2012
NYSTA
Calendar of
Events
Getting More Roots with Less Nitrogen
Turfgrass
Advocacy
2012 NYSTA’s
Lobby Day
A strong root system is vital for healthy turf because roots perform important functions.
They anchor the grass in the soil, absorb water and fertilizer nutrients from the soil, and
transport them to the leaves. In addition, roots produce hormonal signals in response to
soil conditions, transmit the signals to the leaves, and help the grass adapt to conditions in
the soil and on the turf. A weak root system is often the base cause of many turf problems.
Empire State
Plaza, Albany, NY
March
7, 2012
Adirondack
Regional
Conference
High Peaks Resort,
Lake Placid, NY
March
21, 2012
Storm Recovery
Seminar
Union-Endicott
Central School and
En-Joie Golf Club,
Endicott, NY
March
29, 2012
SUNY
Cobleskill/
NYSTA
Turf &
Ornamentals
Spring
Refresher
SUNY Cobleskill,
Cobleskill, NY
April
4, 2012
Z.J. Jiang, Ph.D.
Professor of Plant Science and Turfgrass Management
SUNY Cobleskill
Fertilization is a key management practice that affects root growth, and it is critical to
understand that you can get more and healthier roots with less nitrogen. There is, of
course, a caveat. Not understanding the inverse relationship may lead to unnecessary
applications of nitrogen fertilizers and serious damage to the turf. That, in turn, may cause
more money to be spent on fertilizers and other things trying to repair the damage and
improve the health of the grass.
Evidence of More Roots with Less Nitrogen
The following picture shows the effect of less nitrogen on root growth. Both groups of
creeping bentgrass were obtained from a mature turf and grown in pots with sufficient
nitrogen and other essential nutrients for ten weeks. Thereafter, the plants on the left
received no external supply of nitrogen, while the plants on the right continued to receive
sufficient nitrogen in potassium nitrate and calcium nitrate. Both groups of plants were
supplied with the same amounts of phosphorus, potassium, calcium, and other mineral
nutrients. Four weeks later, the results were dramatic: plants that did not continue to
receive fertilizer nitrogen produced a much larger root system (left) than the plants that
continued to receive nitrate-nitrogen (right).
This picture was taken at the end of an environmentally-controlled experiment, which was
not designed to study the effects of nitrogen supply rates on root growth, but to study the
enzymatic metabolism of nitrogen in leaves and roots of creeping bentgrass under nitrogen
deficiency conditions (Jiang et al., 2011). When nitrogen became deficient in the soil, the
grass could not get enough nitrogen from the soil. To continue growth of young leaves and
roots, the grass uses enzymes to break down proteins in old leaves into amino acids,
which were transported, along with the sugars, to young leaves and roots. It was found
that glutamine synthetase and glutamate synthase were two key enzymes in remobilizing
organic nitrogen from old leaves to roots and young leaves of the grass plant.
SUNY Delhi/
NYSTA Golf
Seminar &
Outing
SUNY Delhi, Delhi,
NY
June
5, 2012
Winning Fields
Seminar
SUNY Fredonia,
Fredonia, NY
June
12, 2012
CNYGCSA "Go
Over the
Research"
Cornell University,
Ithaca, NY
June
21, 2012
Contact Dick Perry at
315-673-4000 for
more information.
Sullivan County
Challenge Steve Smith
Memorial
Tournament
Grossinger Golf and
Country Club,
Liberty, NY
August
22, 2012
Northeastern
Golf Course
Superintendents
Association
POA Annua Golf
Tournament
Glens Falls Country
Club, Glens Falls,
NY
September
24, 2012
Hahn
Memorial
Photo by Z.J. Jiang, Ph.D.
Why Less Nitrogen Leads to More Roots
The remobilization of organic nitrogen in aging leaves may actually be one of the reasons
that less nitrogen leads to more roots. As nitrogen in the soil is depleted, mature leaves
quickly become old due to lack of nitrogen. Organic compounds already in the old leaves,
such as proteins and complex carbohydrates, are broken down into simpler organic
compounds, such as amino acids and sugars. These amino acids and sugars in the old
leaves are then transported out of the aging leaves to the roots and the growing points of
the grass.
When the turf is constantly supplied with nitrogen fertilizers, leaf aging is delayed, and
most of the organic nitrogen compounds, along with the carbohydrates, are retained in the
leaves for leaf growth. As a result, reduced amounts of organic nitrogen compounds and
carbohydrates can be transported to the roots. Without an adequate internal supply of
these organic nitrogen compounds and carbohydrates, root initiation and growth are
reduced or stopped.
Another reason why less nitrogen leads to more roots is that nitrogen in fertilizers is taken
up by roots in inorganic forms, such as nitrate and ammonium, with nitrate being the
predominant form. The absorption of these forms of fertilizer nitrogen by roots requires
large amounts of energy, which comes from carbohydrates transported from leaves to the
roots. Therefore, absorption of nutrients inevitably takes away some energy that may
otherwise be used for root initiation and growth.
The assimilation of nitrate-nitrogen and ammonium-nitrogen into organic nitrogen
compounds also requires energy as well as carbohydrates, both of which are produced by
photosynthesis in the leaves. Because of these energy and carbohydrate requirements,
the turfgrass plants transport nitrate and ammonium ions from the roots to the leaves for
assimilation. Leaves have been found to be the primary site of nitrate assimilation in a
cool-season turfgrass (Jiang and Hull, 1999). As a result, organic nitrogen compounds
produced by the assimilation of nitrate-nitrogen are retained in the leaves for leaf growth at
the expense of the root growth. Foliar application has the same adverse effect.
Getting More Roots with Less Nitrogen
The fact that less nitrogen leads to more roots does not mean that nitrogen fertilization is
not necessary for root growth. As discussed above, turfgrass needs organic nitrogen to
grow roots. Because root growth requires organic nitrogen compounds as well as
carbohydrates and these compounds are produced primarily in the leaves, sufficient
leaves must be produced before root growth can happen.
Scholarship
Tournament
Shadow Lake Golf
Course, Penfield, NY
October
1, 2012
Turf & Grounds
Exposition
Rochester Riverside
Convention Center,
Rochester, NY
November
13-15, 2012
However, after a period of leaf growth, the roots must be encouraged to grow. This should
be done by withholding nitrogen fertilizers for a sufficient period of time so that
carbohydrates and organic nitrogen compounds accumulated in mature leaves can be
transported out of the leaves for root growth and new root development. It is important to
remember that more root growth occurs during a period of nitrogen deficiency following
sufficient leaf growth and accumulation of carbohydrate and organic nitrogen compounds
in mature leaves, as shown in the above experiment. In this case, yellowing of mature
leaves is an indication of active root growth.
A good strategy to grow a strong root system through nitrogen fertilization is to apply
nitrogen at a time period when leaf growth is fast but root growth is not. For cool-season
grasses, leaf growth is fastest when air temperatures are 60-75 degrees and root growth is
fastest when soil temperatures are 50-65 degrees.
When root growth is rapid, nitrogen rates should be reduced or application stopped for a
period of time long enough to encourage translocation of carbohydrates and nitrogen
compounds from mature leaves to roots. The optimum temperature ranges for cool-season
turfgrass species are in the spring and the fall, but it is critical to seize specific windows of
opportunity to apply and then withhold nitrogen fertilizers in order to promote leaf growth
and accumulation of carbohydrates and organic nitrogen and their translocation out of the
mature leaves for root growth.
For example, early spring is a time when air temperatures can quickly reach the optimum
range for leaf growth of cool-season species while soil temperatures may still be below the
optimum range for root growth. That window is a good time for nitrogen application. Once
soil temperatures reach the optimum for root growth, it is time to reduce nitrogen
application rates to suppress leaf growth and encourage translocation of carbohydrates
and organic nitrogen compounds from mature leaves to the roots.
In early fall, there may be a time when air temperatures decrease to the optimum range for
shoot growth of cool-season species but soil temperatures may still be above the optimum
range for root growth. That is a good time to increase nitrogen application to promote leaf
growth and accumulation of organic nitrogen compounds and carbohydrates in mature
leaves.
In late fall, there may be a time when the air temperature decreases below the optimum
range for leaf growth but the soil temperature is within the optimum range for root growth.
That is a good time to increase nitrogen rates to promote production and accumulation of
carbohydrates and nitrogen compounds by mature leaves without stimulating new leaf
growth and thereby promoting root growth.
Conclusion
You can get more and healthier roots with less nitrogen, but the caveat is that you can do
that only after the leaves have accumulated enough carbohydrates and organic nitrogen
compounds. Timing in applying or withholding nitrogen fertilizers is important in promoting
root growth. Many other practices in fertilization affect root growth and so do other
management practices, such as mowing, irrigation, and aeration. All of these practices
must be used with precision to develop a strong root system, which provides a good
foundation for the health of the turfgrass and for best turf management.
References
Jiang, Z., C. Xu, and B. Huang. 2011. Enzymatic metabolism of nitrogen in leaves and
roots of creeping bentgrass under nitrogen deficiency conditions. Journal of American
Society for Horticultural Science 136: 320–328.
Jiang, Z. and R. J. Hull. 1999. Partitioning of nitrate assimilation between shoots and roots
of Kentucky bluegrass. Crop Science 39: 746-754.
New York State Turfgrass Association
PO Box 612, Latham, NY 12110 | (518) 783-1229 | (518) 783-1258 Fax | www.nysta.org
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