Best Management Practices for Agricultural Non-Point Sources of Pollution	Report Contents Report in Word Format
	Caribbean Environment Programme Technical Report #41 1998	All CEP Technical Reports

SECTION 4. BEST MANAGEMENT PRACTICES

4.1 Introduction

Agricultural best management practices (BMPs) are procedures and practices designed to reduce the level of pollutants in runoff from farming activities to an environmentally acceptable level, while simultaneously maintaining an economically viable farming operation for the grower (Bottcher et al., undated). This section discusses BMPs that can be used to control the categories of pollutants described in Section 3.3—sediment, nutrients, pesticides, pathogens, and solid waste.

The concept and use of BMPs are not new to the WCR. Indigenous farmers have traditionally used and still use an array of traditional slope, water, soil, pest, and vegetation management techniques, including composting, crop rotation, polycultures, agroforestry, and watershed management systems (Altieri, 1991). Several indigenous techniques are outlined in Table 4-1. Traditional subsistence and

 

Table 4-1. Some examples of traditional systems of soil management, vegetation, and water use by farmers

Environmental Limitation	Objective	Management Practices
Limited space	Maximize the use of available environmental resources and land	Multiple crops, agroforestry, family orchards, altitudinal zoning, land, rotation
Steep hillsides	Control erosion, conserve water	Terracing, contour strips, dead and living vegetative barriers, mulching, continuous living cover, fallow land
Marginal soil fertility	Sustain fertility and recycle organic material	Natural and improved fallow land, rotation, composting, green and organic fertilizers, pasturing in fallow fields or after harvest, use of alluvial sediments
Floods or excess water	Integrate irrigation and bodies of water	High-field crops
Scarce or unpredictable rain	Conserve water and optimize the use of available humidity	Use of drought-resistant crops, mulching, multiple crops, use of short cycle, etc.
Extremes of temperature and/or radiation	Improve microclimate	Reduction or increase of shade, pruning, spacing of crops, use of crops that tolerate shade, use of windbreaks, live fences, minimum cultivation, multiple crops, agroforestry, etc.
Incidence of blight	Protect crops, reduce pests	Overseeding, damage tolerance, use of resistant varieties, sewing in periods of low pest risk, management of habitat to increase natural enemies, use of repellant plants, etc.

Source: Altieri, M.A. 1988, cited in LACCDE, 1990.

small farm practices employ (1) the use of technology as well as a special spatial and social organization, (2) exact knowledge of resources, (3) adequate consumption, and (4) a nonantagonistic concept of the environment (LACCDE, 1990).

Source controls are often the most effective BMPs for reducing some types of pollution. Examples of source controls include the following:

• Reducing or eliminating the introduction of pollutants to a land area. An example is minimizing the application rates for chemical pesticides, herbicides, and fertilizers.

• Preventing potential pollutants from leaving a site during land-disturbing activities. Examples include conservation tillage and limited land clearing.

• Preventing interaction between precipitation and a potential pollutant. An example is timing chemical applications according to weather forecasts or seasonal weather patterns.

• Protecting riparian habitat and other sensitive areas. Examples include protection of shorelines and highly erosive slopes.

• Protecting natural hydrology. An example is proper water management (USEPA, 1993).

Effective control of nonpoint source pollution in agriculture should focus on controlling soil detachment and overland flow, with considerations for solutional transport and chemical drift. For pollutants that tend to bind to sediment, control of erosion and sediment transport off site can reduce not only impacts from increased sediment loading, but impacts from other pollutants as well due to the interactions of pesticides and nutrients with sediment (Ongley, 1996). The majority of the BMPs described in this document are related to soil conservation practices.

Erosion is not the only factor contributing to agricultural nonpoint source pollution. When a field is actively farmed with the same crop for a number of years, a depletion of nutrients in the soil occurs, requiring the addition of fertilizers to the soil. Loss of soil fertility can also be mitigated by shifting cultivation or crop practices. Shifting cultivation is often characterized by a season-to-season progression of different crops that vary in soil nutrient requirements and susceptibility to weeds and pests (Reijntjes et al., 1992).

The principles of soil and water conservation include increasing infiltration of water for plant use instead of surface runoff which can contribute to nonpoint source pollution. Farmers can reduce erosion, sedimentation, and nonpoint source pollution by 20 to 90 percent by using BMPs to control the volume and flow rate of runoff water, to keep the soil in place, and to reduce soil transport (USEPA, undated).

Best management practices can also encompass a revised approach to traditional agricultural practices. For instance, an effective pest control program might require the use of pesticides as a small component of a comprehensive pest management program. Practices such as crop rotation, proper site selection, proper fertilization, and good cultivation techniques promote a healthy crop and reduce pest infestation, thereby reducing the need for pesticide use. An integrated pest management program protects the environment, reduces pesticide and fertilizer inputs, and enhances economic gain.

The following sections describe structural and nonstructural BMPs that can be used to control agricultural nonpoint source pollution. They focus on pollution prevention, source reduction, and transport control. Although individual techniques are described, their use should be integrated into an agricultural nonpoint source control plan that is appropriate for local site conditions and cropping practices. Many of the methods described minimize or reduce more than one pollutant. The BMPs discussed in this document is not exhaustive and does not preclude any individual or group from using other practices. The selection of BMPs should be based on local cropping practices and site conditions. Table 4-2 provides general guidance on the applicability of the BMPs described based on certain variables. Table 6-1 (Section 6, Meeting Summary) outlines the pollutants, providing sources and various methods for control.

4.2 Nonstructural BMPS

Nonstructural BMPs are modifications in agricultural practices that do not require some type of construction. They focus on source reduction (pollution prevention) and programs and procedures for controlling agricultural nonpoint source pollution.

4.2.1 Education

Education needs to occur on a variety of levels. These include decision makers (elected officials, heads of agencies, and political appointees) who develop policy and regulations and their implementing measures, farm owners and farmworkers, and the general public. The importance of protecting natural resources and the impact of nonpoint source pollution on resource degradation need to be communicated effectively. People need to be educated on the importance of conserving soils and water and protecting sensitive marine ecosystems (coral reefs, sea grasses, bathing beaches, etc.). Linkages between healthy natural resources and a strong economy also need to be communicated. Information on the impacts of nonpoint source pollutants due to some farming practices on these resources needs to be conveyed at all levels. Availability of data, information, resources, technologies, and educational materials must be effectively communicated to the appropriate groups.

Public education and outreach activities and materials can take on a variety of forms, depending on the target audience. Decision makers need general information on the impacts of nonpoint source pollution, how nonpoint source pollution affects the environment, ways of controlling nonpoint source pollution, and how the adverse impacts of nonpoint source pollution affect the economy and aesthetics of the region. Farmers need detailed information on how to select and implement proper nonstructural and structural BMPs, operate and maintain structural BMPs, recognize the limitations of the land and obtain the maximum sustainable yield within those limitations, correctly apply fertilizers and pesticides, manage land properly, and develop and implement erosion and sediment control plans. The general public needs to understand the linkages between their actions, nonpoint source pollution, and degradation of the natural environment.

Education programs should be tailored to the specific needs of the community, the needs of the farmers, and the education level of the target audiences. An effective strategy for public education and outreach regarding agricultural nonpoint source pollution in the WCR should include the following, at a minimum:

 

Table 4-2. BMP acceptability

Acceptabilityd
Economic	Societal
Soil and plant analysis (N, S, P)	Moderatee	moderate	moderate	high
Use of proper fertilization techniques (N)	lowe	low	high	high
Planting ground covers (N, S, P)	Moderate	moderate	moderate	high
Buffer zones (N, S, P)	Moderate	moderate/high	moderate	low
Leguminous trees and plants (N)	Moderate	moderate	high	high
Water management (N, S, P)	lowe	low	low to moderate	low to moderate
Use of organic fertilizers (N)	Moderate	moderate	moderate	moderate
Good housekeeping practices (N, S, P)	lowe	low	high	high
Crop management (e.g., maintaining ground cover) (N, S, P)	Low	low	moderate to high	moderate to high
Vegetating drainage canal banks (N, S, P)	Moderate	moderate	high	low
Good record keeping (N, P)	lowe	low	high	moderate to low
Land use planning (N, S, P)	lowe	low	moderate to low	moderate to low
Animal placement - away from drainage ways (N, Pa)	Moderate	moderate	moderate	low
Proper animal waste handling (N, Pa)	Moderate	moderate	moderate	moderate
Controlled land clearing (S)	Low	low	high	moderate to low
Proper animal grazing practices (S)	Low	low	low	low
Conservation tillage (S)	Moderate	high	moderate	moderate

 

Table 4-2. (continued)

Acceptabilityd
Economic	Societal
Terracing (S)	High	high	moderate to low	moderate
Wind erosion controls (S)	Low	low	moderate	moderate to low
Sediment basins (S)	High	high	high	moderate
Use of organic trash fences (S)	Low	moderate	high	moderate
Diversions (S)	High	high	moderate to low	high
Grassed waterways (S)	Moderate	moderate	moderate	moderate
Contouring (S)	Moderate	high	moderate to high	high
Contour drains (S)	High	high	moderate to high	high
Integrated pest management (P)	Moderatee	moderate	moderate	moderate
Use of biodegradable pesticides (P)	Moderate	low	moderate	high
Reuse of rinse water (P)	lowe	low	moderate	moderate
Crop rotation (P)	Low	low	high	high
Mixed cropping (P)	Low	low	high	high
Use of resistant pesticide varieties (P)	low/moderate	low/moderate	moderate	high
Education of farm workers and farm management (N, S, P, Pa, Sw)	Moderatee	low/moderate	high	high
Pesticide rotation (P)	Low	low	high	moderate
Aerial buffer (no spray) zone (P)	Moderate	moderate	low	low
Proper manure application (Pa)	lowe	low	moderate	moderate

 

 

Table 4-2. (continued)

Acceptabilityd
Economic	Societal
Provision of alternate shade and water for livestock (Pa)	Low	moderate	high	high
Composting and proper disposal of dead livestock (Pa)	Low	low	moderate	moderate
Integrated waste management (Sw)	lowe	low	moderate	moderate
Landfilling waste (Sw)	Moderate	low	low	moderate
Trash catchment basins (Sw)	Moderate	low	moderate	moderate
Proper reuse of pesticide containers (Sw)	lowe	low	high	moderate
Plastics management (Sw)	lowe	low	high	high
River traps on small flow rivers (Sw)	High	high	low	moderate
Composting facilities (Sw)	moderatee	moderate	moderate	high

a N: applicable to nutrient control.

S: applicable to sediment control.

P: applicable to pesticide control.

Pa: applicable to pathogen control.

Sw: applicable to solid waste control.

b Low cost: no construction involved; can be implemented through minimal education (e.g., pamphlets, manuals, etc.).

Moderate cost: little or no construction involved; can be implemented through education programs such as agricultural extension services (public and private), outreach programs, seminars, on-site training, etc.

High cost: construction involved; requires development of plans and the input of BMP designers.

c Low: can be done with little or no change in existing infrastructure; some education may be required.

Moderate: some infrastructure changes may be required; education would be required.

High: infrastructure changes and training and education would be required.

d Low: not necessarily acceptable, primarily because of economic cost or lack of understanding of the benefits achieved by the BMP.

Moderate: generally acceptable but requires some education on the benefits.

High: acceptable.

e Can result in a cost savings for the farmer.

· Development of a commission or similar mechanism for coordinating educational policy for the region.

· Development of national plans and program strategies for education. Plans can include (but need not be limited to):

- Community education programs

- Field demonstrations and follow-up site visits

- School and community workshops

- Outreach and extension programs, including courses for farmworkers

- Use of media (TV, radio, videos, etc.)

- Required school environmental education curriculum

· Development of outreach materials such as fact sheets, guidance documents, and courses for decision makers, farmers, and the general public.

· Education of political and policy leaders in the WCR.

· Appointment of one responsible or lead coordinating agency (e.g., Ministry of Agriculture).

· Economic incentives for implementing education programs.

Accessibility of data and information to user groups.

Achieving the successful implementation of BMPs by farmers hinges on demonstrating to them that adopting such practices can save them money, resources, and time (J. Wright, Cooperative Extension Service, University of the Virgin Islands, personal communication, February 12, 1998). Education and outreach programs can focus on working with farmers to implement the BMPs described in this report.

4.2.2 Water Management

Water management practices reduce erosion and nutrient losses in runoff by minimizing or slowing water flow off fields. They also conserve water. Contour tillage, buffer strips, diversions, and terraces (see Section 4.3.1, Erosion and Sediment Controls) are a few methods to slow and trap nonpoint source pollutants. When water is slowed or stilled, sediments (and associated pollutants) can settle out of the water column, thereby inhibiting their entrance into the coastal waters.

Water management on farms involves two aspects. The first is managing the surface and ground water flow (hydrology) so as to maximize resource use and minimize environmental damage. The second is managing irrigation of crops.

Effectively controlling the flow of water over the land and in the ground, either from runoff or irrigation, reduces erosion potential and sediment transport off site. Management of water on the site is dictated by site characteristics such as soil type, crop or ground cover, topography, and climate. Designing the site so that unnecessary water flow is minimized (e.g., planting crops on the contour, locating infrastructure) can result in less erosion and maximum availability of water resources.

4.2.3 Land Use

Proper land use is an important concept when trying to control nonpoint source pollution. It addresses a variety of issues and concepts. Proper land use planning involves setting goals for the community or country, completing an inventory of existing land uses and natural resources (including agricultural soils), and designating areas suitable for various types of development (including agricultural development) or conservation. Once appropriate land use designations are categorized and mapped, regulations and policies regarding how the land uses are implemented can be developed. For example, areas on steep slopes may be appropriate for only minimal agricultural development and agricultural crops that do not require removal of all the natural vegetative cover. Areas with highly erodible soils should be cleared only as development is to occur (no clear-cutting). Crops should be chosen based on the natural resource limitations and assets of the land; for example, minimal soil preparation and chemical addition should have to occur to achieve a sustainable yield. Area that is prime for agriculture should be left for agricultural development, not residential or commercial development. This prevents forcing agriculture to less desirable locations where cultivation may result in environmental degradation (e.g., steep slopes). By systematically assessing resources, planning development and conservation activities, and managing agriculture in a sound manner, environmental degradation can be diminished.

4.2.4 Erosion and Sediment Control

Nonstructural erosion and sediment control (ESC) focuses on minimizing the amount of exposed soil and the time the soil is exposed. If crops or other ground cover is kept in place, the soil is less susceptible to erosion. Many of these practices are beneficial for controlling other pollutants as well. This is noted in the descriptions.

4.2.4.1 Erosion and Sediment Controls for Cultivated Crops

Conservation Cover/Stabilization Practices. Conservation cover/stabilization practices establish and maintain perennial vegetative cover to protect soil and water resources on land not currently in use for agricultural production (Ongley, 1996). This may be accomplished by preserving existing vegetation or revegetating disturbed soil. Vegetative cover reduces erosion potential by (1) shielding the soil surface from the impact of falling rain, (2) slowing runoff velocity and allowing sediment deposition, (3) physically holding soil in place with plant roots, and (4) increasing infiltration rates by improving the soil’s structure and porosity through the incorporation of roots and plant residues (USVI Conservation District, 1995). Long-term effects of the practice will reduce agricultural nonpoint sources of pollution to all water resources (USEPA, 1993). Areas where natural vegetation preservation is particularly beneficial are floodplains, wetlands, steep slopes, and other areas where erosion controls would be difficult to establish, install, or maintain. Conservation cover/stabilization practices are also suggested for use in drainage structures on agricultural lands where canals or ditches are used to remove excess water. The slopes and bottoms of the canals should be planted with suitable ground cover vegetation. This practice aids in preventing the erosion of ditches and canals and provides uptake for excess nutrients and pesticides that might otherwise run off.

Ground cover and crop residue can reduce erosion and yields of sediment and sediment-related water pollutants. Surface runoff temperatures to receiving waters may also be reduced. Effects will vary during the establishment period and could include increases in runoff, erosion, and sediment yield (USEPA, 1993).

Natural vegetation in a drainage ditch can prevent erosion and provide uptake for excess nutrients and pesticides.
(Click on image to see full photograph (2.7MB))

Conservation Tillage. Conservation tillage, including no-till and reduced tillage, is a planting system that maintains at least 30 percent of the soil surface covered by residue after planting. This practice reduces soil erosion, detachment, and sediment transport by providing soil cover during critical times in the cropping cycle (USEPA, 1993). It increases infiltration into ground water by reducing soil compaction from raindrops.

Reduced tillage consists of either minimizing tillage to a coarse, cloddy finish with machinery or hand tools (to improve infiltration and reduce erosion) or tillage in which only the rows are tilled or holes are dug for crops like banana (Gumbs, 1993). Reduced tillage systems incorporate some pesticides and fertilizers when applied to the soil surface, reducing the effects of runoff.

No-till is a conservation practice common in North America (Ongley, 1996). The no-till method consists of planting crops without prior seedbed preparation, into an existing cover crop, sod, or crop residues, and eliminating subsequent tilling operations (USEPA, 1994). No-till planting is the most effective conservation method to protect against soil erosion (York et al., 1993), but it can result in higher losses of nutrients and pesticides in surface runoff.

Although reduced tillage is practiced on steep slopes in the WCR, no-till is seldom practiced on slopes or flat terrain (Gumbs, 1993).

Cover Crop. A cover crop is a crop of close-growing grasses, legumes, or small grains grown primarily for seasonal protection and soil improvement. Usually, it is grown for one year or less (Ongley, 1996). Maintaining a cover crop prevents or reduces erosion and takes up nitrogen, preventing its undesired movement. In addition, a cover crop traps and recycles nutrients for use by later crops. A cover crop, planted between the rows of a cash crop, can also be used to outcompete weeds. Small-scale farmers can plant a cover crop that can be used for food or feed for animals. Furthermore, the overall volume of fertilizer application may decrease because the vegetation (if nitrogen-fixing) will supply nutrients (USEPA, 1993).

Buffer Zones. Vegetated buffer zones, either planted or natural, can prevent the movement of sediment, nutrients, and pesticides to receiving waters such as bays and streams. The vegetation acts tp slow surface water runoff, allowing sediment to drop out of suspension before entering receiving waters. Pollutants that are transported with sediment are also prevented from entering the receiving waters. Soluble nutrients and pesticides can also be taken up by plants in the buffer zone. Ideally, buffer zones should be areas adjacent to water bodies that are conserved when the land is initially developed for agricultural purposes. If this did not occur, buffer areas can be established by planting indigenous perennial plants along shorelines. There is no set formula for buffer zone width; the width is dependent on factors such as slope, soil, climate, vegetative cover (crops and buffer vegetation), and total drainage area. The buffer zone also protects stream banks from eroding and provides riparian habitat and a floodplain during times of high water flow.

Critical Area Planting. Critical area planting involves planting vegetation, such as trees, shrubs, vines, grasses, or legumes, on highly erodible or critically eroding areas (Ongley, 1996). It reduces soil erosion and sedimentation into surface waters. The plants may take up nutrients, reducing the amount washed into surface waters. During the initial stages of planting, large quantities of sediment and associated chemicals may be transported by runoff prior to plant establishment (USEPA, 1993).

Residue Use. Crop residues (such as leaves and remnant stalks) left or spread on cultivated fields protects soil during critical erosion periods (Ongley, 1996). Crop residues reduce erosion by intercepting rainfall, thereby decreasing soil dispersion and soil compaction. Microbial and bacterial action within the residue takes up nutrients and pesticides, delaying their entrance to surface waters.

Delayed Seedbed Preparation. All crop residue and naturally occurring vegetation can be maintained on the soil surface until shortly before the succeeding crop is planted. This reduces the period that the soil is exposed and susceptible to erosion (Ongley, 1996). Delayed seedbed preparation maintains vegetative cover as long as practical to minimize splash erosion and nonpoint source pollution during critical erosion periods such as the rainy season. Additionally, moisture is conserved, water quality improved, and soil infiltration increased.

Indigenous Weed Management. Indigenous weed management is the practice of allowing weeds to grow in fallowed fields, or intercropping or seeding them. Indigenous farmers have instinctively understood that weeds should be left to grow while crops are young. Weeds cover the soil, prevent it from heating up or drying out excessively, induce a positive competition that stimulates crop growth, and reduce erosion due to rainfall. As the crop matures and weed competition causes a negative impact, farmers hoe the weeds, leaving a protective mulch on the surface to recycle nutrients and naturally fertilize the crop. This natural fertilization is referred to as "green manuring." Compost, leaves, and grass may all be used for fertilization.

Mulching. Mulching is a temporary soil stabilization or erosion control practice in which materials such as cut grass, wood chips, wood fibers, or straw are placed on the soil surface to temporarily stabilize disturbed areas until a seeded crop or vegetation is established (USVI Conservation District, 1995). The benefits of mulching stem from reducing the direct impact of rain, maintaining maximum soil infiltration, and decreasing the quantity, velocity, and transport capacity of runoff water (Manrique, 1993). Mulching is also an effective water conservation tool. It provides added benefits to the crop by holding seeds, fertilizers, and topsoils in place; retaining moisture; and insulating seedlings against high temperatures. It is inexpensive and easy to implement. Mulching provides a method of weed control, and organic mulch is biodegradable. On steep or highly erodible slopes, mulch should be used with some type of anchoring system, such as netting.

Mulching is also an alternative to tilling or hoeing, which has been a common form of weed control. A typical practice is to slash the weeds three to four times a year, leaving a weed mulch on the surface to help avoid soil erosion and to delay weed growth (FAO, 1994). This practice, of course, does not eliminate weeds but inhibits weed growth while cultivated crops gain dominance.

Mulching materials can also be obtained from the crop itself. In banana production, common mulching materials are dead banana leaves, pruned suckers, and old stems (FAO, 1994). In the case of bananas, however, mulch should be used only in vacant rows. Mulch should not be allowed to come into contact with the banana stems since it can create moist conditions that can encourage the entry of banana weevils (FAO, 1994).

Although using mulch has many benefits, certain drawbacks do exist. Mulch can intercept light rains, which evaporate prior to reaching the crop roots. In addition, decaying mulch can immobilize fertilizers and reduce the availability of nutrients to plants.

Strip Cropping. Strip cropping is growing crops in a systematic arrangement of strips or bands across the general slope (not on the contour) to reduce water erosion. Crops are arranged so that a strip of grass or close-growing crop is alternated with a clean-tilled crop or fallow (Ongley, 1996). This method is mainly suited for gentle slopes and areas of lower rainfall (Sheng, 1988).

Conservation Cropping. Conservation cropping is a sequence of crop rotations designed to provide adequate organic residue for maintenance of soil tilth. This practice reduces erosion by increasing organic matter, resulting in a reduction of sediment and associated pollutants to surface waters (USEPA, 1993). It can also disrupt disease and insect and weed reproduction cycles, thereby reducing the need for pesticides. Legumes and grasses are the typical species planted in the rotation (Ongley, 1996).

4.2.4.2 Erosion and Sediment Controls for Livestock Areas

Deferred Grazing. Deferred grazing, also called rotational grazing, removes livestock from an area for a prescribed period of time. This practice reduces nutrient loads from manure and allows vegetation to recover for a period of time. This practice can also be used as a planned grazing system, in which two or more grazing units are alternately rested and grazed for a planned period of time (USEPA, 1993).

Heavy Use Area Protection. Heavy use areas can be protected by using any of three methods—establishing vegetative cover, surfacing the area with suitable materials, or installing structures (USEPA, 1993). This practice may result in a general improvement of surface water quality through the reduction of erosion and sedimentation. Heavy use areas include livestock feeding, shade, and watering areas; pathways leading to water bodies; and similar areas that livestock frequently use.

4.2.5 Pesticide/Nutrient Control

Most BMPs for pesticide and nutrient control are considered nonstructural. However, many of the structural BMPs outlined for erosion and sediment control can also reduce losses of pesticides and nutrients. With minimal effort, the probability of chemical accidents can also be drastically reduced. As with erosion and sediment control, the actual effectiveness of the following BMPs depends on site-specific variables such as soil type, crop rotation, topography, tillage, and harvesting method (USEPA, 1993), as well as education of the farmworkers.

Good Housekeeping Practices. "Good housekeeping" practices are one of the easiest BMPs to incorporate into an agricultural regime. The best way to avoid a problem is to prevent it at its source (USVI Conservation District, 1995). These practices include any preventive measures taken to reduce the possibility of accidental introduction of pesticides or fertilizers to the environment. A few simple steps can be taken to greatly reduce the potential of surface water contamination due to pesticides or nutrients.

• The area where chemical products are stored is a major source of risk: since mishandling of materials or accidental spills may occur in storage areas. Proper storage and handling of chemicals reduces safety hazards. To reduce the risks of misusing chemical pesticides or fertilizers, the materials should be handled as infrequently as possible and all handling or disposal instructions should be carefully followed. Pesticides and fertilizers should always be stored in a dry, covered area, and the recommended application rates and methods need to be followed.

• To reduce the risks of nutrient pollution, fertilizers should be applied only when needed, fertilizer applications should be limited to the necessary area and the minimum recommended amount, fertilizers should be worked into the soil to reduce nonpoint source pollution, seeding and fertilizing should be done in one application, and good erosion and sediment control practices should be implemented to help reduce the amount of sediment and fertilizers that leaves the site (USVI Conservation District, 1995).

• Just as pesticides differ in their effectiveness on a variety of pests, they also differ in their potential to contaminate surface water. Using the appropriate pesticide in a controlled manner with soil conservation practices reduces the likelihood of pesticides being carried into neighboring waterways. Pesticides and fertilizers should never be applied immediately prior to irrigation.

• Used pesticide containers should be disposed of properly.

In any location where intensive agriculture or livestock farming produces serious risks of nitrogen pollution, the following minimal steps should be taken at the farm level (Ongley, 1996):

• Rational nitrogen application. Overfertilization should be avoided.

• Vegetation cover. As discussed in Section 4.2.4, the maintenance of vegetative cover inhibits the build-up of soluble nitrogen by absorbing mineralized nitrogen and preventing leaching during periods of rain.

• Management of the area between crops. Organic debris produced by harvesting is easily mineralized into leachable nitrogen. Steps to reduce leachable nitrogen include planting of "green manure" crops and delaying the ploughing of straw, roots, and leaves into the soil.

• Rational irrigation. Poor irrigation has one of the worst impacts on water quality, whereas precision irrigation is one of the least polluting practices as well as a reducer of the net cost of supplied water.

• Optimization of other cultivation techniques. The highest yields with minimum water quality impacts require optimization of practices such as weed, pest, and disease control; liming; and fertilization.

• Agricultural planning. Erosion control techniques that complement topographic and soil conditions should be implemented.

• Proper record keeping. Accurate records of nutrients or pesticides used, when used, quantity used, and on which crop used should be maintained to establish patterns and needs of the crop being cultivated.

Plant and Soil Analysis. Plant and soil analysis is helpful in determining fertilizer and pesticide usage. It can help in the following ways:

• Nutrients. Soil and plant analyses are helpful in determining the types of fertilizers needed to produce a high yield of a crop with minimal environmental impacts. For example, if soil is tested for pH and the levels of phosphorus, potassium, and nitrogen, and the nutrient requirements of the plant are known (e.g., the plant is a high nitrogen-demanding plant), fertilizers can be applied to the area based on the deficiencies indicated from the soil test.

• Pesticides. Soil and site analyses are helpful in determining proper pesticide usage. Before pesticide use, certain characteristics of the soil should be determined. Locations of aquifers, drinking water wells, sinkholes, drainage wells, and other features that allow surface water and its contents to enter and contaminate the ground water should be identified. The runoff potential, which is increased by steep slopes and highly erodible soils, determines how fast pesticides that can be carried in runoff will leave the site. Pesticides should not be applied in areas directly adjacent to surface waters. A buffer between the site of application and the surface water body should be left untreated. Soils with low adsorptive capacity have a lower ability to bind applied pesticides and prevent them from running off or leaching into the ground water. Highly permeable soils tend to allow water (and, therefore, pesticides) to rapidly percolate through to the ground water.

Nutrient Management Plan. A nutrient management plan provides information to help control or reduce the amount of fertilizers used on a crop. The following practices, components, and sources of information should be considered in the development of such a plan (USEPA, 1993):

• Use of soil surveys and soil testing in determining soil productivity and identifying environmentally sensitive areas. Soil testing should include pH, phosphorus, potassium, and nitrogen data.

• Plant tissue testing.

• Use of proper timing, formulation, and application methods for nutrients that maximize plant utilization of nutrients and minimize loss to the environment, including split application and banding of the nutrients, use of nitrification inhibitors and slow-release fertilizers, and incorporation or injection of fertilizers, manures, and other organic sources.

• Use of cover crops.

• Use of buffer areas.

• Control of phosphorus losses from fields through a combination of erosion and sediment control measures.

Integrated Pest Management. Integrated pest management (IPM), a mixture of chemical and other nonpesticide methods to control pests, has been shown to reduce pesticide use (USEPA, 1994). It promotes the health of crops and animals by using natural and cultural control processes and methods. IPM emphasizes the following strategies (USEPA, 1993):

• Use of biological controls:

- Introduction and fostering of natural enemies

- Preservation of predator habitats

- Release of sterilized male insects

- Use of bait and trap crops

• Use of pheromones:

- For monitoring populations

- For mass trapping

- For disrupting mating or other behaviors of pests

- For attracting predators/parasites

• Use of crop rotation to reduce pest problems.

• Use of mixed cropping.

• Use of improved tillage practices.

• Destruction of pest breeding and refuge sites (which may result in loss of crop residue cover and an increased potential for erosion).

• Use of mechanical destruction of weed seed.

• Pest scouting and parasite/predator monitoring.

• Use of pest resistant crop strains.

• Pesticide application based on economic thresholds; i.e., applying pesticides when an economic threshold level has been reached as opposed to applying pesticides in anticipation of pest problems.

• Use of less environmentally persistent, toxic, and/or mobile pesticides.

• Use of timing of field operations (planting, cultivation, harvesting, irrigation) to minimize application and/or runoff of pesticides.

• Use of more efficient application methods (e.g., spot spraying as opposed to aerial spraying).

• Management of weed hosts.

IPM uses chemical pesticides only where and when the measures listed above fail to keep pests below damaging levels. It involves all stages of agricultural production from site selection to harvest.

A sound pesticide management program matches the pesticide with the pest. This involves proper identification of the pest and then selection of the pesticide, rate, and application method most effective for control (Yelverton, 1993). The need for pesticides, particularly herbicides, can be reduced through proper land preparation before planting. Removing problem weeds prior to planting reduces the need for large quantities of herbicides during the growing season.

IPM not only prevents environmental degradation but also may lead to economic gain for the farmer. Table 4-3 summarizes estimates of reductions in pesticide loss using various management practices and combinations of practices in cotton (North Carolina State University, 1984, cited in USEPA, 1993). Reductions in losses equate to reductions in amount used and therefore a cost-savings.

Proper Application of Nitrogen and Phosphorus. Surface application of nitrogen and phosphorus without incorporation into the soil is the least desirable method of applying fertilizer (Lilly, 1995). Due to the soil bonding properties of phosphorus, it should be incorporated into the soil by tilling, or a similar method, prior to planting. Phosphorus is stable once it is mixed into the soil. Nitrogen, however, is very mobile. Ideally, nitrogen should be applied frequently in small amounts tailored to the crop’s immediate needs (Lilly, 1995). For most crops, nitrogen may be applied in split applications that coincide with the uptake or growth pattern of the crop. A broadcast method of fertilizer (and pesticide) application should not be used when strong winds are present. Wind can cause drift from applicators and misplacement of materials.

 

Table 4-3. Estimates of potential reductions in field losses of pesticides for cotton compared to a conventionally or traditionally cropped field^a

Management Practices	Transport Route(s)	Range of Pesticide Loss Reduction (%)b
Optimal Application Techniquesc	All Routesd	40 to 80 A
Nonchemical Methods	All Routes
Scouting Economic Thresholds	All Routes	40 to 65 A 0 to 30 B
Crop Rotations	All Routes	0 to 20 B 0 to 30 B
Pest-Resistant Varieties	All Routes	0 to 60 A 0 to 30 B
Alternative Pesticides	All Routes	60 to 95 A 0 to 20 B

a The hypothetical traditionally cropped comparison field uses the following management system:

(1) conventional tillage without other soil and water conservation practices;

(2) aerial application of all pesticides with timing based only on field operation convenience;

(3) 10 insecticide treatments annually with a total application of 12 kg/ha based on a prescribed schedule;

(4) cotton grown in 3 out of 4 years; and

(5) long-season cotton varieties.

b Assumes field loss reductions are proportional to application rate reductions.

A = insecticides (toxaphene, methylparathion, synthetic pyrethroids).

B = herbicides (trifluralin, fluometron).

Ranges allow for variation in production region, climate, slope, and soils.

c Defined for cotton as ground application using optimal droplet or granular size ranges with spraying restricted to calm periods in late afternoon or at night when precipitation is not imminent.

d Particularly drift and volatilization.

Source: North Carolina State University, 1984, cited in USEPA, 1993.

Aerial Spray Zones. In some areas, pesticides are applied from airplanes flying low over crops and releasing pesticides. This allows for maximum coverage in minimum time. Care should be taken to minimize release of pesticides to surface waters by establishing aerial "buffer" zones where no spraying would occur within a certain distance of surface waters and populated areas. For example, in Costa Rica, no spray zones have been established within 15 metres of surface waters and 100 metres of populated areas. The limits of the zones can be established by something as simple as markers on poles and trees or something as sophisticated as geographic positioning systems (GPS).

Realistic Yield Goals. All fertilizer recommendations assume a certain yield goal for the crop to be grown. Nutrients should not be overapplied in the quest for an unrealistic yield (Lilly, 1995). Excessive applications or amounts of fertilizer waste money and contribute to water pollution.

Use of Natural Fertilizers. Manure and other waste or by-product materials can be used as natural fertilizers if applied correctly. This practice minimizes the need for chemical fertilizers. For example, farms that grow both sugar and coffee can use a mixture of coffee bean shells and animal manure (e.g., chicken manure) to make fertilizers. Although the natural fertilizer might need to be supplemented with chemical fertilizers, the amount of chemical fertilizer needed is reduced. This approach also helps address the issue of waste disposal from the coffee processing.

Leguminous Plants in Rotation. The planting of grasses and leguminous plants, either individually or together, reduces runoff and provides a source of organic nitrogen, thereby reducing fertilization needs. During the period of rotation when the grasses and legumes are growing, they will take up more phosphorus (USEPA, 1993). They also provide an opportunity for animal waste management because manures and other wastes may be applied for an extended period of time due to the nutrient uptake by the grass and legume species.

4.2.6 Pathogens

Because they are the primary agricultural source of pathogens, pathogen controls focus on livestock and manure management.

Proper Grazing Management. Proper grazing management includes determining the maximum number of animals per hectare based on the amount of manure that can be safely applied per hectare of land. For a sound grazing management system to function properly and to provide for a sustained level of productivity, the following should be considered (USEPA, 1993):

• Know the key factors of plant species management, plant growth habits, and their response to different seasons and degrees of use by various kinds and classes of livestock.

• Know the amount of plant residue or grazing height that should be left to protect grazing land soils from wind and water erosion, to provide for plant regrowth, and to provide the riparian vegetation height desired to trap sediment or other pollutants.

• Know the range site production capabilities and the pasture suitability so an initial stocking rate can be established.

• Know how to use livestock as a tool in range management to ensure the health and vigor of plants, soil tilth, proper nutrient cycling, erosion control, and riparian management, while at the same time meeting the nutritional requirements of the livestock.

• Establish grazing unit sizes, watering, shade, and feed locations to optimize livestock distribution and proper vegetation use.

• Provide for livestock herding to protect sensitive areas from excess use.

Livestock Exclusion. The exclusion of livestock from areas such as waterways and stream banks reduces the amount of sediment and manure that can enter surface waters. Livestock exclusion prevents livestock from entering a water body or walking down its banks, thereby preventing soil compaction and water quality problems due to manure deposition. Alternative shade and water sources should be provided for livestock.

Disposal of Dead Livestock. Dead livestock should be disposed of properly to reduce the potential for ground and surface water contamination from pathogens and nutrients. They should be removed from streams or fields and isolated until disposal is possible. Proper disposal methods include composting and incineration. The general composting guidelines described in Section 4.2.5 can be used when developing composting facilities for dead animals. Incineration facilities require more detailed planning and need to be developed under the consultation of local and national authorities to ensure proper construction, operation, and maintenance. When animals die from contagious diseases, special care should be taken, such as worker protection, quarantine, and similar measures, so as not to contaminate workers or other animals.

Establishing alternative feeding areas can protect sensitive areas (Photographed by Chris Zabawa, USEPA, Office of Water).
(Click on image to see full photograph (3.6 MB))

Manure Management. It is important to consider manure management and the potential for fly, odor, and water quality impacts when raising livestock. A complete manure management system involves collection, storage (temporary or long-term), and ultimate disposal or use (Graves, 1992). A manure management plan should establish fertilizer plans to use manure effectively (Ongley, 1996). Sometimes a small number of animals can cause more difficulties than a large herd, especially when animals are confined in buildings or on small lots (Graves, 1992).

Manure can be stored for later use as a fertilizer. Regular cleaning of a manure storage area reduces the opportunity for insect breeding and odor production. Storage areas should be designed and managed to exclude rodents and to keep rain and surface waters away from the manure (Graves, 1992).

Grazing animals distribute their manure throughout the pasture. Problems result, however, when too many animals exist in too small an area. Animals congregate along streams or watering areas and around feeding troughs and shady areas. Soil erosion and excess manure deposition are likely when the population levels are excessive. Reducing stocking density, moving feeding areas, and paving areas around waterers can reduce these problems (Graves, 1992). It might be necessary to develop alternative watering areas and erect fencing if a stream is present within the pasture.

Waste Utilization. Waste utilization is the practice of using agricultural waste on land in an environmentally acceptable manner while maintaining or improving soil and plant resources (USEPA, 1993). This waste can be in the form of manure or runoff water from agricultural lands. Waste utilization helps to reduce the transport of sediment and related pollutants to surface waters. Proper site selection, timing of application, and rate of application can reduce the potential for degradation of surface and ground water (USEPA, 1993). Additionally, waste utilization may cause microbial reactions in the soil that assist in controlling pesticides and other pollutants by keeping them in place.

4.2.7 Solid Waste

Managing solid waste is an issue of control. Solid waste management not only protects farmers and farmworkers from disease, rodents, and flies but also maintains an aesthetically pleasing environment.

Integrated Waste Management. Solid waste can be managed through an integrated waste management system composed of reducing, reusing, and recycling solid waste used or generated on site. This management system must be supervised, and responsibility for tasks must be assigned to individuals. In implementing an effective waste management plan, an agricultural facility must determine which items are not necessary, which can be reused (e.g., pesticide containers), and what can be recycled. Recycling can be accomplished in a variety of ways. For example, twine and banana bags from a banana plantation were recycled and fashioned into the footbridge below. Items that cannot be reused or recycled should be disposed of at a landfill or other appropriate alternative.

Composting. Organic waste from an agricultural production facility can be composted to be used as mulch or fertilizer. Composting is a controlled process of degrading organic matter by micro-organisms (USEPA, 1993). The organic waste (e.g., leaves, stumps, peels) can be stored in a large garbage can, a constructed structure, or a lined hole that remains dark and allows decomposition to occur. The storage structure should be secured to protect from rodents and odor. As the waste decomposes, it evolves into a humus-like substance that can be used as fertilizer or mulch. Little maintenance is needed, but lime might need to be added to the compost to reduce acidity prior to application on fields.

On one banana plantation, a footbridge was constructed from recycled plastics.
(Click on image to see full photograph (1.5 MB))

4.3 Structural BMPS

Structural BMPs are practices related to something constructed or built. There are a variety of structural BMPs and most require some level of routine maintenance to continue working effectively. The physical structures described in the following subsections are primarily concerned with changing slope characteristics to reduce the amount and velocity of runoff (Manrique, 1993). Slope management, based on a combination of simple and inexpensive cropping practices, can be highly effective in maintaining or improving crop productivity with minimal erosion risk (Manrique, 1993). Physical structures are also used to trap sediment and pollutants before they enter surface waters.

 

4.3.1 Erosion and Sediment Controls

The ability of a country to sustain its agricultural productivity is closely related to topsoil quality and depth, both of which are reduced by soil erosion (Hwang et al., 1994). The focus of any agricultural erosion and sediment control (ESC) plan should be to prevent erosion before it starts. Sediment controls are used to trap the sediment that erodes off the land. An effective ESC plan should minimize the amount of disturbed soil, slow runoff flowing across the site, remove sediment from runoff before it leaves the site, and plan soil disturbance for the dry season (USVI Conservation District, 1995). The BMPs employed must be site-specific to achieve desired effectiveness levels. The actual effectiveness of a BMP depends on site-specific variables such as soil type, crop rotation, topography, tillage, and harvesting method (USEPA, 1993). The following erosion and sediment control techniques also provide beneficial results in relation to nutrient, pesticide, and pathogen control. Combinations of these BMPs can be used to further ensure reductions in nonpoint source runoff of sediment, nutrients, pesticides, and pathogens.

4.3.1.1 Erosion Controls

Contour Farming. Contour farming is the use of ploughing, planting, and other management practices that are carried out along land contours (Ongley, 1996). It includes following established grades, terraces, or diversions. Contour farming reduces erosion and sediment production, which, in turn, reduces the transport of related pollutants to receiving water bodies.

The following is an example of contour planting. Every 10 meters, a farmer marks a contoured, baseline row across the field using an A-frame or an equivalently simple level. Parallel to this level baseline, the farmer then plants five parallel rows uphill and downhill. The short rows are re-leveled and fit into the remaining spaces. The farmer’s planting, cultivating, and hilling-up (sometimes 30 cm high) of each row forms many absorption ditches on the contour. Absorption ditches are expected to store the rain that falls between the rows. The contour planting and hilling-up practices can eliminate 80 to 90 percent of the erosion occurring, even on steep mountain soils. The effectiveness of the method depends on the soil’s infiltration rate; the intensity and duration of rainfall; the steepness and length of the slope; and the human factor, which includes the accuracy of layout and uniformity of height of the ridges (Aldedge, 1988). Contour planting has been successful in many Latin American and Caribbean countries, especially Guatemala, Saint Vincent, Barbados, Puerto Rico, and the Virgin Islands (Aldedge, 1988).

Contour farming of coffee reduces erosion and sediment production.
(Click on image to see full photograph (1.8MB))

Diversions. Diversions are channels constructed across the slope with a supporting ridge on the lower side. By controlling downslope runoff, erosion is reduced and the infiltration into the ground water is enhanced (Ongley, 1996). Maintaining drainage channels prevents or reduces erosion and takes up nutrients. Diversions are particularly effective in preventing sheet and rill erosion by reducing the length of the slope (USEPA, 1993). Figure 4-1 illustrates this concept.

Terracing. Terraces are constructed earthen embankments that retard runoff and reduce erosion by breaking the slope into numerous flat surfaces separated by slopes that are protected with permanent vegetation or are constructed from stone or other materials. Terracing is carried out on very steep slopes and on long, gentle slopes where terraces are very broad (Ongley, 1996). Terracing can actually increase the land area in production. On slopes of 30 degrees, bench terracing increases the productive land surface by 25 percent. Therefore, for every 4 hectares of bench terraces, a farmer gains a fifth hectare. Flatter slopes produce less of an increase in land area; inversely, steeper slopes provide more (Aldedge, 1988).

Figure 4-1. Diversion methods of erosion control (USEPA, 1993).
(Click on image to see full figure.)

Construction of bench terraces requires considerable labor, but maintenance is minimal. In Venezuela, terracing is accomplished by the "controlled-erosion" construction method—building strong rock walls along the contours of the slopes and allowing the normal actions of erosion and cultivation to level the surface (Williams and Walter, 1988) (Figure 4-2). An adequate terrace is exactly level along the front edge and the base of the slope. The cultivated bench must be inclined into the mountain enough to store rainfall (15 percent or more). Protection of the backslope is maintained by a rock wall or planting of perennial species (Aldedge, 1988). "Controlled-erosion" bench terraces are constructed by controlling the natural process of erosion. Rock retaining walls (no higher than 1 to 1.5 meters for gentle slopes, higher for steeper slopes), constructed along the contours of a slope at 10- to 40-meter intervals, provide a block to eroding material. Thereafter, erosion and downslope ploughing provide the fill behind the retaining wall (Williams and Walter, 1988). However, the process takes an extended period of time to evolve naturally and achieving level terraces is delayed indefinitely. The advantage to this form of terrace construction compared with conventional bench terracing is the reduction in the work required for moving soil and subsoil. In addition, it tends to provide cultivation surfaces that are relatively large and stable (Williams and Walter, 1988). In the Venezuela example (Figure 4-2), the rock for the retaining walls was obtained from the field. If rock were not immediately available, labor and transportation costs would be great. Level bench terracing has been successful in several Latin American and Caribbean countries (Aldedge, 1988).

Figure 4-2. Alternative slope patterns on controlled-erosion terraces in Venezuela (Williams and Wlater, 1988).
(Click on image to see full figure.)

Simple terracing systems such as intermittent terraces, convertible terraces, orchard terraces, and hillside ditches are alternatives to the more expensive bench terrace. Intermittent terraces are used for larger tree crops, while orchard terraces are narrower terraces built for a single tree or bush. The cost of these simple terracing systems is approximately one-fifth to one-third the cost of bench terraces, and their effectiveness appears reliable. Runoff studies in Jamaica have shown that hillside ditches with contour mounds or ridges reduce soil erosion by 80 percent in runoff plots under yam cultivation (Manrique, 1993). However, terraces can also have a detrimental effect on water quality if they concentrate and accelerate delivery of nutrients and pesticide pollutants to surface waters (USEPA, 1993).

Wind Erosion Control. Wind erosion controls reduce erosion and nutrient runoff due to wind transport of sediment by protecting crops against winds and stabilizing soil vulnerable to erosion. Common wind breaks include shrubs and trees planted in borders or along property boundaries. Once established, wind breaks become permanent and fruit crops such as bananas are most benefited due to reduced plant stress (Palada, 1992).

Fencing. Fencing encloses or divides an area of land with a suitable permanent structure that acts as a barrier to livestock. It can be built on the contour or up and down the slope. When built across the slope, fencing slows down runoff and causes deposition of coarser-grained materials, reducing the amount of sediment delivered downslope. Fencing can be placed to protect water bodies from livestock activity and, with the proper vegetation along the fencerow, serves as a trap to sediments and solid waste.

4.3.1.2 Sediment Controls

Field Borders. Field borders are strips of perennial herbaceous vegetation or shrubs established along the edges of fields. They slow runoff and trap coarser sediment. However, field borders are generally not effective for fine sediment and associated pollutants (Ongley, 1996). This method is mainly suited for gentle slopes and areas of lower rainfall (Sheng, 1988).

Field borders serve as "anchoring points" for contour rows, terraces, diversions, and contour strip cropping. By eliminating the practice of tilling and planting the ends up and down slopes, erosion from concentrated flow in furrows and long rows may be reduced (USEPA, 1993).

Filter Strips. Filter strips are areas of vegetation for removing sediment, organic matter, and other pollutants from runoff (USEPA, 1993). Like field borders (which are typically grasses), filter strips trap coarser-grained sediment and might not be effective on suspended fine-grained materials. Filter strips are most effective when downslope runoff flows across them as sheet flow, causing the deposition of sediment and polluted runoff.

Grassed Waterways. Grassed waterways, or swales, are natural or constructed channels that are vegetated, graded, and shaped so as to inhibit channel erosion. The vegetation also traps sediment that is washed in from adjacent fields (Ongley, 1996). Grassed waterways require little maintenance, but they must be graded so as to move the runoff off the site.

Sediment Basins. A sediment basin is constructed to remove and store sediment from runoff during rainfall events. Runoff flows to the basin and is held for a period of time, allowing the sediment to drop out of suspension. Sediment basins need to be cleaned out periodically to ensure proper functioning. Their effectiveness is affected by the length of the flow path of the runoff and, therefore, may be reduced when clays and steep slopes are present (J. Wright, Cooperative Extension Service, University of the Virgin Islands, personal communication, February 12, 1998).

As discussed previously, using erosion and sediment control BMPs may result in the control of nutrients and pesticides as well. Table 4-4 summarizes estimates of reductions in pesticide loss from cotton fields using various ESC practices and combinations of practices in cotton.

4.3.2 Pathogens

Management of animal wastes and dead animals can reduce leaching of nutrients, ammonia emission, and health risks due to contamination of surface and ground waters. A variety of measures, including those BMPs referenced in Sections 4.2 and 4.3.1 can be implemented to control animal wastes and contamination from dead animals in runoff.

Waste Storage Ponds. Waste storage ponds are impoundments designed and excavated for the temporary storage of animal or other agricultural waste. This practice reduces the direct delivery of polluted water, which includes any runoff from manure stacking areas, feedlots, and barnyards, to surface waters (USEPA, 1993).

 

 

Table 4-4. Estimates of potential reductions in field losses of pesticides for cotton compared to a conventionally or traditionally cropped field^a

Management Practices	Transport Route(s)	Range of Pesticide Loss Reduction (%)b
Terracing	SR and SL	0 to (20)c
Contouring	SR and SL	0 to (20)c
Reduced Tillage	SR and SL	-40 to +20 AB
Grassed Waterways	SR and SL	0 to 10 AB
Sediment Basins	SR	0 to 10 AB
Filter Strips	SR	0 to -10 A
Cover Crops	SR and SL	-20 to +10 B

SR = surface runoff.

SL = soil leaching.

a The hypothetical traditionally cropped comparison field uses the following management system:

(1) conventional tillage without other soil and water conservation practices;

(2) aerial application of all pesticides with timing based only on field operation convenience;

(3) 10 insecticide treatments annually with a total application of 12 kg/ha based on a prescribed schedule;

(4) cotton grown in 3 out of 4 years; and

(5) long-season cotton varieties.

b Assumes field loss reductions are proportional to application rate reductions.

A = insecticides (toxaphene, methylparathion, synthetic pyrethroids).

B = herbicides (trifluralin, fluometron).

Ranges allow for variation in production region, climate, slope, and soils.

c Refers to estimated increases in movement through soil profile.

Source: North Carolina State University, 1984, cited in USEPA, 1993.

Stream Crossing. A stream crossing is a stabilized area to provide access across a stream for livestock and farm machinery (USEPA, 1993). The purpose is to provide a controlled crossing or watering access point for livestock, thereby controlling bank and streambed erosion, reducing sedimentation, and enhancing water quality.

4.3.3 Solid Waste

Catchment Basins. A catchment basin is a BMP similar to a sediment basin. It traps waste prior to its entering a water body.

River Traps. River traps may also be used to inhibit the flow of solid waste off site, but they cannot be used in streams or rivers with a high velocity of flow. Catchment basins are also effective at preventing the transport of large amounts of organic waste off site.

Stream crossings provide livestock with an alternative access across a stream. (Photographed by Chris Zabawa, USEPA, Office of Water).
(Click on image to see full photograph (1MB))

4.3.4 Siting Structural BMPs

For structural BMPs to be effective in controlling nonpoint source pollution, they must be properly designed, sited, installed, and maintained. Proper design includes making sure the selected BMP will achieve the desired result (e.g., erosion protection). The BMP should be sited in the best location to achieve the maximum pollutant removal and installed in such a manner that it will function properly. If the intended purpose of the BMP is to trap sediment, it should be located in an area where sediment-laden runoff drains and before the runoff leaves the site. Maintenance is critical to BMP effectiveness. If structures are not maintained (e.g., kept free of trash and debris, moving parts kept operable), they will most certainly fail. Sediment needs to be removed from sediment basins and traps, "trash" fences need to be checked to make sure there are no breaks, and contoured areas need to be regraded from time to time.

4.4 Monitoring

Monitoring is defined as "the measurement of a pollutant or its effects on either man or marine resources for the purposes of assessing and controlling exposure to that pollutant" (UNEP, 1985, cited in Coté, 1988). Monitoring is necessary to determine whether the predicted benefits of treatment or other management instruments have occurred to assess the need for further treatment and management, and to provide a basis for new management strategies and instruments to reduce the impact of similar activities that might be proposed in the future (Coté, 1988).

It is important to know whether the BMPs used as part of an overall plan are effective in controlling nonpoint source pollution and in preventing environmental degradation. There are two general types of monitoring—water quality monitoring and program monitoring. Water quality monitoring looks at the levels of specific pollutants or contaminants in a water body and measures the change in pollutant level over time. Program monitoring provides an evaluation of the programs being implemented and allows an evaluation of the types of programs being used to control the impacts of agricultural nonpoint source pollution. Monitoring is done to evaluate the effectiveness of an overall program and to identify areas where improvement or changes are needed. Without monitoring, it is uncertain whether there is pollutant reduction or environmental benefit associated with a given effort.

For monitoring to be effective, a monitoring plan should be developed. The plan contains the goals and objectives for the monitoring program (e.g., to determine the extent to which nitrogen is being reduced in a bay, to determine whether countries are implementing agricultural nonpoint source pollution control education programs), procedures for carrying out the monitoring (e.g., frequency of data collection, methods used), data collection, data analysis, and program evaluation (e.g., whether there a is reduction in nitrogen in the bay, whether country X has developed and implemented an education program).

Water quality monitoring provides specific information on pollutants that are being reduced. Program monitoring (sometimes called technology monitoring) is based on the assumption that structural and nonstructural BMPs are effective at reducing nonpoint source pollutant loadings and that through their implementation, pollutant reduction does occur. For some countries and farm operations, it might be more practical to develop and implement a program monitoring plan. A program monitoring plan in conjunction with a biological monitoring program may also be a cost-effective approach to an evaluation program for BMPs.

Additional information on monitoring technologies and plan development can be obtained from local extension services and nongovernmental organizations. Appendix C contains additional resources that can be consulted.

4.5 Socioeconomic Factors and Implementation

In 1990, the Latin American and Caribbean Commission on Development and the Environment (LACCDE) formulated a strategy to increase productivity and to assess the present and potential environmental impact caused by particular agricultural practices. The strategy proposed adopting the following measures to reduce nonpoint source pollution:

• Prudent use of agrochemicals, assigning preference, for example, to such practices as integrated pest management and the use of organic fertilizers.

• Promotion of tillage techniques patterned on nature’s own methods, such as multicropping and agroforestry.

• Farm subsidy programs to restore watersheds and deteriorated ecosystems.

• Regulation of land use, promoting ecologically suitable crops congruent with land management planning.

• Soil conservation to control erosion produced by wind and water.

• Fixing of a fair price for irrigation water to avoid waste (LACCDE, 1990).

The introduction of a BMP program would be the first step toward achieving the goals of this strategy. To effectively incorporate the use of BMPs into the agricultural sector, however, three major questions need to be answered (Sheng, 1992):

• Which government agency or agencies should be responsible for enforcing or encouraging the use of BMPs?
• How can farmers be effectively motivated to participate in a BMP program?
• What necessary assistance should be given to farmers once they agree to use BMPs?

The need for each country to develop a national policy and a program of measures addressing agricultural nonpoint source pollution is evident. Once achieved, such policies and programs will address the questions listed above.

It is generally recognized that the greatest barriers to the widespread use of soil and water conservation measures in developing countries are socioeconomic. They include insecure tenure, high discount rates, the costs to the farmer of implementing the practices, and government policies that promote nonsustaining farming practices (Hwang et. al., 1994). Several barriers prevent the countries of the WCR from answering the questions above and implementing an effective BMP program. They include insufficient financial or physical resources to control nonpoint source pollution; inadequate institutions, such as laws and policies; and lack of recognition of land-based marine pollution, specifically nonpoint source pollution, as an environmental problem (Hoagland et al., 1995). Land tenure and educational issues also play a major role. Land tenure is an important issue when considering the effective implementation of a BMP program. Many farmers are tenants and have no vested interest in investing in long-term agricultural productivity (DeGeorges, 1990).

Few quantitative studies have been conducted of the relative cost-effectiveness of different erosion control techniques (Hwang et al., 1994) and BMPs in general. According to research conducted in Haiti, the implementation of BMPs may save farmers money (Section 5.4). Through education, the adoption of BMPs, even on tenant farms, might be perceived as more acceptable if an economic gain can be achieved. Furthermore, the study determined that successful adoption of soil conservation techniques and BMPs occurred voluntarily among tenant farmers only when the result increased economic gain, not because of soil conservation per se (White and Jickling, 1995).

Research conducted in two agricultural areas in Haiti found that the implementation of some common BMPs produced much greater economic returns to the farmer (White and Jickling, 1995). Researchers found that the addition of BMPs was beneficial, in terms of both land and labor investments (Table 4-5).

The success of the Haitian program was primarily due to the use of indigenous techniques and subsidies in the form of seed and saplings.

Table 4-5. Economic returns from soil conservation in Maissade, Haiti

Land Use Option	NPV/ha	Return to Labor	Benefit-Cost Ratio
Pure agriculture (no BMPs)	5656	6.1	2.5
Pure agriculture + contour, trash barrier	11,185 (98%)	16.9 (177%)	3.4
Pure agriculture + indigenous trash barrier, hedgerow	12,607 (123%)	22.3 (266%)	3.0

NPV = net present value.

Figures in parentheses indicate percent increase from the pure agriculture (no treatment) case.

Source: White and Jickling, 1995.

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Tables, Figures, Acronyms | SECTION 1. | SECTION 2. | SECTION 3. | SECTION 4. | SECTION 5. | SECTION 6. | SECTION 7. | GLOSSARY | REFERENCES CITED | APPENDIX A | APPENDIX B | APPENDIX C | APPENDIX D