Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: WEDNESDAY, April 5, 1995 TAG: 9504060005
SECTION: CURRENT PAGE: NRV-12 EDITION: NEW RIVER VALLEY
SOURCE:
DATELINE: LENGTH: Long
Let's look at some turf research that helps us to understand proper agronomic treatments to lawns.
Fertilization: When contrasting late-fall fertilization with spring fertilization of cool-season turf grasses, the former has been shown to produce increased root growth, turf density and drought tolerance as well as decreased summer weed problems and disease activity. Fall-fertilized turf remains greener throughout the winter and greens up earlier in the spring.
Work by R.E. Schmidt at Virginia Tech has demonstrated that the application of one pound of nitrogen per 1,000 square feet of unfertilized Kentucky bluegrass in April reduces by 22 percent the number of roots measured at a six-inch depth in May. Where the bluegrass had received one pound of nitrogen per 1,000 square feet in October, December and February, the additional soluble nitrogen in the spring reduced root numbers at the six-inch depth 40 percent.
Similar observations at Ohio State University have shown that fall fertilization programs increased root numbers in June by 75 percent when contrasted with a program that provided one pound of soluble nitrogen per square foot in April. Their work also showed 25 percent increases in storage carbohydrates in the crown tissue in June as a result of the late-fall fertilization program. These stored food reserves are thought to be critical in mobilizing disease resistance mechanisms and generating recuperative potential in summer-damaged turf.
Additional research on tall fescue Kentucky bluegrass mixtures has shown that September- and October-fertilized plots produced half as much crabgrass infestation as plots fertilized in late fall and early spring. The spring fertilization component definitely enhanced crabgrass competitiveness.
There is no doubt that managing cool-season turf grass to provide moderate amounts of nitrogen in late fall (Nov. 1 to Dec. 15) has significant positive impact on root growth and carbohydrate reserve. If this can be coupled with low or no applications of nitrogen in the spring (March 15 to May 15), the positive impact will be maximized.
Mowing: The importance of mowing to the production of quality turf grass is underestimated by the average homeowner. Mowing is basically a stress-creating management factor. Decisions the homeowner makes about frequency, mowing height and disposition of clippings are critical.
Research on Kentucky bluegrass published in 1955 has demonstrated that any time more than 40 percent of the existing green tissue is consistently being removed, there is a significant detrimental effect on the root system. When 50 percent of the green tissue was consistently removed (three clippings per week), after 33 days only 35 percent of the root system was actively growing. Where 60 percent of the existing foliage was removed, all root growth stopped by the 28th day of the experiment. It was demonstrated that improper mowing frequency could have a significant negative impact on root growth. Therefore, homeowners should be advised to mow with a frequency which never removes more than one-third of the existing green tissue. This mowing frequency will enhance root development, minimize summer need for irrigation and increase drought tolerance.
Work in the late 1960s has demonstrated the importance of mowing height in reducing the ability of crabgrass to invade a turf. This work showed significantly less crabgrass germination at 2.5-inch mowing heights when contrasted with 1.5- and 0.75-inch mowing heights. This same principle was illustrated in work on tall fescue Kentucky bluegrass, where season-long mowing heights of one, two and three inches led to 53 percent, 19 percent and 1 percent smooth crabgrass cover in October, respectively.
Increased mowing frequency generally increases stress load on the turf by decreasing shoot, root and rhizome production. This principle was reported by researchers in 1961 when they mowed Merion Kentucky bluegrass at one and two inches five times per week and once a week and contrasted clipping, root and rhizome production. At the two-inch mowing height, clipping, root and rhizome production was reduced 22 percent, 21 percent and 34 percent respectively by the more frequent mowing. At the one-inch mowing height, this impact was even greater, with reductions in clippings, root and rhizome production of 24 percent, 46 percent and 45 percent.
Clippings: Clipping management can have significant impact on nutrient requirements. In 1981 it was reported that, on a Kentucky bluegrass-creeping red fescue mixture, returning clippings for three years led to a 38 percent higher growth rate than when clippings were not returned. This suggests that homeowners returning clippings can expect higher turf grass quality with less nitrogen fertilizer.
With today's increased concern for maintaining environmental quality, appreciation of how agronomic practices can minimize the need for pesticides and fertilizer by improving turf grass health will be increasingly important. Changing your fertilization and mowing practices will help the environment and result in a better quality lawn.
Joe Hunnings is the Virginia Cooperative Extension agent for agriculture in the Montgomery County Extension Office in Christiansburg. If you have quetions, call him at 382-5790.
by CNB