IN DUE TIME
Many turf maintenance recommendations refer to making the last nitrogen application in November when growth slows or stops. Here in Seattle, our perennial ryegrass may continue growing all through the winter months as well as summer months. How do I time my fertilizers to keep up with their growth, and do I need to use slow release nitrogen?
— Seattle, Wash.
It's difficult for turf specialists to make nationwide recommendations due to widespread variations in growing conditions. As you are aware, even variations within the state can provide different challenges for successful turf production. Relying on local university extension publications and other experts can help take the mystery out of turf care in your region. A recent study compared winter fertilizations on turf in Pullman vs. Puyallup and slow-release vs. quick-release fertilizers. They found that November was the latest time fertilizer should be applied in Pullman. Later fertilizations did not produce any response in turf growth. However, the plots in Puyallup benefited from December and February fertilizations as well, regardless of whether quick-or slow-release nitrogen was used. There was some concern over using quick-release nitrogen fertilizers during winter months resulting in increased nitrate leaching. Because the soil conditions are still adequate for ammonium conversion to nitrate, even in late fall and winter, choosing even ammonium sources of N may not prevent nitrate leaching. Those same conditions make it possible for nitrogen to be released from coated urea slow release fertilizers.
I'm seeing a variety of products advertised for treating my greens to increase the number of helpful bacteria. Are these products necessary?
— Charlotte, N.C.
The jury is still out on exactly how beneficial these products are. There have been many studies looking at microbial products applied to help control various pest problems. Some are effective, some are not, depending on the particular circumstances surrounding the problem. Currently, there is no agreed upon number of microbes that is considered “enough” for proper root growth. There has been little research to determine a baseline amount of bacteria surrounding the rhizosphere (the area right around the root which has the greatest amount of microbial activity). Microbe population in the rhizosphere of creeping bentgrass and bermudagrass greens recently has been studied in North Carolina, South Carolina, Alabama and Florida (two locations on research greens and two locations on greens located on actual golf courses). The greens received the same maintenance as any well-cared-for greens would receive, and the bacteria population was measured over four years. The particular type of bacteria present varied a bit according to location and type of turfgrass; however, on all four locations, there were large numbers of culturable bacteria and actinomycetes present in the rhizosphere and the bulk soil all year. Are the products necessary? Hard to say, but if your greens look healthy, they probably have a healthy microbe population below supporting their growth.
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