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VI. Watershed, Regional, and Global Issues

VI. Watershed, Regional, and Global Issues

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curred in the winter for both agricultural land uses. Nitrate losses from southeastem U.S. agricultural watersheds tended to be greater than losses from forested

ones, whereas P loads were similar or slightly less than those coming from the agricultural watersheds (Lowrance et al., 1986). Kilmer et al. (1974) measured consistently higher N and P concentrations in discharge from a more heavily fertilized

watershed than one with lower fertilizer inputs. Hallberg et al. (1983) tracked increases in nitrate-N draining from an agricultural watershed in northeastern Iowa

as agricultural practices changed following the introduction of N fertilizer. However, Thomas and Crutchfield (1974) observed that the "background" nitrate levels from small Kentucky watersheds with crop, pasture, and forested land uses

were highly variable. A strong relationship existed between the geology of the watersheds and the P contents of the stream flow rather than the land use. Stream P

levels corresponded closely to those compiled 50 years earlier when few nutrient

inputs were available to agriculture.

The aerial extent of intensive agricultural operations has been related to nitrate

observed in groundwater (Beck et af., 1985; Pionke and Urban, 1985) and surface

water (Ritter, 1984). Patterns of elevated nitrate in a southwest Georgia study were

coincident with an area of intensive cropland (Beck et af., 1985). Nitrates in

groundwater in a Pennsylvania watershed were approximately four times greater

in wells under cropland than under forest (Pionke and Urban, 1985). The mixing

of recharge from the two areas diluted the nitrate concentration before the flow entered the surface water stream. Nitrate concentrations in drainage from watersheds

in Delaware with >60% cropland were more than 30% greater than those with

<60% cropland (Ritter, 1984). Klepper (1978) determined that both N fertilizer

use for corn and the fraction of watersheds in row crops (primarily corn and soybeans) were significant factors in explaining the variation in nitrate concentration

in surface waters from a central Illinois watershed.

The watershed studies suggest that making meaningful observations of nutrient

cycling in a sustainable agriculture at aggregated geographic scales is difficult.

Lowrance et af. (1986) suggest that watershed-level studies are essential in relating management to external environmental impacts. However, the relationships

may not be simple nor sufficiently sensitive for most decision making. Small plot

and field results do not seem to aggregate well to the higher levels of spatial resolution where the land use patterns are mixed and complex. Furthermore, there must

still be some connection between the activities and the responsibilities (for both

the farmer and the beneficiaries) before changes can be promoted. The appropriate level for observation and for responsibility remains a question. Background

concentrations and differential, as well as relatively slow nutrient transfer rates

may limit the usefulness of observations at the real or perceived scale of the problem. Perhaps an indicator at another level of resolution will be useful. The German guidelines for organic agriculture have selected the farm as the unit to limit

off-farm inputs of both fertilizers and feeds as a means to meet the expectations

they associate with organic agriculture (Nolte and Werner, 1994).




The introduction of clover in Europe during the 17th through 19th centuries

(Kjaergaard, 1995) is a historical illustration of the impact a change in the potential nutrient stocks can have on a region beyond the scale of an individual farm or

watershed. For example, the input of N to cultivated land doubled with the introduction of clover to Denmark during this period and an ecological dilemma of declining yields and degrading landscapes was averted. Grain yields doubled and cattle numbers increased by one-third in less than 35 years. Even the vast increase in

potato production has been linked to the newly available quantities of N. The new

clover-based system relied heavily on animals to utilize the legume forage crop

and provided an opportunity to retain P and K by marketing animal rather than

crop products. Individual cultivators influenced the flow by the allocation of land

resources to the N “collectors,” but it was the introduction of a production factor

from outside the original system that made the change feasible for the individual

to consider.

Nutrient balance information at other spatial scales, such as county, state, andor

country level, can be used to identify where clustering of nutrients may occur when

inputs exceed outputs and/or utilization potential, assess potential nutrient impact

on water resources, and provide a basis for future decision making (Barker and

Zublena, 1995). Almost 20% of North Carolina counties were found to have nutrients in excess of crop requirements with excess P more common (18% of the

state) than excess N (3% of the state) (Barker and Zublena, 1995). When Keeney

(1979) estimated the N budget for Wisconsin, he identified N fixation by legumes

and N fertilizer as significant sources of N for the state (54 and 22%, respectively). However, approximately 40% of the N inputs could not be accounted for and

were assumed to be lost to the environment through denitrification and leaching.

Based on estimates of total N use in all kinds of farming in The Netherlands and

the total removed from farms in produce, 75% of the N is wasted (Whitmore and

van Noordwijk, 1995). Granstedt (1995) estimated that 74,60, and 74% of the N,

P, and K, respectively, imported onto the farms in Sweden are not exported in food

products. Of the nutrients actually taken up by plants only 20,25, and 5% of the

N, P, and K, respectively, are actually exported from the farm to the community

food system. Isermann (1990) recognized that the surpluses of N and Pat the country level in Western Europe are due to increasing levels of nutrient application not

resulting in similar increases in nutrient exports in farm products.

1. Intercontinental Flows

Cooke (1989) highlighted the significance of intercontinental plant nutrient

transfers. Not only is there a concern for soil mining at the farm level, but these

concerns should be nationwide. The value of nutrients lost may not be offset by

the prices paid for the commodities. This transfer affects the countries producing



the commodities, which are often developing countries, and the countries importing the commodities. Furthermore, he estimated that developed countries import

12% more N and more than 60% more K than they export, whereas comparable

depletions exist in developing countries. Only in Pdo the developing countries appear to be gaining while the developed countries are losing. Nutrients in a single

animal feedstuff, casava, imported from Thailand to The Netherlands were equivalent to more than the K fertilizer used in The Netherlands; one-third of the P fertilizers used; and slightly less than 10% of the N fertilizers used. Of course, these

data do not represent the whole range of conditions from various countries. Symptoms of the importing countries may be excessive nutrient accumulation that will

have adverse environmental impacts. In 1983, 40, 72, and 59% of the total imported N, P, and K, respectively, to The Netherlands could be attributed to feedstuffs. Cooke (1989) suggested that all countries need to develop national nutrient

balances as policy guideposts for the future prosperity of their countries. Issues of

sustainability, especially the contribution of maintaining the integrity of the resource base, either from depletion or enrichment, to intergenerational equity

should be a major consideration. Part of the difficulty in implementing policies that

might be derived from such analyses is that the controllers of the nutrient flow may

not correspond with the authority of national jurisdictional boundaries and that future generations and other considerations are routinely underrepresented in the

evaluation of impacts of a wide array of decisions.

2. Finite Geologic Deposits

Although global reserves of P and K are large, the deposits will eventually be

exhausted. It is estimated that, at current rates of mining, the known global reserves

of phosphate and potash will last for approximately 200 years (Louis, 1993). Even

though there are larger “potential” reserves that may extend the time span for mining these nutrients, the rate of growth of demand for P and K may work to limit

the increase in time until deposits are exhausted. Regardless of the time until reserves are depleted, the extent of the potential supply must be compared to the ability of society to sustain the pattern of nutrient flow. Gains in efficiency of P and K

utilization may extend the life of the geological reserves, but if the connections in

the patterns of nutrient flows are not sustainable devoting management and other

resources to enhanced efficiency in order to prolong the reserves may contribute

little to true sustainability.



Patterns of nutrient flow depend on the energy contributed to the process from

a variety of sources. Energy use and flow is the central purpose of the food chain



as solar energy is captured in primary production and moves along to the succession of consumers. Ultimately, energy is dissipated as heat, becomes part of decomposer organisms, or remains in the undecomposed residues. Animals consume

solar energy that was recently concentrated by plants. In addition to relying on capturing current solar energy, agricultural production systems also utilize historic solar energy, recovered from geologic reserves, to create inputs. The inputs have a

variety of functions. These are generally recognized as substituting for labor, for

reducing the deficiency of production inputs such as crop nutrients or water, or creating conditions that could not otherwise exist. However, substituting animal power or machine inputs in corn production for human labor generally reduces the

amount of solar energy captured per unit of expended energy (Pimentel and

Burgess, 1980). Nitrogen fertilizer can eliminate a N deficiency and actually increase the potential for crop production, but its use also tends to decrease the energy captured per unit of expended energy.

Energy accounting can be used to identify the various forms and the amounts of

energy used in agricultural production. The accounting may be conducted for enterprises such as corn, tomatoes, alfalfa, or animal production. Nitrogen fertilizer

is typically a major energy input to cereal production such as corn. This one input

may account for 20% of the total energy in the production inputs and fuel can be

over 40% (Pimentel and Burgess, 1980). For legume crops such as alfalfa the total energy requirements can be approximately 60% of corn production (Heichel

and Martin, 1980).There are usually no N fertilizer inputs to an established stand,

and the fuel requirements for cultural practices become approximately 98% of the

total energy used. Animal agriculture benefits from the controlled environment

conditions provided by modern housing systems (Spedding, 1982). Energy inputs

to animal production vary widely with species and geographic location, but the ratio of energy inputs to outputs is generally much greater than for common crops

(e.g., <0.5 MJ MJ- for cereal crops and 2.8 and 10 MJ MJ-' for milk and broilers, respectively; Spedding, 1982).

Farms are rarely single enterprises and it is essential to evaluate energy consequences of the entire system instead of focusing only on one aspect such as nutrients. For example, changing crop sequences from continuous corn to corn-soybeans in a dairy farm simulation resulted in a more dramatic decrease in energy

requirements (36%decrease) than when a corn-alfalfa rotation was selected (Vinten-Johansen et ul., 1990.The greater reduction in N fertilizer requirement for the

corn-alfalfa rotation was partially offset by the greater requirement for fuel to

manage the forage crop.

The structure of contemporary agriculture has significant implications for the

energy requirements to sustain the connections among the various components. Pimentel(1980) estimated that farm input supplies travel an average of 650 km and

require 257 kcal kg-' for transport. With emerging regional and global markets

(Lanyon, 1995)since Pimentel's original calculation, the energy consumed for this




purpose is likely to have increased. A further link in nutrient flow that is seldom

considered is the energy requirements to “return” the nutrients to some former location. Identifying the relevant controls and the responsible parties is likely to be

an essential part of acting on an understanding of the role of nutrient cycling in a

sustainable agriculture. Thus, the ultimate energy concern regarding the nutrient

flow pattern may have less to do with farm practices that replace fertilizer inputs

than with the extent of the connections between sources of nutrients, production

of cash crops that are transferred to animal production locations, and even the

transfer of animal products to consumers. Another important issue is that the deposits of the two main types of fossil fuels used in production have different projected lifetimes. For example, the natural gas reserves to produce N fertilizer may

well outlast those for the liquid fuels that are the keystone of modern agriculture

and its associated transportation networks (Lanyon, 1995).

The significance of energy use in maintaining the pattern of nutrient flow can

be evaluated using several criteria. For instance, there are environmental consequences that develop as energy is depleted from reserves, as energy and mineral

extraction takes place, as nutrients are used with decreasing efficiency in crop production, or as nutrients accumulate in areas of animal concentration. Consideration of proposed changes will need to include these criteria and to develop relative

priorities for addressing them. Also, if energy scarcity is a concern, then evaluating both the relative magnitude of competing needs and the flexibility for change

may need to be considered. Production agriculture used <3% of the total U.S. energy consumption in the 1970s and was <20% of the energy in the food system

from field to table (Fluck and Baird, 1980).

Reforming the pattern of nutrient flow is likely to involve a reconsideration of

the strategic direction of agriculture. Thus, putting energy use into perspective

with the competing uses across the spectrum of energy uses in society may be a

first step. From this perspective will emerge a new set of questions and associated

technical challenges. Questions such as who decides the characteristics of the new

pattern of nutrient flow, who benefits from the new formulation, and who pays for

the new arrangement are likely to all become part of the debate.




Isermann ( 1 990) cites the long-term possibilities of balancing nutrient applications and use at the field and farm levels by reintegration of animal and crop production, improved animal feeding programs, modified animal housing to reduce

potential ammonia volatilization, increased emphasis on N and P recycling, and

even changes in human diets toward less animal protein. He projects a degree of

success in reducing emissions if these fundamental changes are implemented within 20-30 years. Kaffka and Koepf (1989) suggest that not just a site-adapted pro-



duction program but a mixed plant and animal husbandry are prerequisites for the

success of an approach to sustained production and balanced fertility. This view is

supported by Granstedt (1995) because he suggests that a good balance between

animal production and crop production at local, regional, and national levels is required to reduce the losses of nutrients from agriculture. He envisions that certain

regions of Sweden would emphasize animal production less and animal production would be decentralized in other areas in order to achieve ecologically based,

resource-conserving agriculture. He also believes nutrient balancing can be

achieved through cooperation among farmers with different enterprises and

through returning nutrients from the community to the farm. Stopes (1995) supports the notion of fundamental changes in the food production and delivery system and the human diet if widespread adoption of organic farming systems (as one

form of an agriculture presumably with nutrient cycles) is to become a reality.

There is tension apparent between the value of animal agriculture in conserving

nutrients on the farm and the perceptions that less animal production would be desirable.

Land application of human waste has been viewed as one mechanism to return

nutrients to farms. Witter and Lopez-Real (1 987) suggest that nutrients in sewage

sludge are only 3% of the fertilizer requirement in Britain, but that with increased

emphasis on reducing waste and emphasizing return flows 40% would be possible. The impact of industrial pollution of the waste stream and a variety of policies that keep fertilizer prices low and emphasize productivity will not encourage

“recycling.” Although between 40 and 60% of the N, P, and K of food products in

Sweden is in slaughterhouse and domestic wastes that could be recycled with little risk (Granstedt, 1995), it would require extensive change in the relations between agriculture and the rest of society.

Loehr ( 1969)recognized animal waste management as a “national” problem and

highlighted increasing reliance on readily digestible ration ingredients as a practice to reduce the costs of animal waste management. Increased digestion of nutrients supplied in the rations would reduce the quantity required for the same production. Cromwell et d.(1993) project considerable reductions in required P

supplementation of corn- and soybean-based rations with the use of an enzyme

that increases P availability from these sources. These approaches also are likely

to provide only incremental, short-term improvements. The challenge is to recognize that apparent farm-based solutions may not be that at all if they do not address

the appropriate scale of the problem, which is the transfer of nutrients between specialized farms with different ecosystem elements.

Increasing the efficiency of feed nutrient utilization through changes in the ration components or better balancing of rations has also been suggested. The effect

of livestock production on nutrient balance can be managed by exporting fewer

animal products (cutting production) or reducing losses of nutrients by on-farm

management practices. A biodynamic farm was found to be self-sufficient in nu-



trients because the livestock rate was adjusted to the carrying capacity of the farm

crop production (Granstedt, 1995). Organic farms in Germany cannot purchase

more than 10% of the feed for cattle (Nolte and Werner, 1994), and their production is, therefore, less than that of farms with unlimited potential to purchase feeds.

Sustainable livestock production is an issue of manure management, effects on soil

erosion and soil organic matter, and the export of nutrients in products sold (de Wit

et al., 1995). Postharvest and postplowing N losses have been suggested as a focus for reducing nitrate losses when legume crops are rotated to nonlegume crops

(Kopke, 1995). Other losses from manure application and manure “heaps” need to

be considered. Sustainability must be determined for various agroecological criteria in a system-specific analysis (de Wit et al., 1995).




There are controls on flow patterns that are exerted at different scales. In general, controls exerted at the regional, national, and global levels have ramifications

that influence the choices and decisions made at the farm level (Table IV). The

control that the farmer then exerts over the direction of the farm influences the

choices and decisions made regarding practices in particular fields.

One of the main factors influencing farm decisions affecting nutrient flows is

the perceived economic benefits of particular management options. The growth of

specific crops or raising of animals, the amount of purchased feed for animals vs

farm-grown feed, and the enterprise mix affects the farm nutrient balance. The use

of fertilizers at rates recommended by reputable soil testing laboratories is believed

to help ensure maximum profits from crop sales. Reliance on off-farm feeds frequently enhances the economic performance of an animal farm. In some circumstances, dairy operations may have greater net returns if off-farm feeds are purchased rather than if the dairy cows are fed only from on-farm sources (Westphal

et al., 1989). However, purchased feed arrangements potentially create a gap between the location of crop production and the location of animal production. Because cost is a major factor in purchased feed decisions, rather than the biology of

production, the least costly feed may come from widely dispersed sources. “Return’’ of nutrients to these locations is not considered as part of the cost when they

are purchased. Nor are the full costs of growing and transporting the crops necessarily paid for when feeds are purchased. A variety of government programs, actions, or subsidies commonly mask the true costs of water (as in California), of

transportation (such as the construction of the interstate highway system), or of

maintaining a low-cost energy supply (such as military expenditures to help maintain a flow of oil from the Middle Ease under favorable terms). Consequentially,

there is no economic incentive to maintain biological integrity in the transaction.

Profit maximization is not the only farmer goal influencing the pattern of nutri-



Table IV

Summary of Controls and Their Outcomes on Nutrient Cycling and Flows

at Different Geographic Resolutions


Regional. national,

and glohal


Political process, corporate

decision-making process,

geologic reserves of nutrients

and energy, transportation

and infrastructure

Government programs, international

trade patterns, externalization of

+ certain costs, corporate decisions

about where to locate facilities

and how to organize their

supply of agricultural products.

advertising, etc.



Farmer orientation (outlook).

Enterprise mix (types of crops and

economics (potential sale

animals raised), products exported

price - costs), consumer

+ off-farm, products imported,

preferences, agribusiness

animal density relative

infrastructure and preferences

to land area, etc.


and field

Amounts and forms of

nutrients added, method

and timing of nutrient

additions, tillage system and

surface residue status. types

of crops grown, portion of

crop removed, etc.

K- Soil structure, runoff and erosion,


nutrient stock levels, bioligical

diversity and activity, amount of

active SOM, amount of

total SOM, etc.

ent flow to and from a farm, especially on animal production farms. Although rates

of fertilizer application are likely to be reinforced by the economics of crop production (Legg et d.,

1989),sometimes N fertilizer use in addition to the available

N from legume residue and manure is thought to be a risk-reducing management

tactic for livestock farmers.

Farm-scale nutrient flows are influenced by other factors in addition to individual farmer goals such as profit maximization in crop production or intensive animal production, risk aversion, or some alternative ideology. Government programs

that create incentives for particular practices also influence farm-level nutrient

flows. Actions taken by large corporations to ensure their profits have transformed

the very nature and structure of agriculture. For example, the production of broilers in the United States is almost 100% controlled under production and marketing contracts, with a limited number of integrators or they are raised under integrated corporate ownership (Welsh, 1996).For the most part, the direction of the

hog industry is following poultry, with the decisions as to where animals are raised

and what they are fed coming increasingly under the control of a small number of




Although not shown in Table IV, there can be feedback mechanisms that move

from the field or farm scale upwards and may influence farmer as well as governmental decisions. For example, when soil structure declines, a farmer might

choose to change tillage, crop rotation, and /or the farm enterprise mix. Widespread problems with soil erosion and water pollution have also been recognized

nationally with the implementation of government-financed soil conservation programs aimed at decreasing soil and nutrient loss to water.

If changes in the pattern of nutrient flow are to be made to more closely approximate a cycle for a sustainable agriculture, consideration of the character of

the existing linkages and the incentives behind them will be essential. Nutrient cycling must become a priority in farmer decision making before it can play a significant role in farm performance. For instance, a nearly closed nutrient cycle is a

goal for individual farms in Germany for them to be recognized as organic (Nolte

and Werner, 1994).However, widespread adoption of such a goal cannot be based

solely on resources and personal perspective of individual farmers. It must be a

goal that is supported in the messages communicated to the farmer from the “surroundings.” Efforts to associate nutrient cycling with sustainable agriculture or

management of nutrient flow to meet any criteria other than those present in marketplace transactions will have marginal results unless they are strongly endorsed

outside the farm and then communicated to the farmer.




A sustainable agriculture is not simply an assemblage of numerous possible onfarm techniques, but one that will have to confront the realities of functioning within dynamic social and economic constraints on agricultural activities. The decisions to structure farms in particular ways are shifting from resource-based

constraints to emerging choices based on a variety of social factors. Stopes (1995)

suggests that a new orthodoxy of multiple goals for agriculture that are not limited to production but rather that include environmental and social outputs and a

greater degree of “sustainability” will emerge. Will mainstream society consider

the diversity of approaches that could be utilized to meet production, efficiency,

and consumption goals (Whitmore and van Noordwijk, 1995)?

Many changes in the way farms are managed and in the way society at large interacts with the agricultural sector have been suggested in order to enhance sustainability. A number of these approaches either directly involve nutrient flows and

cycles or have important implications for these flows. For the long-term sustainability of agriculture, ways need to be found to decrease the dependence on fossil



fuels to manufacture fertilizers or other amendments and to transport fertilizers

and feeds over long distances. With the fertilizer industry (especially N) so intimately tied to the price of energy, a sharp increase in the cost of fuel will make

agriculture especially vulnerable. Ways also need to be found to reduce nutrient

pollution of surface and groundwater. Enhanced efficiency of nutrient cycling and

uptake by plants can increase individual cash crop farm profitability by decreasing the amount of purchased inputs.

Finally, although there are large reserves of K- and P-bearing mineral deposits,

the pace of mining these nonrenewable deposits may increase, thus decreasing the

time needed to exhaust the deposits. This indicates that the nutrients should be used

carefully and efficiently.

Changes in agriculture and society that are related to nutrient flows and that

might promote a more sustainable system include those that can happen quickly

as well as those that will take longer to accomplish (Fig. 9). Some of these suggestions appear to hold more promise than others. In general, short-term changes

help to “tighten up” the efficiency of the use of nutrient sources and the cycling of

nutrients in the field setting. Those changes that might occur at the farm level will

take longer to put into effect but will have a more long-lasting impact. However,

farm-based changes may not turn out to be appropriate if the scale of the problem,

such as the transfer of nutrients between specialized farms, is not addressed. Fi-





8a 8b




4c 6 6





field season












Spatial Scale

Figure 9 Relationship between spatial scale of possible changes affecting nutrient flows and estimated time needed to complete changes (see text for explanation of numbers).

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