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. In cereals from this measurement, the optimum N-fertiliser amount at ear emergence can be calculated.
The N-Tester has only been calibrated in the UK for use on winter cereals - winter wheat and winter barley as well as winter triticale and winter rye - 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 N-Tester could be used on any plant to measure the chlorophyll content of the leaf and as such could be a useful management tool, however, no other crop calibrations exist so these would need to be developed locally by the user and any recommendations would need to 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. Trials have shown that by using N-Tester large increases in grain protein content can be achieved.
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 winter wheat and winter barley to provide actual nitrogen recommendations. Ask your local Yara agronomist to support you with calibration and to provide you the fertiliser recommendations based on the N-Tester measurement.
The N-Tester can be used in two main ways:
By taking readings through the season at regular intervals (anything from fortnightly to weekly), the N-Tester can be used as a crop monitoring tool to determine relative changes in crop nitrogen values. This will be in the form of a 3 digit reading.
As a general guide, on cereals, an N-Tester reading above 700 suggests the crop has sufficient N, a reading below 650 suggests the crop is likely to be deficient. Between 650 and 700 requires a judgement based on recent N applications, previous organic manure/slurries, current weather and growing conditions and whether the 3 digit value has increased or decreased since the previous reading.
The N-Tester has the ability to detect changes in leaf nitrogen content well before these are noticeable to the naked eye. It can therefore be an extremely useful tool for helping you to decide application timings.
When using this method there is no need to select crop or crop variety. The N-Tester will give a relative reading on any green leaf which you can then use as the basis for management decisions.
The N-Tester can be used in winter wheat and winter barley to provide an actual nitrogen recommendation for applications at growth stages 37 to 51. This enables you to fine tune the final application for yield. Please note if growing milling wheat varieties, additional N may be required for protein.
Users of older models of the N-Tester can download an excel worksheet which includes the latest variety calibrations and product recommendations
N-Tester calibration worksheet
Users of the new model N-Tester (2013 onwards) can now register for My Yara to download the N-Tester Loader programme which will update the N-Tester with the latest version settings updates to include the latest varieties
N-Tester software download
The instruction manual for the new model N-Tester can also be downloaded as a PDF (808KB)
N-Tester instruction manual