By Mark Lundy
Here's what 8 ppm soil nitrate-N looks like at tillering. The top photo is from a wheat field where the pre-plant NO3-N was 6 ppm in the top foot.
The bottom photo is from an adjacent field with the same soil type, variety, and planting date, but different historical management, where the pre-plant NO3-N was 14 ppm in the top foot.
The extra 32-40 lb of available N per acre predicted by the 8 ppm difference in pre-plant soil NO3-N test can be easily observed in the difference in plant growth and color in the unfertilized portions of the two fields (outlined in red).
A nice, visual example of how real-time measurements of the soil/plant environment can help to inform N fertilization decisions.
Source:ucanr.edu