Foliar uptake of nitrogen on creeping bentgrass and bermudagrass greens
Creeping bentgrass and hybrid bermudagrass show similar uptake of foliar-applied nitrogen.
Stiegler, Ph.D.; Mike Richardson, Ph.D.; and Doug Karcher, Ph.D.
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Foliar fertilization has become an increasingly common means
of providing supplemental nutrition to turfgrass on golf courses.
Photos by M. Richards
fertilization refers to the process of nutrient uptake through the leaves and
is often used to deliver nutrients during periods when root uptake may be
limiting. Anything that restricts root growth or function can potentially lead
to reduced nutrient uptake, even in a nutrient-rich environment. Applying
essential elements directly to the plant foliage can effectively bypass
deficiencies associated with the roots or any soil issues that might prevent
nutrient uptake. Foliar fertilization also provides turfgrass managers with
increased flexibility, precision and convenience of application compared with
traditional granular fertilizer application methods.
fertilization is an increasingly common supplemental nutritional practice in
today’s golf course management. Recently conducted surveys of golf course
superintendents indicated that almost all of those responding use foliar
fertilization somewhere within their nutrient management programs and, in many
cases, foliar fertilization often makes up a major portion of the total annual nitrogen
inputs to putting greens (J.C. Stiegler, unpublished data). Because foliar
fertilizer is routinely applied to intensively
managed areas of the golf course, it is particularly important, from an efficiency
standpoint, to obtain a greater understanding of the time it takes for applied
fertilizer nitrogen to be absorbed by the turfgrass foliage.
The research plots were located
at the University of Arkansas Agricultural
Research and Extension
Center in Fayetteville, Ark.
Although various researchers have examined the practical aspects
(growth and color response) of foliar- and liquid-applied fertilizers (7,8,10,11),
few studies have investigated foliar nutrient uptake dynamics or efficiency and
only recently have scientists addressed this topic under field conditions
(6,9). The majority of the earlier foliar nutrient uptake data in turf looked
at nitrogen absorption by cool-season turfgrass leaves grown in controlled,
moderate temperature environments (3,4,5,12). The previous studies have demonstrated
that 30% to 60% of the nitrogen applied can be absorbed by the leaves. Although
these basic studies have made a significant contribution, more research is
needed to improve foliar nutritional strategies for superintendents who wish to
maximize plant uptake and reduce losses to the environment.
A cup cutter was used to remove turfgrass plugs from the research plots at various intervals after foliar fertilization in order to determine how much of the fertilizer had been absorbed and how quickly it had been absorbed.
Studies to evaluate foliar absorption of nitrogen in the field
would be beneficial to understand how seasonal environmental conditions might affect
this practice. Previous agricultural crop research has demonstrated that
environmental factors and seasonal dynamics of leaf cuticle characteristics can
influence the foliar absorption of nitrogen solutions (1,2). The goals of the
present study were to directly quantify the rate of foliar absorption of urea
nitrogen by putting green turf under field conditions and to determine the
effect of season on the uptake efficiency of foliar nitrogen fertilizer.
Experimental area and nitrogen treatments
This study was conducted at the University of Arkansas
Agricultural Research and Extension Center in Fayetteville, Ark., on both Penn
A-1 creeping bentgrass (Agrostis stoloniofera L.)
and TifEagle hybrid bermudagrass (Cynodon dactylon × C.
transvaalensis) putting greens maintained according to putting
green management practices typical for the region. Mowing was performed six days
per week at a 0.125-inch (3.175-millimeter) cutting height.
Plant-available phosphorus and potassium levels in the root zone
were tested at the beginning of the study and supplemented accordingly. A
mixture of quick- and slow-release nitrogen sources was used to provide the
creeping bentgrass a base fertility program of 4 pounds nitrogen/1,000 square
feet/year (19.52 grams/square meter); the bermudagrass area received 6 pounds
nitrogen/ 1,000 square feet/year (29.29 grams/square meter). Routine
maintenance fertilizer applications were not made during the same week that foliar
nitrogen uptake studies were conducted.
Plots were fertilized at a high and a low rate of nitrogen, but rates of nitrogen uptake efficiency were significantly lower in turf receiving the higher rate.
Because urea is one of the most common forms of nitrogen included
in foliar fertilizer products, it was chosen as the nitrogen source for this
foliaruptake field trial. Throughout the two years of the study, urea enriched
with a heavier isotope of nitrogen (15N) was used for fertilization to allow precise
measurement of nitrogen uptake in the leaves. During the 2007 and 2008 growing
seasons, foliar urea-nitrogen with 15N-labeled urea was applied once a month,
May through September, to 2-foot × 4-foot (0.60 meter × 1.21-meter) plots with
1-foot (0.30-meter) borders. Foliar nitrogen was applied at 50 gallons/acre
(467.69 liters/hectare) with the aid of a spray shield and a single-nozzle CO2-pressurized
sprayer. Spray treatments were made at approximately 7:30 a.m. after the
experimental areas were mowed. Rates of 0.1 and 0.25 pound nitrogen/1,000
square feet (0.5 and 1.25 grams/square meter) were used and designated as a low
and high rate, respectively. Plots received no irrigation or rainfall for a 24-hour
period after treatment so that all nitrogen absorption was limited to foliar
Tissue collection and processing
Immediately before and then after nitrogen application, two
uniformly sized — 4.25-inch (10.8-centimeter) diameter — turfgrass plugs were
randomly taken with a standard golf course putting green cup cutter at 0-, 1-,
4-, 8- and 24-hour intervals, to assess nitrogen uptake over time. A procedure
was developed to precisely remove a uniform, 0.125-inch (0.3175-centimeter) thick
sample of verdure from the top portion of each sampling core obtained during
field sampling. Total nitrogen was determined for turfgrass plant leaf and
The experimental design was a randomized complete block within
each turfgrass species. Treatment factors included nitrogen rate and year, with
sampling time after application and month of year added as repeated measures.
All treatments were replicated four times.
Foliar uptake of nitrogen
Foliar absorption of urea by both species occurred rapidly and followed
a curved pattern of uptake (Figure 1). Absorption was greatest between time
zero and one hour after application, thereafter leveling off and approaching a
numerical maximum by 24 hours. This was consistent for both species and
demonstrates the effectiveness of foliar application to quickly supply nitrogen
to the turf. Based on the amount absorbed at 24 hours, within the first four
hours, creeping bentgrass absorbed 83% and bermudagrass absorbed 94% of the
urea. Bermudagrass foliar uptake of nitrogen peaked at four hours after
application (Figure 1), but foliar nitrogen continued to be absorbed by leaves
of creeping bentgrass up until the last sampling period of 24 hours after
treatment (Figure 1).
Absorption of foliar-applied nitrogen is a complex process
(diffusion and/or mass flow) that is governed by time, solution and molecular
characteristics, along with various other environmental and leaf surface
factors. General principles dictate that foliar uptake should occur as long as
the urea solution remains on the leaf surface. However, from an agronomic
perspective, for a superintendent wishing to maximize foliar uptake of
ureanitrogen on creeping bentgrass greens, delaying necessary management
practices (for example, syringing greens, etc.) for longer spans of time (for example,
24 hours) in an effort to obtain an extra 9% to 10% of nitrogen from a light
foliar application would not be practical or warranted.
For both creeping bentgrass and bermudagrass, absorption of urea
at 0.25 pound nitrogen/1,000 square feet (1.25 grams/square meter) (high rate) was
less efficient than that at 0.1 pound nitrogen/ 1,000 square feet (0.5
gram/square meter) (low rate) when expressed as a percentage of applied
nitrogen. When combined across all sampling times, application months and
years, the low nitrogen rate treatments averaged 50% nitrogen uptake efficiency
on creeping bentgrass, whereas the high nitrogen rate averaged 44%. Absorption by
bermudagrass was similarly affected by nitrogen rate, most notably during June
and August 2008 (Figure 2).
There are no published data on the effects of nitrogen rate on
foliar absorption by turfgrasses, and we can only speculate about potential
reasons for reduced fertilizer uptake efficiency at higher nitrogen rates. The
significant rate effect could be due to differences in precipitation of
nitrogen out of solution. As spray droplets dry on the foliage, the higher
nitrogen rate should precipitate earlier, meaning that a smaller percentage of
the urea remained in solution and, presumably, was able to be absorbed. It is
also possible that the more concentrated urea spray caused minor epidermal cell
damage that may have affected the uptake process; however, visual phytotoxicity
was not observed in any of the experiments.
It should be noted that a greater total amount of fertilizer
nitrogen (0.11 pound nitrogen/1,000 square feet vs. 0.05 pound nitrogen/1,000
square feet) (0.537 gram/square meter vs. 0.244 gram/ square meter) was
recovered within creeping bentgrass plant tissue when nitrogen was applied at the
higher rate; the amount of nitrogen recovered was, however, a significantly
smaller percentage of the amount applied.
Effect of season on uptake of foliar
Significant effects of time (both month and year) on foliar
absorption of urea-nitrogen were found for creeping bentgrass (Figure 3), and
bermudagrass (Figure 2). Fertilizer nitrogen recovered in creeping bentgrass
plants was quite variable depending on month of application and year (Figure
3). Although the range of nitrogen recovered in creeping bentgrass was similar
(36%–59% in 2007; 38%–69% in 2008) between years, trends based on month of
application were markedly different.
In 2007, there was a significant decline in absorption efficiency
as the season progressed (Figure 3), dropping steadily from 59% in May to 37%
in September. In contrast, absorption efficiency in May 2008 was relatively low
at 38%; it peaked in July at 69%, and then declined to 45% in August and 47% in
September. These data suggest that there will be times of the year when uptake
efficiency is reduced, but it is not as simple as attributing these reductions
to month of application within a given year. Many factors (both meteorological
and physical) will likely influence foliar nitrogen uptake efficiency. However,
analysis of select environmental conditions measured on site during each 24-hour
sampling period failed to reveal any consistent trends to help explain the
variability in the data (data not shown). For example, relative humidity is
known to affect foliar uptake of nutrients by its influence on spray droplet
retention and through its effects on hydrating the leaf cuticle for increased
receptiveness to foliar absorption. However, relative humidity values taken at
each application event did not consistently correlate with foliar nitrogen
uptake efficiency values obtained from bermudagrass and creeping bentgrass
(Figures 2, 3) throughout the two-year field trial.
Recently, other researchers (6) used an indirect (rinsate-based)
method to estimate foliar uptake of ammonium nitrogen and nitrate nitrogen by
putting green turfgrasses. They also found absorption differed significantly
between months, and they attributed these differences to changes in ambient air
In our study, average air temperature during application dates in
2008 exhibited a bell-shaped curve from May through September, which coincided with
foliar nitrogen absorption efficiency patterns observed on creeping bentgrass
during that year (Figure 3). However, comparisons of ambient air temperatures
and foliar absorption by creeping bentgrass during 2007 showed no such
relationship. In this study, analysis of environmental conditions and
meteorological data recorded on site failed to show a strong relationship between
any single environmental factor and foliar nitrogen absorption efficiency.
Both creeping bentgrass and bermudagrass golf course greens are
capable of rapidly absorbing urea-nitrogen applied to the foliage. Absorption efficiency
is similar to that reported in previous studies performed on turfgrasses grown
in controlled environments. Most of the foliar-applied urea-nitrogen was
absorbed in the first four hours after application, with the greatest increase
in fertilizer nitrogen within leaves and shoots occurring between time of
application and one hour after application.
As a supplement to traditional root-feeding practices, foliar
fertilization has become an important component of putting green nutritional
programs. Based on our results, we make the following recommendations for
greatest efficiency: use low application rates (0.1 pound nitrogen/1,000 square
feet) (0.5 gram/square meter); wait several hours to maximize foliar uptake and
then water-in, washing any unabsorbed urea-nitrogen or ammonium-nitrogen
remaining on leaf surfaces into the soil or root zone for second-chance uptake
by the root system.
Future research should focus on the effects of certain
environmental influences, leaf cuticle characteristics and/or cultural
practices on foliar nitrogen absorption. These studies could lead to the
development of optimized protocols for turfgrass practitioners to improve the
efficiency of foliar fertilizer applications.
support of this research was provided by the O.J. Noer Foundation, the USGA
Green Section and the University of Arkansas, Division of Agriculture.
research was originally published as “Foliar nitrogen uptake following urea
application to putting green turfgrass species” by J. Chris Stiegler, Michael
D. Richardson and Douglas E. Karcher, Crop Science 2011
51(3):1253-1260 (doi:10.2135/ cropsci2010.06.0377).
Stiegler and his wife, Jenny, were killed in a car accident on Christmas Eve,
2010. The Chris Stiegler Graduate Student Travel Award has been established in
the C5 Division of the Crop Science Society of America to support yearly grants
to deserving graduate students. For information about supporting this effort,
visit: http://turfgrassscience.wordpress. com/2013/06/17/chris-stiegler-turfgrass-science-studenttravel-
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Stiegler carried out this research as a graduate student at the University of
Arkansas. At the time of his death, he was an assistant professor in the soil
and crop sciences department at Texas A&M University, College Station,
Texas. Mike Richardson is a professor and Doug Karcher is an associate
professor in the department of horticulture at the University of Arkansas,