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Agricultural News From The DNRE

Plant growth in farm dams, fertilising grazed pastures courses and more

By Rachel Dawkins - 23rd October 2002 - Back to News

PLANT GROWTH IN FARM DAMS: IS IT A PROBLEM?

The presence of Azolla is evident in many farm dams across Victoria. Azolla is a native aquatic plant found in still or slow-moving water bodies. Azolla appears green or red depending on exposure to the sun, in shaded conditions the leaves are usually green, whilst in direct sunlight they become reddish.

Azolla is a common free floating fern up to 10 to 30 mm in diameter with roots hanging down to about 40 mm below the water surface. Azolla fronds float on the water surface individually or as large mats. Two species of Azolla are commonly found in Australia including Azolla pinnata and Azolla filiculoides. The plants support nitrogen fixing bacterium, which allows it to use nitrogen from the water and air for its own growth.

The occurrence of a vigorously growing population of azolla in a farm dam generally indicates high nutrient levels in the water. Azolla can survive within a water pH range of 3.5 to 10 but optimum growth is in the pH range of 4.5 to 7 and temperature range of 20 to 30 degrees C.

Azolla is not harmful to stock that drink the water or consume the plant. Nor does it have a deleterious effect on domestic house and garden water. However, excess growth of the plant can cause problems including blocked pump inlets and filters, impeded flow where plants bank up at structures, restricted stock access to drinking water if plant density is sufficient and reduced sunlight penetration of dam waters. During times of dying off it may also reduce oxygen levels in the dam.

The need to control excessive growths of Azolla due to associated problems should be carefully evaluated. Re-configuration or relocation of pump suction hoses, inlets and filters and the establishment of off dam watering troughs may be adequate to address common problems associated with this plant.

Azolla in farm dams may well be vital in the ecology of the dam and if controlled, the benefits of Azolla could be lost, including reduced bank erosion, provision of habitat for aquatic life and reduced water evaporation rates and temperatures. In addition Azolla takes up the nutrients in the water for its own growth and therefore restricts the nutrients available for the growth of other nuisance plants and potentially toxic blue green algal blooms. Azolla will also naturally die off during the hotter months.

If excessive Azolla growth becomes a problem and control is deemed necessary, it is best achieved by mechanical or manual removal – such as scraping it off the top of the dam with a scoop net. If Azolla is left to dry for a few hours it dies off. This method has the advantage of removing nutrients in the plants rather than returning them to the water as the plants break down.

To limit periodic excessive growth of Azolla, minimisation of the amount of available nutrients and favourable water conditions in dam is the most effective form of prevention. Where possible:

• Limit the influx of nutrients to the dam by preventing runoff carrying fertilisers and sediment from entering the dam.
• Establish buffer strips of native grass, shrubs and trees above the dam and along drainage lines into the dam to intercept some nutrients and soil particles from pastures and crop land.
• Minimise sunlight on the dam by planting native vegetation on the north and west sides of the dam. Do not plant trees on the embankment.
• Limit stock access to the dam by providing off dam watering troughs to stop stock fouling the water.

LAVINIA ON LEAVE

Regional Plant Standards Officer, Lavinia Zirnsak, has taken leave from the Department for the next 11 months.

Lavinia has been in Bairnsdale since September 2000. Apart from the Regional Plant Standards Officer role, Lavinia was also involved in the lettuce project "Improving Insect Pest Management". This project involved field trials to evaluate new softer biological pesticides as well as the potential for the use of beneficial insects with a view to developing an integrated pest management program for lettuce. The project also looked at opportunities to improve production and quality of lettuce including the incidence of tipburn.

For information on the inter state movement of plants, fruit fly or the lettuce project, contact the Calvert Street office in Bairnsdale on 5152 0600.

FERTILISING GRAZED PASTURES COURSES

The Department of Natural Resources and Environment is running a three day "Fertilising Grazed Pastures" course to help meat and wool producers increase their skills and knowledge of soils and fertilisers. The course will enable producers to make cost effective decisions about how much fertiliser to use, which fertilisers to use and what areas fertilisers should be applied to.

Other topics covered include how to identify and manage problem soils, calculating rates and costs of fertiliser products and determining farm requirements.

This course was run in Gippsland for the first time earlier in the year and proved very popular and relevant to beef and sheep producers in the region. A Warragul producer said that he gained considerable knowledge from the course in soils, nutrient use and requirements and highly recommended it to other producers.

The course is subsidised by FarmBis, bringing the cost down to $40 per farming business (normally $400). The course contains both theory and hands on activities and is suitable for both mainstream and organic producers. It will be run at the Maffra NRE office on Wednesday November 27, Wednesday December 4 and Wednesday December 11.

For more information, please contact Fiona Baker at the Maffra NRE office on 51 470834

Source: http://gippsland.com/

Published by: news@gippsland.com

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