We rely on soil

Soil is vital to Otago’s economy and the health of our land. Over time, different soils have formed across the region due to varying geology, climate, topography and the organisms that live in and on the soil. In the simplest terms, soil has three ingredients:

1. Minerals – rocks broken and weathered to varying degrees
2. Organics – living organisms and decomposed plants and animals
3. Space – voids in the soil that are filled with water or air

In each soil type, these ingredients are made up in specific ways and their relative proportions differ. This affects the ways that each soil type behaves and can be managed.

The New Zealand Soil Classification (NZSC) system recognises 15 soil orders that differ in their characteristics, behaviour and appearance. Around 10 of these soil orders are found in Otago, with eight having regional extents greater than 1%.

The dry basins of Central Otago form dense alkaline Semiarid soils, while the high rainfall alpine valleys host acidic Podzols. Between these extremes, the extensive Pallic and Brown soils are found in hills and high country across the region. Young Raw and Recent soils are formed when the parent material erodes and is deposited on slopes and by rivers. Gley soils are predominantly wet and found where drainage is poor. Melanic soils have dark topsoils formed from limestone and volcanic rock.

Spatial mapping of soil is of great importance to landowners. It means they can manage their operations by understanding the risks and opportunities of different soil types. Soil maps are also used to model nutrient and sediment movement. You can find three soil maps for Otago online – they vary in their cover and reliability.

• The Fundamental Soil Layer combines data from the National Soil Data Repository and the New Zealand Land Resource Inventory databases. It is the only soil map that covers the whole country. It is informative at regional and national scales but less so at finer scales (such as for individual properties). This map will be replaced by S-map.
• The growOTAGO map combines pre-1992 soil maps and soil surveys from the early 2000s. It has full coverage of Otago, mapped by lowlands and uplands. It is the next best soil map after S-map, but should only be used in areas that the S-map doesn’t cover.
• S-map is based on past and ongoing soil surveys. It is the best and most comprehensive soil mapping resource available in Aotearoa New Zealand, but it is not complete – around 30% of Otago is mapped (most of the lowlands). The aim is to complete national coverage by 2030.

A national system for naming soils was developed in 1948 as the Genetic Soil Classification. When this system became outdated, it was used as the foundation for the New Zealand Soil Classification (NZSC) developed in the 1980s.

Regional soil series names that evolved before the NZSC are still often used because they are familiar, are named after the areas where soils are found and allow a finer scale of classification than the primary levels of the NZSC. used in the growOTAGO soil map and was adopted by S-map which launched in 2002. However, S-map , calling the series ‘families’ instead. As a result, these two systems do not always correspond to each other – care must be taken when comparing them.

You can use this tool from Landcare Research to correlate soil names between the NZSC, soil series and S-map. The diagram gives an example of a soil and how it is named at different levels across different systems used in Aotearoa New Zealand.