Co-Injecting the Nitrification
Inhibitor DCD with Ammonia:
An Innovative Approach to Reducing Nitrogen Losses
Dr. Bert Bock, Senior Advisor
Nitrification
inhibitors slow conversion of ammonium to nitrate. This
helps reduce nitrogen losses because ammonium is stored safely in
the soil but nitrate is susceptible to
 significant
losses under excessively wet conditions. Nitrate is mobile
in soil and can move below the root zone with excessive moisture,
especially on sandy soils.
In water-logged soils, nitrate is susceptible to being converted
to gaseous forms that escape to the atmosphere.
The
nitrification inhibitor dicyandiamide (DCD) has been evaluated in
the United States since the 1970’s. The National Fertilizer
Development Center at TVA led the first coordinated effort to
evaluate DCD in the United States and held a symposium in 1981 to
review early results from DCD evaluations. DCD and nitrapyrin
(N-Serve®) are now considered the old reliable nitrification
inhibitors for slowing the conversion of ammonium nitrogen, the
form in anhydrous ammonia, to nitrate nitrogen (1). Examples of
delayed conversion of ammonium to nitrate by DCD and nitrapyrin
are presented in Figure 1 below. The nitrogen rate was 150 lb per
acre. The DCD rate was 11 lb per acre and the nitrapyrin rate was
0.5 lb active ingredient per acre. DCD contains 66 percent
nitrogen so DCD supplied 5 out of the total of 150 lb nitrogen per
acre.
Benefits
from Nitrification Inhibitors
The obvious benefit
of nitrification inhibitors is that nitrogen losses are reduced
when excessive moisture conditions occur. If excessive moisture
conditions do not occur, then nitrogen losses are not reduced.
That means that nitrification inhibitors are more beneficial in
more humid areas where the probability of excessive moisture
conditions is higher. Nitrification inhibitors are more
beneficial in highly permeable soils with rapid downward movement
of water and in soils that tend to get waterlogged. Nitrification
inhibitors are also more beneficial when no “insurance N” is
applied to compensate for when excessive moisture conditions
occur. With no “insurance N”, yields can be reduced significantly
when excessive moisture conditions cause nitrate losses.
Generally, the
potential for nitrogen losses due to excessive moisture are
greater with increasing time between application and when the
plant takes up the nitrogen. For example, nitrate losses tend to
be higher with fall and early spring application than late spring
or sidedress application for corn. Nitrification inhibitors can
significantly reduce nitrate losses and associated yield
reductions from nitrogen applied in late fall or early spring. An
example of a nitrification inhibitor helping avoid a large yield
reduction due to nitrogen losses from preplant nitrogen is
illustrated in Figure 2 below. These data were obtained on a
sandy irrigated soil in Minnesota. Much more nitrogen was
required to achieve optimum yield with the preplant than sidedress
application. The nitrification inhibitor greatly alleviated yield
losses due to nitrogen losses from the preplant application. A
nitrification inhibitor will have less pronounced effects on yield
when the potential for nitrogen loss is less.
Providing more
flexibility for time of nitrogen application is important to many
crop producers. The timing of nitrogen application has to be
balanced with numerous other considerations such other competing
field operations. For example, timely planting is such a critical
factor that nitrogen may be applied earlier than optimum for
reducing nitrogen losses in order to increase the probability of
achieving timely planting. Early spring and fall applications
reduce competition with other field operations. Also, nitrogen
prices are also often lower in the fall and soil compaction often
is less of a problem in the fall than spring. Providing more
flexibility for time of nitrogen application is an important
benefit of nitrification inhibitors. However, in situations with
large potential for nitrogen loss due to excess moisture,
nitrification inhibitors often are not a total substitute for
applying nitrogen close to the time of crop need.
Figure 2. Effects
of nitrogen application time and nitrification inhibitor on corn
yield
response to nitrogen on a sandy irrigated soil
(3).
Nitrification
inhibitors provide environmental benefits. In situations with
significant potential for movement of nitrate below the root zone,
nitrification inhibitors can reduce the amount of nitrogen that
ends up in the ground and surface waters. Another benefit of
nitrification inhibitors is that they reduce nitrogen loss in the
form of nitrous oxide gas (N2O) which is roughly 300
times more potent than carbon dioxide as a greenhouse gas. This
is likely to become a more important consideration as more
emphasis is placed on reducing the level of greenhouse gases in
the atmosphere in an effort to slow global climate change.
Figure 2. Effects
of nitrogen application time and nitrification inhibitor on corn
yield
response to nitrogen on a sandy irrigated soil
(3).
Nitrification
inhibitors provide environmental benefits. In situations with
significant potential for movement of nitrate below the root zone,
nitrification inhibitors can reduce the amount of nitrogen that
ends up in the ground and surface waters. Another benefit of
nitrification inhibitors is that they reduce nitrogen loss in the
form of nitrous oxide gas (N2O) which is roughly 300
times more potent than carbon dioxide as a greenhouse gas. This
is likely to become a more important consideration as more
emphasis is placed on reducing the level of greenhouse gases in
the atmosphere in an effort to slow global climate change.
Rate
Considerations
DCD is marketed in
the United States under the trade name Guardian®. A maximum of 5
lb Guardian® per acre is recommended for banded applications in
general (4). Less than 5 lb DCD per acre may be required when DCD
is co-injected into anhydrous ammonia bands with the Exactrix
system. This is because the Exactrix system injects the anhydrous
ammonia stream at approximately 350 psi into a tight band well
below the opener outlet. We will be testing this concept.
The
rate of Guardian® to use is largely an economic consideration
although the environmental benefits from reduced nitrogen losses
are also important. The web-based
Guardian
spreadsheet provides a framework for evaluating economics (4). In
the example provided, the Guardian® cost is $6.55 per acre. That
means that with corn prices at current levels, an average yield
increase of at least one bushel per acre over years would cover
the Guardian® cost. Anything over that is profit. Requirement
for less applied nitrogen also factors into the economics. The
average yield increase over years likely will be significantly
more than one bushel per acre for early spring and fall
applications in the more humid part of the United States. That
assumes that significant “insurance N” is not applied. Savings
from application of less nitrogen also need to be considered.
The
bottom line is that soil is a terrible place to store nitrogen but
practical considerations often dictate that nitrogen be applied
significantly in advance of nitrogen uptake by the crop. We
believe that DCD co-injected with anhydrous ammonia using the
Exactrix system will be a practical option for providing greater
flexibility of time of nitrogen application and at the same time
avoid significant yield losses due to nitrogen losses associated
with excessive moisture.
References
1.http://www.ag.ndsu.edu/publications/landing-pages/crops/nitrogen-extenders-and-additives-sf-1581
2.
Sawyer, J.E. 1985. Nitrification of ammonium
nitrogen as affected by time of application, location,
temperature, and nitrification inhibitors. M.S. Thesis.
University of Illinois, Urbana. IL
3.
Malzer etal., 1985. Influence of
nitrogen form, nitrogen rate, timing of nitrogen application and
nitrification inhibitors for irrigated corn—Becker,
MN. P. 16-21. In A report on field research Misc. Publ2
(revised). Minnesota Agric. Exp. Stn., Univ. of Minnesota, St.
Paul.
4.
http://www.docstoc.com/docs/155935721/Guardian-Excel-Worksheet---Conklin
Exactrix®
Global Systems LLC
4501 East Trent Ave.
Spokane, WA 99212
www.exactrix®.com
509 995 1879 cell, Pacific.
exactrix@exactrix.com
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