Do You Know Your Soil's Nutrient Needs?

Out-of-balance soils can harm soil structure and a no-tiller's bottom line.

By Darrell Bruggink, Managing Editor/Publisher

IF YOU'RE NOT measuring the nutrient needs of your soils, you may be throwing tons of money away and hurting your soil structure — even if you're no-tilling.

Art Gehring, a consultant from West Bend, Wis., says phosphorus, potassium and nitrogen overapplications are leading to soil imbalances of calcium, magnesium and hydrogen.

"From a chemical standpoint, calcium and magnesium ratios are the leading factors influencing soil structure," Gehring says.

COVER TEST. Art Gehring is working with a cover crop mixture called Nitro Green North consisting of 60% hairy vetch (photo at left), 15% medium red clover, 15% yellow blossom sweet clover and 10% tillage radish (right) as a cover after wheat. Vetch and clover fix nitrogen, while the tillage radish holds nitrogen, potassium and phosphorus and releases it back to next year's corn crop.

Formula For Success

Gehring says there are six main cations that need to be measured and balanced — calcium, magnesium, potassium, sodium, other bases and hydrogen — that when added up equal 100% base saturation. In that equation, calcium should approach 70%; magnesium about 12; potassium 3 to 4; sodium 0.5 to 1; other bases 4 to 5; and hydrogen 10 to 12.

To prove his point of common soil imbalances and the need for soil testing, Gehring took No-Till Farmer into a 10-year no-tilled field in southeastern Wisconsin that was regularly receiving potash applications. However, soil tests were indicating there was an adequate bank of phosphorus and potassium.

Calcium, on the other hand, was well below needed levels at just 32, magnesium was slightly low at 10 and hydrogen was more than triple the norm at 42.

Rather than apply $800 per ton potash (0-0-60), which contains high levels of salt, Gehring says the soil tests indicated liming was where money should be spent.

To get soils in balance, he recommended 1 ton of dolamite lime, which is 20% calcium and 12% magnesium, with 2 tons of calcidic lime. Gehring says dolamite lime is needed to maintain magnesium levels, since they will fall as you increase calcium levels.

Gehring says this would cost the producer about $95 per acre, a much better investment than applying something that isn't needed.

"As far as soil tests go, you need as complete a test as you can get and you need to test for these six cations," Gehring says. "Then you'll have a roadmap to go by. There are too many producers who are not testing for their soil's needs, and are just applying fertilizer without knowing what they need."

Too Much Nitrogen

In addition, 295 pounds of nitrogen was applied to this corn field, the target rate for 240-bushel corn under older university standards. Gehring says nitrogen credits needed to be considered to determine more accurate nitrogen needs.

"If you have 4% organic matter as humus — the residue that's decayed, the corn stalks you can't see anymore or the soybean or wheat straw — that's a 90-pound credit," he says. "That's a credit in and of itself separate from crop rotation or applied fertilizer."

Problems with excess nitrogen go beyond the fact that nitrates can leach. Gehring says nitrates take another key element with them.

"Nitrates take calcium with them because nitrate has a negative 2 charge — it's an anion — and calcium has a plus 2 charge," Gehring says. "It leaves as calcium nitrate. That's why these soils are so imbalanced in terms of calcium. They are putting too much nitrogen out there and are robbing the soil of calcium. Plus, we are not liming."

Value Of pH

Gehring also noted that the soil pH in this field was 5.0. However, he cautions no-tillers not to use that measurement solely as a need for more lime.

"You can't lime based on soil pH alone, as pH is like taking your temperature. It gives you a number, but it doesn't tell you what's wrong," he says. "I place a higher emphasis on your percentage of base saturation — calcium, magnesium and hydrogen."

For example, Gehring knows a Minnesota grower who took 13 tons per acre of dry matter alfalfa off a field with a soil pH of 8.0, an 80% base saturation of calcium and 0% magnesium. He says he'll take those measurements over an 8.0 pH with a 52% base saturation of calcium and 42% magnesium.

"The cation balance is important. I'm not saying you should ignore pH; it's just another tool in the liming decision," he says.