Soil and Water Quality An Agenda for Agriculture (1993) / Chapter Skim
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2 Opportunities to Improve Soil and Water Quality
2 Opportunities to Improve Soil and Water Quality
Pages 35-106
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From page 35... ...
The loss of nitrates, phosphorus, pesticides, and salts from farming systems to surface water and groundwater has, in some ways, supplanted traditional concerns about soil degradation. Efforts to address this larger complex of resource problems have been hampered by concerns about trade-offs.
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From page 36... ...
Soil degradation directly and indirectly affects agricultural productivity and water quality. Increasing nutrient, pesticide, and irrigation use efficiencies addresses the input side of the equation.
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From page 38... ...
The quality of the soil and its management in large part determine whether THREE FUNCTIONS OF SOIL Soils are living systems that are vital for producing the food and fiber humans need and for maintaining the ecosystems on which all life ultimately depends. Soil directly and indirectly affects agricultural productivity, water quality, and the global climate through its function as a medium for plant growth, a regulator and partitioner of water flow, and an environmental buffer.
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From page 39... ...
Soil quality is, nevertheless, as fundamental as air and water quality to future environmental quality and ecological integrity. The threat posed by soil degradation needs to receive the same kind of attention given to air and water quality degradation by national, state, and local policymakers.
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From page 40... ...
and with the environment external to that ecosystem (particularly relative to air and water quality) " (Larson and Pierce, 1991:176~.
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From page 41... ...
The implications of this broader concept of soil on policy development become clearer if one examines in more detail the ways that soils affect agricultural productivity, water quality, and the global climate. Importance of Soil Quality Changes in agricultural productivity, water quality, and global climate are linked to soil quality through the chemical, physical, and biological processes that occur in soils.
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From page 42... ...
Conservation of soil productivity should remain an important long-term goal of national soil resource policy. The effect of soil degradation on agricultural productivity has been underestimated.
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From page 44... ...
Soil and water quality are inherently linked; conserving or enhancing SOIL QUALITY AFFECTS AGRICULTURAL PRODUCTIVITY 1 .0- l .
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From page 45... ...
Soil degradation from erosion leads directly to water quality degradation through the delivery of sediments and attached agricultural chemicals to surface waters. Clark and colleagues (1985)
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From page 46... ...
1 1 1 ~ ~ 1 ~ ~ Reduced moisture & rooting space reduces plant growth Reduced Reduced absorption of absorption of nitrogen & nitrogen & phosphorus by phosphorus by crop plants crop plants Reduced plant growth Increased delivery of nitrogen & phosphorus to surface water or groundwater Increased delivery of nitrogen & phosphorus to surface water or groundwater Reduced waste degradation Increased delivery of pesticides to surface water or groundwater FIGURE 2-1 Changes in soil quality affect water quality. pollutants from their farming systems.
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From page 47... ...
The direct and indirect effects of soil degradation on water quality and global climate change, may, in many circumstances, be more important than the effect of soil degradation on agricultural productivity. Erosion Control Alone Is Not Sufficient Soil management policies should explicitly address compaction, salinization, acidification, loss of biological activity, and soil pollution as well as erosion.
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From page 48... ...
No national estimates of the extent or severity of soil compaction or acidification exist, and researchers have made little attempt to estimate the loss of biological activity. Soil Degradation as an Environmental Problem Protecting soil quality, like protecting air and water quality, should be a fundamental goal of national environmental policy.
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From page 49... ...
Over time, changes in these soil quality indicators will provide the information needed to assess the effects of current farming systems and land use on soil quality, to develop new farming systems that improve soil quality, and to guide the development of national policies to protect soil and water quality. The Secretary of the U.S.
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From page 50... ...
Quantifiable estimates of soil degradation processes in addition to erosion are also needed to direct national soil management efforts comprehensively and to set priorities for soil management and conservation programs. Assess Currently Available Data The Resource Conservation Act appraisal process should assemble all currently available information to assess the current state of and trends in soil quality.
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From page 51... ...
Soil Management at the Farrn Level Public policies for soil management at the farm level have, to date, focused primarily on erosion control. The major thrust of programs such as Conservation Compliance, Sodbuster, and the Conservation Reserve Program has been to reduce erosion rates to the soil loss tolerance level or to adopt farming practices that result in a specified reduction in erosion rates.
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From page 52... ...
~: ~:~ In it: e~ ~ The :~+ ~ m~0 ~ A ~ ~t
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From page 53... ...
The effect of alternative management systems on soil quality indicators could be depicted in simple matrices, as could the significance of these effects on soil and water quality. Measures of soil attributes in the checklist of soil quality indicators should be added to routine soil test reports, and the significance of the measured levels of indicators should become part of the routine interpretations issued with soil test reports.
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From page 54... ...
Ignoring the differences in soil quality between and within fields leads to soil degradation and water pollution by agricultural activities. Promise of New Technology New technology can link digitized soil maps with the exact position of equipment in the field to tailor applications of agricultural chemicals to differences in soil quality (see, for example, Reichenberger and Russnogle [1989]
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From page 55... ...
Development and implementation of these technologies could lead to increases in the total efficiency and effectiveness of agricultural production. Widespread use of such technologies could also lead to the development of extremely accurate data bases that link actual production practices on croplands to their effects on productivity, soil degradation, and water pollution.
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From page 56... ...
-"L Detoxification Leaching, runoff, erosion, volatilization soil-crop system. Nitrogen and phosphorus can leave the soil-crop system in the harvested crop, or they can be lost through erosion, runoff, or leaching (Figure 2-2)
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From page 57... ...
Although the nature of the inputs and outputs vary among farming systems, regions, and fields, mass balances provide a conceptual framework that can be applied across a diversity of farming systems and geographic scales. Increased Input Efficiency Increasing the efficiency with which nutrients, pesticides, and irrigation water are used in farming systems should be a fundamental objective of policies to improve water quality.
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From page 58... ...
To date, the effects of most agricultural conservation programs on water quality have been to reduce erosion and runoff, thereby reducing the transport of nutrients, pesticides, salts, and trace elements to surface water. The nutrients and pesticides retained in the upper portion of the soil profile are subject to additional management efforts that can biologically or chemically reduce their concentrations through microbial degradation or chemical reactions or through subsequent uptake by crops.
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From page 59... ...
The nitrogen delivered in fertilizers, manures, rainfall, and irrigation water; the nitrogen mineralized from soil organic matter and crop residues; and the nitrogen fixed by legumes all contribute to the nitrogen budget of a particular agricultural field. Nitrogen in the form of ammonium ions and nitrate are of particular concern because they are very mobile forms of nitrogen and are most likely to be lost to the environment.
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From page 60... ...
(See Chapter 6 for a discussion of nitrogen mass balance estimates and the Appendix for a complete discussion of how these estimates were made.) In most regions and for the United States as a whole, the nitrogen applied in synthetic fertilizers is less than that harvested in crops.
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From page 61... ...
61 o o us cn o a)
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From page 62... ...
The magnitude of the unaccounted for nitrogen in estimated mass balances; however, indicates the underlying reason for the loss of nitrogen from crop production and illustrates the potential for improvements in nitrogen management. Farm-level nitrogen mass balances in many instances reinforce the picture that emerges from national- and regional-level estimates of nitrogen mass balances.
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From page 63... ...
More important, when livestock or legumes are an important part of the farm enterprise, nitrogen additions from these sources are a fixed part of the nitrogen budget for the enterprise, and adjustments in the total amount of nitrogen applied will likely be made by adjusting the amounts of synthetic fertilizers containing nitrogen that producers apply. Use of legumes and applications of manure may be needed to improve soil quality in addition to their value as sources of nitrogen.
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From page 64... ...
Producers must account for the nitrogen available from manure applications, legumes, soil organic matter, and other sources before recommendations for supplemental nitrogen applications can be made. The impor
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From page 65... ...
The nitrogen balances estimated in Table 2-1 reinforce the importance of accounting for all sources of nitrogen when making decisions about rates of nitrogen fertilization. The nitrogen that is recoverable in manure and legumes supplies roughly the same amount of nitrogen applied to crop fields in synthetic fertilizers containing nitrogen.
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From page 66... ...
If results of statewide surveys in Iowa are representative, more than one-half of the producers would benefit from taking even a conservative manure credit, since they now take no credits (Dully and Thompson, 1991; HalIberg et al., 1991; Padgitt, 1989~. Synchronizing Fertilizer Applications with Crop Needs Supplying the nitrogen needed for crop growth during the period when it is most needed can be an important way to improve nitrogen management.
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From page 67... ...
Applications of manures without incorporation in fall, winter, and spring can be a particularly important source of surface water pollution (University of Wisconsin-Extension and Wisconsin Department of Agriculture, Trade and Consumer Protection, 1989~. Data on the timing of nitrogen applications, however, suggest that preplan" applications are the rule, not the exception, for most major commodity crops (Table 2-3~.
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From page 68... ...
New and Improved Tools Current nitrogen management data suggest that substantial improvements in nitrogen management could be achieved through the more widespread use of current technology for setting yield goals, making and implementing fertilizer recommendations, and increasing postplanting nitrogen applications. Weather and crop yield variabilities, however, create uncertainties about a crop's nitrogen requirements and the amount of residual nitrogen available from the soil that makes refining nitrogen management difficult.
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From page 69... ...
Refining current crop response models to allow greater precision in estimates of optimal nitrogen application rates is an important way to improve nitrogen management. Improving Phosphorus Management Phosphorus, like nitrogen, is both an important plant nutrient and a serious pollutant when delivered to surface water.
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From page 70... ...
Soluble phosphorus is more readily available to stimulate eutrophication, but particulate phosphorus can be a long-term source of phosphorus once it is delivered to surface water (Gilliam et al., 1985; Sharpley and Menzel, 1987)
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From page 71... ...
About 1.6 million metric tons (1.8 million tons) -or 36 percent of total phosphorus inputs-can be accounted for in harvested crops and crop residues, leaving an unaccounted for balance of 2.9 million metric tons (3.1 million tons)
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From page 72... ...
72 cn o 5 U o V)
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From page 73... ...
Efficient management of phosphorus inputs to prevent the buildup of excess phosphorus levels in soil while providing adequate phosphorus for crop growth should be a fundamental part of programs to reduce phosphorus loadings to surface water. The level of phosphorus in surface soil is a critical factor that determines the phosphorus loads in runoff water and the relative proportions of phosphorus lost in solution and attached to soil particles.
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From page 74... ...
cited several studies reporting that increases in soybean or corn yields are small or nonexistent when phosphorus levels in soil are in the medium category (Grove et al., 1987; Hanway et al., 1962; Million et al., 1989; Obreza and Rhoads, 1988; Olson et al., 1962; Rehm, 1986; Rehm et al., 1981~. Phosphorus additions to soils that test high for phosphorus typically do not increase corn or soybean yields in the Corn Belt (Bharati et al., 1986; Hanway et al., 1962; Olson et al., 1962; Rehm, 1986~.
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From page 75... ...
Most states have soil testing procedures and facilities that could be used to establish threshold levels of phosphorus in soil beyond which no crop response would be expected. Application of phosphorus to soils that contain phosphorus in excess of threshold levels should be discouraged or disallowed in extreme cases in which phosphorus loadings are causing severe damage.
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From page 76... ...
These long-term studies suggest that soils with high phosphorus levels can be cropped for a decade or more without the amount of phosphorus in soil reaching a level at which fertilizer additions would result in a crop yield increase. Few comprehensive data are available on how often and how many producers currently use soil tests when deciding how much phosphorus to apply.
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From page 77... ...
The importance of manures as a source of nitrogen and phosphorus in crop production systems varies from region to region (Tables 2-1 and 24~. Nationally, nitrogen from manures supplies about 8 percent of the total nitrogen applied to croplands in synthetic fertilizers, legumes, crop residues, and manures but ranges from 3 to 26 percent among farm production regions.
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From page 78... ...
Losses of nitrogen and phosphorus from feedlots and barnyards can be great, and they can be an important source of water quality problems (Bouldin et al., 1984; Brown et al., 1989; Daniel et al., 1982; Pinkowski et al., 1985; University of Wisconsin-Extension and Wisconsin Department of Agriculture, Trade and Consumer Protection, 1989; U.S. Congress, Office of Technology Assessment, 1990~.
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From page 79... ...
In regions where phosphorus pollution of surface water and groundwater is not a problem, the benefits derived from using manures to enhance overall soil quality and as a primary source of nitrogen for plant growth may outweigh any potential negative effects associated with increased phosphorus levels in the soils. High Capital Costs Effective use of the nutrients in manures requires equipment for collection and application and facilities for storage.
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From page 80... ...
In regions or watersheds where manures supply a significant proportion of nitrogen and phosphorus to crop production, improved manure management to protect water quality should be emphasized. There are few comprehensive national data that can be used to judge how well producers currently manage manures.
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From page 81... ...
They recommended that management of the diet of dairy cattle, with this result in mind, should become an important component of nutrient management on dairy farms. Solutions to the problem of manure management in regions with large concentrations of livestock will require efforts on multiple fronts.
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From page 82... ...
Pesticides applied to cropping systems are volatilized and lost to the atmosphere, lost to surface water bodies in solution or attached to sediments, leached to groundwater, exported with harvested crops, immobilized in the soil, or degraded in soil or by plants. Pesticide properties, soil properties, site conditions, and management practices interact to determine the fate of a pesticide.
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From page 83... ...
Site-specific processes determine how that mass of pesticides that is not degraded or immobilized is partitioned among surface water, groundwater, and the atmosphere. The first step toward reducing the amount of pesticides eventually delivered to surface water, groundwater, or the atmosphere is to reduce the total mass of pesticides introduced into the environment in farming systems.
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From page 84... ...
Improved Pesticide Use Efficiency Aggressive efforts to adopt currently available technologies, systems, and practices to reduce the total mass of pesticides used should be pursued. Immediate gains in reducing the total mass of pesticides used in agricultural production systems can be achieved by using currently available improved pest management practices.
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From page 85... ...
. In 1976, cotton crops received 49 percent of the total mass of insecticides applied to major field crops.
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From page 86... ...
Design Better Pesticides The chemical and physical properties of pesticides have important effects on their ultimate fates when they are applied to farming systems. It is possible to design new pesticides that pose lower risks because they are, for example, less toxic, less likely to be lost to surface water or groundwater, or more effective at lower application rates.
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From page 87... ...
have recently developed a hierarchy of pesticide properties; it lists pesticides according to their surface loss and leaching potentials. These pesticide properties can be matched with soil ratings information available in soil surveys so that producers can select those pesticides with the lowest potential for loss to surface water or groundwater.
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From page 88... ...
In the San loaquin Valley, disposal of irrigation water has become a critical problem and the recent discoveries of selenium and other toxic trace elements in -irrigation drainage water has increased the difficulty in managing irrigation-induced soil and water quality problems (National Research Council, 1989b)
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From page 89... ...
A combination of carefully controlled, efficient irrigation with an appropriate match between the crop grown and water quality will minimize the amount of drainage water requiring disposal and, thereby, reduce the potential for water pollution and soil degradation (National Research Council, 1989b)
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From page 90... ...
It is impossible to be certain, however, that improved input management alone will be enough to meet water quality standards in all regions. Both technical and economic constraints have an impact on the degree to which input management, particularly for nitrogen, phosphorus, and pesticides, can be refined.
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From page 91... ...
There may be significant lag times between improvements in input management and changes in water quality. Phosphorus and pesticides in stream sediments, nitrates in surficial aquifers, and phosphorus or salts that have built up in soils, for example, will continue to contribute to water pollution for a period of time after input management is improved.
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From page 92... ...
Technologies that afford greater precision in managing inputs can help solve this problem, but input management alone may not be sufficient to prevent water pollution. Managing cropping systems through rotations, cover crops, and multiple crops may be needed to augment efforts to improve input management.
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From page 93... ...
The potential benefits of cover crop use in these regions, if technical obstacles can be overcome, are great. Research to develop innovative cropping systems to meet long-term soil and water quality goals is needed.
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From page 94... ...
Other observers anticipate improved informationgathering devices in the crop field that will interface with farm machinery capable of varying the application of inputs to achieve higher efficiency. These two approaches are not mutually exclusive and both are important for guiding efforts to improve the environmental perfor POTENTIA1 BENEFITS OF COVER CROPS Cover crops are legumes, grasses, cereals, or other crops that are added to crop rotations to protect the soil, reduce pest infestations, and improve water quality.
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From page 95... ...
Cover crops prevent water pollution by a combination of effects that have already been discussed. Reducing erosion and runoff also reduces the amount of sediment and agricultural chemicals that reach surface water.
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From page 96... ...
Erosion and runoff also deliver nutrients, pesticides, and salts to surface waters. Increased runoff volume and energy from croplands disrupt water flow regimes, increasing discharge peaks and stream channel erosion.
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From page 97... ...
Reducing erosion from croplands is a fundamental first step toward improving soil and water quality. However, managing the volume and energy of runoff water is
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From page 98... ...
Such field and landscape buffer zones hold great promise for improving water quality in agricultural watersheds. (See the section on field and landscape buffer zones later in this chapter and in Chapter 12.)
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From page 99... ...
Immediate gains in soil and water quality can be attained if producers adopt currently available conservation tillage and residue management systems. If producers incorporate such conservation systems into current farming systems, resistance to episodic events will increase and runoff energy and soil erosion will be reduced.
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From page 100... ...
A concentrated effort to increase the use of conservation tillage in watersheds where water quality degradation is greatest would lead to even greater benefits. Develop New Cropping Systems Most natural ecosystems resist erosion through biotic control over the abiotic environment (Bormann and Likens, 1979~.
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From page 101... ...
Immediate gains in preventing soil degradation and water pollution can be achieved by incorporating the probability of episodic events into the design of farming systems. Current computer simulation capacities and available climatic data could be used to analyze the probability of episodic events that would lead to damaging erosion or runoff events.
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From page 102... ...
events accounted for more than 50 percent of the total erosion. Thus, in most years, conservation systems designed for average annual soil loss would be overdesigned, yet during years with severe storms, the damage might be catastrophic.
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From page 103... ...
Managing the landscape by creating or restoring buffer zones is a promising way to increase the effectiveness and lower the cost of programs to protect soil and water quality.
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From page 105... ...
Research to develop design and management standards for field and landscape buffer zones should be accelerated. The use of field-scale buffer or filter strips can be useful for reducing runoff, and for trapping the sediments, nutrients, and pesticides that move in surface runoff from specific fields.
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From page 106... ...
The cost of replacing the water quality benefits of existing vegetation with efforts on the farm level to increase soil quality, input use efficiency, and resistance to erosion may be high. Balance Needed The creation of field or landscape buffer zones should augment efforts to improve farming systems.
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