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Healthy soil demands some TLC

Ron Smith dfp-ron.smith-soil.loss_.jpg
A water infiltration demonstration at the 2018 Milan No-till Field Day showed the advantages of cover crops.
Without adequate nutrients, water and protection from the elements, soil productivity declines.

Like people, soil functions better when it's healthy. And also like people, without adequate nutrients, water and protection from the elements, soil productivity declines. Forbes Walker, associate professor, biosystems engineering and soil sciences at the University Tennessee Institute of Agriculture, says proper management will improve soil health.

Forbes, in a presentation during the recent virtual Milan No-till Field Day, said farmers have options available to improve soil and increase yield potential. He cited cover crops, reduced tillage and rotation as key factors in improving or maintaining healthy soil.

He defines soil health as "the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals and humans," according to USDA.

Microbes make a difference

He adds that the soil ecosystem includes microbes that need food, shelter and water. Microbes are essential. "There is more life in a teaspoon of soil than humans on earth," he says. "Organic matter is critical for those soil microbes to perform functions necessary to produce food and fiber. Practices that improve or conserve soil carbon are critical for building and improving soil health."

Erosion plays havoc with that ecosystem, and tillage contributes to soil loss. "Tillage destroys organic matter and damages soil structure," Forbes says. He says if farmers till they should do it "only when soil moisture is low enough to prevent compaction."

Forbes showed a chart indicating soil loss from various tillage systems. The data come from a Gibson County, Tenn., trial with Grenada soil in a field with a 2% to 6% slope. The trial included cotton, corn and soybean production.

Soil loss

Conventional tillage resulted in a 64 tons per acre soil loss per year in a corn crop, 95 tons per acre in soybeans, and 100 tons per acre with corn.

No-till was much better, 1.4 tons of soil loss per acre per year in corn, 14 tons in soybeans and 19 tons in cotton. Adding a cover crop made a significant difference, dropping soil loss in corn to .97 ton per acre per year, 3.8 tons in soybeans and 4.8 tons in cotton.

Tennessee a no-till state

Forbes says Tennessee farmers have adopted no-till in the past few decades. "Tennessee data show 75% of the state's row crop acreage is planted no-ill," he said. "I think it's higher, probably around 85%."

Cover crop adoption has lagged, however. Forbes says only 10% to 15% of Tennessee row crop acreage includes a cover crop. "We have a way to go."

Farmers have numerous options for cover crops including grasses (cereals such as rye, oats, wheat, millet and sorghum), legumes (vetches, clovers, cowpea and lupin), and brassicas (radish and turnip). He says buckwheat is another option, sometimes used in organic row crop production.

Cover crop benefits

Cover crop advantages include improved weed control. "Weeds compete for nutrients and water," Forbes says. "Cover crops aid weed control by shading, allelopathy (inhibiting weed germination or growth) and may cut costs by reducing the need for some herbicides."

He says the combination of no-till and cover crops offers significant advantages. "We see increases in total organic carbon, wet aggregate stability, and soil health."

Better yields

Yields also improve. He cites a long-term continuous cotton study that shows yield differences in tillage systems. "With no cover crop, we see yields decline over time," Forbes says.  "Long term, even in poor growing years, we see improved yields with cover crops."

Crop rotation also contributes to improved soil health. "Vary crops in time and space," Forbes says. "A corn and soybean rotation is common in Tennessee and breaks the disease, weed and pest cycle.

"Also, include cover crops during fallow periods. Keep the soil surface covered with a growing crop for most of the year to reduce erosion. Cover crops also maintain or increase soil organic matter content and nutrient availability when cash crops are not grown."

Weed control

Cover crops improve weed suppression and legume cover crops add nitrogen to the soil.

Forbes says in some cases farmers may choose to graze cattle on cover crops during the winter. "Grazing may make cover crops more valuable."

Maintaining adequate fertility improves soil health. "Don't guess, soil test," Forbes says. "Make sure you understand the soil test information. Know the difference between sufficiency (applying what's necessary to reach yield goals) and maintenance."

He recommends maintaining the proper soil pH and following state recommendations on fertilizer rates.

"Remember the four Rs for fertility — right rate, right type, right time, and right place."

He also recommends using precision agriculture technology to target nutrient applications.

In addition to improved erosion control, increased organic matter and potential weed suppression, the combination of no-till and cover crops also improves water infiltration.

He showed a slide of a soil loss demonstration from the 2018 Milan No-till Field Day. Several containers represented various tillage and cover crop options. Simulated rainfall demonstrated water runoff rates for each option. Vertical tillage showed significant runoff.

"No-till and cover crop examples showed almost zero runoff," Forbes said.

Water that falls on no-till/cover crop fields infiltrates and stays put. "With the combination of no-till and cover crops we're doing some great things with water management."

Forbes says adopting practices that improve and maintain soil health offers numerous benefits and a big factor is carbon.

"If we can increase or maintain soil carbon, we can improve soil health," he says.

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