Soil types form patterns in the landscape that are related to changes in environment, geology and landscape history. The patterns are predictable and can be used to make soil maps and guide land management.
If we could look at the soil over a broad area from a high-flying aircraft we would see variations, mainly due to changes in climate and geology. For example, dry valleys may contain Pallic soils that give way to Brown soils on wet mountain slopes.
For more detail, we would need to fly lower. From here, changes in soil relate to topography, the age of the land surface and the type of parent material. For example, we would see Recent soils in alluvium beside streams, mature Brown soils on a flat river terrace and in rock debris on a hillside, Raw soils and Recent soils in erosion scars, and Gley soils in small wet gullies. To see even more detail we could examine soils in a paddock and find variation in texture, thickness of layers and wetness. These changes can cause variation in pasture and crop yield.
Catenas are common in hilly countries like New Zealand. They are a sequence of soil types linked like a chain from hill crest to valley floor. A drainage catena is the transition from well-drained soils higher on a hill to successively wetter soils, with increasing mottling and greyness on a valley floor. Changes in soil depth and texture are also common. Catenas and other patterns help people precisely predict soil locations, understand the hydrology of water catchments, and learn the history of landforms.
Positioning technology is used to map variations in soil properties. These detailed maps enable farmers to adjust irrigation and fertilisation. This precision helps reduce the costs and adverse environmental effects of soil management.
Maps and databases
Soil changes are plotted by soil surveyors and marked on soil maps. Soil profiles are taken by sampling to a depth of 1 metre across a range of landforms. Relationships between soils and landforms are used to predict the locations of main soil transitions. Analyses, descriptions, and maps of New Zealand’s soils are stored in a national soils database.