Cyamopsis tetragonoloba AKA Cluster Bean
Guar seems to be definitely worth trying as a cover crop. The few past growers I can contact in Australia seem to think so. For cover cropping or otherwise, it can grow good biomass, as suggested by this 2009 article in Crop Science Society of America, which compares biomass, nitrogen accumulation and digestible dry matter of guar, cowpea, pigeonpea, mungbean and soy.
Apparently drought tolerant, it supposedly thrives in semi arid regions, and has been grown in Australia. (Best yields with monsoon rains – that certainly isn’t us). It is usually grown for green manuring, and guar gum. The international crop is so big/significant that in India it has its own futures market, but the Wiki guar page has little to say about it.
It apparently has good root growth, then takes off upwards, growing to 70 – 200cm. It is a poor competitor. Likes sand, & alkaline soils, but not waterlogging.
It must be well and individually inoculated, is a long season grower, Oct to May in Qld. The cvs can be bushy or erect.
So, will it suit us here? It will suit our alkaline soils and droughty ‘semi arid’ summers, and very probably won’t go to seed because of the amount of daylight hours needed, which suits our needs. If it is truly a poor competitor, then it may suffer like many legumes grown in a mix. That will be a topic for future density trials.
Because of the nature of the guar gum market, not only is (Australian grown) seed dear relative to other legumes, but scarce at the moment and grown under licence. IF it grows, and IF it is suitable as a cover, seed availability may be quite an issue. The upside is that if the local cc seed market grew (remember, the USA has had a cover crop seed industry for a decade already), it may be positive and encouraging for the industry as a whole, creating another market for the seed. Thanks goes to Tony Matchett, from the Australian Guar Co (and also here, which further explains how they are in partnership with West Texas Guar) for supplying me with some seed to trial. I think the timing has been right to achieve this: 12 months ago I was on a trail of contacts in Qld (& thanks to all of them: Bruce Proud, Peter Mailler [now chairman of Grain Producers Australia,] Peter Thompson), and having seed right now is a good outcome: as much as guar has been tried in Australia, no one sells it commercially, not even by a gardeners packet (but I could be wrong…)