SINO-AUSTRALIAN WORKSHOP
The Shine Dome, 6-8 December 2005
Improving the productivity and sustainability of rainfed farming systems for the western Loess Plateau of Gansu province
by Dr William Bellotti, School of Agriculture and Wine, The University of Adelaide
Evaluate conservation tillage
Conservation tillage describes a system where crops are grown without tillage and crop stubbles are retained in the field to protect the soil from erosion and maintain or improve soil fertility. Experiments, now in their fifth year, have been established at Dingxi and Xifeng to compare conservation tillage with traditional tillage practices.
Overall, no-tillage and straw retained (NTS) treatments have performed well across locations, phases (seasons), and crops. It is clear that crops can be successfully grown without tillage and with stubble retained on these Loess soils and in these climate conditions. Another encouraging result is that the benefits of retaining stubble and no tillage occur quickly. Improvements in surface soil water and reduced crust formation are evident in just one season of treatment. Research effort in 2005 and 2006 will shift to on farm research to evaluate how farmers adapt the principles of conservation tillage to local conditions.
Integrate legumes into cereal based cropping systems
Replacement of bare fallow with forage legumes has the potential to increase animal and crop production while also improving soil fertility. Our research in Gansu has focussed on the productivity, soil water dynamics, and nitrogen balance of lucerne – wheat rotations. A major experiment was completed in 2004. Grain yields of 3.7-4.2 t/ha in the absence of N fertiliser and after three consecutive wheat crops indicate the potential for these soils to mineralise N after a lucerne phase. The response to fertiliser N in these same rotations (5.6-5.9 t/ha) reveals that mineralised N supply alone is inadequate to meet wheat N demand in these systems. After two years and four months of fallow, and a near full soil water profile, grain yield without fertiliser was 5.1 t/ha, and increased to 6.3 t/ha with addition of fertiliser N. The interactions between climate, soil water, soil nitrogen and wheat yield will be analysed with APSIM and long term rotation and N fertiliser strategies identified.
Develop capacity for simulating agricultural production systems
From the outset of the project, field research has been integrated with system simulation modelling. We have successfully developed, tested, and applied the Agricultural Production System Simulator (APSIM) to local farming systems. Good progress has been made possible through excellent field experimentation and data management. The stage of deriving soil and crop parameters has been largely completed. Performance of the model against observed data has been very good for soil water and plant growth, but several areas require ongoing improvement, including surface soil conditions and runoff and evaporation; winter dormancy physiology in winter wheat and lucerne; and simulation of inorganic nitrogen dynamics.
Given the promising performance of the model some preliminary long-term simulations (Xifeng 1961-2003, Dingxi 1970-2003) have been undertaken. A study of long-term average water balances under a range of crop rotations and lucerne has provided new insights and reinforced findings based on experimental results. For example, the water balance is dominated by soil evaporation at Dingxi, runoff and drainage are very small components at this dry site. At the wetter Xifeng site, lucerne can reduce runoff and drainage compared to annual cropping, with implications not only for the local farmer, but also for the wider context surface and groundwater flow systems.
Possible future research in western China
Our ACIAR research project has highlighted the interactions between animal and crop enterprises on local Gansu farms. In addition to the well known benefits of forage legumes on soil fertility and subsequent crop production, and the obvious benefit of animal manure returned to the soil as fertiliser, some more subtle and complex interactions have become evident.
For example, inclusion of forage legumes on a portion of the farm may be the key to farmer adoption of conservation tillage farming systems. Currently, crop stubbles have high value as animal feed and farmers are reluctant to leave crop residues in the field. Provision of a productive, high quality forage legume may facilitate a new animal feeding regime allowing some crop stubbles to be retained in the field. It is clear that this concept requires further research to evaluate the system under farmer managed conditions but the potential benefits are significant and widespread.
The ability to critically evaluate current and new farming systems using system simulation tools such as APSIM and GrassGro has much to offer in the development of more productive and sustainable farming systems both in China and Australia.
