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| Wednesday, 29 December 2004 |
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Queensland's cotton growers helping solve water loss mystery
Cotton producers of St. George and Dirranbandi, Queensland care playing a vital role in solving the mystery of water lost beyond the plant root zone. Department of Natural Resources scientists are using a device called a lysimeter to help understand and reduce deep drainage or wasted water in irrigated cropping areas. Twenty-one drainage lysimeters have been placed under the root zone of cotton plants in the Condamine McIntyre-Balonne irrigations areas. The project is funded by the Queendsland Government in its newly initiated Rural Water Use Efficiency Program, Stage Two (RWUEII), and the work is backed by the Australian cotton industry, the Co-Operative Research Centre (CRC) for Irrigation Futures and the CRC for Cotton. Principal scientist with the Department of Natural Resources and Mines, Dr. Des McGarry, said many growers had done the hard work of introducing controlled traffic, permanent crop beds and break crops but the time had come to get to the bottom of deep drainage. "Deep drainage is a form of poor environmental management that can be sustainably managed today through altering on-farm practices," Dr. McGarry said. "Excessive deep drainage of irrigation water is both an inefficient use of a limited resource and it has strong potential to contribute to rising water tables, salinity and water quality problem." The research has grown from four farm sites three years ago to seven in recent months. The sites represent the key cotton growing soils and reflect a diverse picture of soil types, farm practices and climate. Craig Brimblecombe's property 'The Anchorage' and Bill Knights 'Farm 280 are the two St. George sites. Additionally there are five others - one at each of Dirranbandi, Pittsworth (Pampas), Dalby, Goondiwindi, and Macalister. "The Anchorage' is a good example of cracking brown clay, an old alluvium geologically, while 'Farm 28' is more typical of the old St. George irrigation area. Dr. McGarry and experimental Sri Lankan scientist Dr. Thusitha Gunawardena travel from Brishane after each irrigation to continue their research. They were in St. George last Tuesday. At each site, three recording drainage lysimeters have been installed with the crop, 50 metres in from the top, middle and tail ditch-end, beneath the root zone of the cotton plants. Lysimeters are large undisturbed soil cores instrumented with a suction drainage and logging system made from a PVC pipe of 30cm diameter. These are placed 120cm to 150cm below the soil surface and capture water which passes through the lysimetere-so bypasses the root zone. Water moves through to a collection point at the field edge via a small diameter underground irrigation pipe. A suction tower provides the vacuum to extract the water from the lysimeter to the collection points. It features a solar panel on top and a small electric motor, a water reservoir and two reid switches. The pump automatically activates when this water level becomes low. At the collection point, a data logger records (electronically) the volume of water passing beyond the root zone, as well as the time and the date of the event. This information is down-loaded directly into a laptop computer and the actual water that passed through the lysimeter is measured and collected for later analysis of chloride. Each site also features, a rain gauge which records volume, time and date details. A full weather station, based at Farm 28, measures and records humidity, solar radiation, rainfall, wind direction and speed information so weather may be related to evaporation and drainage. Answering the question of deep drainage takes a triangulated approach of research and cross referencing 0 lysimeters, irrigation advance and chloride analysis. The advance rate of the irrigation water down the field is measured with wetting front apparatus. This data is put through the Surface Irrigation Computer Simulation Model (SIRMOD) that has been developed at the NCEA (the National Centre for Engineering in Agriculture) in Toowoomba. This allows prediction of the water infiltration at any point in the field. This data is then combined with Evapotranspiration data (from the weather station) to calculate deep drainage by difference. A second method estimates deep drainage using the SODICS model based on the difference in soil chloride profiles (to 1.8 metres) at the start and ends of the cotton seasons. Early analysis of the experimental data shows deep drainage amounts, over a single cotton season, can vary from 50mm to 260mm. The collecting of data on a wide range of environmental and farm management conditions will continue for several years. (Courtesy - Balonne Beacon) |
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