AGRICULTURE IRRIGATION

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Irrigation makes agriculture possible in areas previously unsuitable for intensive crop production. Irrigation transports water to crops to increase yield, keep crops cool under excessive heat conditions and prevent freezing.

Less than 15% of U.S. cropland is irrigated, although irrigation is essential for crop production in some of the most productive areas of the country. For instance, in Arizona, home to some the highest corn yields in the country (208 bushel per acre state average in 2001 compared to 152 for Illinois), much of the crop is under continuous irrigation from planting until harvest.

The need to irrigate is usually driven by the necessity to meet the water needs of the crop from year to year (some areas of the country simply receive too little rainfall during the growing season to support economical crop growth). In other situations, irrigation is viewed as insurance against occasional drought. In areas where rainfall is plentiful in most years, irrigation can bring benefits by reducing risk, meaning that a farmer is better able to control income fluctuation. Other benefits include:

* Improving crop quality (most noticeable for vegetable crops)
* Significantly increasing crop yields, particularly on sandy soils which have low moisture-holding capacities
* Increasing opportunities for double cropping (planting soybeans after wheat in the same year)
* Providing a means of liquid fertilizer application

In 1997 there were about 55 million irrigated crop acres in the U.S. Irrigation is concentrated in certain areas like central California, Nebraska and the Great Plains, and the lower Mississippi valley.

Although irrigation has always been most common in the West, U.S. irrigated acreage in the East has also grown from 11 percent of acres in 1969 to 22 percent of acres in 1997.

Irrigation water is obtained from either ground water or surface water. Wells drilled on the farm are a common source of water in many areas, and are usually the only source used in the Great Plains. Offsite sources such as rivers, pipelines, canals operated by irrigation districts and private water companies, are also used, mainly in western states. The percentage of water source used for irrigation varies across the U.S.

Operations and Timing

Irrigation water is applied throughout the growing season to meet crop needs. Moisture needs depend on the type of crop and its stage of development. In the Eastern Corn Belt, for example, it takes 20-22 inches to produce an optimal corn crop, 18-20 inches for a soybean crop, 12-13 inches for small grain, and 24-26 inches for alfalfa. Irrigation can reduce crop stress if rainfall does not provide this amount of moisture during the growing season.

It is not only total moisture, but also the timing of moisture application (or rain) that is necessary for optimum crop yields. Crops have critical periods during the growing season when soil moisture must be maintained to ensure optimal yields. For corn, the most critical period is from just before tasseling through silking. For small grain, it is from boot to heading stage, for alfalfa, the start of flowering and after cutting, and for pasture, after grazing.

Equipment Used

There are four primary types of irrigation:

* Surface irrigation,
* Sprinkler irrigation,
* Drip or trickle irrigation, and
* Subsurface irrigation (or “subirrigation”).

Surface Irrigation – With surface irrigation, water flows directly over the surface of the soil. The entire surface can be flooded (most often used for crops that are sown, drilled, or seeded) or the water can be applied through furrows between the rows (for row crops).

Sprinkler Irrigation – With sprinkler irrigation, water is sprayed through the air from pressurized nozzles, and falls like rain on the crop.

Subirrigation – With subirrigation, the water table is artificially raised either through blocking ditches or by supplying water through the perforated pipes also used for subsurface drainage.

Irrigation types can be further distinguished by whether the equipment is permanently installed in one place (stationary system) or whether it is used until the necessary amount of water is applied, then moved to a different area (traveling system). Stationary systems such as permanent spray installations or trickle systems require less labor, but usually cost much more to install. Traveling systems such as center pivot sprinkler irrigation, linear-move, or cable-tow require more labor but less capital expense.

Potential Environmental Concerns

Environmental concerns related to irrigation include depletion of the water source (falling water tables or reduced water levels in streams or reservoirs), soil erosion due to over-application, runoff and leaching of chemicals, and salinization of the soil (salt-buildup) and minerals and nutrients in the irrigation return flow that drains from the irrigated area.

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Best Management Practices

1. Minimize water use. Apply only enough water to meet crop needs. This can be determined through regular soil moisture monitoring or through a “checkbook” system to monitor water applied and crop needs.
2. Irrigation efficiency. Use efficient irrigation systems such as drip irrigation to minimize evaporation.
3. Apply at rate the soil can absorb. Runoff due to excess irrigation can cause soil erosion.
4. Uniform Irrigation. Make sure water is applied uniformly. This makes the water more efficient, and reduces the chance of runoff and leaching in certain areas where water may be overapplied.
5. Provide good drainage. Salinization in areas of low rainfall can be minimized by providing good drainage along with the irrigation, to leach salts down through the soil profile.

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Crop Glossary

Acre – The unit of measure most typically used to describe land area in the United States. An acre is equivalent to 43,560 square feet and is about 9/10 the size of a football field.

Acre-Inch – A volume measurement typically associated with irrigation operations on cropland. An acre-inch is equivalent to 27,154 gallons. When an inch of water is applied to cropland via irrigation, each acre receives 27,154 gallons. (Alternatively, a measure of the volume of water applied to the soil/growing crop using irrigation – approximately equivalent to 27,154 gallons.)

Agribusiness – An enterprise that derives a significant portion of its revenues from sales of agricultural products or sales to agricultural producers.

Anhydrous Ammonia – A fertilizer used to provide nitrogen for crop production. The product, stored under high pressure as a liquid, changes state during application and is injected into soil as a gas. It is popular due to the fact that it is composed of 82 percent nitrogen compared to other nitrogen fertilizers such as urea that contain only 46% nitrogen and ammonium nitrate with 30-33% nitrogen content.

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Boot – The time when the head is enclosed by the sheath of the uppermost leaf.

Bt Corn – Field corn that has received a gene transferred from a naturally-occurring soil bacterium called Bacillus thuringiensis. The gene causes the corn plant to produce one of several insecticidal compounds commonly called Bt toxins. The toxins affect the midgut of particular groups of insects such as European corn borer that can be harmful to corn.

Bushel – A unit of dry volume typically used to quantify crop yields. One bushel is equivalent to 32 quarts or 2,150.42 cubic inches. A bushel is often used to represent the weight of a particular crop; for example, one bushel of No. 2 yellow shelled corn at 15.5% moisture content weighs 56 lb.

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Cash Crop – An agricultural crop grown to provide revenue from an off-farm source.

Center Pivot – A type of irrigation system that consists of a wheel-driven frame that supports a series of sprinkler nozzles. The frame rotates about a central point to distribute water over a large circular area.

Channel Erosion – Erosion in channels is mostly caused by downward scour due to flow shear stress. Side wall sluffing can also occur during widening of the channel caused by large flows.

Conservation Tillage – Any tillage and planting system that covers 30 percent or more of the soil surface with crop residue, after planting, to reduce soil erosion by water. Where soil erosion by wind is the primary concern, any system that maintains at least 1,000 pounds per acre of flat, small grain residue equivalent on the surface throughout the critical wind erosion period.

Conventional Tillage – Full width tillage that disturbs the entire soil surface and is performed prior to and/or during planting. There is less than 15 percent residue cover after planting, or less than 500 pounds per acre of small grain residue equivalent throughout the critical wind erosion period. Generally involves plowing or intensive (numerous) tillage trips. Weed control is accomplished with crop protection products and/or row cultivation.

Corn Belt – The area of the United States where corn is a principal cash crop, including Iowa, Indiana, most of Illinois, and parts of Kansas, Missouri, Nebraska, South Dakota, Minnesota, Ohio, and Wisconsin.

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Depression – A low area in a field where surface drainage away from the area does not occur.

Drawbar – A tractor component typically located at the rear and near the ground that permits attachment of implements for pulling or towing.

Drawbar Work – Any operation performed by a tractor that requires force to be exerted by wheels/tracks to propel an implement through or over the soil.

Drilled – Planted with a grain drill. Grain drills differ from row crop planters in that they do not meter individual seeds, but drop small groups of seed in a process referred to as bulk metering. Drills plant crops in closely spaced rows (typically seven to 10 inches on center) that will not be mechanically cultivated.

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Ensiling – The process of creating silage via anaerobic fermentation.

Eutrophication – The process by which lakes and streams are enriched by nutrients (usually phosphorus and nitrogen) which leads to excessive plant growth.

Federal, Food, Drug, and Cosmetic Act (FFDCA) – It specifies the levels of pesticides, chemicals, and naturally occurring poisonous substances in food products. It also regulates the safety of cosmetic products.

Source: University of Vermont Environmental Safety Facility Exit EPA

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) – The objective of FIFRA is to provide federal control of pesticide distribution, sale, and use. All pesticides used in the United States must be registered (licensed) by EPA. Registration assures that pesticides will be properly labeled and that, if used in accordance with specifications, they will not cause unreasonable harm to the environment. Use of each registered pesticide must be consistent with use directions contained on the label or labeling.

Source: EPA’s Agriculture Web site

Feed Grain – Any of a number of grains used for livestock or poultry feed. Corn and sorghum are feed grains.

Flowering – This is the stage when the crop starts flowering. In corn, tassel emergence and pollen shedding takes place at this stage. Two to three days after pollen shedding, silk emergence takes place. At this stage, typically occurs 51-56 days after planting the corn seed, pollination between silks (female) and tassels (male) takes place.

Forage Crop – Annual or perennial crops grown primarily to provide feed for livestock. During harvesting operations, most of the aboveground portion of the plant is removed from the field and processed for later feeding.

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Genetically-Modified Organism (GMO) – A term that refers to plants that have had genes implanted to improve their performance by making them resistant to certain pesticides, diseases, or insects.

Grazing – Any vegetated land that is grazed or that has the potential to be grazed by animals.

Source: Forage Information System Exit EPA

Ground Water – The water under the surface of the earth that is found within the pore spaces and cracks between the particles of soil, sand, gravel and bedrock.

Gully Erosion – They are formed when channel development has progressed to the point where the gully is too wide and too deep to be tilled across. These channels carry large amounts of water after rains and deposit eroded material at the foot of the gully. They disfigure landscape and make land unfit for growing crops.

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Hay – The product of any of a variety of perennial crops, typically grasses or legumes, that can be used a feed for ruminant animals.

Heading – The stage in which the head pushes its way through the flag leaf collar.

IPM – An integrated approach to controlling plant pests using careful monitoring of pests and weeds. It may include use of natural predators, chemical agents and crop rotations.

Source: Pennsylvania Farm Bureau Glossary of Terms Exit EPA

Leach – The downward transport of dissolved or suspended minerals, fertilizers, pesticides and other substances by water percolating through the soil.

Karst – Areas with shallow ground water, caverns, and sinkholes.

Mulch Tillage – Full-width tillage involving one or more tillage trips which disturbs all of the soil surface and is done prior to and/or during planting. Tillage tools such as chisels, field cultivators, disks, sweeps or blades are used. Weed control is accomplished with crop protection products and/or cultivation.

Source: Conservation Technology Information Center (CTIC) Exit EPA

Non-Point Source Management Program – Under the Non-point Source Management Program, states can receive funding to control non-point sources of pollution to protect surface and ground water, including programs to control pesticide contamination of the ground and surface water.

No-Tillage – Crop production system in which the soil is left undisturbed from harvest to planting. At the time of planting, a narrow strip up to 1/3 as wide as the space between planted rows (strips may involve only residue disturbance or may include soil disturbance) is engaged by a specially equipped planter. Planting or drilling is accomplished using disc openers, coulter(s), row cleaners, in-row chisels, or roto-tillers. Weed control is accomplished primarily with crop protection products. Other common terms used to describe No-till include direct seeding, slot planting, zero-till, row-till, and slot-till.

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Pasture (or Pastureland) – Land used primarily for the production of domesticated forage plants for livestock (in contrast to rangeland, where vegetation is naturally-occurring and is dominated by grasses and perhaps shrubs).

Pesticide – A general name for agricultural chemicals that include:

* Herbicide – for the control of weeds and other plants
* Insecticide – for the control of insects
* Fungicide – for the control of fungi
* Nematocide – for the control of parasitic worms
* Rodenticide – for the control of rodents

Postemergence – Refers to the timing of pest control operations. Postemergence operations are accomplished during the period subsequent to the emergence of a crop from the soil and must be completed prior to point at which crop growth stage prohibits in-field travel (unless alternative application means – aerial or irrigation-based – are used).

Power Take-Off (PTO) – A splined shaft that extends from a tractor drive train and is designed to couple with the splined drive shaft of an implement. The connection permits mechanical power to be transmitted from tractor to implement.

Preemergence – Refers to the timing of pest control operations. Preemergence operations are accomplished during the period subsequent to the planting of a crop and prior to the emergence of that crop from the soil.

Preplant – Refers to the timing of pest control operations. Preplant operations are accomplished during the period subsequent to the harvest of one season’s crop and prior to the planting of the next season’s crop.

Primary Tillage – The mechanical manipulation of soil that displaces and shatters soil to reduce soil strength and to bury or mix plant materials and crop chemicals in the tillage layer. Tends to leave a rough soil surface that is smoothed by secondary tillage.

Ridge Tillage – The soil is left undisturbed from harvest to planting except for strips up to 1/3 of the row width. Planting is completed on the ridge and usually involves the removal of the top of the ridge. Planting is completed with sweeps, disk openers, coulters, or row cleaners. Residue is left on the surface between ridges. Weed control is accomplished with crop protection products (frequently banded) and/or cultivation. Ridges are rebuilt during row cultivation.

Source: Conservation Technology Information Center (CTIC) Exit EPA

Rill Erosion – The removal of soil by concentrated water running through little streamlets, or headcuts. Detachment in a rill occurs if the sediment in the flow is below the amount the load can transport and if the flow exceeds the soil’s resistance to detachment. As detachment continues or flow increases, rills will become wider and deeper.

Row Crop – Agricultural crop planted, usually with mechanical planting devices, in individual rows that are spaced to permit machine traffic during the early parts of the growing season

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Safe Drinking Water Act – The objective of the Safe Drinking Water Act is to protect public health by establishing safe limits (based on the quality of water at the tap) for contaminants that may have an adverse effect on human health, and to prevent contamination of surface and ground sources of drinking water.

Secondary Tillage – The mechanical manipulation of soil that follows primary tillage. Performed at shallower depths than primary tillage, secondary tillage can provide additional soil pulverization, crop chemical mixing, soil surface leveling, and firming, and weed control. In conventional tillage systems, the final secondary tillage pass is used to prepare a seedbed.

Seeded – Generic term for introducing seed into the soil-air-water matrix, typically via a mechanized process that will maximize the likelihood of subsequent seed germination and plant growth.

Self-Propelled – A term that is typically applied to farm machines with integral power units that are capable of moving about as well as performing some other simultaneous operation such as harvesting or spraying a crop.

Sidedress – To apply fertilizer to a standing crop, usually by surface application of liquid fertilizer products or subsurface application of liquid or gaseous fertilizers placed near crop rows.

Silage – A feed prepared by chopping green forage (e.g. grass, legumes, field corn) and placing the material in a structure or container designed to exclude air. The material then undergoes fermentation, retarding spoilage. Silage has a water content of between 60 and 80%.

Silking – It is considered the first reproductive stage

Sinkhole – A surface depression caused by a collapse of soil or overlying formation above fractured or cavernous bedrock.

Soil Test – A soil test indicates the availability of nutrients present in the soil and the availability of those nutrients to crops grown there.

Sown – Planted using a broadcast seeding machine that distributes seed upon the soil surface. The seed may then be incorporated into the soil to ensure adequate seed-soil contact for germination.

Strip Tillage – The process in which only a narrow strip of land needed for the crop row is tilled.

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Tasseling – A condition when the tassel-like male flowers emerge.

Tillage – The mechanical manipulation of soil performed to nurture crops. Tillage can be performed to accomplish a number of tasks including: seedbed preparation, weed control, and crop chemical incorporation.

Transgenic Crop – Contains a gene or genes which have been artificially inserted instead of the plant acquiring the gene(s) through pollination. The inserted gene(s) may come from an unrelated plant or from a completely different species.

Urea – A form of nitrogen that converts readily to ammonium.

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Crop Production
tractor in a field

Source: USDA – Natural Resources Conservation Service

Crop production is a complex business, requiring many skills (such as biology, agronomy, mechanics, and marketing) and covering a variety of operations throughout the year. In this module, the practice of crop production will be described by discussing eight components in the crop production cycle:

For each component, the operations and when they need to be carried out, the machinery or equipment farmers use, potential environmental concerns related to that component, and best management practices recommended to minimize environmental problems will be described.

* Background
* Major Crops in the U.S.
* Crop Production Systems
* Crop Production Steps
o Soil Preparation
o Planting
o Nutrient Management
o Pest Management
o Irrigation
o Drainage
o Harvest
o Storage of Fuel and Chemicals
* Agricultural Pesticide Use
* Study Questions
* Glossary
* References
* Printer Friendly Version
Does not include Glossary and References

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