e.g., NO3-, PO42-, SO42-). Positively charged cations are attracted to negatively charged anions. Cation Exchange Capacity (CEC) is simply the soil's ability to hold onto (i.e. adsorb) and exchange cations (essential minerals and positively charged ions) such as, calcium, potassium, iron, sodium, magnesium etc. Once adsorbed onto soil surfaces the minerals are not easily lost when the soil is leached by water, and therefore soils with medium to high CEC provide minerals to plant roots. These minerals can then be replaced or exchanged by other cations (i.e. cation exchange) in time.
Phosphorus is a key nutrient for the successful growth of crops and pastures. P retention (phosphate retention) is an estimate of the soils capacity to fix phosphate, so if a soil has a high P retention (86-100%) the soil adsorbs, retains, holds onto the phosphorus (i.e., the available phosphorus for plants is therefore low). If the soil has a low (0-30%) P retention, the soil lets the phosphorus escape (e.g., a large proportion often ends up in rivers and lakes).