Hardseeded annual legumes, an on-demand break option with significant benefits
Author: Belinda Hackney and Jane Quinn (Graham Centre for Agricultural Innovation) | Date: 17 Feb 2015
Take home messages
- Summer sowing of hardseeded annual pasture legumes using seed harvested on farm is proving to be a robust method of establishing pastures for use as ‘on-demand’ break options in crop-pasture rotation systems for the low and medium rainfall areas of NSW.
- On-farm results show hardseeded legumes are regenerating vigorously following a cropping phase without the need for resowing with substantial benefit to the cropping enterprise.
- Summer sowing appears to have potential for suppression of both early and late germinating problem weeds in cropping systems and as such may assist in reducing the impact of increasing herbicide resistance.
- Both research experiments and on-farm monitoring shows annual legumes are capable of supporting very high levels of livestock production with livestock offering additional weed control options.
A major objective of current studies at the Graham Centre is investigating strategies to improve profitability and sustainability of mixed farming systems. A key area within this objective is assessing the impact hardseeded annual pasture legumes can have on both crop and livestock performance. Hard seeded annual legumes such as biserrula (Biserrula pelecinus), bladder clover (Trifolium spumosum), gland clover (T. glanduliferum) and French serradella (Ornithopus sativus cvs. Margurita and Erica) have the capacity to be used as ‘on demand’ break options in cropping systems providing valuable nitrogen and disease breaks for the cropping system whilst also providing high quality fodder for grazing livestock.
Three key questions in developing strategies for widespread use of these legumes by the mixed farming industry are:
- How can they be readily and reliably established?
- What is their impact on the cropping system?
- What is their impact on the livestock system?
These three questions will be addressed in the remainder of this paper using results of on-farm monitoring in southern NSW.
Mike O’Hare at Beckom has been growing hardseeded annual legumes since 2009 and now has half his farm sown with a biserrula (cv. Casbah) seedbank and the other half, a mixed bladder clover (cv. Bartolo) and gland clover (cv. Prima) seedbank. There is also a small area of French serradella. Mike’s rotation is to sow the annual legumes in late February-early March using seed harvested on farm. The biserrula seed is scarified to approximately 50% germination prior to sowing while the bladder and gland clover is sown unscarified. (Note: Our replicated experiments covering central and southern NSW have shown excellent establishment of unscarified biserrula in summer sowing situations, which differs substantially from the Western Australia experience). Inoculant used has been ALOSCA® of the appropriate group.
The legumes are allowed to grow and set seed in the first year with grazing pressure dependent on seasonal conditions. Legumes are then allowed to regenerate in the second year and sprayed out using a knockdown in September (i.e. no seed set in the second year). Paddocks are then sown to canola and in the following year, wheat. Following this, legumes are left to regenerate. Thus the legumes are only permitted to set seed every fourth year. Last year (2014) was the first opportunity to measure the effect of this type of rotation on legume regeneration following the cropping phase at a reasonable scale.
Regular measurements were taken on regenerating biserrula, bladder clover and French serradella areas. Measurements taken included autumn, late winter and peak spring herbage availability. Differences in crop yield and cropping inputs for the cropping phase are discussed while the results of on-farm monitoring of lamb liveweight gain is also reported.
Results and discussion
Agronomy – on farm impacts of use of hardseeded legumes in cropping systems
The ability of legumes to regenerate as an ‘on-demand’ break in the cropping rotation was clearly demonstrated on-farm at Beckom in 2014. All areas evaluated had been in legume pasture in 2010 and allowed to set seed with some grazing occurring. In 2011, legumes regenerated and were grazed from germination (in rotation) through to mid September when all herbage was sprayed out (prior to seed set).
Canola was sown in 2012 and wheat in 2013. The farmer reported a 0.5 t/ha increase in canola yield following the legumes compared to his conventional non-legume paddocks with only starter fertiliser used at sowing. The wheat yield was no different to conventional paddocks. These results support earlier studies (Hackney et al. 2012 a, b, c) which showed at least comparable performance of wheat after hardseeded legumes with no fertiliser addition compared to paddocks where legumes were not grown and all nitrogen was supplied via inorganic nitrogen sources.
In terms of regenerating legume productivity (Figure 1), bladder clover and French serradella were very similar at all measurement periods. Biserrula had 600-1000 kg DM/ha more feed on offer in late autumn compared to French serradella and bladder clover, respectively. Again in late winter, biserrula produced an additional 1000 kg DM/ha compared to the other two species and compared at peak spring. The feed on offer from biserrula was on average 1600 kg DM/ha greater than the other two species. The high feed availability of all species, but particularly biserrula, in the autumn-winter period is of substantial value to livestock enterprises in the mixed farming zone and also has implications for increased N-fixation for following crops.
Biserrula has higher hard seed content than both bladder clover and French serradella and therefore it is probable that there was greater seedbank available for germination following the cropping phase compared to the other two species. The results found here again differ somewhat from the WA experience. In WA, both bladder clover and French serradella are used primarily in 1:1 rotations as their hard seed levels (~55% in WA conditions) tend not to give good regeneration results if the cropping phase is extended for longer.
Biserrula, in WA situations may be used in cropping phases lasting from 2-5 years with capacity to still regenerate. The results from Beckom indicate bladder clover and French serradella are persisting well in the seed bank even with a one year in four seed set. There is considerable complexity in the hard seed breakdown/seed coat formation/total seed production area that needs to be well defined to understand at a regional level the optimal rotation strategy for these species. This is currently one focus of our research.
At Beckom, feed on offer at the end of winter in the regenerating biserrula paddock used was 4000 kg DM/ha with biserrula contributing >90% to total herbage availability. Seasonal conditions deteriorated considerably from late August onwards. Ewes and lambs were introduced to pasture on 3 September 2014 and feed availability at that time was 3880 kg DM/ha. At the conclusion of measurements and following lambs weaned, approximately 1700 kg DM/ha remained.
Liveweight gain differed between sexes and was averaged 350 g/head/day overall (Figure 2).
Biserrula can cause primary photosensitisation in sheep and this was observed in the lambs with 4% affected with mild photosensitisation. The farmer is aware of this risk and part of his strategy in managing this risk is having areas of non-biserrula pasture; i.e. the bladder/gland clover mixed pasture. If animals begin to show early warning signs of photosensitisation which includes drooping ears and slight depression, sheep are moved into another paddock. In some instances this is another biserrula paddock that may contain some other species such as annual ryegrass. A feature of biserrula, and particularly of the variety Casbah, is its lower level of palatability compared to some other common pasture species. This difference in palatability can be used as a weed removal strategy with sheep eating plants such as annual ryegrass preferentially, thus reducing its impact on the following cropping system. Additional research undertaken in replicated experiments also shows biserrula and other hardseeded legumes when used in summer sowing situations has direct physical suppression on weeds including annual ryegrass compared to pastures sown in late autumn.
Programs of study underway at the Graham Centre are well on the way to offering to producers strategic methods of introducing hardseeded annual legumes into mixed farming systems to optimise crop, livestock and pasture production while exploring tactical use of these species to combat weeds which impact on crop performance. So far, results of these projects have shown the potential of summer sowing compared to conventional sowing as a means of introducing these legumes into the farming system, while offering a tactical means to reduce weed incidence.
In addition, monitoring of producers’ large scale sowings have shown these species can considerably boost following crop productivity with reduced reliance on fertiliser nitrogen and operate very effectively as an on-demand break option in a cropping rotation. This is a major step forward from the traditional crop-pasture rotation system practised in south-eastern Australia where pastures have traditionally been re-sown following a cropping phase with often mixed results.
In the break year, there is the potential for these legumes to contribute to high levels of livestock production as evidenced by on-farm results. An additional bonus, particularly with biserrula, and specifically it seems, with Casbah biserrula, is the ability to use grazing to tactically remove problematic weeds in the pasture phase thus reducing their impact in following crops. More research is needed on a regional basis to identify the best options for specific crop rotation – soil-climatic-livestock associations, but what is evident is the tremendous capacity of these legumes to complement cropping systems in southern Australia.
Hackney, B., Rodham, C., Piltz, J. (2012a). Using biserrula to increase crop and livestock production. Meat and Livestock Australia.
Hackney, B., Rodham, C., Piltz, J. (2012b). Using bladder clover to increase crop and livestock production. Meat and Livestock Australia.
Hackney, B., Rodham, C., Piltz, J. (2012c). Using French serradella to increase crop and livestock production. Meat and Livestock Australia.
The current research at the Graham Centre on hardseeded legumes in this paper is funded by Meat and Livestock Australia and Australian Wool Innovations under the projects B.PSP.0013 Pasture legumes in the mixed farming zones of WA and NSW: shifting the baseline and by Meat and Livestock Australia B.AHE.0236 Understanding photosensitisation in livestock grazing the pasture legume Biserrula pelecinus.
Graham Centre for Agricultural Innovation, Locked Bag 588, Wagga Wagga NSW 2678
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