Achieving high yields and good stand persistence in lucerne boils down to maintaining adequate nutrition. Though soil testing remains the foundation of any fertility programme, herbage testing provides additional insight and is valuable to investigate underperforming stands or identifying potential deficiencies before they limit production.
Unlike a soil test, which measures the nutrients present in the soil, a herbage test measures the nutrients the plant has actually taken up. When used with soil tests and paddock history, it provides valuable information on the nutritional status of a lucerne stand and helps identify deficiencies affecting production.
Most test when a lucerne stand is not performing as expected. Signs may include reduced dry matter production, poor regrowth following grazing or cutting, uneven growth between paddocks, or visual symptoms of nutrient deficiency. Testing helps determines whether nutrition is contributing to the problem.
However, it is not only useful for troubleshooting. Early-season testing helps identifies nutrient deficiencies before they become yield-limiting and provides an opportunity to address issues and maximise production over the remainder of the growing season.
Where a deficiency is identified, foliar fertilisers provide a rapid correction, particularly for trace elements such as Boron (B), Copper (Cu), Manganese (Mn), Molybdenum (Mo), and Zinc (Zn). Molybdenum is especially important in lucerne because of its role in Nitrogen (N) fixation. Foliar applications sometimes help overcome short-term nutrient shortages or periods when nutrient
uptake is restricted.
However, foliar fertilisers are not a replacement for a sound soil fertility programme.
Lucerne removes significant quantities of Phosphorus (P), Potassium (K), Sulphur (S) and other nutrients through grazing and conserved feed. These nutrients must be replaced to maintain productivity. The quantities required are far greater than can realistically be supplied through foliar applications alone.
In many cases, a herbage test indicates the underlying issue is not a trace element deficiency, but rather a shortage of major nutrients such as P, K or S, moisture stress, pest damage, or declining stand vigour. In these situations, a foliar fertiliser is unlikely to address the root cause of the problem.
As with any diagnostic tool, do not use herbage testing in isolation. The most reliable interpretation comes from considering the herbage test alongside soil test results, paddock history, seasonal conditions, and field observations.
Used correctly, herbage testing identifies nutritional limitations, targets fertiliser investment where it is most needed, avoids unnecessary applications, and improves lucerne productivity and persistence when combined with soil testing and good paddock records.
For help with testing and analysis, contact your local PGG Wrightson Technical Field Representative.
Tech Tips
- Sulpher (S) deficiency can resemble N deficiency. Pale pastures may need S, not additional N.
- Nitrogen performs best when soils are moist and temperatures are rising. Timing influences response and return.
