Production: seed to soil contact critical for legumes

Beef Central, 15/03/2013

A central Queensland producer demonstration site has revealed how producers can boost legumes in pastures dominated by buffel grass.

Maximising the contact between soil and seed is the key to establishing legumes to combat rundown of sown pasture and minimise time and money wasted on costly legume seed that doesn’t survive.

Fitzroy Basin Association Grazing Land Management Officer Joe O’Reagain said the MLA-funded Bundaleer Producer Demonstration Site (PDS) had shown treatments that increased soil disturbance or placed the seed directly in contact with the soil doubled plant establishment compared with broadcasting.

“The more careful we are at ensuring good seed-soil contact, the better the initial establishment,” Joe said.

“There are greater costs associated with getting better soil-seed contact, such as machinery and fuel expenses, however it appears to pay off.”

The exact costs of the different treatments will be established in the next 12 months of research. The PDS, on Matthew and Maryellen Peart’s Arcadia Valley property ‘Bundaleer’, investigated different approaches to establishing legumes in buffel grass dominated brigalow soils.

The site consisted of two adjoining buffel grass paddocks on heavy brigalow clay soils. Three legume species (butterfly pea, burgundy bean and siratro) were planted together across the two paddocks via broadcast, direct drill seeder and crocodile seeder. The control had no legumes sown.

A crocodile seeder is an implement with a large cylindrical drum to which shovel-like tools are attached. Seed placed in the drum escapes through holes at each shovel as the implement is towed along behind a 4WD or tractor.

Both paddocks were heavily grazed prior to planting, however only one was subjected to a herd of 200 head/ha for 12 hours immediately after sowing, to see if hoof impacts would boost soil-seed contact.

Making it count

Initial establishment counts showed that direct drilling doubled the initial establishment rate compared with simply broadcasting the seed, but high density grazing immediately after sowing had no impact on legume establishment.

However, with the crocodile-seeder treatment, high-density grazing did improve initial seedling counts, doubling legume establishment from 62,500 to 118,000 plants/ha.

There is good producer interest in the trial because much of Central Queensland’s sown pastures are affected by pasture rundown, and many producers are keen to get more legumes into their pastures.

“Grazing productivity and profitability are reducing from declining pasture production, carrying capacity and live weight gains,” Joe said.

“Traditional pasture renovation methods, such as blade ploughing, are expensive and economically unsustainable, and their pasture renovation effect is short-lived. By establishing legumes, producers have an opportunity to improve diet quality and provide some nitrogen to their soils on an ongoing basis.”

Best options

Across all treatments, siratro has been the most abundant legume to date, with burgundy bean appearing in moderate proportions and butterfly pea plant densities being very low.

More recent results showed large declines in plant numbers (which is expected as seedlings compete with each other and other plants) but the impact of soil disturbance is still marked. The benefit of high-density grazing on seedling numbers from the crocodile-seeder option had disappeared by this time.

Even with excellent seasons (1,700mm rainfall for 2010), only 6.5% of the viable seed had germinated and survived at last count. But, despite severe attrition, Joe said current plant populations were still acceptable and were better on average where mechanical disturbance had occurred.

Queensland Department of Agriculture, Fisheries and Forestry pasture agronomist, Stuart Buck, said it was important to consider the benefit of seed-bed preparation to reduce competition from the existing pasture and to store soil moisture when weighing up the costs and returns of different establishment methods.

“While removing grass through cultivation or herbicides increases the preparation costs, it significantly reduces the risks of failure, particularly during poor-average seasons,” Stuart said.

Top tips for growing legumes

Strategic spelling is important for legume survival as stock preferentially graze them.

If you are going to sow legumes, do your homework:

• find the most suitable legumes for the soil type and grazing system

• talk to neighbours and professionals with experience

• look carefully at seasonal forecasts and know when you can expect season-breaking rain

• learn about rhizobia, otherwise your legumes may not produce nitrogen properly.

When planning legumes for your own pastures, remember the PDS operated in a period of excellent seasons, a small amount of sampling was carried out, and there was no replication.

Source: Meat & Livestock Australia


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