The challenge with in-season N application is to adjust the top-dressing application rates to yield potential as well as the crop status in season to over-fertilisation, but also preventing crop stress and maximise ROI.
FluroSense Nitrogen recommendation is a guideline to adjust the recommendations, based on specific criteria to each field (soil, variety, Nitrogen uptakes) and seasonal conditions (weather, prices).
With the objective to define the optimal Nitrogen rate for in-season N application in winter wheat, 3 doses of urea were applied in strips on July 23 (middle of the winter season in Australia) with the following application rates (Fig.1):
- 1kg (pink)
- 20kg (red) and
- 40kg (blue)
FluroSense nitrogen recommendation module – N Rx recommended the application of 24 kg/ha of urea on July 23, compared to the grower standard practise of 40kg/ha.
Nitrogen response analysis
Using satellite imagery, FluroSense measured the chlorophyll index (CCCI) for each application rate. CCCI is a vegetation index, well correlated with the chlorophyll content of the leaves. By analysing its evolution of this index over the course of the season, agronomist can get an estimate of the nitrogen availability to the crop in the field:
- By July 19, chlorophyll is decreasing and suggests that the field develops nitrogen deficiency and requires an additional application.
- On July 29, only one day after the effect of the Nitrogen application is already visible with a 24% increase in the chlorophyll index.
- After July 29, the chlorophyll index of the crop that received 20 and 40 kg/ha remains similar throughout the rest of the season, indicating that the lower application rate (closer to the one recommended by the FluroSense N Rx model) would have been sufficient.
Nitrogen application outcomes
As the analysis of the chlorophyll status of the crop in this case study demonstrates:
- CCCI is a reliable and responsive measure of nitrogen status of wheat.
- The evolution of the CCCI shows that wheat becomes deficient in nitrogen prior to the application date. This deficiency could have been used to anticipate the application and move it to 10 days earlier to avoid stressing the crop.
- A top-dressing application in July was appropriate as clearly demonstrated by crop’s chlorophyll response
- The optimal application rate was defined – 20kg of urea (23 kg/ha recommended by the model) compare to the grower standard rate of 40kg that didn’t bring additional benefits
- By applying the Nitrogen at the FluroSense recommended rate (24kg) instead of standard grower practices (40kg), the grower could have saved 16 kg/ha or 1,600 kg on a 100 ha field (-$560 on this field alone).
In this case study, FluroSense nitrogen recommendation model suggested optimal nitrogen rate, which would have helped the grower to avoid over-fertilisation, and maximised the ROI. The model takes into account numerous parameters, including in-season satellite data, pre-season N application, and economic factors to provide greater accuracy in nitrogen management while making it easy for agronomists to use.