Some rain around Australia’s northern region saw some last minute mungbean crops go in.
The GRDC Mungbean Grownotes suggests we base fertiliser recommendations on:
- soil test results
- fallow length
- yield potential
- paddock history.
That’s comprehensive, but with an opportunity crop there’s not always the chance to cover all the bases.
Typical starter fertiliser rates for mungbeans are low in nitrogen (N), phosphorus (P), sulfur (S) and zinc (Zn). We don’t use much, or sometimes any, N because we expect legumes like mungbeans to fix their own nitrogen.
If you put mung beans in, here’s what to look for, and what you can do about some possible nutrient issues. Use Ask an Expert if you’d like feedback from our Community of Practice.
Mungbean is a legume. They should fix enough atmospheric N for their own growth. To do so they need to be sucessfully innoculated and in low background N soils. N deficiency shows up as leaves that are pale green to yellow all over, with oldest leaves most affected. Check roots to see if there’s effective nodulation. If not consider a top-up with urea ahead of rain or irrigation to move the crop along.
High stubble loads can also trigger a need for more nitrogen. Extra N can help crop development if soil N is immobilised by microbes to break down crop stubble.
In some late plantings the crop can flower in as early as 35 days. This can make it a challenge for the crop to reach an adequate height and canopy closure. Extra N can help achieve rapid early growth.
Fungi friends help mungbeans with P & Zn
Mungbeans depend on beneficial fungi to access P and Zn from the soil. Long fallows, canola and lupin crops, can reduce the activity of those fungi. Severe lack of friendly fungi shows up as long-fallow disorder. Crops fail to thrive even with enough moisture.
If you suspect there could be low fungal activity use extra starter P. P deficiency appears as purple stripes along stems, darker green leaves and delayed maturity. Foliar sprays may help to overcome mild deficiencies in-crop.
Zn deficiency appears as stunted plants with dead tissue between the veins. Nutrient top-ups could help if there’s signs of Zn deficiency.
P and Zn fertilisers can’t entirely compensate for the lack of fungi.
S deficiency is most likely with double-cropping and high yields. Upper leaves and petioles look yellow before older leaves. Applying of 5–10 kg S/ha usually corrects S deficiency.
Fertiliser top-ups are less effective if there are subsoil constraints. Subsoil problems restrict root growth. With fewer roots, plants extract less moisture and nutrients from the soil:
- Salinity affected plants are patchy, stunted, and quickly wilt on hot days. EC levels >2 dS/m can cause a yield loss in mungbean.
- Sodicity reduces plant-available water, limiting growth and yield. Soils are classed as sodic with exchangeable sodium percentage (ESP) over 6%. But lower ESP levels can be a problem, particularly when magnesium is also high.
- Acidity can be a problem with pH <5.5 (measured in 1:5 soil–water), and induce nutrient imbalances.