HERE we are back into another year and at over half way through summer, we still have not received any wide spread significant rain. So the general call goes out, when is it too late to plant this or that crop?
The first hurdle to avoid is early frost events for any summer crop. In some southern areas of Queensland that can be as early as Anzac day and is fairly debilitating event on all crops, that are not physiological mature. So that is a relatively easy end point date. What about our short and quick legume crops like mung beans? It is all to do with day degrees. So day degrees can be thought as thermal time or even as heat units in terminology, as the cotton industry quotes some time ago. Day degrees add up and the plants develop as these day degree numbers get higher. So for mung beans we need a base temperature, which is the lowest temperature that in this genus classification of plants called Vigna, has no growth. For mungs it is considered that around 8 degrees Celsius is base temp. So given we need nearly 600 day degrees to get to a first flowering point and 1200 day degrees for physiological maturity, then the equation is fairly simple.
If the max temp during the day is 35 degrees and the night time minimum is 20 degrees and the base temp is 8, then for these specific temps you would accrue 19 day degrees per day towards your approximate 600 day degree requirement for first flowering. That is about 1 month duration, which is when I would then like 2 to 3 inches of steady rain for our mung bean crop. Before you start the three decimal point calculator up, this is a rough calculation and of course our days are never going to be even as this every day. Remember that area of leaf canopy developed is crucial to a final yield and radiation/heat from the sun (day degrees), soil moisture levels and nutrients like N, P, K, S and Zn are very important partners to produce leaf canopy. Then it is another 600 day degrees from that flowering point to maturity. About 1200 unit degrees in total is required for physiological maturity in mungs. When you have worked in central Queensland with mungs and then in southern Queensland as I have, it is quite acceptable from experience to say in early and late planted mung bean crops, there will be at least a week's difference in flowering points between the two regions, with CQ being the quicker of course. So are you any the wiser for this information as too when is too late to plant? At least you have some of the parameters to make a judgement call on your take on the weather in the future at your location. So on sunny warm days, there is going to be more day degrees generated, than on several overcast or wet days. Even northern aspects on sloping country compared to a southern aspect can influence your length of time in the paddock of your mung bean crop. In 2016 for February, significant late rain provided many CQ growers for opportunity to plant a late mung bean crop. After so many dry months and lack of any crop, it was a local personalised decision to plant mung beans, so whilst I can ramble on about day degrees and nutrients etc, financial survival and solid end pricing for mungs really made the plant decision fairly easy for the low risk involved. The same situation may arise for all of us this summer with our valuable mung bean crop. Look after your soil nutrition and inoculation process, plus establish good pre plant sub soil moisture levels, so to push your favourite summer legume as fast as it can grow.
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