Low Nitrogen Rates Are Best for Zoysiagrass Establishment

By Elizabeth Guertal, Professor, Crop, Soil and Environmental Sciences Auburn University, AL 36849 • guertea@auburn.edu

The Rationale

Previous research with zoysiagrass establishment was fairly clear in all the results: lower rates of nitrogen (N) are all that were needed for establishment of the grass, whether from sprigs or plugs. What, exactly, were ‘low rates’? Faster establishment of zoysiagrass occurred at N rates below 2 lbs N 1,000 ft -2 year -1 , regardless of the N source or timing of that N application. In general, exceeding 2 pounds of N per 1,000 square feet per year was either deleterious for or did not speed zoysiagrass establishment.

One issue with all of this previously published work is that the vast majority of it was done with only ‘Meyer’ zoysiagrass, an older, wide-bladed variety of Zoysia japonica. While there is certainly nothing wrong with that research, the fact is that many new and improved zoysiagrasses are now on the market, and there is no research that evaluates best N rates for newer cultivars of zoysiagrass. So, the Objective of this two years of work was to evaluate rates of N fertilization for the best establishment of three newer zoysiagrass cultivars, which were L1F, Jamur and Zeon.

The Experiments

To conduct the research, we installed a total of three experiments at the Auburn University Turfgrass Research Unit (TGRU), located in Auburn, AL in 2015 and 2016. In 2015 two studies were installed: 1) an early spring establishment study, and 2) a late summer establishment study. In 2016 the early spring establishment study was repeated. For all experiments the soil type was a Marvyn sandy loam, and the research areas were fumigated (Basamid) prior to experiment start so that bermudagrass was eliminated. Irrigation was provided as needed to prevent turfgrass stress.

The experiment was a factorial combination of N rate (0, 1/8, 1/4, 1/2 and 1 lb N 1,000 ft -2 ) for the spring experiments. The summer 2015 experiment was adjusted as shown below, with a total of nine applications made to each experiment, and zoysiagrass cultivar (L1F, Zeon and Jamur). All zoysiagrasses were provided by the growers, washed free of soil, and pre-separated into two-inch plugs for planting. For each experiment the zoysiagrasses were planted as small plugs (two inches in diameter) planted at a six-inch grid in each plot. There were four replications of all the cultivar and N rate treatments. All N was applied as granular urea, with that fertilizer irrigated in with 1/4 inch of water after application.

Collected data included weekly establishment via line transect collection and shoot density. To collect the line transect data, two marked dowels were placed at right angles to each other between the plugs in each plot. If a piece of zoysiagrass tissue touched one of the 25 marks on a dowel it was counted as a ‘hit’ and totaled towards percent establishment. Shoot density was determined by removing three 2.25 inch diameter cores from each plot (again, within the plugged area), and counting all shoots in each core.

The Results

Of the cultivars evaluated, Jamur has the widest leaf blade, and was the most aggressive in establishment. When only zoysiagrass cultivars (establishment was averaged over N rate) were examined, establishment was in the following order: Jamur > Zeon > L1F (from fastest to slowest). Differences in the establishment rate of Zeon and L1F were less pronounced, and establishment in those two cultivars was often at the same rate. When plugged in the early spring (late May/first of June) Jamur was almost fully established within 11 to 12 weeks (> 95% cover), while Zeon and L1F both took around 15 weeks to reach 85% cover. Fall plugging of zoysiagrass did not result in a 95% stand prior to frost. However, there was no damage, and growth simply renewed in the following spring.

There was often an interaction between N rate and cultivar, which means that some cultivars reacted differently to N rates than other cultivars. This was almost always because Jamur was less sensitive to increased N rates, and establishment often increased as the N rate increased to 0.25 lb N 1,000 ft -2 (every other week, a total of 4.5 pounds of N 1,000 ft -2 in total). In comparison, establishment of L1F and Zeon was often only improved when N was added at 1/8 to 1/4 lb N 1,000 ft -2 (a total of 1.125 pounds of N 1,000 ft -2 ). These results match those for previous work with Meyer zoysiagrass, which showed that establishment was best when N was applied at between 0 and 2 lbs N 1,000 ft -2 year -1 .

Adding N beyond 1/4 to 1/2 lb N 1,000 ft -2 never improved establishment, and in many cases harmed the zoysiagrass stand. Sometimes applying higher rates of N created plots that were darker green, but the establishment was not any faster – extra N simply went to color and leaf growth. While not observed in 2016, in 2015 overapplication of N caused yellowing and loss of stand density in some cultivars (see picture). Ultimately, all of the zoysiagrasses recovered from this in the following spring.

Finally, while shoot density sometimes increased as N rate increased, the results were not always consistent, and shoot density was often unaffected as N rate increased beyond the 1/4 lb N rate (see Figure 1, next page). So, what N rate is best for establishment of newer zoysigrass cultivars? Well, it still pretty much matches that found years ago with Meyer – 2 lbs of N 1,000 ft -2 in total for establishment in 12 to 15 weeks. Early spring planting is more effective than later summer, but we did not see any adverse effects from winter damage. The coarser texture Jamur could use a higher rate of N than the finer textured L1F and Zeon cultivars, but overapplying lots of N (> 4 lbs N 1,000 ft -2 year -1 ) never improved establishment, shoot density or quality.

Picture from the Spring 2015 study (taken in May of 2016) showing the effects of over fertilizing with N on quality of zoysiagrass cultivars.