17

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.

5. 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 soit 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 fevels 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%, 769%, 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.

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. Wolkowski, K.A. Kelling, L.R.
Massie, and §.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.


11

Modeling of the 1985 and 1990 data indicates chlorophyll 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 chlorophyl! 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 tevels 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.”

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 mode! with a
hydrodynamic model of the Gulf of Mexico circulation, expansion of the model 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.



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

Tom W. Bruulsema, Ph.D., Potash & Phosphate Institute

The topic 3 report is very detailed and comprehensive. However the problem
addressed demands extreme attention to detail and rigorous analysis. While the report
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 Com 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 spectral
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 total N prior to 1967
and therefore cannot support that statement. In fact a visual assessment of the
trend in Fig. 4.2 would suggest an increase of roughly 2 fold over the past 40 years.

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


18

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 corn 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 Joern, 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 cor 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:

1. 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


15

fertilizer and legume credits roughly meet the N requirements of the corn
crop. Excesses in each case afe 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.

. 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 corn
differed between soil mapping units. He concluded that optimum N rates did differ
for the two soils studied. He created his own local 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


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 Nationa! Agricultural Statistics Service and Economic Research Service data, there
has been an improved efficiency of N, P and K utilization by com, per bushel of
production, since the early 1980s.

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

Page 11, 2TM 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 com had already been applied in the Cornbelt 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 Combelt 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 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


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).

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 mode!
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 modem 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 run-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.
Russelie’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/hafyr, while a crude N balance for 1998 suggests U.S. harvested soybeans
removed 170 kg/ha/yr more than was applied as fertilizer N. It is highly likely,
though difficult to substantiate, that soybean N fixation is considerably higher than
78 kghhalyr. ~

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 exptain the greatest amount of variation in the regression model.


were higher than those for the North Atlantic basin, as the soils of the MARB have
above average organic matter content.

5. Page 15 states that N input from anima! 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.

6. 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.

7. 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?

8. 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 Arny Corps of Engineers is suggested to verify
this point.

The calculation of “soi! 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 mineralizationimmobilization turnover (MIT) as a
continuous internal 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.

2. Current evidence indicates that agricultural soils have switched in the fast 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 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 soils could potentially
threaten this C accumulation capacity, as N is critical for stabilizing increased soil


16

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 corn/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 com/soybean rotation. All of this would lead one to conclude that the
predominant corn/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. This is normally
determined from N response equations by finding the rate producing $1 net retum
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 retums 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


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.S. Malhi, and R.C. Izzauraide. 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 soi! 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.


P.O. Drawer 2440
Conway, AR 72033-2440
POTASH & PHOSPHATE INSTITUTE Phone: S01-330-8110

Fax: 501-329-2316
esnyder@ppi-far.org

July 29, 1999

John Field

National Ocean Service

National Centers for Coastal Ocean Science
WS 13446 SSMC4

1305 East-West Highway

Silver Spring, MD 20910

Dear Mr. Field:

Enclosed with this cover are general and specific comments on the Topical Scientific Reports for an
Integrated Assessment of the Causes and Consequences of Hypoxia in the Gulf of Mexico. Our technical
comments have also been sent to The Fertilizer Institute for their consideration in responding to the six
CENR reports.

We have specifically addressed Topics 3, 4 and 5. Topic 6 authors used a macro-economic modeling
approach to look at costs and benefits for reducing nutrient loads to the Gulf of Mexico. The model will
likely be challenged by agricultural economists and others who may be more familiar with the impact of
crop acreage reductions and nutrient-use reductions in a global farming economy. There are numerous
assumptions in the model that just do not agree with conventional agricultural wisdom and we formally
register concern about the potentialty inaccurate model projections.

Please record our comments, reply to confirm receipt, and forward our comments to authorities within

EPA, NOAA, and the Office of Science and Technology. If you have any questions please feel free to call
me at 501-336-8110.

Lifeb L Aly

Clifford S, Snyder, Ph.D.
Mi i

Enclosures

CC: Dr. Tom Bruulsema

Dr. Paul Fixen
Dr. Scott Murrell
—
Members: Agrium inc. ° Cargill, Incorporated . CF Industries, Inc. . Farmland Hydro, Inc.

IMC Global inc. * Mississippi Chemical Corporation © Potash Corporation of Saskatchewan Inc.



through IV. Cropped lands (i.e. Land Capability Classes I-IV) are inherently more
productive, usually more fertile, and may frequently have a higher actinomycete and
bacterial population. These charactersitics 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, 2TM paragraph

The authors should also mention that soils in the Eastern and Southern sub-basins
usually have lower soil 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 journals.
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 resuit, 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 com 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 corn N-use efficiency has
been improving since the early 1980s. Nationally, com 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. The 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


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, 4TM paragraph

Dr. John Lory, at the University of Missouri, has submitted a manuscript to the Journal
of Environmentat Quality, in which he and colleagues review the science behind
“critical” soil test P fevels. 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 pattern 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

's it valid to use the results of Randall and lragavarapu (1995), which involved a single
rate of 200 kg N/ha, to “calibrate and validate” the ADAPT model developed by Davis
(1998)? Can Davis’results be used to extrapolate to a range of N application rates?
More information should be provided regarding the independent data used to develop
the ADAPT model.

Page 32, 2TM 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 |


5. The soil 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 fag 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
Ttegression mode! 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 targe negative intercept of the final model contradicts the initial assumption of
limited in-river losses of N by denitrification and other processes.

Finally, the report provides very little discussion of the decline in the residual surplus of
the catculated 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 poo! 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.

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


19

limited. There are many researchers willing to do significant projects if money were
available.

2. 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.

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

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


REVIEW OF THE HYPOXIA ASSESSMENT REPORTS

--FROM THE COMMITTEE ON ENVIRONMENT AND -- -

NATURAL RESOURCES HYPOXIA WORK GROUP
MAY 1999

Topic 3. Flux and sources of nutrients in the Mississippi
Atchafalaya River Basin

Topic 4. Effects of Reducing Nutrient Loads to Surface
Waters within the Mississippi River Basin and the Gulf of
Mexico

Topic 5. Reducing nutrient loads, especially nitrate-nitrogen,
to surface water, groundwater, and the Gulf of Mexico

BY THE POTASH & PHOSPHATE INSTITUTE

June 7, 1999


12

Figure 1. Hypoxic Area in Gulf of Mexico Declined

square miles

Since 1993 Floods
N. Rabalais, LUMCON

6000

4000 +

2000 +

14,000

ern
B85

2,000

000 tons of fertilizer
Cy

4,
o

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

1983 to current, Excluding 1993 data

1,000 tons of n

1,600
1,400
z
1,200 8
1,000 &



14

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 N L" from insurance N
applications applied for 6 consecutive years. Applying manure at 100 kg N haTM
above recommended rates was estimated to increase drainage water N
concentrations by 25 mg N L" over the 6 year period.

Data from 1977-79 from Waseca, MN showed 16-20 mg N L" increased nitrate
concentrations in drainage water when higher (224 and 336 kg N ha”) fertilizer N
tates were applied. Applying 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 N L7.

3. Reducing N rates by 10% from recommended rates produces modest yield losses
and reduces nitrate concentration in drainage water (pp20-22).
Estimates from com response to fertilizer N at Lamberton and Waseca were used to
predict effects of lower 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 3mg 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 (56 bu/A) and
decrease drainage water nitrate concentrations by 3 mg 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 corn
experiment were used to predict that 10% and 20% reductions from currently
recommended N rates would produce 0.3-0.4 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 fo 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 com. Tables 1 and 2 of the paper indicated that:


Figure 1

Fertilizer Application Rates for Corn
160 aN : —— -

140 + 4 p205

Average Rate Applied (Ib/A)

1960 1970 1980 1990 . 2000

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

Figure 2

N Fertilizer Use Efficiency for Corn

14 4
1.2
1.0
0.8
0.6

0.4 T T 7
1960 1970 1980 1990 2000

bu per Ib of nutrient

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


FERTILIZER N EFFICIENCY FOR CORN

Potash & Phosphate Institute
June 7, 1999

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

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.

Arecent 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 com-soybean rotation averaged in the middle of lowa State University’s
recommended use range. For continuous corn 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 less N credit for the manure than was recommended probably due to
uncertainty about the actual N content of the applied manure. Although, there is
still 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 Corm/com Corn/soybean Corn/com _Corn/soybean
Com yield, bu/A 142 143 131 142
N fertilizer use, Ib/A 121 119 135 129
ISU recom., Ib/A* 0-90 0-80 150-200 100-150

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


10

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 soil 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 all chlorophyit 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,
aeeeee 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 coutd 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”.

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 _20% 50%
1985 25 45
4980 60 140



13

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

T. Scott Murrell, Ph.D., Potash & Phosphate Institute
Preliminary Comments

The goal of theTopic 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 “Managing the
Time of Nitrogen Application”. The main points in both sections are summarized below.
Section 3.1.3

4. 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