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Rural Industries Research & Development Corporation
by Angela Avery & Geoff Ronnfeldt,
Agriculture Victoria, Rutherglen
and
Jim Virgona & Oliver Owen, NSW
Agriculture
November 2001 RIRDC Publication No 01/155 RIRDC Project No: DAV-144A
Trifolium subterraneum (sub clover) is an important legume for farming systems in South Eastern Australia. The sub clover seed industry is small when compared to other agricultural industries but is of great importance to Australian agriculture as it supplies affordable, high quality legume seed to many grazing and cropping enterprises. Economic viability and long-term sustainability are major challenges for this industry with industry analysis revealing increased production costs, declining seed yield and a fall in the number of growers.
The principles behind sub clover seed production have changed little over the last sixty years. There has been a significant increase in mechanisation of the harvesting process as well as adoption of improved agronomic practices. Despite these advances little research or extension has been directly targeted towards the sub clover seed industry over the last four decades. It was from this basis that the project Improved sub clover seed production evolved. There were two objectives of this project, (the first related to research and the second related to industry development):
• To increase production of quality subterranean clover seed by 50% in northern Victoria and southern NSW.
• To develop a grower network in the subterranean clover seed production industry and to facilitate shared learning and communication.
The methodology was based on integration of research and industry development and as a consequence was largely driven by industry and their needs. While the initial project proposal was developed with industry, critical information gaps relating to seed production were unclear. As a consequence the first stage of the project involved an extensive literature review. The second stage coordinated and facilitated an industry workshop to share and build the project around knowledge gaps and industry priorities.
The general aim of the experimental work was to explore management options needed to increase seed yield through enhanced herbage, nutrient and weed management. In Victoria, all research was conducted at an irrigation site at Katamatite. In NSW, research was conducted at two dryland locations at Mangoplah and Wagga. The sites were linked through common design and measurements and through shared extension activities. Experiments were clustered into three broad management areas, herbage, nutrient and weed management.
Herbage management
Dry residual herbage at seed harvest decreases the efficiency of the harvesting process. Management systems that enabled residual herbage to be reduced, yet maintain seed production, offer large benefits to the industry. A range of herbage management treatments were considered over two years based upon grazing, cutting (mulching and silage), herbicides and plant hormones. Unfortunately there was no one treatment that was able to reduce residual herbage and maintain or increase seed yield. From this work two favourable herbage management practices were identified; herbicide (such as Sprayseed) in June/July for irrigated and dryland seed crops and early silage production for irrigated seed crops. Silage cutting of dryland crops significantly increased the risks of soil moisture depletion before the completion of seed development. The work also concluded that herbicides (Sprayseed and Paraquat) in spring at or post 5% flowering significantly reduces seed yield. Seed reduction as a result of this practice was however similar to seed reduction caused by heavy weed infestation. Therefore on weedy sub clover seed crops late spraying can be justified. The use of plant hormone sprays and mulching, which is a relatively common practice in the industry had no effect on seed yield or residual herbage. These results have the potential to be dependent upon cultivar and the growing season, further work is required to refine optimal management practices
Nutrient management
Survey work has indicated that most seed production paddocks have low soil phosphorus and that phosphorous applications to sub clover seed crops are also low. At the last Victorian workshop held for sub clover seed growers fertiliser rates of 200 kg/ha were recommended, but there are currently no clear guidelines as to the minimum and optimum levels of phosphorus for seed production or the phosphorus levels removed by sub clover seed production. Findings from this study indicate that 300 kg/ha of superphosphate (27 kg P/ha) (the highest rate used) is below maintenance levels for both dryland and irrigated sub clover seed production. Phosphorus removal from sub clover seed was identified to be between 13 and 21 kg P/ha/year, depending upon the fertilisation application, and soil P levels declined across all treatments. There is a need for further work to understand the extent of P loss and attribute this loss between product removal (herbage, seed and herbage residue), and dust generated in the harvesting process before sound fertiliser recommendations can be made.
Seeds were analysed for total P and it was shown that fertiliser application affects seed P content and that seeds with a high P contents are likely to germinate and grow more rapidly as seedlings.
Practical implications of this are limited given that seed quality in the market place is currently only related to germination and weed contamination. Fertiliser application to increase seed P may be a worthwhile practice in the production of pre-basic and basic seed.
Weed management
This study highlights the critical nature of the timing of weed removal in sub clover seed crops and recommends that further work be undertaken across several growing seasons and for more cultivars.
Preliminary findings indicated that to gain optimal control of annual grass weeds in sub clover seed crops, herbicides should be applied before flowering. The work on broadleaf weeds determined that seed yield was reduced by 0.36 t/ha as a direct result of broadleaf weed presence.
Industry development
The final area of this project was extension and network building. To this end the project has been effective in bringing the Victorian and NSW clover seed industries together to learn new technology, to share experience and to address some of the major challenges confronting the industry in the next decade. Some examples of these activities included seminars, workshops, site visits, bus trips and combined industry meetings.
In 2000, a second project was funded by RIRDC for 18 months to develop sub clover seed production guidelines. These guidelines provide a valuable and effective means to further extend the findings from this project to seed growers and to the end-users of sub clover seed.
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