Photo credit: FREEPIK
The zero spot fertilization method for wheat is based on the following principles: The nitrogen supply to the wheat during the growing season is done in three steps.
1) The first application in early spring at the time of the start of wheat growth (BBCH30 (middle of March) about 25-40% of the estimated total nitrogen intake.
2) The main application, 40-55% of the estimated total nitrogen intake, is applied at BBCH 30 (middle of April) so that it is available when shooting at BBCH32.
3) The final supplementary application is made in the flag leaf stage at BBCH39) (middle of May).
The final supplementary amount of Nitrogen is calculated according to the result of the measuring of the Zero spots. The zero spot is defined as a square area of 3×4 meters within the field that has not been subjected to the application of nitrogen fertilizer. The supplementary rate is distributed according to biomass from satellites.
The total nitrogen requirement is calculated after the zero spots have been evaluated and revealed the soil’s nitrogen supply. The nitrogen requirement is calculated according to 3 different formulas depending on the winter wheat variety and on the final use of the wheat. The winter wheat varieties are classified into three categories based on protein content at optimal nitrogen levels: 1) Low protein wheat (<10% protein) at optimum, 2) Medium protein wheat (10-12% protein) at optimum and 3) High protein wheat (>12% protein) at optimum. In addition, the nitrogen calculation is adapted according to the use of the wheat. A) Own feed and bread wheat 22 kg N/tons harvest, B) Feed for industrial and starch wheat medium or high protein varieties 20 kg N/tons harvest. C) feed for industry and starch wheat Low protein wheat 15 kg N/tons harvest.
In practice, non-fertilized zero spots for nitrogen are laid out in the fields in the spring in connection with nitrogen fertilization of the winter wheat. At each nitrogen fertilization, it is ensured that the zero spots do not get any nitrogen. When wheat approaches BBCH39, measurements of nitrogen uptake are made in the zero spots. Nitrogen uptake is measured indirectly with Yara’s N-tester and via image analysis in Yara’s Atfarm app. The values from the measurement are then entered into a formula developed by Yara, where the characteristics of the variety and the use of the wheat is also taken into account as described above. In the formula, the farmer also specifies the estimated harvest and previous fertilization. In this way, the supplemental nitrogen requirement is determined. The supplemental requirement is then used as a basis for determining the optimal distribution of the nitrogen application based on Satellite data via Atfarm or Cropsat.
In these programs, the value from the zero box is calibrated against the satellite images so that the zero box represents the correct part of the field. Then a VRA file is created and the farmers spread their supplementary application based on the VRA (Variable Rate Application) file.
By laying two zero spots when spreading organic fertilizer (one that only gets organic fertilizer and one that gets no nitrogen at all), we also have the opportunity to calculate the contribution of the organic fertilizer and remove it from the need for supplementation. This is done by measuring the nitrogen uptake in both zero spots.