Agriculture Irrigation on the Increase

Linda F. Benedict, McClure, Olivia J.

In the constructed wetland at the Red River Station in Bossier City, runoff enters the system by way of three grassed drainage ditches (red dashes). Runoff then enters a shallow wetland with an average depth of 18 inches. The deep wetland is up to 9 feet deep and provides conditions for further improvement in water quality. From culverts runoff then flows to the Flat River. Illustration by Kathy Kramer

Olivia McClure

Agriculture is one of the biggest users of Louisiana’s water resources, which many people worry are in danger, both in terms of quantity and quality.

There has been a steady increase in agricultural irrigation in the past few decades in Louisiana. The number of irrigated acres has gone from 702,000 in 1974 to 1.2 million in 2013, according to the U.S. Department of Agriculture.

Major Louisiana row crops like corn and soybeans are water-intensive, and new high-yield varieties demand even more water.

“The value of irrigation can’t be overestimated,” said Rogers Leonard, LSU AgCenter associate vice chancellor for plant and soil sciences. “You can’t afford to lose crop yields to droughty conditions. Irrigation is used as a risk management tool because it stabilizes the variation in yields over time.”

To reach those higher yields, many farmers rely on decades-old irrigation methods that use excessive amounts of water to meet crop needs. Much of the water never touches crops and leaves the field as runoff, carrying soil and expensive fertilizers with it. Sometimes, that nutrient-laden water ends up in nearby streams that drain into larger bodies of water, causing low-oxygen conditions.

In some areas of Louisiana, the increase in irrigation has lowered the groundwater supply, which leaves higher concentrations of naturally occurring salt — sometimes high enough to make water unsuitable for irrigation.

These problems are exacerbated by the increasing water needs of industry and urban populations that use groundwater from the same aquifers.

While new technologies and research can help achieve greater efficiency, change will not be quick or easy. Farmers face incredibly complex decisions about how and when to irrigate their crops.

Irrigation history

Farmers didn’t always irrigate. Nature did it for them with rain.

“History indicated that farmers could get normal yields of soybeans from natural rainfall in some years, but in years with less rain, those yields may be off by 50 to 75 percent,” Leonard said. “That loss in annual income from yield variability will not allow farmers to consistently make a profit. Long-term sustainability is only possible at higher yield levels. To get to those levels consistently, they have to provide those plants with sufficient inputs.”

Today, many farmers invest in the equipment needed to irrigate, and more than 40 percent of Louisiana’s row crop acreage is now irrigated, according to AgCenter irrigation engineer Stacia Davis. Good soybean prices in the past several years, for example, have made it critical to get the highest yields possible.

Beneficial as it is, irrigation can cause problems. One is with salt. In northeastern Louisiana and coastal parishes, salt in groundwater is a big concern because it hurts crop health.

Salt domes lie beneath Louisiana’s surface, along with 12 major aquifers that all flow southward. Historically, rain would push saltwater to waterways and the Gulf of Mexico, but rainfall patterns have been changing since 2000, and there have been extended periods of drought in some areas of Louisiana, said retired AgCenter water specialist Bill Branch.

With more farmers putting down wells for irrigation in recent years, groundwater isn’t being replaced fast enough to dilute the salt. Some recent test wells in Franklin Parish have been too salty for irrigation, Branch said.

In northern Louisiana, this problem is compounded by competition for groundwater from paper mills and growing municipalities, as well as rice farms in southern Arkansas. Branch said the Sparta Aquifer, which covers 16 northern parishes, has been “over-drafted.”

Surface water, which is more renewable, can be used if a stream, bayou or lake is close to the farm. In the Shreveport area, more farmers are using surface water thanks to the Natural Resources Conservation Service’s Red Bayou project, which uses water from the Red River to fill smaller bayous that farmers can pump from. But in other parts of the state, a well is often the only option.

Washing away investment

No matter where the water comes from, how it is used can pose other problems. Water does crops little good if it doesn’t stay in the field.

A popular way to irrigate is pumping water into a field to flood furrows. While common in Louisiana, furrow irrigation is inefficient, Davis said. It can be difficult to know when to turn the pump off, which allows water to run off, and some of the water standing in furrows is lost to evaporation.

Drip irrigation uses small pipes placed next to rows so water drips toward crop roots. It wastes less water, but involves a higher cost.

However, farmers contending with salty groundwater can’t use drip irrigation because salt precipitate will clog the system. Rust can do the same thing in areas where the soil is rich in iron.

Overhead sprinkler irrigation systems, which Davis estimates are used by 15 to 20 percent of Louisiana farmers, must operate at the correct pressure to be efficient, which makes maintenance important. Older systems can be retrofitted with new sprinkler packages to conserve water and energy, she said.

“Your method depends on your crop and soil,” Davis said. “There’s not one solution.”

Compounding the problem is farmers’ prevailing logic that irrigation is always good, even if it isn’t really necessary. Irrigation is one variable amid many that farmers can control — and the mentality tends to be that more irrigation always equals more profit.

That may not be true. Naveen Adusumilli, an economist at the AgCenter Red River Research Station in Bossier City, said one irrigation event can cost as much as $4 per acre.

Irrigating a 200-acre farm one time would cost about $800 — and if the soil is still moist from a previous irrigation, that $800 probably could have been saved. Water cannot soak into wet soil, so it will run off.

This past summer at the Red River Research Station, Davis found that cotton growing on the station did not need irrigating because there was enough rainfall. Most farmers in the region irrigated anyway, but achieved similar yields to the cotton Davis studied.

“A lot of farmers irrigate using the calendar,” Davis said. “They need to make a more informed decision and know what the soil moisture and weather actually is.” That is especially true if farmers apply soil amendments like poultry litter, which hold water, Davis said.

Davis and Adusumilli are encouraging farmers to use sensors to keep an eye on soil moisture. Irrigation can be delayed if the soil is very moist. If conditions are dry, irrigation may be required sooner than usual, and sensors can help farmers ensure their crops always have enough water.

Although there are no approved regulations governing their use, unmanned aerial systems, or drones, could also help farmers monitor irrigation and know when to turn the pump off, Leonard said. Flying a drone equipped with a camera would save the time it takes a farmer to drive around a field — and potentially get stuck in a muddy turn row — to see if water has completely traveled down the field.

Environmental impact

The problems with using too much water extend beyond economics.

Flowing water causes erosion, which is bad for farmers because it removes fertile topsoil. Excessive irrigation can add additional salt to the field, which harms soil health. Another issue is that eroded soil can fill drainage ditches, Leonard said.

Runoff also takes fertilizer inputs like nitrogen and phosphorus away from crop fields and into waterways, where low-oxygen conditions known as hypoxia can result.

“You can lose more than 10 percent of applied nitrogen through surface runoff,” said AgCenter agronomist Syam Dodla.

Nitrogen also leaches easily into deep layers of soil, Dodla said, which lowers the soil quality. If the soil becomes less fertile, farmers must apply even more fertilizer and perhaps irrigate more, which harms the soil even more in the long-term.

Soil erosion caused by furrow irrigation, which Dodla said is sometimes only 45 percent efficient, adds to the problem. Dodla is trying to find out if farmers can skip rows when they irrigate, which would reduce erosion, nutrient runoff and the amount of water they use, and still reach proper soil moisture levels.

Different soil types — and there are many in Louisiana — absorb water at different rates, so rows may need to be closer or farther apart to achieve sufficient moisture in skip-row irrigation.

Applying soil amendments such as compost, animal waste or charcoal made from plant matter can also help hold moisture and reduce evaporation, said AgCenter water quality expert Changyoon Jeong.

While it is best to reduce runoff, another strategy is to make good use of it. The water that runs to the ends of rows can be reused in a practice called tailwater recycling.

“These are storage systems for excess water from field runoff that can be used later,” Jeong said. “It can be useful for crop growth when it’s very dry.”

Leftover chemicals must be removed from the recycled water before it is used on crops. One way to do that is with a constructed wetland, where nutrient particles collect and decompose.

There are many types of constructed wetlands, Jeong said, that can be used as part of tailwater recycling or simply to clean up water before it flows into waterways.

Jeong has been studying the efficiency of the constructed wetland at the Red River Research Station, which consists of two ponds — a shallow pond that contains a diverse mix of plants to trap and uptake nutrients, and a second, deeper pond that provides conditions for further improvements in water quality. Through culverts the water drains out to the Flat River.

Farmers can clean water as it runs off sloped fields by planting sections of grass called filter strips at the edges of fields and along waterways. The grass catches excess nutrients and sediments so they deposit in the strip instead of flowing out with the water, Jeong said. Depending on the angle of the slope of the land, the width of filter strips can range from 20 to 60 feet.

While these kinds of practices can save farmers money, they also cost money to implement. Still, they could be critical to the future of agriculture.

“Until recently, there’s been a misconception that Louisiana has plenty of water,” Adusumilli said. “We don’t. Groundwater is decreasing, and competition for use of it is increasing. Once it’s gone, it may be gone forever.”

Future for irrigation

The water situation in Louisiana is better than in some places. Western states are dealing with one of the worst droughts in recent history. Arizona, for example, has introduced usage fees to conserve dwindling water resources.

In Louisiana, water itself is essentially free — farmers only have to pay for the energy and infrastructure used in irrigation.

Many Louisiana farmers have been working toward greater efficiency for years. Some work with the NRCS and the state Department of Agriculture and Forestry’s Office of Soil and Water Conservation to develop conservation plans. The AgCenter’s Master Farmer program, which includes workshops and field days, helps producers implement researchbased management practices.

These programs give farmers the tools they need to address environmental concerns voluntarily, which is preferable to additional regulations that may limit crop production in the future.

“If you’re pushing your yields higher and you want to maintain those levels, you have to have an irrigation strategy,” Leonard said. “We have to meet the food needs of a growing world population. But at the same time, we know we have to be more efficient in our use of water resources here at home.”

Olivia McClure is a graduate assistant in LSU AgCenter Communications.

This article was published in the winter 2015 issue of Louisiana Agriculture Magazine.

3/19/2015 10:32:40 PM
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