The huge diversity in soil types and productivity across the Hunter region results in diverse productive capacity and stocking rates. Soils are also a key determinant of cattle enterprise options and the area required for a sustainable grazing enterprise.
The more favourable soils for grazing enterprises have a soil depth of at least 60cm, a balanced composition of clay, silt and sand, at least 2% organic matter, and a pH (CaCl2) of between 4.5 and 7.5. There should also be no significant deficiencies of phosphorus, sulfur, nitrogen, potassium, zinc or molybdenum.
Many soils in the Hunter region fall into this category, but many soils also have natural or induced deficiencies that require correction before pastures can support sustainable grazing enterprises.
The mineral composition of underlying parent rock types (as indicated in Table 1) and the influence of climatic conditions during soil formation over many millions of years largely determines local soil types.
Soils in the valley range from fertile alluvium and deep, fertile basaltic clay loams, through many intermediate soils, to shallow, light textured, stony and impoverished sandy granites. The transition from one soil type to another can also be gradual or very dramatic, sometimes within short distances.
Table 1 Characteristics of soils based on rock type
Heavy textured (basalt) soils
Black earths, red/brown and other heavy-textured soils common around Merriwa, Cassilis and in elevated parts of the Upper Hunter developed from tertiary basalt and subsequent alluvium. These are usually highly fertile in their natural state, but often respond initially to sulfur. Including nitrogen-fixing legumes in the pasture mix can further increase productivity.
Zinc deficiency is relatively common in crops grown in these soils, especially if alkaline. Molybdenum deficiency is also a possible problem. Red-brown earths around Scone and Murrurundi formed from sedimentary rock; however, pockets of basaltic and alluvial soils also occur. Similar red brown earths of basalt origin also occur in more elevated parts of the Lower Hunter for instance around Gloucester or Dungog.
Medium to light textured soils (granite or sedimentary rock origins)
These soils are developed from various shale, sandstone or granite parent rock types and are more widespread in the mid to Lower Hunter and Gloucester areas.
Soils derived from granite and sandstone are usually naturally low in fertility and require fertilising with phosphorus, sulfur, nitrogen, molybdenum and sometimes zinc and potassium to sustain productive pastures and hence reasonable stocking rates. They are also typically quite acidic, which can reduce pasture productivity unless carefully managed. In acid soils, the availability of nutrients may be lower and aluminium toxicity may occur. Liming may be justified in some situations. These soils often have shallow topsoils that expose pastures to moisture stress.
Soils derived from shales, slates (traps), and some sandstones, are usually low to moderate in fertility and require consistent fertilising to sustain productive pastures and support profitable grazing enterprises. Such soils can have reasonable clay content (which can help retain moisture), but are often very shallow, stony (or skeletal) and can be quite acidic.
Alluvial soils
Alluvial soils adjoining rivers and creeks are usually highly fertile in their natural state and ideal for both pastures and crops. They originate from various parent rock types further up the catchment (including basalt, granite and sedimentary), but usually have considerable organic material in their make-up and excellent depth of topsoil. Having alluvial soils within a grazing property is of particular value as the production of fodder crops and improved pastures can supplement the more seasonal / lower levels of pasture growth in the remainder of the property and increase overall carrying capacity. Retaining the connectivity between flood prone alluvial areas and adjoining flood free lands is also important.
