Soils of Hawke's Bay

Across Hawke's Bay, many different types of soils have evolved. A knowledge of these soils is critical to understanding the growing environment for your trees, crops and pasture. While soils are complex, there are some basic things you need to understand.

These are:

1. Physical Soil Characteristics, type, and general location in the landscape;
2. Soil Drainage (linked to providing a soil water balance);
3. Soil Moisture Availability (linked to providing a soil water balance);
4. Potential Rooting Depth;
5. Natural Drainage Classes;
6. Soil Orders.

Physical Soil Characteristics

These are important as they affect the growth of plants and trees. Two major components are:

• soil texture, which influences the availability of plant nutrients, the development of the soil structure, and the ease with which a soil can be cultivated; and
• soil structure, which describes the way the soil is held together.

Combined, they provide an indication of soil porosity (pore space), bulk density (compactibility), and consistency (plasticity). Knowledge of these will help with making management decisions on issues such as erosion control, trace element and nutrient deficiencies, and stock-grazing regimes. Remember, the soils will vary across your property.

Soil Drainage

This refers to how quickly water is removed from a soil. This is dependent upon the position of the soil within the landscape. Soil drainage is determined by four factors:

• inputs comprising rainfall, irrigation, seepage and runoff;
• the flow of water through the soil;
• outlet from the soil; and
• the level of compaction that has occurred.

Soil colour is a good indicator of soil drainage patterns. For example, poorly drained soils have grey subsoils, whereas well drained soils have brownish subsoils.

Soil Moisture Availability

This is complex. Put simply, the soil has capacity to store water within the potential rooting depth, where the moisture level can vary. Soil moisture availability is affected by soil depth, climate, slope and aspect. As the land steepens, the soils generally become shallower, and soil moisture retention capacity reduces, particularly if the slope is facing north or west. Moisture availability is important if you live in drought prone areas, and will determine your selection of crop/pasture/trees species.

Potential Rooting Depth

This relates to the available depth of soil in which plants grow. It is important for species selection. Topsoil depth is particularly important, as this is the main growing environment. On some sites, soils are too shallow for successful planting.

Natural Drainage Classes

Source: "Soils of the Heretaunga Plains" by E. Griffiths

Soil Orders

The soils of Hawke's Bay are grouped into ten orders based on the New Zealand soil classification system, as outlined in the following subpages. The "old classification" soil groups such as "yellow grey earth" and "yellow brown earth" together with common soil names are included.