Is Your Soil Susceptible To Nitrogen Loss?

Is Your Soil Susceptible To Nitrogen Loss?

Soil type and cation exchange capacity or CEC of various soils affect their ability to retain nutrients.

Nitrogen (N) loss happens in three major ways: volatilization, leaching and denitrification. All soils are susceptible to nitrogen loss. In fact, as much as 50% of applied N fertilizer may be lost through volatilization, leaching and surface runoff in a given year, according to the USDA Agricultural Research Service.

SAVE YOUR NITROGEN: Clay soils have a higher CEC than sandy soils. But that doesn't mean farmers with clay soils shouldn't worry about nitrogen loss. Though there is a smaller leaching potential in clay soils, nitrogen is still susceptible to loss from denitrification in soils with high organic matter and high CEC.

"Nitrogen is expensive," says Barney Gordon, professor emeritus at Kansas State University. "Economically and environmentally, you don't want to lose it. From an agronomic standpoint, you don't want the crop to suffer from nitrogen deficiency and lower yields. You want a constant supply for crop uptake." While nitrogen loss can occur on any soil type given the right conditions, Gordon explains sandy soils with a low cation exchange capacity (CEC) and low organic matter content are the most susceptible to nitrogen loss from leaching.

"With sandy soils, you have large sand particles and large pore spaces, which means more space for rain to wash through and take the nitrogen with it," says Darren Hefty, co-host of Ag PhD TV, which airs weekly on RFD-TV. "Since sandy soils typically have low CEC and organic matter, there's a reduced capacity to latch onto those positively charged ions like ammonium."

Consider CEC, the cation exchange capacity, of your soils
CEC is a part of a soil test measuring the number of cations in the soil that are available to exchange with soil particles, explains Gordon. Cations are positively charged atoms or molecules. Since clay soils and organic matter are negatively charged, these types of soils have higher CEC.

Volatilization is also a risk for surface applied nitrogen. In this reaction, nitrogen is lost to the atmosphere, so warm, moist soils and especially fields with unincorporated surface applications are more likely to lose nitrogen through volatilization. That doesn't mean farmers with clay soils shouldn't worry about nitrogen loss. Though there is a smaller leaching potential in clay soils, nitrogen is still susceptible to loss from denitrification in soils with high organic matter and high CEC.

~~~PAGE_BREAK_HERE~~~

Hefty says farmers should take the CEC of their soil into account when making decisions about how much N to apply. However, he warns that CEC is an indicator of how much nitrogen the soil can safely hold, not an indicator of how much nitrogen a crop needs. "When we look at the historical rule of thumb, 10 times the CEC can be applied in one shot. If a grower has a CEC of 20, that soil can safely hold 200 pounds of N at one time," Hefty explains.

Steps you can take to protect against loss of nitrogen
Especially in fields that are more susceptible to nitrogen loss, experts suggest farmers carefully manage their nitrogen with split applications and the use of a stabilizer. Both Hefty and Gordon recommend using a stabilizer with every application of nitrogen fertilizer, regardless of soil type.

"N stabilizers keep nitrogen in the ammonium form longer," Hefty says. "Plants want to take up nitrogen in the ammonium form. They're capable of using nitrogen as ammonium or nitrate, but they need to expend energy to convert nitrate to ammonium. That extra energy ultimately results in lower yields."

When choosing a stabilizer, look into the types of N loss that it will protect. Some stabilizers will only protect against volatilization. "NutriSphere-N protects against all three types of nitrogen loss where other products protect against just one type of loss. It's easy for me to recommend NutriSphere-N," Hefty says. "It makes environmental, economic and agronomic sense."

Different nitrogen stabilizers protect different types of N loss
NutriSphere-N Nitrogen Fertilizer Manager from Verdesian Life Sciences, keeps more of the nitrogen in the ammonium form longer. Ammonium is able to bind to negatively charged soil particles, keeping it from leaching. "NutriSphere-N especially helps nitrogen retention in sandy soils," Gordon says. "The product certainly improves retention of nitrogen in sandy soils, but it can still only hold so much. A stabilizer will help keep the nitrogen available to the plant longer, but you shouldn't count on it to make up for a bad agronomic decision. With sandy soils, split applications are important. You can't apply it all in the fall like with clay soils."

~~~PAGE_BREAK_HERE~~~

Regardless of soil type, nitrogen loss is virtually guaranteed. Experts advise farmers to reduce their losses in the next growing season with smart agronomic practices: Use a stabilizer, split apply your nitrogen fertilizer and focus your nitrogen rate per acre on what the crop needs, not what the soil can hold.

Normal Range of CEC Values for Common Soil Groups

Soil Group

CEC (meg/100g)

Light colored sands

3-5

Dark colored sands

10-20

Light colored loams and silt loams

10-20

Dark colored loams and silt loams

15-25

Dark colored silty clay loams and silty clays

30-40

Organic soils

50-100

Source: David B. Mengel, Department of Agronomy, Purdue University

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish