Paddocks of underperforming, stunted, pale legumes could be suffering from a Molybdenum (Mo) deficiency. Yellow plants may indicate a lack of Nitrogen (N) but, sometimes it is actually a lack of Mo limiting the plant’s ability to fix and utilise that N effectively.
What makes Mo so important for growth?
Mo plays a small, but vital role in the plant’s ability to metabolise N. Every plant needs Mo to convert the N absorbed from the soil into amino acids and proteins. Plus, legumes like clover and lucerne, need Mo to fix the biological N from the atmosphere into something the plant can use. Because this process uses far more Mo than the process of making amino acids into proteins, clovers and lucerne are more likely to face deficiencies.
A little goes a long way
Fortunately, plants only require tiny quantities of Mo. However, because Mo deficiency significantly limits plant growth it is important to consider your soil type. Soils with low Mo are typically sedimentary soils. However, farmers with ash, pumice, and organic soils often have deficiencies, too. Molybdenum availability decreases as soil pH declines, so it is important to remember acidic soils are more prone to deficiency.
Animal well-being and Mo
Historically, excessive applications of Mo on pasture contributed to Copper (Co) deficiencies in livestock, leading to farmers to be cautious about its use. However, now we have a better understanding of the nutrient, you can mitigate this risk by applying only the recommended amounts and conducting regular herbage testing.
Is it Mo deficient?
If your clover and lucerne stands are not performing as expected or you spot yellowing, sad crops, it is worth investigating a Mo deficiency. Reliable soil tests are unavailable, so the only way to confirm deficiency is through a legume-only herbage test. Early spring is an ideal time to correct a deficiency, as clover and other legumes are beginning active growth and N fixation.
TECH TIPS
- Regular soil testing helps you understand the effectiveness of your fertiliser program and shows the long-term fertility trends across your farm. However, before soil testing, ensure no phosphate and potassium fertilisers have been applied in the previous three months as this can lead to elevated test results.
- Protect soils from pugging damage. Graze wet paddocks early before soil moisture gets too high.
