Agronomists and growers use fertiliser test strips to see if a crop might respond to additional nutrients. Test strips are bands of a specific nutrient, put out in the cropping paddock. A nutrient is applied at a higher rate than the fertiliser base rate in the paddock. Ideally, another strip has no nutrient applied to it. If crop plants clearly respond to the higher rate test strip, topping up that nutrient might boost crop performance. If plants in the higher rate test strips are not growing better than the rest of the paddock, there might be no need for more of that nutrient. If plants in the rest of the paddock are not growing better than the nil strip, maybe the fertiliser rate was too high.
Which nutrients do test strips work on?
Test strips can be used for any nutrient but it makes the most sense for nutrients than can be applied in-crop. Nitrogen (N) test strips are the most common. They help growers decide on N top-up rates to use during the season. Potassium (K) and sulphur (S) strips are also useful, as are copper (Cu) and boron (B) where appropriate. For nutrients where there’s only one opportunity to apply during the season, like phosphorus (P) and granular applied trace elements such as zinc (Zn), test strips help gauge if rates need to change upwards or downwards for future crops.
South Australian grower Justin Wunduke used both N and S strips and found responses to both nutrients.
Tips for using test strips
- Put in test strips either just before sowing (e.g. N, K and S), at sowing (P, granular trace elements), or during the season (e.g. N, foliar trace elements).
- Run the strip across a typical part of the paddock. If the paddock is zoned for different fertiliser management strategies, run the strip across these areas so that the responses can be seen in all zones.
- Put the strip in a place you frequently drive past, to keep an eye on changes.
- Apply more fertiliser than the paddock rate e.g. an extra 50 to 100 kg/ha of N.
- Leave a nil strip to assess if the base fertiliser rate is appropriate.
- Ideally use one nutrient per test strip. This helps single out which nutrient is causing the response.
- If you want to use nutrient combinations, do strips for the individual nutrients as well. Then you can tell which nutrients get a response and if that response is better when nutrients are combined.
- Use the same fertiliser application technique as the rest of the paddock.
- Make the strip the width wide enough to ensure at least one full cut of the harvester is in the strip. This makes it easier to compare yield results and can be seen on a yield map.
- P strips work better when drilled rather than topdressed.
- For nitrogen test strips, include the test strip when you topdress.
What to look for in the test strip
- Assess the strip throughout the season, especially at the very start of stem elongation.
- Look for clear visual differences in growth compared to plants outside the strip. Be aware that a visual response may only be “cosmetic” – real responses are seen in final yield.
- You can use NDVI devices to get more quantitative observations. Summit Fertilizers use GreenSeeker® to assess paddock N strips and give fertilizer recommendations.
Making the most of test strip data
At harvest, keep a sample of grain from the test strip for testing. Take the grain sample from well within the test strip to reduce edge effect. Use grain analysis to calculate nutrient performance indicators.
Compare the treated and untreated strips to assess responsiveness and profitability. Response is the amount of extra yield between the two areas. Profitability is the value of the extra yield compared to the cost of the extra fertilizer.
Insights from N rich and poor strips