Realistic yield goals need to be set given the moisture conditions going into the season and long term average for a particular crop in a certain area. Nutrient requirements for these yields can be estimated using this type of table. Nutrients used by previous crops. When determining fertilizer levels it is also important to look at previous years yields along with previous fertilizer application levels. If a 50 bushel durum crop was fertilized at a 40 bushel level, the difference needs to be made up so the soil N pool is consistent from year to year.
Soil tests are important periodically to verify the previous three points.
Soil tests are a guideline only because of the various errors that can occur in their procedure and need to be implemented in a broad approach to fertility. If unsure, we err to using higher rates. Maximum yield is determined by the fertility available in the earliest stages of crop development. Foliar applications mainly affect protein therefore proper rates have to be applied with the seed. In both cases, the fertilizer rate was varied proportionately cutting the seeding units speed.