Growing in a New Bermudagrass Green
Dr. Grady L. Miller
The study started with the question, Can we establish a bermudagrass on a USGA green with just nitrogen? We all know that bermudagrass requires ample nutrients for optimum growth and performance. Since USGA greens are almost void of nutrients, growing turfgrass on them increases the need for careful nutrient management. This is particularly true when establishing the turf. Because nitrogen (N) is the nutrient needed in greatest quantity, it is the nutrient that is most often applied and the one generally associated with increased growth rates. For this reason, a quick grow in is normally thought to correspond to high N rates. Previous research has shown the importance of K in nutrition programs, and the current trend is to apply K at rates similar to that used for N. So, what about the need for phosphorous?
A couple of years ago when the Envirogreen was constructed at the Turfgrass Envirotron, I had the opportunity to test out the theory that N, above all, else is most important for growing in a green. The Envirogreen was built to USGA specifications (without a choker layer) in the summer of 1996 with the assistance of Barbaron and industry donations. Half the green (6,000 square feet) was sprigged with Floradwarf and the other half to Tifdwarf. Soil samples were collected before sprigging. Since I was going to initiate a grow-in study, I was really only interested in knowing that the pH values were within a desirable range (6.0 - 6.5). I knew I could go back later and evaluate the soil nutrient status if I had growth differences during the grown-in.
Grow-in treatments consisted of applying N at a rate of 1 pound per 1,000 square feet each week with varying rates of phosphorus (P) and potassium (K). The fertilizer was applied as an approximate N-P-K ratio. The ratios evaluated were 1-0-1, 1-0-2, 1-1-1, 1-2-1, and 1-3-1. Treatments were replicated four times on each grass. Our target was to have the turf fully established in 7 weeks with an August 6th sprigging date. The turf was evaluated for density weekly.
As you can see in table 1, the two grasses grew in at similar rates. In terms of overall density, coverage was very slow until the third to fourth week. Total cover at seven weeks was still not achieved even from the best treatment. This was most likely due to the late sprigging date. What was the best treatment? Well from the third week on, the best growth was achieved from the 1-1-1 ratio of N-P-K. In Floradwarf plots, there was 33% greater density at three weeks compared to the next best treatment and 24% greater density in Tifdwarf plots. While the 1-2-1 and 1-3-1 plots filled in well, they still did not experience the same coverage as the plots fertilized with the 1-1-1 ratio. The 1-0-1 and 1-0-2 plots grew in very poorly. By seven weeks they averaged only about 36% coverage, 61% less than Floradwarf plots and 53% less than Tifdwarf plots fertilized with the 1-1-1 ratio.
What does this mean? It means that turf will respond to P fertilizer when it is grown in a P deficit situation and that you cannot substitute N or K for good balanced nutrition. The initial P and K in the soil would have been categorized as very low (<10 ppm). At the conclusion of the study, extractable K concentrations in the soil ranged from very low to low according to soil test recommendations. This illustrates the difficulty in maintaining a high concentration of K in sandy soils. Extractable soil P values for the respective treatments were as follows: 1-0-1 (very low), 1-0-2 (very low), 1-1-1 (low), 1-2-1 (high) and 1-3-1 (very high). The higher P concentrations did not contribute to a faster grow in. This response further illustrates the value of a balanced nutrition program and the need for soil testing. Phosphorus is a valuable fertilizer when needed, but should not be used when it is not needed, since it a non-renewable resource and can potentially contribute to pollution problems.
Table 1. Visual density values for Floradwarf and Tifdwarf following
Acknowledgement: I thank The Scotts Co. for providing fertilizer for this evaluation and the many other industry supports who contributed to the construction of the Envirogreen.