Use Water Efficiently

January 2, 2016 02:46 AM

Ensure the water that’s left over from crop production doesn’t carry away nutrients 

Sound water management includes making sure water carries away as few nutrients as possible when some of it inevitably leaves your farm. That point was driven home to Farm Journal Field Agronomist Ken Ferrie when he measured nutrients in field runoff, a stream, road ditch and pond in the Midwest. Based on his findings, it’s evident:

  • Water pollution from crop production is a real concern. Until he conducted his own tests, Ferrie was inclined to emphasize the pollution contribution of point sources such as sewage treatment plants and municipalities. “Our tests make it clear both farms and cities must do their parts to preserve clean water,” he says.
  • Water management and nutrient management go hand in hand. “Nutrients don’t get into water bodies by themselves,” Ferrie says. “They’re carried by water. If crops use the water and nutrients they can’t leave the field. Using water and nutrients more efficiently also adds to higher yields and profit.” 

Ferrie’s tests were eye-opening for many. One of them was conducted several years ago, before Ohio environmental regulations forbade applying fertilizer to frozen or snow-covered soil. Ferrie captured runoff water from two frozen soybean stubble fields covered by 2" to 4" of snow. On one field, the operator had applied 150 lb. of diammonium phosphate  and 400 lb. of 0-0-60 (potash) per acre on top of the snow. 


Two weeks after application, the snow started to melt and water ran off the field. The runoff was clear, containing no soil because the ground was frozen. The second field had no fertilizer applied. (See chart above.) 

“Lost potassium fertilizer is a wasted expenditure,” Ferrie says. “But the phosphorus [P] is a water-quality concern because it’s dissolved phosphorus [ortho P]. That water-soluble form is the most active in the environment [compared with particulate P attached to soil particles].” 

Nitrate in drinking water is a health concern for pregnant women and children. Together, nitrate and P (especially dissolved P) promote algae blooms. In places such as Lake Erie, algae blooms hinder recreational activities such as swimming, fishing and water skiing, and they cause a bad taste to drinking water. Algae decomposition depletes water of oxygen, creating hypoxic zones (low-oxygen zones, where aquatic creatures either migrate away or die) in water bodies such as the Gulf of Mexico.

That field runoff could have been prevented by following the 4Rs of nutrient management: right product, right rate and—in this instance—right time (when there’s no snow on the ground) and right place (inject the fertilizer so it can’t run off). 

CRP filter strips flanking a drainage ditch help retain eroding soil and water runoff containing particulate phosphorus and other nutrients.  

In Illinois, Ferrie tested water in a small stream that usually runs about 6" deep and 2½' to 3' wide. During normal flow, he found 9.2 ppm nitrate, 0.04 ppm particulate P (attached to soil particles), 0.09 dissolved P and 42 ppm suspended solids. 

But following a heavy rain, when the stream was 5' deep and 15' wide, particulate P was 0.33 ppm, dissolved P was 0.36 ppm and suspended solids were 128 ppm. “Not only did the phosphorus concentration increase, but the volume of flowing water was much greater,” Ferrie says.

Nitrate concentration fell slightly, to 8.1 ppm, but with much more water flowing, more nitrate was being carried downstream. 

“There are no municipalities nearby, so all that water ran off farm fields, after failing to infiltrate into the soil,” Ferrie says. 

In this situation, buffer strips, another nutrient best management practice (BMP), might have helped by filtering out eroding soil containing particulate P. To prove it, on the same day Ferrie sampled water in a farm pond protected by buffers of cattails, willows and switchgrass. 

Even though a field was being farmed only 30' away, there were no detectable levels of nitrate, P or suspended solids in the pond water. “If there had been nitrate in the water earlier, it could have denitrified into the atmosphere,” Ferrie says. “That’s what constructed wetlands, another 
BMP, accomplish.” 

None of this means crop production is the only source of nitrate and P in streams and rivers. “Golf courses, lawns, sewage plants, storm water runoff—even natural decomposition and lightning—all contribute nutrients to water bodies,” Ferrie says. In addition, about half the surface area of cities such as Baltimore and Washington, D.C., are hard-surfaced, so rainfall neither infiltrates nor gets filtered. 

        Fast Facts About Runoff
  • An easy-to-overlook aspect of water management is keeping it as free of nutrients as possible when it leaves your field, as some water will.
  • Agriculture is one of several sources of excess nutrients in water.
  • Nitrate and phosphorus pose the biggest threats to water quality.
  • Excess nitrate might be a health hazard for pregnant women and children.
  • Nitrate and phosphorus together can make algae blooms, which can create hypoxic zones such as the one in the Gulf of Mexico.
  • Most of the water- and nutrient-management practices that protect water quality also help improve farm profitability and overall soil health.

An Illinois study showed 48% of the phosphate and 80% of the nitrates in the state’s water bodies come from agriculture. Farmers can’t prevent all water and nutrients from leaving their land, Ferrie emphasizes. But it behooves every farmer to do all he can to keep water, and the nutrients it carries, at home. 

“With phosphorus, base every fertilizer application on a soil test to avoid overapplying,” Ferrie says. “Sample by soil type, rather than grids; if possible, use variable-rate application technology to apply the right rate on each soil.” 

Controlling soil erosion with conservation tillage and surface residue helps prevent particulate P from leaving farms attached to soil particles. But in soil with high P levels, dissolved P can be carried downward by water, becoming a threat to exit the property through tile lines. Some states have calculated a formula called a P index, which helps growers zero in on fields where P loss is most likely. 

In those fields, cover crops can take up dissolved P and carry it through to the next growing season. In a field of cornstalks, Ferrie found a cover crop of annual ryegrass reduced the dissolved-P level in the top 6" of soil from 0.7 ppm to 0.3 ppm. At the 6" to 12" depth, the annual ryegrass reduced the dissolved-P level from 
0.2 ppm to 0.04 ppm.  

The 4Rs—the right product, rate, time and place—also reduce the risk of nitrogen loss. “In various field-scale studies, we have proven the same total amount of nitrogen, split into multiple applications and applied at the correct time throughout the growing season, can increase corn yield by up to 39 bu. per acre,” Ferrie says. “The increased yield more than pays for the additional application passes.”

As with P, cover crops can tie up nitrate—if some is left over because drought reduced corn yield, for example—and prevent it from being leached away. 

Everything you do to help water infiltrate soil decreases the chance it will run off and carry away soil and nutrients. Some prevention practices, such as removing dense layers and converting to no-till, strip-till or a vertical tillage system, are obvious. Others are less so. 

Planting the appropriate population and variety for each soil type, using variable-rate technology, causes more soil water to be transpired upward through plants.

For example, planting the appropriate population and variety for each soil type (using variable-rate planting technology) maximizes transpiration of soil water upward through plants. Variable-rate technology also helps irrigators apply water where it is most likely to be used by crops. Besides storing nutrients, cover crops improve soil structure of a field, which increases infiltration and water storage capacity.

Ultimately, some water will wind up exiting many fields through tile lines. “Recently developed gated tile systems let you hold back some of the drainage water, so some of the nitrogen it carries can denitrify into the atmosphere,” Ferrie says. 

“In the spring, you open the gates to let the soil dry out for planting. In a dry year, gated systems can be used to manage the depth of the water table, keeping more water available for plants,” he adds. 

As a limited yet vital input, water demands a high level of diligence. The Water Management series details how farmers can manage earth’s most valuable resource to boost yields and profit. water_management


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