19

of N application rates? More information should be provided regarding the
independent data used to develop the ADAPT model.

Page 32, 2" paragraph

The authors contrast loss of N from forested watersheds with loss from
agricultural watersheds. However, they fail to mention that forested watersheds
often involve Land Capability classes V, VI, and VII. The NRCS and most - ~
university agronomists recognize that agricultural crops are typically found on
Land Capability Classes | through IV. Cropped lands (i.e. Land Capability
Classes I-1V) are inherently more productive, usually more fertile, and may
frequently have a higher actinomycete and bacterial population. These
characteristics contribute to a higher nitrification potential than in many forest
soils. Comparisons of nitrate losses between forested watersheds and cropped
agricultural watersheds, without regard to Land Capability Class or soil
characteristics, is risky at best. Perhaps the authors considered these factors, but
they should explain the similarities or differences in soil characteristics, which
may influence nitrification potentials and interpretations regarding BMPs for
reductions in nitrate losses.

Page 33, 2" paragraph

The authors should also mention that soils in the Eastem and Southern sub-
basins usually have lower soll organic matter levels than soils in the Midwest and
Northcentral states. Differences in soil organic matter and climate may also
explain a large portion of the variation in nitrate yields among the sub-basins.

Page 33, 3 paragraph

The authors’ statement that nutrient inputs from the lower Mississippi states (i.e.
Arkansas, Louisiana, and Mississippi) flow directly into the Mississippi is grossly
inaccurate. The large majority of the cropped acreage in the lower basin is
actually separated from the Mississippi River by the Corps of Engineer's levee
system. Consequently, surface and subsurface drainage must take a tortuous
path before reaching the Mississippi River.

Page 33 through 37

The HUMUS model developed at Temple, TX apparently has not been subjected
to independent validation, nor has it been published or peer reviewed in refereed
joumats. The authors state, “There are many reasons why the results from these
two studies may not directly correspond to the results of other studies, especially
results of studies of specific local sites and watersheds.” As a result, the
discussions on these pages should be considered preliminary and quite tentative,
at best.

It is highly unlikely that a 30% reduction in N inputs in the Cornbelt states would
reduce the national corn production by less than 1.5%. Further, how can a 30%
reduction in N use on sorghum increase yields by 2.2%? The U.S. currently uses
about 1.1 Ib N in producing a bushel of corn. The long-term data indicate that
com N-use efficiency has been improving since the early 1980s. Nationally, com


36

limited set of policies targeted at reduced nitrogen application rates. It
identifies very high direct costs yet ignores potentially high indirect costs on
employment and output in the input supply industry, the livestock sector, and
the grain handling and processing industries. It identifies no significant
economic benefits to fisheries in the gulf region, but implies significant other
unmeasurable benefits. It would require a tremendous leap of faith to accept
that such unidentifiable benefits would come remotely close to exceeding
even the partial costs identified in the study.

12.Modeling is an imprecise art, particularly the modeling of a complex
relationship such as nitrogen application rates and nitrogen loads. Do the
lead authors understand the model and how confident are they of the results
as a firm basis for the kind of regulation that is being suggested?

13. The nitrogen balance table reported on page 3 reports that fertilizer accounts
for 30% of the total annual nitrogen input into the MB. Even if nitrogen
fertilizer did account for 30% of the total load, then simple math implies that
reducing the load from fertilizer by 20% would result in a 6% drop in the total
load. That relatively small drop raises big questions about the potential and
unmeasurable benefits of such a decline relative to the large and identifiable
direct, and even larger indirect, costs.

14.Section 2.3 (pp. 9-13) is especially weak, completely ungrounded and
contradictory. The example used in the first two paragraphs on page 9
suggests farmers are way down the yield response curve or production
function (Stage |) and that they are grossly under-utilizing nitrogen fertilizer
(e.g. implied marginal factor cost of $.18 per acre vs marginal revenue of
$2.00 per acre in the first paragraph and implied marginal factor cost of $1.80
to $3.60 per acre Vs marginal revenue of $20.00 to $30.00 per acre in the
second paragraph). .Five paragraphs later, the authors indicate that nitrogen
application rates are excessive and imply that farmers are operating at stage
Ill on the yield response or production function and are maximizing physical
yield rather than economic yield. The conclusion is that farmers are grossly
over-using fertilizer (even though as they note most production decisions are
based on fertilizer recommendations from university agricultural extension
personnel!). Which is the case? This is a good illustration of the lack of rigor
and grounding in the analysis. Data do exist and they show that nitrogen
application rates generally have stayed flat even as yields have increased
during the last 20 years. Farmers have become more efficient and no doubt
have moved close to maximizing economic yields. The implication of gross
under- and over-use is not supported by the numbers. There may be further
efficiency gains possible (e.g. Blackmer’s late spring nitrogen soil tests), but
additional costs may outweighed incremental benefits and explain why these
technologies have not been widely adopted by U.S. farmers.


13

many of the non-MARB watersheds of the North Atlantic consist of acid soils
and soils of lower natural fertility than those of the MARB. It is likely that
“pristine” MARB N yields were higher than those for the North Atlantic basin,
as the soils of the MARB have above average organic matter content.

Page 15 states that N input from animal manures has decreased slightly over
the last 40 years. However, this assessment was made assuming constant
per-head manure nutrient output. The livestock industry has made dramatic
changes in per animal output in the past 40 years. Dairy cows now produce
much more milk per animal. Swine and poultry are produced in much shorter
production cycles. One cannot assume that manure output per animal has
not changed; it is very likely to have increased significantly.

In several places (p. 31, 36), the report emphasizes the importance of ortho
phosphorus (P) over total P and considers it more available to algae and
aquatic plants, citing Correll (1998). However, the same report by Correll
(1998) emphasizes that total P is the more important quantity to measure and
regulate in terms of its impact on eutrophication.

The choice of nutrients was rather limited. Certainly N, P and silica may be
important, but how can their relative importance be assessed when no
consideration is given nutrients like organic carbon (C) and its impact on
BOD? Given its interactions with sediment, how can P be interpreted without
consideration of sediment loads and concentrations?

The regression model predicting annual flux and yield of P (p.35) assumes
zero net sedimentation in the entire Mississippi river. Most rivers do have
continual sedimentation, and this is normally a large sink or loss mechanism
for P. The statement on p. 36 that deposition of sediment does not occur
except in basins with large main stem reservoirs appears questionable.

_ Consultation with river management hydrologists and US Army Corps of

Engineers is suggested to verify this point.

The catculation of “soil mineralization” as a N source has several major
problems.

1.

Separation of mineralization from immobilization as inputs and outputs from
the system on this scale is inappropriate. Current models of soil organic
matter and N transformations recognize mineralization-immobilization
turnover (MIT) as a continuous intemal cycling (Jansson and Persson, 1982). -
Instead of considering gross mineralization and gross immobilization, the
report should have focussed on the net mineralization or immobilization of
nitrogen produced by MIT in MARB soils.

Current evidence indicates that agricultural soils have switched i in the last 15
years from being net producers of carbon dioxide to being net accumulators
(Allmaras, 1999). In other words, soil organic matter is no longer undergoing
net loss; it is increasing. Soil organic matter stabilizes with a C:N ratio of
10:1. The new evidence on C balance suggests that the current balance of
MIT in agricultural soils results in no net loss of N. The model in the report
implies a mineralization rate more than twice that of immobilization, a


Figure 1. Hypoxic Area in Gulf of Mexico Declined

square miles

Since 1993 Floods
N. Rabalais, LUMCON

8000

6000

4000 7

2000 7

o4

» © KS & ASX NHmM *F H SK &
SS PD eT ST TT NK PF ST PS OF Ss
LFF FF SF FSssgsIss Fs

Figure 2. Fertilizer N Use and Nitrate-N Load to the GOM

14,000
= 12,000
10,000

88

4,000

1,000 tons of fertilizer
3

1983 to current, Excluding 1993 data

1,600
1,400
1,200
1,000

£

1,000 tons of nitrate-N

23


Nutrient management planning

The practice of preparing and following written, flexible, voluntary crop
nutrient management plans is a growing one in U.S. agriculture. This
stewardship practice enables farmers to be better managers, minimizes costs,
increases efficiency and reduces nutrient loss.

An effort to bring greater professionalism into this process was a major
reason the fertilizer industry was supportive of the efforts of the American Society
of Agronomy to start the Certified Crop Advisor program. This program requires
an application to demonstrate a knowledge base necessary for assisting farmers
in an advisory capacity. To date, more than 12,000 individuals have passed the
rigorous testing and background requirements and have maintained their
certification through a program of continuing education.

Measurement of crop nutrient management planning is elusive. TFI and
many of the agricultural farm and commodity organizations participate in the
Core 4 program of the Conservation Technology Information Center. The
nutrient management component of Core 4 has two objectives: 1) market
nutrient management planning to farmers by educating them about the
components and benefits; and 2) measure the increased adoption of nutrient
management planning. Voluntary efforts such as this are the best and most
effective way to increase nutrient management planning.

Conservation Buffers

The installation of conservation buffer strips is a growing success story
that invoives commitments from both the private and public sectors. The U.S.
Department of Agriculture has set a target of 2 million acres of buffer strips in the
Conservation Reserve Program by 2002. There is widespread support of that
goal and independent efforts to implement buffers among farmers and
agribusiness.

Research demonstrates the effectiveness of these conservation buffers.
Research by Leeds et. al. at The Ohio State University summarizes field
research done in Indiana, lowa, Maryland and Virginia. The results show filter
strips reduce sediment between 56 and 95 percent, depending upon soil
characteristics, slope, rainfall and runoff conditions and filter width. Results for
nitrogen and phosphorus removal were highly variable, ranging from 0 to 83
percent for phosphorus and 27 to 87 percent for nitrogen.


have different recommendations, how can charges of “overapplication” be
assumed for the entire basin?

. Arelated factor is that there have not been any long term studies showing
that a permanent 20% reduction in N use across the MB would not have any
long term impacts on yields. While some studies may show that a decrease
in nutrient applications for a year or two show no significant decrease in yields
there is an issue of “mining the soil” over the long run and its potential
negative impact on soil quality.

. On page 30, the authors state that net farm incomes actually increase after
forcing farmers to lower N use by 20% and forcing 6% of land out of
production in the MB region. Even taking into account slightly higher farm
incomes outside of the MB region, this result is counter-intuitive. It appears to
be based entirely on the assumption that virtually all farmers could reduce N
application rates by 20% with little or no impact on yield, which is not
supported by the analysis. It appears (the paper doesn’t provide the

information) that the crop price elasticity used from the model is a short term
gne rather than the long term elasticity. It is unlikely a 6% reduction in

cropped land in the Mississippi Basin would result in a 9% increase in
average US com prices over the long term (and a 5% increase in wheat and
19% increase in sorghum). This is an important assumption in order to get an
increase in farm income in their 20% scenario and could be checked fairly
easily with USDA, FAPRI or WEFA. Furthermore, it is questionable whether
the model accurately estimates the impact on crop yields from shifting crop
rotations to the extent shown in the model (more continuous cropping of
soybeans, rather than corn/wheat with soya rotations). Also questionable is
the yield impact of lower nitrogen application rates by 20%. Why is there no
table showing the yield impact and are their results similar to other yield
models that are available?

. The whole issue of lower quality soil by lowering fertilizer application rates is
one that may need to be examined. The lowering of N in the soil also
reduces its ability to sequester carbon (fixed ratio). This would increase
carbon dioxide in the air, thus exacerbating the problem of carbon dioxide in
the atmosphere, thus moving the U.S. away from Kyoto Treaty goals.

. Itis interesting that at the beginning of the paper there is a recognition that
precision agriculture could help to reduce nitrogen run-off (see Precision
Nitrogen Application section) . The discussion ends with the comment that
“Despite the intuitive logic of matching N application to site-specific crop
needs, variable application was not uniformly superior to uniform application
in terms of increasing net returns and improving water quality in Goodwater
watershed.” There is no further discussion of how precision agriculture might
be used to reduce nutrient run-off without attempting to legislate lower
application rates. Nor is there any discussion about other technologies that


20

yields have been increasing. The authors have not considered the impact of
nitrogen use restrictions on the future opportunity of farmers to capture improved
genetic yield potential. Th authors also fail to consider the farmer's ability to
improve production efficiency and yield potential with better management (e.g
site specific crop management). Failure to consider these factors in the model
can result in false conclusions and destine the American farmer to failure by
destroying his/her ability to compete in the global market.

The authors assume that farmers are applying too much N. The authors also
imply in Table 3.3 that a reduction in N use would result in higher crop prices.
How is it possible that such a small change in total com production (1.5%) could
have any impact on corn price? Table 3.3 also shows that 41 to 56% of the
farmers would lose profits due to imposing N stress-based restrictions on N
rates. The remaining percentage of farmers presumably would have increased
profits. The authors suggest a 34% reduction in N use will result in only a 2 to
5% decrease in N discharge from the Upper Mississippi and Ohio Rivers. This
further supports the evidence, which indicates the principal source of N
losses from farm fields, in these same sub-basins, is nitrate derived from
soll organic matter mineralization.

Page 54

Figures 3.29 and 3.30 indicate there is a poor relationship between growing
season mean total P concentration and chlorophyll a concentration in the
Mississippi River itself. This appears to contrast with data from other rivers
(Figure 3.30). The authors do admit that there is “ considerable scatter “ in the
relationship between ail chlorophyll a and total P data. Certainly, Figure 3.30
illustrates that it is not valid to transpose the relationship between chlorophyll a
and total P in reservoirs, to chlorophyll a and total P concentration in the
Mississippi River. These graphs illustrate that the Mississippi River behaves
differently from other monitored rivers and especially differently from reservoirs.
Relationships in lakes and reservoirs should not be extrapolated to rivers, ......
and especially not to the Mississippi River.

Page 60

The authors state that Task Group 5 concluded that more than 50% of the N
loading to the Gulf could be achieved through implementation of a number of
proven best management practices working in concert. This statement negates
the need for imposed N-use- reductions to achieve water quality goals in the
Mississippi River and the Gulf of Mexico.

Page 62, 1* paragraph

The authors admit the forecast results ....“do not contain any information on the
time frame required for the system to fully respond to imposed changes in
nutrient loadings’.


26

recommended N rates would produce 0. 30 .4 metric ton ha’ (5-12 bu/A) com
yield reductions and 2.5-5.0 kg N ha” yr" reductions in nitrate losses.

Comments

1. The practice of applying insurance fertilizer N is not supported by the cited
paper.
The paper cited (Legg, T.D., J.L. Fletcher, and K.W. Easter. 1989. Nitrogen
budgets for economic efficiency: A case study of southeastern Minnesota. J.
Prod. Agric. 2:110-116) examines the fertilization practices of 4 farmers.
Three of the farmers had livestock, the fourth did not. The 3 livestock
producers had approximately 25% of their land area in corn. Tables 1 and 2
of the paper indicated that:

fertilizer and legume credits roughly meet the N requirements of the
corn crop. Excesses in each case are approximately equal to the N
applied as manure.

This statement indicates that over-applications did not result from intentionally
applying fertilizer N at rates above those recommended but from failure to
consider manure as a nutrient source. The paper also points out that the
farmer who did not raise any livestock did not apply enough fertilizer N to
meet currently recommended rates.

2. Over-applications of N occur for many reasons
It must be remembered that farmers are most concerned with maximizing
their profit. Where it occurs, N is over-applied because 1) farmers do not
believe that current recommendations are appropriate for their production
levels, 2) local data needed to refine university recommendations are not
available or do not exist, 3) university recommendations are based upon yield
goals and farmers may set yield goals based on the yields of their best, rather
than their average years, 4) dealers, agronomists, or other consultants do not
have good guidance on how to incorporate manure as a nutrient source into
the nutrient management plans they create for growers.

Farmers understand that local conditions can lead to best management
practices (BMPs) different from university BMPs. Most farmers want data
upon which to base their decisions. However, the data they want is local data
specific to their situations. Without such data, farmers will try their own
refinements in attempts to increase their production levels and profitability.
Increased N rates have been a part of such strategies in some cases.

An example of the effectiveness of local data comes from Indiana from an
agronomist who has conducted small plot research to refine local N
recommendations. He observed that soil types differed in their response to
N. He conducted a split-plot experiment (2 soil mapping units (whole plot), 4
N rates (sub-plots), replicated 4 times, conducted for 5 years) to examine how
N response in com differed between soil mapping units. He concluded that
optimum N rates did differ for the two soils studied. He created his own local


22

This reviewer is in complete agreement with the final paragraph on page
82,

“Results presented in this report are from an ongoing research program and
should be considered preliminary and provisional in nature. To reduce
uncertainties in these results, future modeling should include linkage of the water
quality model with a hydrodynamic model of the Gulf of Mexico circulation,
expansion of the mode! spatial domain, and refinement of'the horizontal and
vertical spatial resolution of the model. The water quality model itself should be
expanded to include a sediment diagenesis submodel, multiple phytoplankton
groups and silica as a limiting nutrient.”

Literature Cited

Burkart, M. R. and D. E. James, 1999. Agricultural-nitrogen contributions to
hypoxia in the Gulf of Mexico. J. Environ. Qual. 25:850-859.


35

may also help lower nitrogen run-off without the need for evasive government
regulations/controls on individual farmer's management practices. Precision
agriculture is a potentially very important tool, but other technologies such as
controlled released nitrogen fertilizers are not even mentioned. Furthermore,
the potential to better utilize manure (using new techniques) so that nutrient
run-off is reduced from this agricultural source is also barely mentioned.
Surely these are important possible avenues which should be
studied/supported for their potential to lower excess nutrient run-off without
attempting to legislate something as variable and field specific as nutrient
application rates.

8. Technical difficulties of somehow forcing farmers to apply less nitrogen
fertilizer are not addressed. This is a very important factor. The authors
seem to imply that the government can go to individual farmers and tell them
to apply 20% less nitrogen than they have been using. They admit a tax on
fertilizer is not a viable option, largely due to the very inelastic demand for
fertilizers. The last decade has seen a shift away from the government
getting directly involved in farmers production decisions, and this would be an
extremely difficult task to accomplish considering the recent trend. The
enormous drain on public resources seems not to have been considered in
the cost equation.

9. Comments are made throughout the paper that there is no firm method of
determining the extent to which fertilizers may have contributed to hypoxia
and they acknowledge that this condition happens naturally to a certain
extent. They also recognize that there is no way of measuring the success of
any program, as there are many variables that contribute to hypoxia.
Furthermore, they recognize that there are limited financial returns to lowering
nutrient levels in water, even if it could be done and measured. “The
assessment suggested that given the available data, there was no effect in
the shrimp, snapper, or menhaden fisheries data that could be attributed with
high confidence to hypoxia” (pg. 24). Then they go on to say that “ The fixed
target level of nitrogen loss reduction, 20%, was suggested by Topic Group 5
as a reasonable level that could attained given current technology and would
have the potential to decrease the incidence of hypoxia in the Gulf.

10. This paper appears to be intentionally “naive” as the consequences of such a
policy. The economic impacts would be hugely negative to the farm sector
(not positive). There would also be major political and policy problems which
are not even raised with such a new fertilizer control policy for a problem
which is not well defined and potential future benefits which cannot be directly
measured.

11. There is no evaluation of the economic benefits of reducing nutrient loads
and the study should not be titled and advertised as such. It is just a cost
assessment of achieving arbitrary reductions in nutrient loads through a very

:


17

REVIEW OF TOPIC 4 REPORT:

EFFECTS OF REDUCING NUTRIENT LOADS TO SURFACE
WATERS WITHIN THE MISSISSIPPI RIVER BASIN AND THE
GULF OF MEXICO

Cliff S. Snyder, Ph.D., Potash & Phosphate Institute

Page 6, Section 2.3.1

The authors state that N and P loadings to the Gulf have increased and silica
loading has decreased this century, and that the trends have accelerated since
the 1950s. These statements are not accurate. Considering the 1993 record
flood year an aberration from the norm, and excluding 1993 data from the years
1983 to 1996, the trend in nitrate-N flux to the Gulf since 1985 has been clearly
downward. Further, based on National Agricultural Statistics Service and
Economic Research Service data, there has been an improved efficiency of N, P
and K utilization by corn, per bushel of production, since the early 1980s.

These data support the fact that there has not been an increased nitrate-N flux fo
the Gulf Mexico since 1983. (See supporting Figures 1 and 2).

Page 11, 2" paragraph

The authors state that in 1985 and 1990, Mississippi River flow was above the
long-term flow of 664,000 cubic feet per second. On a percentage basis, the
1985 flow was 31 percent above the long-term average, and the 1990 flow was
36 percent above the long-term average. Comparisons of flow in 1985 and 1990
with the flow in 1988 (Table 2.1), show that the combined Mississippi and
Atchafalaya inflow to the Gulf was 83% greater in 1985 and 49% greater in 1990,
than in 1988. Total N loading to the Mississippi ~Atchafalaya Basin was 487%
greater in 1985 than in 1988, and 356% greater in 1990 than in 1988. Similarly,
total P loading was 357% greater in 1985 and 423% greater in 1990, than in
1988.

Peak Gulf of Mexico inflow, via the Mississippi and Atchafalaya discharges, in
1990 was measured in June rather than in April, the historic norm. This change in
peak flow occurred after much of the N for corn had already been applied in the
Combelt states. Consequently, the “flushing” of nitrate-N from farm fields in the
Combelt states in 1990 , may have represented the worst-case scenario for loss
of N from the Cornbelt states. The record rainfall and flooding experienced in
1993 in the Combelt states, and the consequential increased flow and N
discharge to the Gulf of Mexico in 1993, suggest that trends observed from 1985
to 1995 may therefore represent aberrations in the long-term rainfall and river
discharge trends. Since about 1970, the total water discharge to the Gulf appears


Section 2: Specific comments on individual reports

The comments in this six are the result of TF] seeking reviews from several
scientists within the industry and from the Potash and Phosphate Institute. The
varying styles and formats are the result of variations among those individuals.
While these could have been submitted individually, we thought it useful to
package them together for convenience.

Report 1

1. The area of hypoxia in the Gulf of Mexico is not static and is not
growing (p. xvii). Data presented in the body of the report (Section 3.0
Dimensions and Variability of Hypoxia) do not support the summarization of
the aerial extent i in terms of an average range of 8,000 to 9,000km? or 16,000
to 18,000 km*. Figure 2 (p. 6) presents a more comprehensive snapshot of
the hypoxic zone during time of “expected maximal extent.” However, neither
Figure 2 nor the associated text provides square kilometer ranges for the
frequency quartiles. Please provide these ranges, and incorporate these
estimates into the summary of the general dimensions of the hypoxic zone.

In addition, the aerial estimate of the “maximal extent” of the hypoxic zone for
1998 is listed as 12,500 km? (p. xvii), yet is not used to calculate average
values, or in Figures 2 or 3. The only mention of this estimate in the text of
the report is to say that the 1998 aerial extent was similar to 1992. . Inclusion
of 1998 data shows that the aerial extent of hypoxia is not growing. Please
incorporate the 1998 estimate into any calculations of average aerial extent,
depiction and calculations of extent quartiles, and in any text discussing the
long-term trend in hypoxic conditions in the Gulf of Mexico.

2. The area of hypoxia is influenced by several! natural, physical and
chemical parameters that constantly refine the aerial and vertical extent
of hypoxia. The data presented represent the aerial reach of hypoxia during
the “expected maximal extent” of the condition. Section 3.2 discusses
variability in the mid-summer hypoxic zone, including Figure 4 that shows
shifts in the extent of the hypoxic zone. The report discusses localized
weather patterns, current pattems, tidal influences and diumal patterns in
qualitative terms in relation to the vertical and aerial extent of hypoxic waters.
Please provide the aerial extent of the hypoxic zone over the three
observation periods, as well as some estimate of the geographic shift of the


32

Report 6
Comments on “Evaluation of Economic Costs and Benefits of
Methods for Reducing Nutrient Loads to the Gulf of Mexico”

The authors of the paper “Evaluation of Economic Costs and Benefits of
Methods for Reducing Nutrient Loads to the Gulf of Mexico” quote many relevant
articles and, in a few cases, make some good points. However, they skip over
certain key factors or make incorrect assumptions conceming some of the most
basic building blocks of their conclusions. In addition, they use a model that is
inappropriate for the task at hand. The result is a study that identifies few, if any,
benefits from a proposed 20% reduction in N use in the MB, and significantly
underestimates the total cost of such a proposal. Specific comments regarding
the study follow.

1. The economic costs of a 20% reduction in N use in the MB are estimated
using the USMP model. On page 32, the authors note, “In addition, the
results of a model such as USMP are not detailed enough for a real
application of the results to the ground.” This is a crucial point and a very
significant limitation of the USMP model with respect to the analysis in
question. The reason is that it is the ground, or the micro-level, where the
initial impacts of a 20% reduction in N use in the MB would actually take
place. If the initial impacts are not measured correctly (i.e., changes in crop
yields), then all other downstream impacts of a 20% reduction in N use will
also be miscalculated.

2. The paper concludes by stating that “The bottom line is that nitrogen loss
reduction in the 20% range is doable and there are relatively cost effective
ways to achieve it” (p.50)._In addition to the results.of the USMP model, the
authors note the results of economic studies to argue that the 20% goal is
doable. For example, on page 11 the paper notes, “Based on ERS surveys of
Nebraska farmers, Fuglie and Bosch found that nearly half of the surveyed
farmers used N fertilizer recommendations from a preplant N test and were
achieving N fertilizer reductions of 18 to 33 percent with no loss in yield.
Shortle, et. al., found that 36 percent of farmers used late spring soil tests,
and were able to reduce N fertilizer use 40 percent.” The authors use these
case studies to imply that since these farmers reduced their use of N fertilizer
without any reduction in yields, it would not be an economic hardship for all
farmers to do so. However, they are missing the point. The point is, farmers
have already and continue to reduce the fN they use per unit


29

Review of the recommendation “use of alternative crops such as
perennials”

This recommendation was constructed from data presented in Sec. 3.1.2
“Changing Cropping Systems”. In this section, data were presented that showed
lower soil nitrate concentrations with alfalfa and a grass/alfalfa mix compared to
row crops.

This recommendation does not account for the management strategy needed by
many livestock producers. As manure is increasingly being used as a nutrient
source, more acres will have to be located to spread manure. A manure
application prioritization scheme created by the University of Wisconsin (R.P.
Wotkowski, K.A. Kelling, L.R. Massie, and S.M. Combs. Developing a plan for
assigning manure spreading priorities. University of Wisconsin Extension
Publication A3626) reduces priorities for fields with legumes. Therefore, it seems
inconsistent for livestock producers, some of whom have been identified as over-
applying N, to increase their legume acres as they have an increased need to
find fields on which to apply manure in an agronomic manner. What livestock
producers need is a cropping sequence that takes up and removes large
amounts of N and P from manure applications. Leguminous perennials would be
counter to the N removal needs of these producers. Grass cover crops would be
a more reasonable focus.


pointed avoidance of using the term “cause,” their conclusions are contradicted
both by the Alabama report and report number 4, which cite increased
precipitation and increased river flows over the past three decades as a major
contributor to increased nitrate flux.

A careful reading of all the reports reveais that hypoxia in the Gulf of Mexico is a
naturally occurring phenomenon that possibly has been enlarged overtime by a
complex series of anthropogenic activity. So what factors contribute to Gulf
hypoxia?

e Natural processes that occur when freshwater flows into salt water bodies.
As the Alabama report points out, increased freshwater flow from the tate
‘60s until today has increased the stratification that sets the stage for
hypoxia.

e Nutrient additions. The nitrogen cycle is not leak-proof, and more people
living in the Mississippi River Basin (MRB) inevitably mean more nitrogen
cycling through and leaking from the system. The heavy reliance on this
single factor, however, is not borne out. There is a consistent view across
the reports that nitrogen concentrations in the river have increased, but
that virtually all of the increase took place in the late 1950s and early
1960s. Since that time, concentrations have been fiat to slightly lower.
Thus, the increased flux and increased size of the hypoxic zone observed
in 1993 can only be attributable to increased river flow.

e “Channelization of the river.” Certainly changes made to the river over the
past century to enhance navigability of the river have had a dramatic
impact on nutrient flux. These changes have had the greatest impact in
the delta region, where the channelization of the river has deprived the
coastal marshtands of the steady supply of the nutrients and sediments
that built and are utilized by the marshes.

In addition, the channelization of the river results in more rapid and direct
delivery of solutes into the Gulf and less interaction with historical
wetlands and the floodplain where nitrate can be removed. As a result,
the physical changes made to the river to enhance navigation also
enhance nitrate delivery into the Guif.

e Organic Carbon. A significant finding of the Alabama report is the
potential role of terrigenous organic carbon in oxygen loss in Gulf waters.
Catcutations performed for that study indicate a major portion of the
hypoxic area could be the result of organic matter being delivered to the
Gulf by the river.

All of these factors are mentioned in the CENR reports, but only major
consideration is given to nutrient loading. Even so, the authors of report 4


In addition to demonstrating successful removal of nutrients and
sediments, this work demonstrates the variability that exists across the
agricultural landscape. This variability demands local contro! and flexibility in
order to achieve nutrient loss reductions. One-size-fits-all regulatory approaches
cannot succeed.

2. The CENR process has been closed to public input

These reports, like the overall Gulf of Mexico Hypoxia Assessment Pian, are
closed federal efforts that would benefit from the inclusion of the wider
stakeholder community.

The assessment plan and the writing of the six reports are under the control of
federal agencies. After giving a team of about 35 authors more than a year to
write the six assessment reports, a 90-day comment period for stakeholders is
insufficient opportunity for input. While it is currently unclear who will write the
integrated assessment and when, that effort should be broadened to include
scientists and others from the private sector who have studied the issue of
hypoxia.

Attached as appendix A is a report entitled “The Role of Solutes in Gulf of Mexico
Hypoxia” (“Alabama Report”) published by a group of researchers at the
University of Alabama with a grant from TFI. This report serves as an
independent review of many of the issues addressed in the six assessment
reports. It recognizes that some of the contributing factors mentioned in the
assessments, including the role of terrestrial organic carbon, the channelization
of the river, and increased precipitation in the Mississippi River basin, have a
greater impact on hypoxia than recognized in the six assessments. It also
suggests areas for additional research as we try to learn more about the causes
and cures for Gulf hypoxia.

3. The six assessments are inconclusive and fail to consider
multiple hypotheses for causes of hypoxia.

The federal assessments focused narrowly on a single cause of Gulf hypoxia and
failed to prove the stated hypothesis. Thus, they serve as interesting scientific
inquiry but fail to provide a foundation for regulatory efforts to “solve” hypoxia.

On the fundamental question of what causes Gulf hypoxia, the reports are highly
inconclusive. Thus, the underlying hypothesis of nutrient additions being
responsible for hypoxia is not proven. Clearly, the authors of report number 1
make a heroic effort to attribute the cause to nutrients and increased
concentrations of nitrate in the Mississippi River. However, in addition to their


18

to have increased compared to data from 1900 to 1970 (see Figure 32 on page
47 of the Report by Rabalais et al., CENR Topic#1. Characterization of hypoxia.
May 1999). These facts, plus the statements by the authors in the second
paragraph on page xvi, indicate that hypoxia development and persistence may
not be affected by nutrient loadings as much as by water flux to the Gulf, water
movement and other physical processes on the Louisiana Intercontinental Shelf.

Page 21, 3% paragraph

The statement that P is transported to surface waters by direct discharge from
animal waste storage lagoons, implies that the majority of these lagoons breach
or overflow. While there have been accidents highly publicized by the media, the
majority of animal waste lagoons do not directly discharge to surface waters.
Instead the lagoon contents are land-applied though irrigation systems or by
manure spreaders. Such discharges are regulated as point sources by EPA and
state water quality authorities.

Page 21, 4" paragraph

Dr. John Lory, at the University of Missouri, has submitted a manuscript to the
Journal of Environmental Quality, in which he and colleagues review the science
behind “critical” soil test P levels. His paper provides solid evidence that such
limits ignore the major influence on the potential for loss of P from land surfaces:
water flow. Mention of the Sharpley et al. (1994) paper, is of interest, but the
authors should also mention the need to identify critical source areas and
potential for transport losses. This point is reinforced by the author’s statements
in the first paragraph, on page 23.

Page 28, section on N and manure application

The geographic pattem of precipitation is cited as THE major influence on nitrate
loading to rivers and land-use characteristics were secondary. This reinforces the
transport considerations mentioned in the review comment above, regarding
page 21.

Page 29, section on mineralization of organic matter.

The contribution of N from soil organic matter mineralization is related accurately
in this section. As pointed out in the review comments for the Topic 3 Report, soil
organic matter levels have likely either stabilized or are generally increasing on a
time scale of many years. However, year to year and field to field fluctuations in
soil conditions can result in substantial release of inorganic N, at times under
conditions where the N cannot be efficiently used by plants. A more recent
publication reinforces the scientific acceptance of soil organic matter as a major
source of nitrate-N in the Mississippi River basin (Burkart and James, 1999).

Pages 30 and 31

Is it valid to use the results of Randall and Iragavarapu (1995), which involved a
single rate of 200 kg Nha, to “calibrate and validate” the ADAPT model
developed by Davis (1998)? Can Davis'results be used to extrapolate to a range


percent reduction in nutrient flux, and there is no confidence that this
reduction leads to improvement in Gulf hypoxia.

The second flaw in the recommendation is its definition of affordability.
Report 6 states “Our analysis accounts for economic impacts on the
producers and keeps changes in acreage and exports within historic bounds
of recent past adjustments; something of concern to many in the agricultural
sector.”

It appears the recommendations are judged affordable because they would
keep the number of acres and exports within the bounds of what farmers
have experienced in the past. Thus, farmers will be limited to the low end of
their economic experience. A cap will be placed on their income, and that
cap will be at the low end of their recent experience. The recommendations
would relegate farmers to economic poverty and the benefit of this policy is a
complete unknown. There is no indication it would reduce hypoxia, and we
know hypoxia reduction would not have an economic benefit to the fishing
industries. This does not make sense.


24

REVIEW OF TOPIC 5 REPORT:
REDUCING NUTRIENT LOADS, ESPECIALLY NITRATE-
NITROGEN, TO SURFACE WATER, GROUNDWATER, AND THE
. GULF OF MEXICO

urrell, Ph.D. ash hate Institute
Preliminary Comments

The goal of Topic 5 Report was to devise possible strategies and outline further
needed research to reduce nutrient loads to the Gulf of Mexico. The executive
summary (pp. xi-xiii) contained 8 recommendations specific to this goal. This
review will focus on only one of these recommendations, #1 (pp. xi-xii) which
states:

Several on-farm practices for the reduction of discharges of
nitrogen to streams and rivers should be implemented. These
practices, which could lead to reduction of 15-20% of nitrogen
sources, include 20% reduction in fertilizer nitrogen application,
optimum timing of fertilizer application, use of alternative crops
such as perennials, wider spacing of subsurface drains, and better
management of livestock manures whether stored or applied to the
land.

The wording of this recommendation in the executive summary is essentially the
same as the wording in the Sec. 6.2, Recommendations (p. 101).

In conducting this review, the assistance of other soil fertility researchers who
have been involved in N research and recommendations in the Northcentral US
was requested. Only 2 of the 14 researchers had time to respond to this request. _
More would have responded, given more time (2 not providing comments
specifically stated this). It should be noted that the review period corresponded
to spring planting and treatment applications, leaving researchers with great
expertise little time to provide in-depth comments on this important document.
The two researchers who were able to provide information are both from the
University of Minnesota and have been involved in the N recommendations for
the state. They commented specifically on the content in Sec. 3.1 (pp. 12-26)
and Secs. 6.1 and 6.2 (pp. 100-103). The comments they provided are
incorporated into the following review.

Review of the recommendation “20% reduction in fertilizer nitrogen
application”

This recommendation appears to have been constructed from data presented in
Sec. 3.1.3 “Reducing Nitrogen Fertilizer Application Rates” and Sec. 3.1.5


\

The Fertilizer Institute

Gary D. Myers
President

July 23, 1999

Mr. John Field

Gulf of Mexico Hypoxia Working Group
National Centers for Coastal Ocean Science
WE 13446 SSMC4

1305 East-West Highway

Silver Spring, MD 20910

RE: TFI Comments on the Integrated Assessment of the Causes and
Consequences of Hypoxia in the Gulf of Mexico

Dear Mr. Field:

The Fertilizer Institute (TFI), on behalf of its member companies, submits these comments
in response to a Environmental Protection Agency (EPA) notice regarding the six topical scientific
reports by the National Science and Technology Council’s Committee on Environment and Natural
Resources for an assessment of the causes and consequences of hypoxia in the Gulf of Mexico.

TFl is a voluntary, non-profit trade association of the fertilizer industry. TFI’s nearly 250
member companies manufacture more than 90 percent of the domestically produced fertilizer.
TFI’s membership includes producers, manufacturers, distributors, transporters, and retail dealers of
fertilizer and fertilizer materials.

Our comments begin with a section of general comments, a section of specific comments
on the six reports, and finally our recommendations. In addition, we submit to you as part of our
comments a report on the Role of the Mississippi River in Gulf of Mexico Hypoxia, published by
the University of Alabama Environmental Institute. TFI appreciates the opportunity to submit these
comments and we look forward to working with EPA throughout this process.

. Myers
GDM::pdg
| 501 Second Street, NE + gmyers@tfi.org
Washington, DC 20002 www.tfiorg

202.675.8250
202.544.8123 fax


1

Report 2

1. The evidence provided in Report 2 of hypoxia dating back to the early
1960s seems to contradict evidence provided in Report 1. Specifically,
the INDEX generated for Figure 2.1 seems to indicate that some evidence of
hypoxia existed in the early 1960s, while Report 1 states that the first credible
reports of hypoxia were anecdotally mentioned in the 1970s and that the first
true measurements were in 1985. Please provide relevant literature citations,
gathered data, and/or modeling results that determine with some confidence
level the time frame of nutrient-induced hypoxia, or (suggested) re-examine
the evidence that hypoxia may be a natural phenomenon.

2. Report 2 seems to discount the relationship between hypoxia and
nutrient enrichment. It is stated that “...the correlation between the time
series of AREA with time itself is nearly 0.8, so that any other time series
exhibiting a secular change over this relatively short time period will be
correlated with AREA” (p. 19). Based on this comment, please present
relevant literature citations, gathered data, and/or modeling results that
explain the uncertainty associated with correlating nitrogen production and
use data with hypoxic conditions in the Gulf of Mexico, Also, please explain
the uncertainty associated with using an “assume[d] 2% growth rate of
nutrient concentration” for the INDEX equation.

3. Report 2 indicates that the area data for the period 1985 to 1997 Is “too
short to establish a credible relationship between the severity of
hypoxia and variables relating to fisheries” (p. 14). Given this statement,
please provide relevant literature citations, gathered data, and/or modeling
results that quantify the uncertainty of using this time series establish a
credible relationship between hypoxia severity and any variable—especially
nutrients.

4, Report 2 indicates that unlike any other hypoxic area in the world, the
Gulf of Mexico seems to rebound ecologically each year. Please relevant
literature citations, gathered data, and/or modeling results that explain how
the largest hypoxic zone in the world can be so apparently benign to the
affected ecosystem. Please indicate how these data affect the uncertainty of
the use of area data for establishing establish a credible relationship between
hypoxia severity and any variable—especially nutrients.


10

zone over the three periods. Please discuss the change in extent and
location in terms of applicable physical parameters and how (a)typical these
types of changes are over the course of a summer.

Please provide relevant literature citations, gathered data, and/or modeling
results that describe the relative effects of these factors over a given time
period. This discussion should then be tied to descriptions of the mid-
Summer snapshot data provided for 1985-1998 and especially how these
factors can be expected to influence the distribution of the frequency of
occurrence of mid-summer hypoxia.

Temporal variability is described quantitatively using data from continuous
recording oxygen meters at Stations C6A or C6B. These meters are located
in an area identified in Figure 2 as being >75% hypoxic frequency. Therefore,
these meters are situated in the most stable area of the hypoxic zone. Please
provide relevant literature citations, gathered data, and/or modeling results
that discuss the representativeness and uncertainty associated with using
these data to describe the full aerial extent of the hypoxic zone. Given the
fact that there are no data available for May, June, mid to late August, no
hypoxic conditions recorded after the first week of October and only limited
data for April, please provide relevant literature citations, gathered data,
and/or modeling results that quantify the confidence limits of the estimated six
month hypoxic period, over the entire aerial extent estimates provided, based
on data from Station 6.

Carey et al. recently published “The Role of the Mississippi River in Gulf of
Mexico Hypoxia” (Alabama report). This report, which we are attaching as an
Official part of our comments, concludes that hypoxic episodes are a natural
phenomenon caused by a variety of factors, including physical, chemical,
biological and meteorological conditions. Specifically, the roles of increased
rainfall patterns in the upper Mississippi Valley, increased organic carbon
loading, and increased flow in the Mississippi River are not yet fully
understood. Please integrate the findings of this study into Report 1, as
appropriate and provide some qualitative or quantitative estimation of the
proportional influence each exerts in causing hypoxia. We further request the
integrated assessment writing process be opened to scientists such as Dr.
Carey who have made important contributions to the understanding of Gulf
hypoxia.


31

. Increased funding for basic fertility research. This review has shown the need
to account for interacting variables in fertility recommendations as well as the
need for local refinements. Currently, research for comprising
recommendations is too limited. There are many researchers willing to do
significant projects if money were available.

. Train and use county extension agents, consultants, and dealers to conduct
local research on best management practices. These professionals could
receive guidance from university personnel to create meaningful local BMPs
based upon local research.

. Educate those creating nutrient management plans, specifically in techniques
for using manure as a nutrient source.

. Although this requires no money, the NRCS, USDA, and EPA must recognize
local modifications in recommendations as BMPs if they meet current
scientific standards.


30

Review of the recommendation “better management of livestock manures
whether stored or applied to the land”

This recommendation was constructed from data presented in Sec. 3.1.4
“Managing Manure Spreading”. The discussion in this section centered around
using manure as a nutrient source. There are many considerations for using
manure as a source of nutrients. The best management practice in a
corn/soybean rotation is to store manure in a covered storage facility and empty
it once a year by injecting the manure in the spring on com acreage at rates
needed to meet either the N or P needs of the crop. Few producers have the
facilities or equipment to manage manure in this fashion. Adjustments to manure
management will require large capital investments in storage facilities, injection
equipment, and other needed equipment. Besides the initial capital investments,
manure has a variable nutrient analysis. The nutrient content of a single load of
manure can vary widely (Dr. Brad Joem, Purdue University, personal
communication). Many producers are concerned that because of variable
analyses, N or P needs of the crop may not be met, even with calibrated
applications. The advantages to commercial fertilizers are 1) guaranteed
analysis, 2) the ability to blend fertilizer sources to meet specific needs of more
than one nutrient, and 3) ease and uniformity of application. It should be
recognized that using manure as a nutrient source is a very complicated process
with many obstacles. Definition and implementation of BMPs will require time.

General Comments

The recommendations in this.section have not been considered in the context of
their interaction. There are some rather significant management practice
changes that producers will incur if this document becomes the basis for
regulations. Producers will have to take on costs associated with 1) reduced
crop yields from lower N rates, 2) reduced crop acreage from restoration of
wetlands and the establishment of riparian zones, 3) reduced acreage for
applying manure from use of rotations involving leguminous perennials, 4) higher
capital investments in manure storage and application equipment, 5) increased
hiring of labor to accomplish a large number of tasks during a short time period in
the spring. All of these costs will lead to a significant management decision:
increase the acreage in the farm. Increased acreage will allow the producer to 1)
maintain current farm production levels with lower corn yields and reduced crop
acreage per field, 2) apply more manure on the land in the farm, 3) spread
increased overhead costs over more acres. Certainly, this proposal favors farms
with large working capital to make these needed investments. Farmers with
smaller working capital are less likely to be able to afford these changes. It is
necessary to put these proposed changes in front of economists to determine
their efficacy and who is likely to benefit most.

If large sums of money are to be spent on the Mississippi basin, there are a few
efforts that should be supported. They are:


who modeled the effect of nutrient reductions on hypoxia said “there are large
uncertainties in the magnitudes of these responses.” Clearly, the
anthropogenic contribution to Gulf hypoxia is not well understood; we do not
know the extent of natural vs. manmade contributions, and there is not a
clear understanding of the relative contributions of a complex set of factors.
Thus the reports are inconclusive. They fail to prove the hypothesis, and
raise many questions and research opportunities about the complex set of
contributing factors.

4. The variability among the six assessments results in an
inconsistent and disconnected line of reasoning.

Report 1 clearly attempts to make the case for nutrients as the sole cause of
hypoxia, but fails in light of factors discussed elsewhere. Report 2 contains
the clearest conclusion in all the assessments: “The economic assessment
based on fisheries data, however, failed to detect effects attributable to
hypoxia.” This conclusion proved most troublesome to the authors of report
6, who were asked to weigh the costs and benefits of reducing hypoxia after
being given “zero” as the benefit. And yet they went on to suggest an
“affordable” program that combines a 20 percent reduction in fertilizer use
with a 5 million acre wetlands restoration program. There are two huge fiaws
with this recommendation:

First, it does nothing to reduce hypoxia. The authors of report 4 question the
effectiveness of reduced applications of fertilizer on water quality. “Among
the controllable measures, fertilizer application rate is a major factor, but the
effectiveness of reducing rates depends on climactic conditions and the
extent to which baseline applications exceed recommended rates.” In other
words, reduced application rates only reduce nutrients in water when two
other factors are in play: one, farmers are applying fertilizer above agronomic
rates, and two, it does not rain.

There are also major uncertainties about the effects of nutrient loss
reductions on Gulf hypoxia. Again, from report 4: “It was found that
dissolved oxygen and chlorophyil concentrations on the LIS do appear
(emphasis added) to be responsive to reductions in nutrient loadings from the
MAR; however, there are large uncertainties in the magnitudes of these
responses for a given nutrient loading reduction. These uncertainties are due
to lack of information on controlling physical, chemical and biological
processes, and to natural variability in hydrometeorological conditions in the
northern Gulf of Mexico.”

Thus, the recommendation to reduce fertilizer application by 20 percent is
made not on the basis of ecological impact, but on the basis of “affordability.”
The recommendation does not achieve the previously stated goal of 20


21

Page 62 and page 63

The authors state, that a simulated 50% N loading reduction for 1985 conditions,
increased dissolved oxygen conditions in the Gulf of Mexico by less than 5% for
constant boundary layer conditions, and 45% for reduced boundary layer
conditions. The authors further state that, “Differences in responses of average
dissolved oxygen concentrations between constant and reduced boundary layer
conditions are not constant among different years.” These differences are
illustrated as follows:

Effects of nutrient load reductions on percentage changes in dissolved
oxygen (under reduced boundary layer conditions)
Nutrient_Load Reduction

Year 0Y 0!
1985 25 45
1990 60 140

Modeling of the 1985 and 1990 data indicate chlorophyl! a response to nutrient
load reductions is similar between years. However, there are marked differences
and considerable variations in load reduction effects on dissolved oxygen. The
absolute differences in predicted percentage effects on dissolved oxygen
approach 100%, as illustrated above. The authors state that chlorophyil a is
coupled to nutrient concentrations in Gulf waters, but that phytoplankton growth
rate is controlled by underwater light attenuation.

These modeling results indicate the effects of nutrient load reductions on
dissolved oxygen levels in the Gulf of Mexico, 1) can not be accurately
predicted, and/or 2) they are not predominantly under influence by N
loading. Dissolved oxygen levels appear to be under greater effect from
advective flow and flow direction along the Louisiana Intercontinental
Shelf, than from nutrient loading.

CONCLUSIONS on page 79

To quote the authors, “Violations of numerical water quality standards for
dissolved oxygen, pH, nitrate, and un-ionized ammonia are uncommon in MRB
rivers and streams under current and recent conditions. It should be noted
however, that there are no numerical standards for nutrients in water bodies
relative to their potential to cause eutrophication problems (e.g. the nitrate
standard applies to drinking water)". The authors go on to state, that about 30 to
55% of the HCUs of the Ohio, Lower Mississippi, and Tennessee basins exceed
a recently proposed eutrophication criterion (Dodds et al., 1998) for total P in
flowing waters, and 16-40% exceed the total N criterion.

Conclusions page 80

To quote the authors again, “For a given reduction in MAR (Mississippi and
Atchafalaya River) N or P loadings, there are large uncertainties in the
magnitudes of dissolved oxygen and chlorophyll concentration responses.”



38

Section 3: Additional Recommendations

1.

Make the process more open. The integrated assessment writing team
should include scientists outside the federal structure who have done work on
Gulf hypoxia. This would bring the broader scientific viewpoints and
hypotheses to bear on the process. The integrated assessment must
acknowledge the existence of other contributing factors and not be limited to
examining only the role of nutrients.

Make the peer reviews from the six scientific assessments publicly available.
The scientific process is known for being an open search for the truth. The
public should also have access to the data and viewpoints expressed in those
reviews.

The integrated assessment should include the conservation achievements of
farmers that have been made to date.

. The integrated assessment should examine the additional federal and private

resources that can be used to achieve more farm-level conservation.

The integrated assessment and action plan developed should rely heavily on
existing conservation programs, including CRP, EQIP, WRP and CTA.
Currently, these programs do not have the funding or manpower necessary to
meet farmer demand. It is through incentives and partnerships in these types
of programs that farmer practices will be changed in ways that reduce nutrient
losses.

The integrated assessment and action plan must recognize the need to
increase agricultural productivity, not limit it. In addition to a growing world
population and overseas markets that will enable farmers to achieve greater
market income, there are federal programs that are creating increased
demand for agricultural products. Commodities such as corn and soybeans
are being touted as sustainable, renewable sources of fuel and motor oil, and
will soon assist in the reduction of carcinogens and greenhouse gases. The
action plan should envision a growing agricultural production base.

Significant data gaps are acknowledged in the six assessments and noted
here. The action plan should include requests for money for additional
research and water quality monitoring. Monitoring of Gulf hypoxia should
continue due to the very limited data currently available.


39

8. The U.S. Department of Agriculture should be the lead agency in assembling
the Action Plan. Successes in achieving nutrient loss reductions are
dependent upon the individual behavior of millions of landowners and
operators. It is USDA that operates the programs and has the personnel with
the expertise to deliver the assistance farmers will rely upon.


27

recommendations based upon soil type, rather than yield goal, the current
university guideline. The result: reductions of 10-40 Ib N/A compared to
current university recommendations. Productivity has remained the same or
increased and profitability has increased. Farmers in the agronomist’s trade
territory use his recommendations exclusively. This has led to reduced N
applications on thousands of acres. This example shows that solid local data,
produced by reputable agronomists, is the key to creating N
recommendations that 1) fertilize a crop appropriately and 2) are accepted
and used by farmers.

. Recommending a 20% reduction in N fertilizer for the Mississippi basin
extrapolates well beyond the inference space of the data presented,

The effects of a 20% reduction in N fertilizer (from recommended rates) were
estimated only for one site (Waseca, MN) in one experiment (6 site-years
total). Only 10% reductions were investigated in the other two cited studies (2
sites in Minnesota totaling 9 site years). The Waseca study where the 20%
reduction was investigated was in a continuous com rotation. The
predominant rotation in the Mississippi basin is corm/soybean, not continuous
corn. A corn/soybean rotation is fertilized with N once every 2 years, not
every year as in a continuous corn rotation. Thus, the predominant rotation in
the basin uses N half as often as the rotation used as the basis for the 20%
reduction. In addition, the paper also states on p. 19 that higher nitrate losses
were found in one study from a continuous corn rotation compared to a
cormsoybean rotation. All of this would lead one to conclude that the
predominant corm/soybean rotation is capable of producing lower nitrate
losses than those from this study in Minnesota.

The more conservative recommendation of a 10% reduction in N fertilizer use
is not well-supported either. Only 15 site-years of data from 2 sites in
Minnesota were used to create this recommendation for the Mississippi basin.
Normally, university recommendations for a state are based on many more
sites and years of data than presented here. It is logical to expect that a
blanket recommendation for the Mississippi basin would be based on
hundreds of site-years collected from all of the states in the basin, rather than
15 site-years from one state.

. The N rate reduction analysis is flawed.

The components of the analysis were: 1) create equations from corn and
drainage water nitrate responses to fertilizer nitrogen, 2) look up currently-
used N recommendations for yield goals appropriate to the experiment, 3)
estimate yield and drainage water nitrate concentrations from recommended
N rates, 4) estimate yield and drainage water nitrate concentrations from a
reduced (10-20%) N rate, 5) determine reductions in yield and drainage water
nitrate from using reduced N rates.

In the analysis for Lamberton, MN, the optimum rate of N was calculated to
be 112 kg N ha" (p. 20). Optimum usually implies an economic optimum.


Fertilizer Application Rates for Corn

< 160 4mN

2

mol

2&

3

<<

2

O

iv

oO

Do

®

oO

Zz oO 1 7 ;

1960 1970 1980 1990 2000
Figure 1
Data source: National Agricultural Statistics Service and Harold Taylor, Personal
Communications.
Figure 2
N Fertilizer Use Efficiency for Corn

_ 14

c

£12 .

= 1.0 % a*

° a am -

2 08 aes =

g .

= 06 = a

ao

0.4 r ; 1
1960 1970 1980 1990 2000

Data source: National Agricultural Statistics Service and Harold Taylor, Personal
Communications.



14

situation that is not compatible with stabilized soil organic matter levels

(unless soil OM C:N is increasing, of which there is no evidence). In fact,

limiting N inputs to agricultural soits could potentially threaten this C

accumulation capacity, as N is critical for stabilizing increased soil organic

matter (Paustian and others, 1992; 1997) as well as for increasing crop yield

and crop C contribution to the soil to build up soil organic matter (Nyborg and
others, 1995). nt

3. The soil mineralization calculation involves a multiplication by cropped land
area, assuming that only cropped land mineralizes N (p. 48). As the amount
of cropped land is correlated to N fertilizer use, it is not surprising that the
regression model finds these two variables correlated and cannot distinguish
between their contributions to the flux of N in the rivers (p. 67).

4. The report cites literature on the so-called “priming effect” whereby N fertilizer
additions stimulate N mineralization (page 48). This priming effect has been
debated extensively in the literature, and many reports are based on
erroneous interpretation of 15N tracer experiments (Jansson and Persson,
1982). In most agricultural soils, available C rather than N limits microbial
decomposition of organic matter and hence N mineralization. In fact, lack of
N may limit C accumulation in soils (Paustian and others, 1992; 1997; Nyborg
and others, 1995).

The bias against modern row crop production practices is demonstrated in
the following.

1. While all aspects of agriculture that could lead to potential losses are
considered, the consideration of other sources is much more limited. For
example, the estimates of N and P from point sources are limited to permitted
discharge from facilities in the NPDES database (p.53 section 5.3.1).
Violations of current regulatory limits and illegal dumping are ignored and are,
in effect, estimated to be zero. Point sources from facilities outside the
NPDES database are not considered.

2. Land uses other than agriculture, including forestry, municipal landfills, urban
tun-off, geological nitrate etc. are simply assumed to contribute little and are
not investigated in any degree of detail. Therefore it is not surprising that
agriculture appears to be the larger contributor.

3. The N contribution from legumes is underestimated. In Minnesota, Dr. M.P.
Russelle’s recent work with alfalfa indicates that substantial N fixation takes
place even when soil nitrate is high. This work was ignored in the model, and
it was assumed that legumes never fix more N than needed (p.45). Yet it is
well known that when forage legumes are plowed down or killed, N
mineralization is enhanced and nitrate can accumulate. The estimates used
for the most important legumes, soybeans and alfalfa, are considerably below
the middle of the range of literature values (Table 5.4). In fact, estimated N
fixation for soybeans works out to 78 kg/ha/yr, while a crude N balance for
1998 suggests U.S. harvested soybeans removed 170 kg/ha/yr more than


16

The report's first objective, to identify where the most significant nutrient
additions to surface water occur, was achieved. However, its second and
admittedly more difficult objective, to estimate the relative importance of specific
human activities, was not achieved. It is unfortunate that the report's conclusions
neglect this and make estimates of the latter without scientific grounds.

Literature Cited
Allmaras, R. 1999. USDA-ARS News Release, May 17, 1999.

Correll, D. 1998. The role of phosphorus in the eutrophication of receiving
waters: a review. J. Environ. Qual. 27:261-266.

Jansson, S.L., and J. Persson. Mineralization and Immobilization of Soil
Nitrogen. Ch. 6 in Nitrogen in Agricultural Soils, F.J. Stevenson, ed. ASA
Monograph No. 22.

Nyborg, M., E.D. Solberg, $.S. Mathi, and R.C. Izzauralde. Fertilizer N, Crop
Residue, and Tillage Alter Soil C and N Content in a Decade. p. 69-83, Chapt. 6
in: R. Lal, J. Kimble, E. Levine, B.A. Stewart (eds.) Soil Management and
Greenhouse Effect, CRC Press, Inc.

Paustian, K., W.J. Parton, and J. Persson. 1992. Modeling soil organic matter in
organic-amended and N-fertilized long-term plots. Soil Sci. Soc. Am. J. 56: 476-
488.

Paustian, K., H.P. Collins, and E.A. Paul. 1997. Management controls on soil
carbon. p. 39-41, Chpt. 2 in: E.A. Paul, K. Paustian, E.T. Elliot, C.V. Cole (eds.)
Soil Organic Matter in Temperate Agroecosystems, CRC Press, Inc.


Farmers have increased the amount of grain produced per unit of N from 0.76
bushels per pound of N in the late 1970's to approximately one bushel per pound
of N today. That represents an efficiency increase of 32%.

Grain production per unit of fertilizer N applied will never increase to what it was
in the early 1960's. Farmers today are rebuilding soil organic matter and soil
organic N with conservation tillage systems. These systems do not mine soil N
like the plowed systems of the 1960’s did. Instead, they fix atmospheric carbon
and in so doing reduce carbon dioxide emissions by the U.S. Farmers in the
1960's could use less fertilizer N because of the soil N released by their intensive
tillage systems. Changes in crop rotation practices have also impacted N need.

A recent survey of lowa farmers gives additional insight into today's N
management practices (Table 1). Where no manure was available, fertilizer N
use for a corn-soybean rotation averaged in the middle of lowa State University’s
recommended use range. For continuous com without manure, farmers
averaged less than the recommended range and may have been losing yield
from insufficient N. Fertilizer N use where manure was applied was less than
where it was not applied but exceeded recommended rates. Farmers generally
took fess N credit for the manure than was recommended probably due to
uncertainty about the actual N content of the applied manure. Although, there is
stil! room for improvement in N management practices, especially where manure
is involved, this survey does not support an across the board mandatory
reduction in fertilizer N use.

Table 1. Nitrogen use on com in lowa in 1996, with and without manure.

Manure used Manure not used
Parameter Com/com _Corn/soybean _Com/corn _Corm/soybean
Com yield, bu/A 142 143 131 142
N fertilizer use, Ib/A 121 119 135 129
ISU recom., Ib/A* 0-90 0-90 150-200 100-150

*jowa State University 1997 N recommendations where all N is applied before emergence.
Data source: M. Duffy, lowa State University, personal communication.


37

15. The FAIR Act has reduced incentives to crop as intensively as in the past.
Therefore, some of the adjustments discussed in the paper may already have
occurred or will occur in the near future. It seems (again, no detail is given)
the base case is of a 1995/96 vintage and we know that conditions have
changed radically since then.

16. The authors appear content to shift potential "problems" or "risks" to other
tegions. The increase in commodity prices causes more intensive input use
outside the MB, but that apparently is OK.

17.Costs of $4.9 billion to achieve the 18.8% reduction from fertilizer sources (or
a 5.6% reduction in total loadings) seem very high relative to the lack of
benefits identified by the authors. In addition, other indirect costs noted
above are ignored.

18.Report 6 calls for a 20% nitrogen use reduction and the reclamation or
creation of five million acres of wetlands as the solution for the hypoxic zone.

Please provide the regulatory authority options that the Federal government
would have to pursue these policies.

19. The cost of wetlands construction is lowered in Report 6 by counterbalancing
secondary benefits of wetlands, such as increased habitat for flora and fauna.
However, no mention is given to the cost of establishing, monitoring and
complying with a 20% fertilizer use reduction. For each regulatory authority
listed in response to the comment above, please provide an estimate of the
cost of establishing, monitoring and complying with a 20% fertilizer use
reduction. Please integrate these estimates into the brief discussion of costs
versus benefits in Report 6.

20. EPA is currently preparing Guidance for establishing nutrient criteria guidance and
TMDLs for nutrient-impaired waters. There is no discussion in Report 6 of how the
proposed 20% nitrogen use reduction and the reclamation or creation of five million
acres of wetlands would be integrated with these two initiatives. It can be argued that
the policies suggested in Report 6 would establish a nutrient criterion for nitrogen in
the Mississippi River and artificially set agriculture’s maximum allowable daily
contribution across 41% of the landscape. Please explain how these would be
integrated and, specifically, justify the selection of a 20% nitrogen use reduction and
the reclamation or creation of five million acres of wetlands in terms of superceding
expected establishment of eco-region or watershed based nutrient criteria and the
individual states’ right to partition the TMDL across point and non-point sources.


25

“Managing the Time of Nitrogen Application”. The main points in both sections
are summarized below.

Section 3.1.3

1. Many farmers use excess N (p. 19).
Sec. 3.1.3 begins by stating that many farmers-choose to use “extra” N as
“insurance”. Too little N results in lower yields, poorer grain quality, and
reduced profits. Too much N results in no yield or quality reductions but can
negatively impact the environment (p. 19). Legg et al., 1989 is used to
support the statement that farmers use excess N as insurance.

2. Use of insurance N increases nitrate levels in drainage water (pp20-22).
Data from 1974-79 were presented from Lamberton, MN that showed high
nitrate concentrations in drainage water from plots receiving large fertilizer N
rates (224 and 448 kg N ha’) each year for 6 years. These data were used
to estimate increased nitrate concentrations in drainage water of 6-20 mg NL”
‘ from insurance N applications applied for 6 consecutive years. Applying
manure at 100 kg N ha” above recommended rates was. estimated to
increase drainage water N concentrations by 25 mg NL" over the 6 year
period.

Data from 1977-79 from Waseca, MN showed 16-20 mg NL” increased
nitrate concentrations in drainage water when higher (224 and 336 kg N ha’)
fertilizer N rates were applied. Applying i insurance N 45 kg N ha” above the
currently recommended 190 kg ha” rate was estimated to produce a 7 mg N
L" increase in drainage water nitrate concentration. Applying manure at 100
kg N ha” above the recommended rate was expected to increase drainage
water nitrate concentrations by about 17 mg NL’.

3. Reducing N rates by 10% from recommended rates produces modest yield
losses and reduces nitrate concentration in drainage water (pp20-22).
Estimates from corn response to fertilizer N at Lamberton and Waseca were
used to predict effects of tower N rates upon yield and drainage water nitrate
concentration. At Lamberton, reducing N rates by 10% compared to currently
recommended rates would reduce yields only slightly and decrease drainage
water nitrate concentrations by 3 mg NL’. Reducing N rates 10% from
currently recommended rates at Waseca was predicted to reduce com yields
by 0.3-0.4 metric ton/ha (6-6 bu/A) and decrease drainage water nitrate
concentrations by 3mg NL.

Section 3.1.5

The three points developed for Section 3.1.3 were reiterated for another study at
Waseca (pp. 23-24). Nitrogen response data from 6 years of a continuous com
experiment were used to predict that 10% and 20% reductions from currently


Section 1: General Comments

1. Voluntary changes in farming practices are reducing nutrient
losses.

Farmers have an economic self-interest in achieving the goal, stated in the six
assessments, of reducing nutrient losses. Farmers have made great progress in
this area and will continue to make improvements. These improvements in
management practices will ultimately serve the dual purpose of making farmers
more efficient and reducing nutrient loads to the Gulf.

We fully support the goal of reducing nutrient losses from fields. Farmers have
an economic self-interest in achieving this goal: nutrient losses from fields
represent lost production and lost money to farmers. This incentive to reduce
losses is at odds with the viewpoint expressed in reports 5 and 6 that farmers
have an economic incentive to apply too much nitrogen. Farmers do not have an
economic incentive to over apply — overapplication represents money that will
surely be lost in the form of nutrient losses. Farmers have an incentive to
maximize production, meaning get the most possible production out of the least
possible input.

Nutrient loss reduction is the result of many complex, site-specific factors,
including application rates, nutrient sources, soil types, and precipitation. Thus,
mandated use restrictions, such as those suggested in Reports 5 and 6, are
unlikely to achieve loss reductions and are certainly not the most efficient way to
achieve loss reduction. Rather, loss reductions can be best achieved and are
being achieved over time by farmers adopting new methods and new
technologies that make them more efficient.

Farmers are making gains in efficiency by implementing a number of practices.
Some of these practices are purely voluntary and the result of technological
advances and farmer education. Others are being accomplished in partnerships
with federal, state and local governments. What follows is a discussion of
efficiencies that have been achieved and some of the major practices being used
to achieve those efficiencies.

rtilize! i r Col

U.S. farmers have been improving their nitrogen (N) fertilizer efficiency for the
last two decades. Average fertilizer use per acre on com in the U.S. has been
essentially constant since the late 1970's (Figure 1). However, corn yields have
continued to climb resulting in an increase in the bushels of corn produced per
unit of fertilizer N applied (Figure 2).


33

output produced. is Wi ntinue to in: her
efficiency!

The information put together by PPI, included earlier in these comments,
clearly demonstrates that U.S. com farmers, who account for over 40 percent
of U.S. N use, have increased their efficiency by 32% since the late
1970's. This increase in efficiency can be demonstrated in another way. In
1980, U.S. com farmers used 5.2443 million tons of N to produce 6.395 billion
bushels of com. In 1998, they produced 9.738 billion bushels, a 52 %
increase in production over the 1980 level, with approximately the same
amount of N (5.2668 million tons). If farmers were still using 1980 cropping
practices with respect to N use, it would have taken an additional 2.7415
million tons of N to produce the 9.738 billion bushels of com produced in
1998. That is, N use efficiency in com production increased by over 34
percent from 1980 to 1998 without any laws requiring this to take place. The
laws of economics, which encourage farmers to maximize their profits, as well
as voluntary best management practices, have resulted in these efficiency
gains. Placing an additional constraint of a 20% reduction in N use ona
system that has already experienced a 32-34 percent increase in
efficiency since 1980 would surely have significant consequences for crop
yields and production. To argue otherwise would be to ignore the law of
diminishing retums.

. The paper suggests that the large majority of farmers in the MB region apply
20% more nitrogen than required on a regular basis. The authors admit, “the
extent to which producers are currently over-fertilizing is unknown.” While
some farmers apply more nitrogen than is recommended or optimal, it has not
been demonstrated that this practice is common in the MB region. As a
matter of fact, the 1997 AREI nutrient use report indicates that 47% of com
farmers conduct soil tests for nitrogen. Of those that do, 69% report they
apply the recommended level, 18% apply less than the recommended levet
and only 13% report they apply more than the recommended level. The 20%
over-utilization figure quoted throughout the study would imply that com
farmers apply over 27 Ibs of N per acre more than needed (average nitrogen
rate was 136 Ibs/acre in 1996). This is a key “assumption” of the report since
the study seems to imply that there would be little negative impact on crop
yields over the long term with farmers lowering application rates of N by 27
lbs. per acre on com, and similar reduction in other crops. At the $0.18 per
Ib. cost of N quoted in the paper, it also implies that farmers throw away
$5/acre in N costs (plus their time and expense of purchasing the product). A
full review of the literature, and possibly additional studies, on how much
nitrogen farmers should and do apply is a key piece of information that has
not been adequately addressed in this paper. Also missing from the paper is
a discussion of the role of state land-grant university recommendations, and
the variabllity of those recommendations from state to state. This has been a
subject of many agronomic debates over many decades. !f bordering states


28

This is normally determined from N response equations by finding the rate
producing $1 net return for the last $1 increment spent on N fertilizer. It is
widely accepted that the economic optimum rate is best for the producer,
since it maximizes profits. Rates greater than the optimum may produce
slight yield Increases, but such increases produce negative net returns and
are not profitable for the farmer. The recommended rate used for the N
reduction calculation was 135 kg N ha’, a rate 23 kg N ha” greater than the
optimum for the site. The 10% reduction examined used 125 kg N ha”, a rate
still 13 kg N ha" greater than the optimum. This discussion shows that the N
reductions examined were not appropriate for this site and were not expected
to impact yields or profitability. This site should not have been 40% of the
data used for the rate reduction recommendation. This site demonstrates the
variability in response possible at different locations and different years.
Recent data from Windom, MN demonstrates that the same rate reductions
showing no impact at the Lamberton site could produce large impacts at other
sites that are more responsive to N fertilization.

Drainage water N concentrations at the sites studied do not accurately assess
current recommendations. These studies examined the impacts of the same
N rates applied every year, without regard to residual soil nitrate levels.
Current university recommendations adjust N rates based upon residual
nitrate concentrations in the soil profile.

. The 20% rate reduction does not consider the influence of other factors.
Balanced nutrition has always been the key to optimizing nutrient
management. It is not known if the studies considered in the paper examined
the effects of other factors. If they did, those factors should be included in the
discussion. If they did not, they were too narrowly focused to apply to all of
the conditions existing in the Mississippi watershed. An example showing the
importance of examining interacting factors comes from Johnson et al. (J.W.
Johnson, T.S. Murrell, and H.F. Reetz, Jr. 1997. Better Crops 81:3-5). This
study demonstrated that higher levels of soil test K led to lower economic
optimum N rates and reduced residual soil nitrate concentrations. Focusing
on N alone will lead to recommendations not appropriate when other factors
interact.

The possibility of other interacting factors is demonstrated in a recent
survey of soil test levels in North America. This survey determined the
percentage of soil samples tested by laboratories that are expected to
respond to P, K, and lime additions. These percentages were, for the states
in the Mississippi watershed, 35-77%, 7-69%, and 1-63%, respectively, for P,
K, and pH. These data demonstrate that N interaction with other nutrients are
expected in areas of all of the states in the basin. None of the data presented
in the paper accounted for the effects of applications of P, K, or lime on
optimum N rates.


12

REVIEW OF TOPIC 3 REPORT:
FLUX AND SOURCES OF NUTRIENTS IN THE MISSISSIPPI
ATCHAFALAYA RIVER BASIN (MARB).

sem D h: i

The topic 3 report is very detailed and comprehensive. However the problem
addressed demands extreme attention to detail and rigorous analysis. While the
teport provides and summarizes much useful information, its conclusions are not
supported by the science presented. In fact, there unfortunately appears to be a
bias within the study toward attributing modern row crop production practices
with most of the responsibility for the current level of nitrogen (N) loading. While
that premise may indeed be true, the appearance of bias detracts from the
acceptability of the report.

Conclusions that must be taken seriously include:

1. The average total N yield for the basin of 4.97 kg/ha/yr is quite conceivable.
Most agronomists would agree that this rate of leakage of N from most row
crop production systems could be occurring, even when averaged over non-
cropped land in many parts of the basin.

2. The major nitrate and nitrogen loads in the basin come from the geographical
area of the Corn Belt, as illustrated clearly in Fig. 4.5.

General weaknesses in the report include:

1. Data interpretation is often questionable. For instance, on page 24 Fig 3.3 is
interpreted as a “direct relation” between nitrate concentration and
streamflow. The fit is not nearly that tight. Visual examination of Fig 3.3
hardly supports a positive association between the two, as there are times of
high concentration at low streamflow. This important association, considering
its use in the flux estimates, is not reported to have been rigorously analyzed
with statistical methods, even methods as simple as a Pearson correlation
coefficient. It would seem that these data should be analyzed by more
advanced statistical methods including spectra! analysis, as there appear to
be significant cycles in the data.

2. The statement in the executive summary on page 13 that nitrate flux is about
three times larger than it was 30 years ago is an exaggeration of data shown
in Fig 4.2, where the increase appears to be no greater than 2.5 times.

3. On page 31, it is stated that the average total N yield for the MARB had
increased 3 fold over the past 40 years. Figure 4.2 indicates no measure of
totat N prior to 1967 and therefore cannot support that statement. In facta
visual assessment of the trend in Fig. 4.2 would suggest an increase of
roughly 2 foid over the past 40 years.

4. In the same paragraph on p.32, current MARB N yields are compared with
“pristine” North Atlantic basin yields. The comparison is not meaningful, as


15

was applied as fertilizer N. It is highly likely, though difficult to substantiate,
that soybean N fixation is considerably higher than 78 kg/ha/yr.

4. The most precisely known variable in the regression model is fertilizer N
sales, as disclosed on p. 66. It is not surprising that the variable with the least
amount of error would explain the greatest amount of variation in the
regression model.

5. The soll mineralization calculation assumes that only cropped land
mineralizes N. Thus it is not surprising that soil mineralization is correlated to
N fertilizer use, and to crop agriculture in general.

Problems with the regression model used to attribute sources of nutrient
loading (pages 67-74 section 6.3) include:

1. The 42 basins are not all independent. Several are inclusive of a separate
upriver basin (examples include 17-18, 20-21, 25-26, 27-28). This leads to
autocorrelation within the data and thus underestimation of error variance.
No mention is made in the report of use the Durbin-Watson d statistic to test
for autocorrelation.

2. The dependent variable, nutrient flux, is an average of the 17-year period
1980 to 1996. The independent variables are estimated from the 1992
census. While the appropriate time lag is an unknown, it would seem
obviously invalid to argue that independent variables (nutrient inputs) in 1992
were causes of effects on the dependent variable in 1980 to 1991.

3. A preferred method of computing the relative contribution of each variable in
the regression model would be to use the various types of sums of squares in
SAS to estimate proportion of variation explained, rather than basing all
conclusions on the size of the coefficients relative to the mean input values of
the independent variables.

4. The large negative intercept of the final model contradicts the initial
assumption of limited in-tiver losses of N by denitrification and other
processes.

Finally, the report provides very little discussion of the decline in the residual
surplus of the calculated N balance over the past 40 years (Figure 6.4A). It
would seem to contradict the-increasing trend in measured N and nitrate flux over
the same time period. Examination of cumulative residuals (Figure 6.4B) implies
a long-term storage pool of N, filled to a “steady-state” capacity (page 65) over
the course of 20 years or more. However it is extremely difficult to conceptualize
where such a large pool of N might be stored. It was not soil organic N (which
did not likely increase between 1955 and 1975). Possibly this huge pool could
be groundwater nitrate, but the report gives no discussion of the contribution of
baseflow relative to that from surface runoff and tile drainage. It is difficult to
imagine that baseflow from deep groundwater sources could be a major
contributor. It is recommended that experienced hydrologists be consulted on
this question.