Pasture legumes tested for flexibility

So it came as no surprise, in a moisture-deficient northern district at Binnu last week, to hear about opportunities for growing a pasture legume.

Particularly as this is the area where, arguably, the best lupins are grown.

It's an area of traditional continuous cropping on a cereal-legume rotation with canola now a big rotation component.

With persistent chemical resistance issues, livestock is returning to the vocabulary of many of the younger generation as a possible option for another income stream, while applying integrated weed management pressures on weed seed burdens.

Department of Agriculture and Food (DAFWA) senior pasture research agronomist Angelo Loi and Nabawa/Chapman Valley farmer Jason Stokes are trialling biserrula, a pasture legume with an ability to persist in the often dry and frequently variable seasonal conditions.

The plant produces very high, hard-seed levels and has the potential to alter the crop-pasture rotation systems to a more flexible model.

It may allow farmers to more readily alter the crop-to-pasture and therefore crop-to-livestock ratios on their farms.

In comparison to subterranean clover, biserrula is deeper rooted and this assists in it being able to withstand moisture stress.

The deeper root system also allows it to better access moisture and also enables it to remain green later in the season.

Stressing the early nature of this research, Dr Loi said 300 hectares of arable pasture was dry-sown with biserrula last year, targeting as much seed production as possible to set up a seed bank.

"The reason why we chose biserrula is because it is a vigorous grower with a grazing benefit in autumn and spring with a DSE of 8-10/ha for the season," he said.

But the impressive nature of biserrula is its nitrogen-fixing.

How much do plants fix?

"About 20 kilograms of urea per tonne of dry matter," he said.

"As long as the plant is well nodulated, that organic nitrogen is available for next year's crop."

This means 5 tonnes per hectare of dry matter from the 2016 crop makes 100 kilograms per hectare of urea is available this year with the same residual amount for the following two years.

"Our trials and those done is other States show this to be true," he said.

"We trialled biserrula, serradella and bladder clover to investigate whether there is an N (nitrogen) response in wheat and barley crops.

"We compared no nitrogen with applications of 50, 100, 150 and 250kg/ha and trials were held in Brookton, Dandaragan, Babakin and Ardath.

"In each case, there was no or minimal response to added nitrogen."

GRDC trials were held last year at Lake King, Chapman Valley and Scaddan following a 2015 sowing of biserrula.

At Lake King, wheat with no nitrogen yielded 3.4t/ha with protein at 10.9 per cent.

"The same yield was also achieved with a rate of 150kg/ha of nitrogen with protein at 11pc.

There was no yield response to added nitrogen for treatments of 50, 100 and 200kg/ha.

At Chapman Valley, wheat with no nitrogen yielded 5.1t/ha with no statistical responses from all added nitogen treatments (at 50kg/ha, yield was 5.2t/ha, at 100kg/ha was 4.7t/ha and at 150 and 200kg/ha yield was the same as the no nitrogen plot).

Another trial at Chapman Valley involved a biserrula-canola-wheat rotation with the no nitrogen plot of wheat outyielding all other treatments at 5.4t/ha (yields from low to high treatments were 5.2t/ha, 5t/ha, 4.9t/ha and 4.7t/ha).

These results underlined the beneficial nature of pasture legumes for stock grazing.

In answering a question regarding photo-sensitivity, where compounds in the feed can react to the skin of an animal, Dr Loi said it should be a management practice to move mobs to diversified feed sources if early symptoms were detected.

"Photo-sensitivity normally kicks in at flowering in June or July but there's no uniform period and it can vary from paddock to paddock,'' he said.

"So you need to keep an eye on your mob."

While the northern trials were on red loams with 5.5 pH at the surface and lower at sub-levels, Dr Loi said pasture legumes could be grown on sand.

"On your best cropping country, you can rotate with biserrula and on your bad sands you can sow serradellas," he said.

"The heavy country can be sown to bladder clover and medics.

"There are still a lot of questions but the trials are encouraging and point to not putting on unnecessary nitrogen."

Research in WA has shown farmers have been able to crop for up to four years following initial seed set and still have sufficient regeneration of biserrula.