Water Management

December 10, 2009 06:00 PM

Yield maps and aerial images, such as normalized difference vegetation index (NDVI) maps, make spotting problem areas in a field easier. "Inevitably, hybrid differences are the first thing that show up. Drainage is second,” says Farm Journal Field Agronomist Ken Ferrie.

In other words, to make the biggest yield difference fastest, improve water management. Apparently, a number of farmers are acting on that advice.

"All the drainage contractors I've spoken with recently are quite busy,” says University of Illinois ag engineer Richard Cooke. "There was a little lull a couple years ago, but drainage has picked up a lot because of the [wet] weather and the increase in the price of corn and soybeans. Higher commodity prices make drainage projects pay for themselves much faster.”

The advent of do-it-yourself drainage, in the form of tile plows, has made drainage management easier for farmers. "Our sales are on track to be about triple last year—and that already was our best year ever,” says Denny Bell, who manufactures Gold Digger tile plows.

"For what land sells for, a lot of farmers say it makes more sense to improve the productivity of land they already have, instead of buying more,” Bell says.

Another factor contributing to drainage growth is yield monitors, Cooke says. By revealing the impact of wet soil on crop yield, "monitors have launched a trend toward more systemic tile systems, instead of random drainage or just running a line to a wet spot,” he says.

Why drainage matters. The effects of wet soil in fields extend beyond the poor-yielding spots.

"Yield maps don't show the impact of poorly drained areas on an entire field,” Ferrie says. "The field may average 140 bu. per acre. But when you look closely, you see that some areas averaged 200 bu., but others made from zero to 90.”

Wet areas also determine the timing of every operation, from tillage through harvest. "That can be crucial in a wet year like 2009,” Ferrie says. "Say you have 70% or 80% of a field ready to plant but the remainder is too wet. You save the field for later. If you had planted on time, maybe the best parts would have yielded 240 bu. per acre. But you sacrificed that opportunity, waiting for 20% of the field to dry.”

Yield maps show the difference in yield between well-drained and poorly drained areas, but they can't tell you how much better yield would have been if you had planted four or five days earlier. "In 2009, waiting a few days for wet spots to dry out sometimes made the difference between planning in April or June,” Ferrie says. "In the end, the field was still planted wet, but it was also planted late.”

"If a field dries uniformly, it's easier to make the decision whether to plant or not,” says Mike McLaughlin, who farms near Leroy, Ill. "It also makes it easier to set your tillage tools. A variation in moisture is just one more variable to deal with. The fewer variables there are, the easier it is to farm.”

A double whammy. When you finally do plant a wet area, it's probably still wet enough to make it difficult to get a good seedbed, Ferrie points out. "Working wet soil results in compaction,” he says. "If you plant it wet, it will be difficult to close the seed trench. Both situations result in yield loss.”

"It all goes hand in hand,” McLaughlin agrees. "If you work a field wet and put in a compaction layer, there may be nitrogen beneath that layer, but the corn roots can't get to it.”

Nor can yield maps explain the cause of the lower yield in poorly drained areas, Ferrie says—especially if you have water molds that destroy corn or soybeans early. "Maybe the area was only wet for two weeks after planting,” he says. "But those two weeks were important to the stand.”

Wet spots cause nitrogen fertilizer to be lost through denitrification, resulting in reduced yield or frantic efforts to apply more nitrogen. Adding nitrogen can bring back a lot of yield in those areas but that increases cost.

Without pulling soil nitrate samples, you can't tell whether stunted yellow corn is due to loss of nutrients or the effect of the water itself. "Standing water results in a lack of oxygen for root growth,” Ferrie says.

If you have to replant a wet area, you not only have increased expense but you face the prospect of delayed harvest. The late harvest delays fall tillage, so everything is behind schedule.

Poor drainage makes it nearly impossible to fertilize efficiently. "Knowing a spot usually drowns out, you consider not applying nitrogen,” Ferrie says. "But in a dry year, that area will grow a tremendous crop. You have to farm the area as if it is going to produce, but the odds are against you.”

Farmers sometimes give up cash-rented land because the amount of quality acres makes the good land cost too much. "If you have 15 wet acres that produce little or nothing in an 80-acre field, it raises the rental rate on the productive acres,” Ferrie explains.

Where tile isn't the answer. The benefits of tiling vary by soil type, of course, Cooke points out. Naturally, heavy, poorly drained soils benefit the most.

Exceptions include fields where the land is such that you have to travel too far to find an outlet for a tile system and unusual soil conditions, such as high sodium content or iron ochre.

"Sodium causes particles to disperse and clog tile lines,” Cooke explains. "In soils with iron ochre, an iron-based bacteria forms like a film and clogs inlets.” Those soils are rare.

Got a landlord who doesn't see the value of tile? Show him yield maps and NDVI images and this article. Then show him a cost/benefit analysis produced with one of the calculators on www.FarmJournal.com.

Managing Drainage May Boost Yield

Managing drainage water on a farm near Hume, Ill., produced a 20-bu. soybean yield increase in 2009, in a study conducted by University of Illinois ag engineer Richard Cooke. The controlled-drainage area yielded 49.1 bu. per acre, compared with 29.5 bu. per acre for "free,” or unregulated, drainage. The practice also reduced tile water flow and nitrate loading by almost 70%.

Managing drainage water will hopefully reduce the escape of nutrients into the Mississippi River and the Gulf of Mexico. There, excess nutrients contribute to hypoxia, or oxygen depletion.

To manage drainage, the flow of water out of tile lines is regulated by installing control structures with movable weirs, or "stop-logs.” The weirs are closed following harvest to retain more water in the tile lines and soil. They are opened prior to spring tillage and planting. During the growing season, the structures can be set to hold the water table about 2' below the soil surface, so water is accessible to plant roots, rather than draining off the field.

Drainage water management is best suited for flat fields, since a control structure is required for every 2' change in elevation. But recently developed farm-over control structures will make it more practical to install additional structures in sloping fields.

Computer modeling suggests managing drainage on Midwestern fields could boost yield as high as 5%, Cooke says, but the effect depends on rainfall. Various studies have documented annual nitrate load reductions of 15% to 75%, depending on location, soil type, climate and cropping practice.

Drainage water management qualifies for Environmental Quality Incentives Program funding in some states. It is expected to be an approved practice for the Conservation Stewardship Program. 

Data Coming Soon from Farm Journal Test Plots

The drainage systems being studied by the Farm Journal Test Plots team have been in place for six years, so they are about to start yielding water management secrets, says Farm Journal Field Agronomist Ken Ferrie.

"We are looking at the effects of depth of tile and spacing of tile lines in three situations—on an easy-to-drain farm, a hard-to-drain farm and a farm that may be impossible to drain due to sand lenses,” Ferrie says.

The studies use sensors to measure soil moisture at 1', 2' and 3' depths, halfway between tile lines. The tile lines are spaced 120', 60' and 30' apart.

"Preliminary data shows that the closer the tile lines, the easier it is to control soil moisture, at the 1' and 2' depth, after each rain event,” Ferrie says.

"As we obtain more years of data, we will find out how each system performs in wet and dry years, and how performance translates into yield and profit. Eventually, the study also will shed light on exactly how much time may be wasted with each tile spacing in waiting for soil to dry out for planting in the spring.”

You can e-mail Darrell Smith at dsmith@farmjournal.com.

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