This enables fast and accurate field specific recommendations to help fine tune application during the growing season. This can result in more accurate field scale recommendations, improving profitability and minimising environmental effect.
The nutritional status of the plants determines the timing and amount of fertilizer. With the N-Tester it is possible to identify the nitrogen requirements of plants directly on the field easily, safely and quickly. The nitrogen fertiliser demand is never constant and can vary considerably from year to year and field to field. By splitting the N-fertilisation into more dressings, it is possible to optimise the N-fertiliser rate according to the actual plants needs on any field in any year.
A plant analysis with the N-Tester gives valuable information about the current nutritional status of the plant.
The N-Tester has been calibrated in South Africa on wheat and potatoes. On these crops it can be used to determine the nitrogen status of the plant and from this a variety specific nitrogen recommendation can be calculated.
In theory, the N-Tester could be used to measure the chlorophyll content of the leaf and as such could be a useful management tool, however, no other crop calibrations exist. Currently it is being tested in South Africa on barley and maize and recommendations would be confirmed by locally conducted trials.
A series of field trials was conducted to assess the advantage of using N-Tester to fine tune nitrogen applications. Applying the correct level of nitrogen to a cereal crop can have a significant benefit both on yield and on grain quality. Ensuring the protein content of grain meets grain buyers specifications can have a significant impact on crop profitability.
N-Tester operates by measuring the chlorophyll content of the leaf, as this is related to the nitrogen status of the plant. The measurement point should be in the middle of the blade of the youngest, fully developed leaf. Thirty random measurements from across the field, taken using the usual ‘W’ pattern, give an average value that is used to indicate how much Nitrogen the crop requires. Deriving a fertiliser recommendation is only possible if no other nutrient is limiting the crop growth.
The N-Tester measurements are strongly influenced by crop variety and growth stage. For this reason the N-Tester measurements must be calibrated to take account of this variation.
Yara have developed calibrations for wheat and barley to provide actual nitrogen recommendations at growth stages 33 - 51. This enables you to fine tune the final application for yield and protein / grain N content.
As a general guide, on wheat, an N-Tester reading above 650 suggests the crop has sufficient N, a reading below 600 suggests the crop is likely to be deficient. On Barley, a N-tester reading above 550 suggests the crop has sufficient N, a reading below 500 suggests the crop is likely to be deficient.
Interpretation of N-tester readings is further based on crop potential, crop rotation system, recent N applications and current weather and growing conditions. Ask your local Yara agronomist to support you with calibration and to provide you the fertiliser recommendations based on the N-Tester measurement.