Managing Water
Managing Water
Irrigation
and Drainage
Deficits and excesses of
water are the various significant yield-limiting factors to crop production worldwide.
It is estimated that more than half of the global food supply depends on some
type of water management. In fact, the first major civilizations and population
centers emerged when farmers started to control water, resulting in more
consistent yields and stable food supplies. Examples include Mesopotamia—literally
the “land between the rivers” (the Tigris and Euphrates), the lower Nile
Valley, and China. High yields in drained and irrigated areas allowed for the
development of trade specialization, because no longer did everyone need to
provide their own food supply. This led to important innovations like markets,
writing, and the wheel. Moreover, new water management schemes forced
societies to get organized, work together on irrigation and drainage schemes,
and develop laws on water allocations. But water management
failures were also responsible for the
collapse of societies. Notably, the salinization of irrigated lands in
Mesopotamia and filling up of ditches with sediments— cleaned out by enslaved
Israelites among others—resulted in lost land fertility and an inability to
sustain large centrally governed civilizations.
Today, many of
the most productive agricultural areas depend on some type of water management.
In the United States, average crop yields of irrigated farms are greater than
some corresponding yields of dryland farms by 118% for wheat and 30% for corn.
At a global scale, irrigation is used on 18% of the cultivated areas, but those
lands account for 40% of the world’s food production. The great majority of
agricultural lands in the western U.S. and other dry climates around
the world would not be
productive without irrigation water, and the majority of the U.S. horticultural
crop
acreage—especially in
California—is entirely dependent on elaborate irrigation infrastructures. Even
in humid regions, most high-value crops are grown with irrigation during dry
spells to insure merchandise quality and steady supplies for market outlets, in part
because the soils have become less dehydration resistant from intensive use.
To address
excess water problems, the best fields in the U.S. corn belt have had drainage
systems installed, which made those soils even more productive than they were
naturally. Drainage of wet fields allows for a longer growing season because
farmers can get onto those
fields earlier in the spring
and harvest later in the fall without causing extreme compaction.
The benefits of irrigation
and drainage are thus obvious. They are critical to food security as well as to
the agricultural intensification needed to protect natural areas. Concerns with
climate change, which is resulting in greater occurrences of deficits and
excesses of precipitation, will increase pressure for more irrigation and
drainage. But they also exact a price on the environment. Drainage systems
provide hydrological shortcuts and are responsible for increased chemical
losses to water resources. Some irrigation systems have resulted in drastic
changes in river and estuarine ecosystems, as well as land degradation through
salinization and sodium buildup, and have been sources of international
conflict. In the case of the Aral Sea—formerly the fourth largest inland
freshwater body in the world—the diversion of rivers to use for irrigated
cotton farming in the former USSR resulted in a 50% decrease in the area
of the sea. It also became
severely contaminated with drainage water from agricultural fields.
Irrigation
There are several different
types of irrigation systems, depending on water source, size of the system, and
water application method. Three main water sources exist: surface water,
groundwater, and recycled
wastewater. Irrigation
systems run from small on-farm arrangements—using a local water supply—to vast
regional schemes that involve thousands of farms and are controlled by
governmental authorities. Water application methods include conventional
flood, or furrow, irrigation—which depends on gravity flow—and pumped water for
sprinkler and drip irrigation systems.
Surface Water
Sources
Streams, rivers, and
lakes have traditionally been the main source of irrigation supplies.
Historical efforts involved the diversion of river waters and then the
development of storage ponds. Small-scale systems—like those used by the
Anazasi in the southwestern U.S. and the Nabateans in what is now Jordan—involved
cisterns that were filled by small stream diversions
Small-scale irrigation systems nowadays tend
to pump water directly out of streams or farm
ponds. These water sources are generally sufficient for cases in
which supplemental irrigation is used—in humid regions where rain and
snowmelt supply most of the crop water needs but limited amounts of additional
rainwaterater may be needed for good yields or high-quality crops. Such systems,
generally managed by a single farm, have limited environmental impacts. Most
states require permits for such water diversions to ensure against excessive
impacts on local water resources.
Large-scale
irrigation schemes have been developed around the world with strong involvement of state
and federal governments. The U.S. government invested $3 billion to create the
intricate Central Valley project in California that has provided a hundredfold
return on
investment. The Imperial Irrigation District, located in the dry desert of
Southern California, was developed in the 1940s with the diversion of water
from the Colorado River. Even today, large-scale irrigation systems, like the
GAP project in southeastern Turkey is being admitted. Such
projects often drive major economic development efforts in the region and
function as a major source for national or inter-national food or fiber
production. On the other hand, large dams also frequently have detrimental
effects of displacing people and flooding productive cropland or important wetlands
Groundwater
When good
aquifers are present, groundwater is a relatively inexpensive source of
irrigation water. A significant advantage is that it can be pumped locally and
does not require large government-sponsored investments in dams and canals. It
also has less impact on regional hydrology and ecosystems, although pumping
water from deep aquifers requires energy. Center-pivot overhead sprinklers
(figure 17.3, right) are often used, and individual systems, irrigating from
120 to 500 acres, typically draw from their own well. A good source of
groundwater is critical for the success of such systems, and low salt levels are
especially critical to prevent
the buildup of soil salinity. Most of the western U.S. Great Plains—much
of it part of the former Dust Bowl
area—uses
center-pivot irrigation systems supported by the large (174,000-square-mile)
Ogallala aquifer, which is a relatively shallow and accessible water source. It is, however, being used faster than it is recharging
from rainfall—clearly an unsustainable practice. Deeper wells that require
more energy—plus, more expensive energy—to pump water will make this mining of
water an increasingly questionable practice.
Recycled
Wastewater
In recent years, water scarcity has forced
governments and farmers to look for alternative sources of irrigation water.
Since agricultural water does not require the
same quality as
drinking water, recycled wastewater is a good alternative. It is being used in
regions where (1) densely populated areas generate significant quantities of
wastewater and are close to irrigation districts, and (2) surface or
groundwater sources are very limited or need to be transported over long
distances. Several irrigation districts in the U.S. are working with
municipalities to provide safe recycled wastewater, although some concerns
still exist about long-term effects. Other nations with advanced agriculture
and critical water shortages—notably Israel and Australia—have also implemented
wastewater recycling systems for irrigation purposes
Irrigation
Methods
Flood, or furrow, irrigation
is
the historical approach and remains widely used around the world. It
basically involves the simple flooding of a field for a limited amount of time,
allowing the water to infiltrate. If the field has been shaped into ridges and
furrows, the water is applied through the furrows and infiltrates down and
laterally into the ridges. Such systems mainly use gravity flow
and require nearly flat fields. These systems are by far the cheapest to
install and use, but their water application rates are very inexact and typically
uneven. Also, these systems are most associated with salinization concerns, as
they can easily raise groundwater tables. Flood irrigation is also used in rice
production systems in which dikes are used to keep the water ponded.
Sprinkler irrigation systems
apply
water
through pressurized sprinkler heads and require conduits (pipes) and
pumps. Common systems include stationary sprinklers on risers and traveling overhead sprinklers (center-pivot and lateral; ). These systems allow for more precise water application rates than
flooding systems and more efficient water use. But they require larger up-front
investments and pumps use energy. Large, traveling gun sprayers can
efficiently apply water to large areas and are also used to apply liquid
manure.
Localized irrigation—especially
useful for tree crops—can often be accomplished using small sprinklers
) that are connected using
small-diameter “spaghetti tubing” and relatively small pumps, making the system
comparatively inexpensive.
Drip, or trickle, irrigation
systems also
use
flexible or spaghetti tubing combined with small emitters. They are
mostly used in bedded or tree crops using a line source with many regularly
spaced emitters or applied directly near the plant through a point-source
emitter. The main advantage of drip irrigation is the
parsimonious use of water and the high level of control
Drip irrigation systems are relatively
inexpensive, can be installed easily, use low pressure, and have low energy
consumption. In small-scale systems like market gardens, pressure may be
applied through a gravity hydraulic head from a water container on the small
platform. Subsurface drip irrigation systems, in which the lines and emitters
are semi-permanently buried to allow field operations, are now also coming into
use. Such systems require attention to the placement of the tubing and
emitters; they need to be close to the plant roots, as lateral water flow from
the trickle line through the soil is limited.
Manual
irrigation involves
watering cans, buckets, garden hoses, inverted soda bottles, etc. Although it
doesn’t fit with large-scale agriculture, it is still widely used in gardens
and small-scale agriculture in underdeveloped countries.
Fertigation is an efficient method to
apply fertilizer to plants through pumped systems like sprinkler and drip
irrigation. The fertilizer source is mixed with the irrigation water to provide
low doses of liquid fertilizer that are readily absorbed by the crop. This also
allows for “spoon-feeding” of fertilizer to the crop through multiple small
applications, which would otherwise be a logistical challenge.
Environmental
Concerns and Management Practices
Irrigation has numerous advantages, but
significant concerns exist as well. The main threat to soil health in dry
regions is the accumulation of salts—and in some cases also sodium. As salt
accumulation increases in the soil, crops have more difficulty getting the
water that’s there. When sodium accumulates, aggregates break down and soils
become dense and impossible to work. Aloft the centuries, many
irrigated areas have been abandoned due to salt accumulation, and it is still a
major threat in several areas in the U.S. and elsewhere.
Salinization is the result of the evaporation of irrigation water, which leaves
salts behind. It
is especially prevalent with
flood irrigation systems, which tend to over-apply water and can raise saline
groundwater tables. Once the water table gets close to the surface, the capillary
water movement transports soil water to the surface, where it evaporates and
leaves salts behind. When improperly managed, this can render soils
unproductive within a matter of years. Salt accumulation can also occur with
other irrigation practices—even with drip systems, especially when the climate
is so dry that leaching of salts does not occur through natural precipitation.
The removal of salts is difficult, especially
when
lower soil horizons are also saline.
Irrigation systems in arid regions should be designed to supply water and also to remove
water—implying that irrigation should be combined with drainage. This may seem
paradoxical, but salts need to be removed by application of additional water to
dissolve the salts, leach them out of the soil, and subsequently remove the
leachate through drains or ditches, where the drain water may still create
concerns for downstream areas due to its high salt content. One of the
long-term success stories of irrigated agriculture— the lower Nile Valley—provided
irrigation during the river’s flood stage in the fall and natural drainage
after it subsided to lower levels in the winter and spring. In
some cases, deep-rooted trees are used to
lower regional water tables, which is the approach used in the highly salinized
plains of the Murray Darling Basin in south-eastern Australia. Several
large-scale irrigation projects around the world were designed only for the
water supply component and funds were not allocated for drainage systems,
ultimately causing salinization.
The removal of
sodium can be accomplished by exchange with calcium on the soil exchange
complex, which is typically done through the application of gyp-sum. In general,
salinity and sodicity are best prevented through good water management.
Salt
accumulation is generally not an issue in humid regions, but over-irrigation
raises concerns about nutrient and pesticide leaching losses in these areas.
High
application rates and
amounts can push nitrates and pesticides past the root zone and increase
groundwater contamination. Soil saturation from high application rates can also
generate denitrification losses.
A bigger issue with
irrigation, especially at regional and global scales, is the high water
consumption levels and competing interests. Agriculture consumes approximately
70% of the global water withdrawals. Humans use less than a gallon of water per
day for direct consumption, but about 150 gallons are needed to produce a
pound of wheat and 1,800 gallons are needed for a pound of beef. According to the U.S. Geological Survey, 68% of high-quality groundwater
withdrawals in the U.S. are used for irrigation. Is this sustainable? The
famous Ogallala aquifer mostly holds “ancient” water that accumulated during
previous wetter climates. As mentioned above, withdrawals are currently larger
than the recharge rates, and this limited resource is therefore slowly being
mined.
Several large
irrigation systems affect international relations. The high withdrawal rates
from the Colorado River diminish it to a trickle by the time it reaches the
U.S.-Mexico border and the estuary in the Gulf
of California. Similarly,
Turkey’s decision to promote agricultural development through the diversion of
Euphrates waters has created tensions with the downstream countries, Syria and
Iraq.
Irrigation
Management at the Farm Level
Sustainable irrigation
management and prevention of salt and sodium accumulation require solid
planning, appropriate equipment, and monitoring. A first action is to build the
soil so it optimizes water use by the crop. As we discussed in chapters 5 and
6, soils that are low in organic matter and high in sodium have low
infiltration capacities due to surface sealing and crusting from low aggregate
stability. Overhead irrigation systems often apply water as “hard rain,”
creating further problems with surface sealing and crusting
Healthy soils
have more water supply capacity than soils that are compacted and depleted of
organic matter. It is estimated that for every 1% loss in organic matter
content in the surface foot, soil can hold 16,500 gallons less of
plant-available water per acre. Additionally, surface compaction creates lower
root health and density, and hard subsoils limit rooting volume. These
processes are captured by the concept of the optimum water range—which
we discussed in chapter 6—where the combination of compaction and lower
plant-available water retention capacity limits the soil water range for
healthy plant growth. Such soils, therefore, have less efficient crop water use
and require additional applications of irrigation water. In fact, it is
believed that many farms in humid climates have started to use supplemental
irrigation because their soils have become compacted and depleted of organic
matter. As we discussed before, poor soil management is often compensated for
by increased inputs.
Reducing
tillage, adding organic amendments, preventing compaction, and using perennial
crops in rotations can increase water storage.
A long-term experiment showed that reducing tillage and using crop rotations
increased plant-available water capacity in the surface horizon by up to 34 %. When combining organic matter, consider stable sources that are
mostly composed of “very dead” materials such as com-posts. They are more
persistent in soil and are a primary contributor to soil water retention. But
don’t forget fresh residues (the “dead”) that help form new and stable
aggregates. Increasing rooting depth greatly increases plant water availability
by extending the volume of soil available for roots to explore. When distinct
plow pans are present, ripping through them makes subsoil water accessible to
roots. Practices like zone tillage increase rooting depth and also result in
long-term increases in organic matter and water storage capacity.
These practices
have the most significant impact in humid regions where supplemental irrigation
is used to reduce drought stress during dry periods between.
rainfall events. Building a healthier soil
will reduce irrigation needs and conserve water because increased plant water
availability extends the time until the onset of drought stress and greatly
reduces the probability of stress. For example, let’s assume that a degraded
soil with a plow pan (A) can provide adequate water to a crop for 8 days
without irrigation, and healthy soil with deep rooting (B) allows for 12
days. A 12-day continuous drought, however, is much less likely. Based on
climate data for the northeastern U.S., the probability of such an event in the
month of July is 1 in 100 (1%), while the probability for an 8-day dry period
is 1 in 20 (5%). The crops growing on soil A would run out of water and suffer
stress in July in 5% of years, while the crops on soil B would be stressed in
only 1% of years. A healthy soil would reduce or eliminate the need for
irrigation in many cases.
Increasing surface cover—especially with heavy mulch—significantly
reduces evaporation from the soil surface. Cover crops can increase soil
organic matter and provide surface mulch, but caution should be used with cover
crops, because when growing, they can consume considerable amounts of water
that may be needed to leach salts or supply the cash crop.
Conservative
water use prevents
many of the problems that we discussed above. This can be
accomplished by monitoring the soil, the
plant, or whether indicators and applying water only when needed. Soil sensors—like
tensiometers, moisture blocks, and new TDR or capacitance probes—
can evaluate soil moisture conditions. When the soil moisture levels become
critical, irrigation systems can be turned on and water applications can be
made to meet the crop’s needs without excess. The crop itself can also be
monitored, as water stress results in increased leaf temperatures that can be
detected with thermal or near-infrared imaging.
Another approach
involves the use of weather information—from either government weather services
or small on-farm weather stations—to estimate the balance between natural
rainfall and evapotranspiration. Electronic equipment is available for
continuous measuring of weather indicators, and they can be read from a
distance using wireless or phone communication. Computer technology and
site-specific water and fertilizer application equipment—now available with
large modern sprinkler systems—allow farmers to tailor irrigation to acre-scale
localized water and fertilizer needs. Researchers have also demonstrated that
deficit irrigation—water applications that are less than 100%
of evapotranspiration—can provide equal yields
with reduced water consumption and promote greater reliance on stored soil
water. Deficit irrigation is used purposely with grapevines that need limited
water stress to enrich quality-enhancing constituents like anthocyanins.
Many of these practices can
be effectively combined. For example, a vegetable grower in Australia uses beds
with controlled traffic. A sorghum-Sudan cover crop is planted
during the wet season and mulched down after maturing, leaving a dense mulch.
Subsurface trickle irrigation is installed in the beds and stays in place for
five or more years (in contrast, annual removal and reinstallation are
necessary with tilled systems).
No-tillage is performed, and vegetable crops
are planted using highly accurate GPS technology to ensure that they are within
a couple of inches from the drip emitters.
Drainage
Soils that are naturally
poorly drained and have inadequate aeration are generally high in organic
matter content. But poor drainage makes them unsuitable for growing most crops
other than a few water-loving plants like rice and cranberries. When such soils
are artificially drained, they become very productive, as the high
organic matter content provides all the good
qualities we discussed in earlier chapters. Over the centuries, humans have
converted swamps into productive agricultural land by digging ditches and
canals, subsequently also combined with pumping systems to remove the water
from low-lying areas. Aztec cities were supported in part by food from chinampas, which are canals dug in
shallow lakes with the rich mud used to build raised beds. Large areas of
Holland were drained with ditches to create pasture and hay land to support
dairy-based
agriculture. Excess water was removed by
windmill power, and later by steam- and oil-powered pumping stations. Today, new drainage efforts are primarily accomplished with subsurface
corrugated PVC tubes that are installed with laser-guided systems. In the United States land drainage efforts have been significantly
reduced as a result of wetland protection legislation, and large-scale
government-sponsored projects are no longer initiated. But at the farm level,
recent adoption of yield monitors on crop combines has quantified the economic
benefits of drainage on existing cropland, and additional drainage lines are
being installed at an accelerated pace in many of the very productive lands in
the U.S. corn belt and elsewhere.
Benefits of
Drainage
Drainage results in the
lowering of water tables by removal of water through ditches or tubes. The main benefit is the creation of a deeper soil volume that is
adequately aerated for the growth of common crop plants. If crops are grown that
can tolerate shallow root-ing conditions—like grasses for pastures or hay—the
water table can still be maintained relatively close to the surface or drainage
lines can be spaced far apart, thereby reducing installation and maintenance
costs, especially
in low-lying areas that
require pumping. Most commercial crops, like corn, alfalfa, and soybeans,
require a deeper aerated zone, and subsurface drain lines need to be installed
3 to 4 feet deep and spaced from 20 to 80 feet apart, depending on soil
characteristics.
Drainage increases
the timeliness of field operations and reduces the potential for compaction
damage. Farmers in humid regions have limited numbers of dry days for spring
and fall fieldwork, and inadequate drain-age then prevents field operations
prior to the next rain-fall. With drainage, field operations can commence
within several days after rain. As we discussed in chapters 6 and 15, most
compaction occurs when soils are wet and in the plastic state, and drainage helps
soils transition into the friable state more quickly during drying periods—except
for soils with high plasticity, like most clays. Runoff potential is also
reduced by subsurface drainage because compaction is reduced and soil water
content is decreased by the removal of excess water. This allows the soil to absorb
more water through infiltration
Installing drains in poorly
drained soils, therefore, has agronomic and environmental benefits because it
reduces compaction and loss of soil structure. This also addresses other
concerns with inadequate drainage, like high nitrogen losses through
denitrification. A large fraction of denitrification losses can occur as
nitrous oxide, which is a potent greenhouse gas. As a general principle,
croplands that are regularly saturated during the growing season should either
be drained or revert to pasture or natural vegetation.
Types of
Drainage Systems
Ditching was used to drain lands for many
centuries, but most agricultural fields are now drained through perforated
corrugated PVC tubing that is installed in trenches and backfilled. They are still often referred to as drain “tile,” which dates
back to the practice of installing clay pipes during the 1800s and early
1900s. Subsurface drain pipes are preferred in a modern agricultural setting,
as ditches interfere with field
operations and take land out of production. A
drainage system still needs ditches at the field edges to convey the water away
from the field to wetlands, streams, or rivers
If the entire field requires
drainage, the subsurface pipes may be installed in grids with mostly parallel lines. This is common for
flat terrains. On undulating lands, drain lines are generally installed in
swales and other low-lying areas where water accumulates. This is generally
referred to as random drainage
(although
a better term is targeted drainage). Interceptor drains may be installed at the bottom of slopes to
remove excess water from upslope areas.
Fine-textured
soils are less permeable than coarse-textured ones and require closer drain
spacing to be effective. A common drain spacing for a fine loam is 50
feet, while in sandy soil
drain pipes may be installed at 100-foot spacing, which is considerably less
expensive. Installing conventional drains in heavy clay soils is often too
expensive due to the need for close drain spacing. But alternatives can be
used. Mole drains are developed by
pulling a tillage-type implement with a large bullet through soil in the
plastic state at approximately 2 feet of depth. The implement
cracks the drier surface soil to create water pathways. The bullet creates a
drain hole, and an expander smears the sides to give it more stability. Such
drains are typically effective for several years, after which the process
needs to be repeated. Like PVC drains, mole drains discharge into ditches at
the edge of fields.
Clay soils may
also require surface drainage, which
involves shaping the land to allow water to discharge over the soil surface to
the edge of fields, where it can enter a grass waterway. Soil
shaping is also
used to smooth out localized
depressions where water would otherwise accumulate and remain ponded for
extended periods of time.
A very modest system
of drainage involves the use of ridges
and raised beds, especially on
fine-textured soils. This involves limited surface shaping, in which the crop
rows are slightly raised relative to the inter-rows. This may provide a young
seedling with enough aeration to survive through a period of excessive
rainfall. These systems may also include reduced tillage—ridge tillage involves
minimal soil disturbance—as well as controlled traffic to reduce compaction
Concerns with Drainage
The extensive drainage of
lands has created concerns, and many countries are now strictly controlling new
drainage efforts. In the U.S., the 1985 Food Security Act contains the
so-called Swampbuster Provision, which strongly discourages the conversion of
wetlands to cropland and has since been strengthened. The primary justification
for such laws was the loss of wetland habitats and landscape hydrological
buffers.
Wetlands are
among the richest natural habitats due to the ample supplies of organic sources
of food, and they are critical to migrating waterfowl that require food and
habitat away from land predators. These wetlands also play important roles in
buffering the hydrology of watersheds. During wet periods and snowmelt, they
fill with runoff water from surrounding areas, and during dry periods they
receive groundwater that resurfaces in a lower landscape position. The
retention of this water in swamps reduces the potential for flooding in
downstream areas and allows nutrients to be cycled into aquatic plants and stored
as organic material. When the swamps are drained, these nutrients are released
by the oxidation of the organic materials and are mostly lost through the
drainage system into watersheds. The extensive drainage of glacially derived
pothole swamps
in the north
central and northeastern U.S. and Canada have provided significant
increases in flooding and losses of nutrients into watersheds.
Drainage systems also
increase the potential for losses of nutrients, pesticides, and other
contaminants by providing a hydrologic shortcut for percolating waters. While
under natural conditions water would be retained in the soil and slowly seep to
groundwater, it is captured by drainage systems and diverted into ditches,
canals, streams, lakes, and estuaries. This is especially a
problem because medium- and fine
textured soils
generally, allow for very rapid movement of surface-applied chemicals to
subsurface drain lines. Unlike sands, which can effectively
filter percolating water, fine-textured soils contain structural cracks and
large (macro) pores down to the depth of
a drain line. Generally, we would consider
these to be favorable because they facilitate water percolation and aeration.
However, when the application of fertilizers, pesticides, or liquid manure is
followed by significant precipitation—especially intense rainfall that causes
short-term surface ponding—these contaminants can enter the large pores and
rapidly (sometimes within one hour) move to the drain lines. Bypassing the soil
matrix and not filtered or adsorbed by soil particles, these contaminants can
enter drains and surface waters at high concentrations.
Management practices can be implemented to reduce the potential for such losses
(see the box “To Reduce Rapid Chemical and Manure Leaching to Drain Lines,”
next page).
Artificial
drainage of the soil profile also reduces the amount of water stored in the
soil and the amount of water available for a crop. Farmers who want to drain
water out of the soil in case of excess rain but would like to retain it in
case of drought play a game with the weather. Controlled drainage allows for some flexibility
and involves the retention of
water in the soil system through the use of weirs in the ditches at the sides
of fields. In effect, this keeps the water table at a higher level than the
depth of the drains, but the weir can be lowered in case the soil profile needs
to be drained. Controlled drainage is also recommended during winter fallows to
slow down oxidations of organic matter in muck (organic) soils and reduce nitrate
leaching in sandy soils.
Summary
Irrigation and drainage allow for high yields
in areas that otherwise have shortages or excesses of water. There is no doubt
that we need such water management practices to secure a food supply for a
growing population and provide the high yields needed to arrest the conversion
of natural lands into agriculture. Some of the most productive lands use
drainage and/or irrigation, and the ability to control water regimes provides
great advantages. Yet there is a larger context: These practices exact a price
on the environment by diverting water from its natural course and increasing
the potential for soil and water contamination. Good management
practices can be used to reduce the impacts of altered water regimes. Building
healthy soils is an important component of making soil and water management
more sustainable by reducing the need for irrigation and drainage. In addition,
other practices that promote more judicious use of water and chemical inputs
help reduce environmental impacts
