Soils: December 1999

We have written about the importance of yield goals but believe a review is needed. Those of you who have soils tested and want a fertilizer recommendation know that the expected yield (yield goal) has almost the same influence on the fertilizer recommendation as the soil test values. In many instances, the testing facility personnel assume a yield goal or send only the test results to the sample owner if they receive no yield goal with the soil sample.

We need yield goals and production records as we prepare nutrient management plans (already required for some manure application plans). The following article is reprinted with permission from Oklahoma State University (Zhang, H., G. Johnson, and B. Raun, "Setting a Realistic Yield Goal," Crop Statement 2, no. 15 [1999]: 3).

What is a realistic yield goal?
A yield goal is the yield you hope to harvest. However, what you hope to grow and what you end up with are two different things. Crop yields are largely determined by your management style, crop varieties, soil properties and weather conditions. Therefore, your yield goal should be practical and achievable. This is the so-called Realistic Yield Goal. Since soils vary considerably in their physical and chemical properties from farm to farm and field to field on the same farm, it is important to set a realistic yield goal for each field every year.

Why use a realistic yield goal?
The primary reasons for setting a realistic yield goal are economics and environment. Yield goals are needed if you are going to decrease the cost of production to improve farm profitablity. For example, fertilizer deficiencies for nitrogen and sulfur are identified not only on the results of soil testing but also on expected yield goals. The soil testing lab cannot make those interpretations if crop code and yield goal are not marked on the soil sample bags. Many soil samples received by the lab do not have a yield goal marked, and some counties use the same yield goal for everyone who submits a sample. If yield goals are too high, money can be spent needlessly on fertilizer. Over-applying nutrients in the form of fertilizer and animal manure can have a negative impact on the environment. Fertilizer use can be a significant part of your production cost. On the other hand, if the yield goals are too low, nutrients recommended are not sufficient for the most profitable yield, and farm profitability may be reduced. Therefore, yield goal has a direct impact on your projected cost of production.

How do I set a realistic yield goal?

• Aim for above average yields so crop yields will slowly increase over time.
   
• Keep a good production record of each field on the farm for at least five years. Some fields may produce more than others because of differences in soil-quality and other factors.
   
• Adjust the past average to set a yield goal. The practical range for a yield goal should be somewhere above average to near the maximum yield in the last three to five years. Two common methods for calculating realistic yield goals are:
  1. to add 10 to 30% to the recent average yield; and
  2. to take the average of three highest yields in the last five consecutive years. These two methods are illustrated in the following table. Regardless of the method you employ, it is important to be consistent from one year to the next.