Then we observed the change of the state of crops in each zone. To assess the dynamics of the vegetation index, we used satellite images from May 14th and control measurements of yields on June 26th.
After our observations, the following conclusions were made.
- Zones with a high vegetation index didn't react to high nitrogen fertilizer rates. The index did not change for subzones with high (150 kg) and low (50 kg) doses.
This indicates that high and medium fertilizer rates were ineffective – nitrogen was not used by plants. In addition, we recorded a lodging of wheat in these areas during the harvest.
- Zones with an average vegetative index reacted to a high nitrogen fertilizer rates with an increase of the index.
Later we found that the areas with an average vegetative index and a high dose of nitrogen fertilizers yielded better than those with medium and low doses of nutrition.
- Only 45% of zones with a low vegetation index reacted to a higher nitrogen fertilizer rates with an increase of the index.
Mainly, these were areas located in the lowlands. Crops there were flooded or were in poor condition after wintering. For the areas that were located on the hills, we didn't record an increase in the vegetative index after changing the fertilizer rate. The amount of harvested grain only confirmed this observation.
We measured soil moisture by our sensors
located on the hills, and they showed that crops were experiencing moisture deficiency. Thus, they did not react to higher nitrogen rates.