Australian Mungbean Association
Australian-grown mungbeans have quality written all over them!
When is it too late to plant mungbean?
27 January 2017
by Paul McIntosh, Pulse Australia
As the summer advances, and significant widespread rains haven’t occurred, the question of ‘when is it too late to plant’ arises.
For any summer crop, an early frost is fairly debilitating for crops that are not physiologically mature. In some southern areas of Queensland that can be as early as Anzac day and so this provides a reasonable end point date for the crop to be fully mature.
Working backwards from the likely date of the first frost, mungbeans require nearly 600 day degrees to reach the first flowering stage and 1200 day degrees to reach physiological maturity.
Day degrees can be thought as ‘thermal time’ or ‘heat units’. This is calculated using a base temperature (the temperature below which the crop doesn’t grow) and the average daily temperature (daytime maximum + night-time minimum divided by 2). The base temperature for mungbeans is around 8 degrees C.
On a day where the maximum daytime temperature is 35 degrees C and the night-time minimum is 20 degrees C, the average temperature for the day is 27.5 (i.e. 35 + 20 divided by 2). If you then subtract the base temperature of 8 degrees C you have accrued 19.5 day degrees toward the total of 1200 day degrees for the crop to reach physiological maturity.
If this average day degree accrual continued it would take about a month to reach the 600 units required for flowering to begin. At this point another couple of inches of rain would be generally required to see the crop through to the end of the season.
Of course, our day degrees are never going to be the same every day. Remember that area of leaf canopy developed is crucial to a final yield and also affects how much radiation/heat from the sun [day degrees] the crop can capture. Soil moisture and nutrients like N, P,K, S and Zn are very important partners to produce leaf canopy.
In different seasons and different regions the day degrees will accumulate at different rates with more generated on sunny warm days than on overcast or wet days. Even northern aspects on sloping country compared to a southern aspect can influence how quickly the mungbean crop will mature.
In February 2016, significant late rain provided many CQ growers with an opportunity to plant a ‘late’ mungbean crop. After so many dry months and lack of any crop, it was a local and personal decision for many to plant mungbeans. In this situation financial survival and solid end pricing for mungbeans really made the plant decision fairly easy for the low risk involved. The same situation may arise for many growers this summer with our valuable mungbean crop. Look after your soil nutrition and inoculation process, and ensure there is adequate pre-plant sub-soil moisture, to push your favourite summer legume as fast as it can grow.