Potential for vetch to reduce nitrogen costs
An important part of the equation in Australian grain growers’ declining terms of trade in recent seasons has been the rising price of fertiliser.
Many soils in our cropping regions are limited by nutrient deficiencies, so nitrogen fertiliser is usually an inescapable cost component in farming budgets.
Of course, there are alternatives to applying a lot of nitrogen. Legumes play a critical role in cereal rotations by providing disease and pest breaks to cereal crops but also by returning nitrogen to the soil, and one of the most effective legumes for this purpose is vetch.
Rade Matic, who leads the vetch breeding program at the South Australian Research and Development Institute (SARDI), says trials across five sites over three years had shown an average increase in soil mineral nitrogen (as reported in commercial soil tests) in the 0-10cm soil layer of 17kg/ha after a vetch grain crop.
From two sites over two years, there was an average increase of 30 kg/ha after vetch hay production and a substantial 51kg/ha average increase following green manuring. At current prices for urea, these nitrogen inputs would be worth approximately 33, 59 and $100/ha respectively and they only represent a tip of the iceberg – there could easily be twice as much more nitrogen from the vetch in the deeper layers of the soil profile (10-60cm).
It doesn’t stop there. Field trials conducted by CSIRO Plant Industry at Narrabri in New South Wales on vetch in cotton rotations found that vetch’s ability to fix nitrogen exceeded all other legumes in the trials, including field peas, faba beans, clovers and medics.
Vetch commonly fixed up to 200 kg/ha of atmospheric nitrogen in the trials, and there were several other notable outcomes. Soil organic matter in cotton fields with vetch in the rotation increased by 14% and subsequently, cotton grown after vetch showed improvement in its uptake of key nutrients including nitrogen, phosphorus and beneficial trace elements.
Soil structure was also improved, making cultivation easier, as was the soil’s water-holding capacity.
Demand for vetch appears to be increasing. According to Seedmark’s Bryan Robertson, high nitrogen prices and difficulties with fertiliser supply have helped to create a great deal of interest in vetch among Australian growers over the past six months.
Bryan says there has also been an increase in interest from European farmers for Australian vetch seed, which can fetch prices of $1,500-2,000/tonne for Australian growers. Again, European demand is being driven by high nitrogen fertiliser prices along with the recent fall in the Australian dollar.
The vetch breeding program at SARDI released the new variety Rasina β late in 2006 to be marketed by Seedmark. Rasina was developed with support from growers and the Australian Government through the Grains Research and Development Corporation (GRDC).
Rasina β is a rust-resistant, ascochyta-resistant, soft-seeded vetch variety suited to low-medium rainfall areas of southern Australia. Trials prior to its release showed Rasina β was superior to any other vetch in terms of grain yield, early establishment and dry matter production. It is also tolerant to shattering.
However, another important quality of Rasina β and other vetch varieties such as the high-rainfall Morava β is their ability to offer substantial improvements in soil fertility, structure and organic matter. Further varieties being developed in the GRDC program will be targeted at grain production in lower rainfall cropping areas (a variety which matures earlier than Rasina β) as well as a replacement for Morava β.
One of the difficulties in using legumes to replace nitrogen and deliver other benefits has been the relatively poor yields associated with growing them in low-rainfall areas which dominate much of the Australian southern cropping belt.
However with Rasina β, growers now have access to a versatile vetch variety which is better suited to low-rainfall environments and which has considerable capacity to reduce their reliance on nitrogen fertiliser. Further funding from SA Grains Industry Fund (SAGIT) aims to assess and develop new vetch (Vicia) species for forage and grazing in low-rainfall environments.