Three-year bare patch beats ryegrass

Alan Harman reports that a non-crop phase can help crop farmers practically eliminate ryegrass. He quotes David Ferris of Weeds CRC.
Issue date: 18 April 2008

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Introducing three-year, non-crop phase can drive down annual ryegrass seed banks, giving pasture farmers a weapon against herbicide-resistant populations and allowing a return to rotational cropping, Australia’s Weeds Cooperative Research Centre (Weeds CRC) reports.

Weeds research offers alternatives for both grazing and non-grazing enterprises.
In Australia, reports of ryegrass herbicide resistance are increasing while soil fertility, grain protein levels and crop yields decline. David Ferris of Weeds and the Western Australian Department of Agriculture says a non-crop phase provides an array of weed control methods, many of them non-chemical, to reduce weed numbers before sowing.

“Like most weeds, annual ryegrass is vulnerable to grazing,” Ferris says. “A three-year non-crop phase can reduce weed seed set and competitiveness, while encouraging growth of desirable pasture species. For grazing systems, it’s effective to introduce a sub-clover phase with grazing and weed seed-set control in spring – preferably using paraquat herbicide.”

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Ferris says grazing increased sub-clover coverage from about 20% to between 50% and 95% over three years. As a result, the annual ryegrass seed bank was so depleted that when cropping began in year four, there was only one annual ryegrass plant per square metre, compared to over 1 000/m2 in the first year of the non-crop phase.

A grazed sub-clover phase also supplied adequate nitrogen to subsequent crops, improving crop yield and quality.Crop farmers can also introduce a non-crop phase to fight weeds, but they’re advised to persist with the treatment for two to three years to adequately deplete the annual ryegrass seedbank. “For non-grazing systems, the best options are to introduce a Cadiz serradella pasture or a field pea or canola crop, brown-manuring them each year,” Ferris says.

One-year breaks with these crops all met the nitrogen demands of the subsequent crop, improving its yield and quality. |fw

How cows respond to concentrates

As concentrate costs rise, Dr Robin Meeske’s research can help farmers get the most out of their cows’ feed. Roelof Bezuidenhout reports.

Dairy farmers should carefully weigh up pasture quality and availability when deciding on the level of concentrate feeding, says Dr Robin Meeske of the Institute for Animal Production, Outeniqua Farm, George, in the Western Cape.

Writing in Grassroots, the Grassland Society of South Africa newsletter, he says rising concentrate costs make it essential for farmers to get a good return on concentrate feeding. “Concentrate feeding’s effect on milk production depends on pasture quality and allocation, level of concentrate feeding, quality and composition of the concentrate, stage of lactation and the cow’s genetic potential,” he explains.

“The poorest milking response to concentrate comes with high-quality pasture and high pasture allocation.”explains that high-fibre pasture takes longer to digest than pasture with a lower fibre content. The best fibre digestion takes place when the rumen pH is above 6. When it drops to below 5 many of the fibre-digesting bacteria die, halting the process. Cows then stop eating and experience acidosis.

“When pasture fibre content is high rumination increases and the cow’s digestive system can tolerate more concentrate feeding,” says Dr Meeske. “Research shows the fibre content of ryegrass pasture may vary from 40% in June to 55% in November, and in kikuyu it may be as high as 65% in March.“When Jersey cows fed 4kg of concentrate grazed high-quality ryegrass, the pH of their rumen was below 5,8 from 6pm to midnight. But when cows grazed kikuyu on 4kg of concentrate, the rumen pH stayed above 6,2. Concentrate feeding to Jerseys grazing high-quality ryegrass shouldn’t exceed 6kg/cow/day.

Feeding just 4kg/cow/day may be more cost effective, but 6kg concentrate on kikuyu during summer and autumn won’t compromise rumen pH.”Farmers should determine cows’ response to concentrate feeding by monitoring milk production when making changes, Dr Meeske concludes.Contact Dr Robin Meeske at [email protected]. |fw

India runs with GM cotton,veggies

In 2007 India had 6,2 million hectares under insect-resistant Bt cotton. This involved some 3,8 million smallholder farmers, cultivating an average of 1,6ha each. In 2006 alone the financial benefit to farmers of higher yields and fewer pesticides was calculated at R63 billion. The Bt gene has been bred into 131 hybrids sold by 23 companies. GM cotton now accounts for 66% of the total cotton area.

However, India is also developing vegetable varieties to fight insect pests and diseases. Public institutions, private companies and public-private joint ventures are researching crops such as black gram, cabbage, cauliflower, eggplant (brinjal), spanspek, okra, potato and tomato. Studies into eggplant are the most advanced. A major vegetable for millions and cultivated on 500 000ha in India, its production is constrained by fruit and stalk borer. A Bt gene provided significant protection in field trials and will reduce insecticide use by half, benefiting households and the environment.

Other vegetables in field trials include insect-resistant cabbage, cauliflower and okra, potatoes containing a gene from a wild relative that confers late blight resistance, and tomatoes resistant to the leaf curl virus. grain crops under trial include insect-resistant maize, castor beans, groundnuts and rice. Rice’s chitinase gene is being tested in tomato and groundnuts to provide potential resistance to fungal infection. – Wynand van der Walt ([email protected])
Source: ISAAA Brief 37, 2008. |fw