Big Hopes for Biserrula

Extremely drought-tolerant, this amazing legume might be a great way of growing your own nitrogen in areas where dryland winter wheat can grow, saving you money in the process, writes John Fair.

It appears that many READERS HAVE  the same weakness I have for finding something new to try. Because after the first article in this series, I received a number of enquiries about biserrula (Biserrula pelecinus), the legume I used as an example of how to grow nitrogen instead of buy it.

One of the challenges South African farmers face is a narrow choice of legumes, and grain farmers need more legume options to grow nitrogen. Buying less nitrogen can immensely improve the profitability of producing grain. This isn’t only because of the obvious saving in fertiliser input costs, but because the biological fertility of soil is improved.

One Harrismith farmer did a trial some years ago where one land was planted to serradella for three years, and used exclusively for grazing ewes and lambs in the winter. A few lands were also partially planted to serradella for two years maize was planted in tramlines and serradella was planted in the pathway between to improve the grazing value of the maize residue.

In the same year, the average maize yield of all the lands that hadn’t been planted to serradella was 4,5t/ha. The yield of lands partially planted to serradella for two years was 5,1t/ha. The land on which serradella had provided excellent winter grazing for three years yielded 7,2t/ha. But I can hear some farmers in the Bothaville and Hoopstad regions grumbling, “John, get real, serradella doesn’t grow here!” My advice to them is to try biserrula.

A hardy legume
Where dryland winter wheat can grow, biserrula has a good chance of succeeding. Because it has a deep taproot, this legume is seriously drought tolerant. In Western Australia it grows well in areas with an annual rainfall of 300mm or more. It seems biserrula is more drought-tolerant and robust than serradella. Farmers in the southern and Western Cape should take note that biserrula is well-suited to deep sandy soils and has a wide range of adaptability, from acidic to alkaline soil.

Seriously hard seeds

There’s another characteristic that makes this self-regenerating annual winter legume an attractive proposition for farm research and development – it produces a mass of hard seeds. Seed yields can be as high as 1,5t/ha with a seed count of around 1 million/kg. Because the seeds are so hard, as many as 45% survive cattle and sheep ingestion. Sheep dung pellets can contain as many as 70 viable seeds per pellet! Some seeds are like olieboom (Datura’s) – they’ll last for just about forever in the soil.

This worries me a little – if biserrula grows successfully and is allowed to produce a lot of seed, we could have a very persistent weed on our hands. However, bright farmers will solve this problem by planting Roundup Ready maize so they can spray out any biserrula weeds at planting time. After harvesting, they’ll hopefully have a blanket of dark-green pasture that they’ll have to get rid of by chasing in four-legged weed-eaters!

A few years like this and buying nitrogen will be a thing of the past. Am I daydreaming? Not if biserrula behaves like grazing vetch has done on a farm near Kriel on the Highveld.Next time round, some more about biserrula and the magic of grazing vetch.

Contact John Fair at Harrismith’s SA Biofarm Institute on 058 622 3585 or e-mail [email protected].