Paul McIntosh talks temperature and how it helps mung bean development
Cooler weather delays flowering
ONE of these years it is going to rain really significantly in early January and then everyone can plant whatever they want in summer crop choices and vexing questions like “can I plant mung beans?” in early February will not be an issue.
Mungs, like other crops, accumulate heat units to generate growth and ageing.
So with a base temp of 10.5 degrees, then you need about 600 day degrees for flowering to be in full swing.
Add another 500 to 600 day degrees for physiological maturity (PM) which equals about 1200 day degrees.
Not much different to chickpeas – an interesting fact as well.
You accumulate these milestones of growth stage as this thermal time increases.
So what has all this to do with when or when not too plant to, on the calendar?
If we have a coolish end of summer and even cooler autumn, it is going to take longer for our mung bean plants to reach the flowering stage and even longer to physiological maturity time.
Cooler conditions with adequate soil moisture lead to a longer plant life and therefore a longer period of time your mung bean crop needs to set pods and seeds to reach maturity.
At this time of year for planting for any of our remaining summer crop options in southern Queensland, a frost on Anzac Day would create a fair bit of havoc with your summer crop trying to reach PM stage.
In previous years, planting dates around now really do need a frost-free period to at least the middle of May.
Remember we are betting on a continuous warm environment with adequate soil moisture to propel our favourite summer legume through the various growth stages.
So what can you do to assist your mung beans in reaching physiological maturity as quickly as possible?
Well you can have input into some things and then there are other uncontrollable environmental details that you are at the mercy of, like future weather conditions.
Topography is a key element and lower creek or river flat ground compared to north-facing slopes will certainly impact on your mung bean crop’s development speed and crop safety.
North-facing slopes should develop more quickly of course, especially when compared to the other side or a south-facing hill.
So a good even strike is your first requirement and a planting depth as shallow as possible would be important from a well structured and soft soil surface.
The last thing you want is a crusting soil surface in this late plant situation.
Some pop-up starter fertiliser positioned at least two inches below and to one side of the seeding zone would be handy, to provide that early and even flush of growth as a seedling.
I have debated about adding a lot of nitrogen fertiliser in the root zone of this future mung bean crop and I must say the jury in my mind is still out on the need for this heavy nutrition rate to speed up the growth process.
Certainly we would achieve more dry matter production and probably more yield, however if you look at speed of crop development with the extra bio mass created by large amounts of plant available nitrogen and hopefully some moisture, you may not achieve much PM earliness here in the trade-off.
You want nothing to slow the plant growth down and that may include some post-emergent herbicides.
So weed control timing needs consideration in this endeavour of trying to beat the onset of frost or cool temperatures in the autumn time.
By my reckoning over the past 15 years, there have been at least three occasions of early frosts in April somewhere in southern Queensland impacting on our late sown crops.
The risk is there, however so are the rewards of planting our short and quick mung bean crop.
Do some assessment in your own country, along with your mung bean accredited agro to share the load.
IN THE PADDOCK: Mungs emerging from a 2017 wheat stubble block.