Persons recommending fertilizer for bermudagrass often comment that the grass has a minimum requirement for nitrogen before efficient production responses are obtained.
When the producer has limited funds we usually suggest treating only the acres that can receive the most efficient rate of nitrogen. A common response to the question "What did you apply on your bermudagrass last year?" is 150 pounds of 17-17-17, or a similar statement. How do you know if that was a wise investment? We could go into a discussion about soil testing, yield goals and productive potential of the soil, but this article is limited to efficient nitrogen rates. Research and observations have indicated that a certain amount of nitrogen must be applied to satisfy requirements of other plant parts before additional forage is produced.
The yield information shown in Tables 1 and 2 is from replicated research plots at the NF Pasture Demonstration Farm. This data does not show yields from any plots receiving less than 50 pounds of actual nitrogen per acre because other research has shown nitrogen rates less than 50 pounds per acre are usually inefficient. A quick search of regional experiment station reports since the early 1960's found no bermudagrass fertility studies with nitrogen rates less than 50 pounds per acre.
Treatments of 50 or 75 pounds were applied in late April and ammonium nitrate was the source. Treatments greater than 75 pounds were applied as split applications, one-half in late April and one-half in June. Soil type and test years are listed on the tables.
Table 1 shows four years of results comparing no nitrogen, 75 pounds and 150 pounds. Yields show a large variation between years but three of the four years show good responses from nitrogen applications. In those three years, 150 pounds of nitrogen produced more pounds of forage per pound of applied nitrogen than 75 pounds.
You can use those relationships to calculate the nitrogen cost per pound of additional forage.
Table 2 shows yields from a different soil and during a different time period. During those years and at that site, 100 pounds of nitrogen per acre was more efficient than 50 or 200. Again, notice the variation between years.
It is possible that splitting the higher rates into two applications had an influence on the efficiency. One year of data from Oklahoma State University Experiment Station Progress Report P-561 (Table 3) shows 100 pounds of spring applied nitrogen is more efficient than 50 pounds.
The data shown in these tables supports the general recommendation made by NF specialists, and many others, that you should always apply at least 50 pounds of actual nitrogen per acre when fertilizing bermudagrass. Exceptions to this statement would occur when legumes are in the system or soil tests show significant nitrogen in the soil. I encourage you to use soil testing and other guidelines to help you invest your fertilizer dollars wisely.