This project addresses problems associated with growing wheat and maize on an area of about 13 million hectares in the North-West Provinces of China that receives an annual rainfall of less than 600 mm. Excessive cultivation of the relatively poor soils has led to soil degradation and water and wind erosion. Loss of water and organic matter has resulted in low grain yields and a depressed rural economy.

Zone tillage - a traditional method of optimising water use - is labour intensive using present techniques, and is no longer economic. It entails the arrangement of semi-permanent run-off/run-on zones, sometimes involving the use of plastic mulch, or the movement of `mellow soil'.

The project was the result of a visit by Prof. Gao Huan-Wen to the Farm Mechanism Centre, University of Queensland Gatton College (UQG), in 1990, and subsequent correspondence with Dr JN Tullberg of UQG. While Prof Gao's major interest was in conservation tillage systems applicable to northern China, and UQG work was concerned with `controlled traffic' cropping, both systems address the same underlying problem - that of optimising sustainable rain-fed grain production in an environment where moisture is limiting, soil degradation is a major problem, and current large inputs of energy, capital or manpower are undesirable. UQG scientists have already shown that controlled-traffic cropping - i.e. restricting movement of farm machinery to set paths at 2-3 m intervals in the cultivation area - reduces soil structural degradation and the energy requirements of crop establishment.

The project aims to develop conservation tillage systems - i.e. systems providing optimal crop production while conserving soil, water, energy and other system inputs - to increase the sustainability of agriculture in China. At the same time, Chinese zone-tillage methods will be combined with the controlled-traffic method of tillage to improve the sustainability of Australian cropping systems.

The Chinese collaborators will evaluate the effects of conservation cropping techniques, including non-inverting tillage and the maintenance of crop residues on the soil surface, on crop yields and soil degradation. In the first year they will select appropriate soil-engaging components of tillage and planting equipment.

As the work develops, they will go on to assess treatments involving varying levels of soil disturbance, residue cover and manure use, including some elements of deep tillage and controlled traffic. The scientists will measure soil degradation and its effect on crop yield in terms of water-use efficiency, soil density and porosity, and organic matter level.

In Australia, techniques for the investigation of conservation tillage systems are well developed. The Australian collaborators will further investigate the conservation and cost benefits of controlled traffic, its interaction with conservation tillage, and its extension into `zero traffic' crop production, which depends on gantry-mounted equipment to further increase the width of non-compressed rootbeds.

Experimental work will focus on soil and crop response to controlled traffic and zone tillage under a range of tillage intensities. In the first year the researchers will develop equipment and an experimental area that will allow valid comparisons of energy input, soil water properties and crop performance. They will link this work to research on the use of gantry (or zero traffic) crop production systems, which are likely to be the basis of future zone tillage systems.

Differences in scale and stage of development dictate that conservation tillage in China will be based on the use of much smaller and lighter tractors than those used in Australia. Under these circumstances, traffic-induced soil degradation may be a smaller problem. This is why Chinese research will focus on the tillage aspects. Traffic aspects will be considered later, combined with an investigation of the effects of deep loosening.

The expected benefits to China include an increase in wheat and maize yields and a reduction in erosion potential associated with residue retention. Pilot trials (with manual zone tillage) have indicated a yield increase in wheat of up to 20% from conservation tillage.

An increase in grain yield would provide additional income and, if 50% of farmers adopted the practice and gained a 10% grain-yield increase, annual grain output of the North-Western Provinces would increase by more than 1.5 million tonnes. Experiments on deep tillage and traffic control will indicate the value or otherwise of deep loosening, and the impact of traffic on the persistence of any beneficial loosening effects when using relatively light field equipment.

Benefits to Australia will include a reduction in tillage depth and intensity made possible by the absence of random heavy-wheel traffic. Increased surface soil stability and infiltration rates can be expected when wheels do not travel over the whole field area. There would be reduced runoff, and hence reduced water erosion.