Grain Farming on Cracking Clay Soil Downs Grain Farming on Cracking Clay Soil Downs

Soils and vegetation
A long period of geological, weathering and natural erosion processes has resulted in a diverse range of soil and vegetation types throughout the Peak Downs area, centred on Capella.

The area is perhaps best known for its ‘open downs’ country, which was originally undulating plains covered with various blue, Mitchell and other grasses, interspersed with occasional and open woodlands of mountain coolibah, bloodwood and silver-leafed ironbark. These plains give rise to wooded and often stony ridges.

The soils on the undulating plains are mostly heavy black, brown and grey cracking clays of varying depth, and are commonly of low to moderate fertility. They overlay crumbling basalt and fine sedimentary rock parent material, from which they have been formed through weathering processes over many millions of years.

There are also smaller areas of undulating scrub plains originally vegetated by brigalow and other softwood scrub species. These soils were formed from the deposition of weathered fine-grained sediments, and are more variable in texture as a result of a variety of parent material and weathering regimes. They are generally deeper and more fertile self-mulching cracking dark clay soils, which make them more suited to grain cropping and improved pasture production.

There are also open woodland areas of poplar box and ironbark, overlying red-brown earths that formed from sandstones and other conglomerates. They grow native and introduced pasture grasses and are used for cattle grazing.

The open downs plains were the first areas developed for grain farming, and later with the scrub soil plains, now form the basis of grain farming in the district.

Rainfall variability is a major feature of the climate. Annual mean rainfall is around 600mm, with the majority falling in summer. Summer rain often occurs in intense summer storms.

Winters are short, with only a few frosts in low-lying areas. In contrast, summers are hot, with average daily maximum temperatures in mid-summer of 34-35°C and often exceeding 40°C.

The climate has a significant impact on farming in the area. Yield variation between localities and seasons is high, closely reflecting rainfall variability. Yields are usually lower than in southern Queensland, reflecting the harsher climate for cropping. As a result of rainfall uncertainty, crops often need to rely on stored soil moisture for significant periods, so a good profile of soil moisture at planting time significantly improves yield reliability. Although the soils are well-suited for cropping, the shallow nature of some soils limits their water-holding capacity, and crops grown in them often suffer moisture stress late in the growing period. Intense summer storms can cause significant soil erosion.

Main crops grown
The main crops now grown in the district include grain sorghum, wheat and chickpea, and smaller areas of mungbean and sunflower. Grazing crops of forage sorghum, oats, and grazing legumes (lab lab and butterfly pea) are also grown. Past cropping programs have also included linseed and safflower. Sunflower was a major crop from the 1980s to the early 2000s, but production has declined since then due to a run of poor seasons, diseases, and low stubble cover levels after harvest.

Farming systems
Some farms only grow grain or graze cattle, but the majority of farms have both enterprises, reflecting the range of land and soil types on the farm. Typical farms include cropping areas of between 1000 and 2000 hectares, with varying numbers of cattle being run according to availability of grazing land. Cattle are almost exclusively tick resistant tropical breeds, having proven most adapted to the local environment. They are run as either pure-bred cattle or crosses with temperate or European breeds. Grain and grazing activities are usually run as separate enterprises, although cattle often graze sorghum stubble, forage crops or grazing legumes grown on cropping land.

Large-scale broadacre farming commenced in the district in the 1950s, and until the mid 1980s was based on conventional tillage for seedbed preparation and weed control. Farmers have readily adopted an opportunity cropping strategy, which involves growing appropriate crops according to rainfall and soil moisture availability rather using a strict cropping rotation.

Recognition of the need to maximise stubble cover on the soil surface for erosion control, and for farmers to manage increasingly larger areas in a timely manner, has seen stubble mulch and zero-tillage farming become more popular. Modern sustainable farming methods now encompass zero-tillage utilising controlled traffic, where all machinery wheels run on the same track, reducing compaction and improving water infiltration and crop performance.

These practices usually use large machinery, and often utilise satellite guidance to facilitate and improve the efficiency of farm operations. These methods maintain high stubble cover levels on the soil surface to encourage infiltration of heavy rainfall, and minimise soil erosion and evaporation losses.

Local farming families have lead the way in helping to develop sustainable farming methods which have been of enormous benefit to grain farmers, both locally and throughout the Central Queensland region.

The White family hosted a large-scale Run-Off and Soil Loss experiment conducted by the Department of Primary Industries through most of the 1980s at Springvale. This research identified the impact of different farming methods (conventional, reduced and zero tillage farming) and crop type (sorghum, sunflower and wheat) on grain yield, rainfall capture and soil erosion in the local environment.

The Storey family at Moonggoo has collaborated in a long-term paddock-scale research project since 1997. The trial is a key component of the Central Queensland Sustainable Farming Systems Project, funded by the Queensland Department of Primary Industries and Fisheries and the Grains Research and Development Corporation. It has helped to develop modern sustainable farming systems that include controlled traffic farming, opportunity cropping and soil fertility management.

Information courtesy of Graham Spackman, agricultural consultant, Emerald. January 2008.