The first Verdure column of the year is traditionally dedicated to turfgrass science history. So, “back in the day” to the 1960s, John H. Madison Jr., Ph.D., (1918-2005) conducted research to determine the best seeding rates for the “most commonly utilized” turfgrasses of that time.
Today, turfgrass seeding rates are typically recommended in pounds per 1,000 square feet (or grams per square meter). Over 60 years ago, turfgrass seeding rates ranged from 10 to 20 pounds per 1,000 square feet (49 to 98 grams per square meter) in a “more-is-better” philosophy. Damping-off seedling diseases were common then, and seeding was a game of “survival of the fittest.” Too much seed results in excessive seedling competition, and seedlings cannot develop until some factor, usually disease, thins the population so surviving plants have space to grow and thrive. Too little seed results in too much space, so the turfgrass slowly fills in; however, the site is open to weed invasion.
This research was conducted at the University of California, in Davis. Four factors affecting turfgrass seedling establishment were investigated: turfgrass species, season of establishment, seeding rate and seeding depth.
Three turfgrasses were the focus: Kentucky bluegrass (Poa pratensis; common-type) and Penncross and Seaside creeping bentgrasses (Agrostis stolonifera). The turfgrasses were seeded in late March and again in early October in two separate but adjacent sites, and both on a silty clay loam. Individual plot size was 4 feet × 4 feet (1.2 meters × 1.2 meters), with two replications per treatment.
The experimental treatments consisted of seeding each of those three turfgrasses at four rates: 1, 2, 4 or 8 pounds per 1,000 square feet (4.9, 9.8, 19.5 or 39 grams per square meter). In addition, all seeded plots were covered with plaster sand at four rates: 0, 0.125, 0.25 or 0.5 inch (0, 3.1, 6.4 or 12.7 millimeters) to evaluate seeding depth.
At each site, the soil was tilled, raked, leveled and rolled, and 1 pound nitrogen per 1,000 square feet was applied from a 10N-10P2O5-10K2O granular fertilizer. The fertilizer was applied again each month after establishment at 0.75-pound nitrogen per 1,000 square feet (3.7 grams per square meter). All turfgrasses were mowed at 0.875-inch (2.2-centimeter) height-of-cut for the March seeding, and 1.375 inches (3.5 centimeters) for October.
Turfgrass plant populations were evaluated periodically over several months by counting plants within 2-inch- (5.08-centimeter-) diameter plugs, and measuring verdure, a chlorophyl index and root weights. A seed germination test revealed the actual seed germination rate was 80% for Kentucky bluegrass, 96% for Penncross and 90% for Seaside. Today, pure live seed (PLS) is used to indicate the percentage of viable seeds in a given weight of seed.
The March or October seeding time was not a significant factor in this study. The best seeding rate for Penncross was 1 pound seed per 1,000 square feet, and 1 to 2 pounds seed per 1,000 square feet for both Seaside and Kentucky bluegrass. Madison stated, “The turf maturing in the shortest period is the one that starts with fewer than the final numbers of plants and reaches its mature density by growth and tillering (or stolonizing).” In other words, heavily seeded turf produces a dense plant population, but those plants are weak and take several months to mature and spread and tiller. Therefore, the goal with seeding should be to get those newly emerged seedlings up and running and maturing as soon as possible. Also, seed covered with sand at 0.125 to 0.25 inch was best for seed germination, emergence and establishment.
The overall result of Madison’s work led to improved seeding rate recommendations for the turfgrass industry. He was one of the first scientists to conduct turfgrass research through the lens of ecology.
One more interesting historical point: Madison is credited with utilizing the term “verdure” to describe the “living grass remaining above the soil after mowing,” first published in Madison and Hagan (1962). Verdure is French for “greenery,” verdant is English for “green with growing plants,” and vert refers to “green vegetation.”
Sources
1. Madison, J.H. 1966. Optimum rates of seeding turfgrass. Agronomy Journal 58:441-443.
2. Madison, J.H., and R.M. Hagan. 1962. Extraction of soil moisture by Merion bluegrass (Poa pratensis L. ‘Merion’) turf, as affected by irrigation frequency, mowing height, and other cultural operations. Agronomy Journal 54:157-160.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 23-year member of GCSAA.