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Improving soil structure with cover crops

"The thing is that with the cover crops we have living roots in the soil as many months as we can.”

When it comes to profitability, money can be a lot like the water that lands in farmers’ fields, according to Dr. Bill Robertson, Extension cotton specialist with the University of Arkansas System Division of Agriculture.

“Jason (Krutz) got us started this morning, talking about getting water on the fields,” Robertson said, speaking at the Arkansas Soil and Water Education Conference and Irrigation Expo. “Others talked about being more efficient in getting water off the fields.

“But we haven’t talked much about keeping water in the fields,” said Robertson. “I agree there’s a need for more profitability. A ton of money changes hands, but you don’t get to keep a lot of it in your pocket. That’s kind of what happens with our water — we don’t keep enough of it in our fields.”

That’s one of the areas where cover crops can be beneficial, said Robertson, who spoke after Dr. Jason Krutz at the conference at Arkansas State University. Krutz is director of the Water Resources Research Institute at Mississippi State University.

The average intake of silt loam soils, where most of Arkansas’ cotton acres are grown, is about one-half inch to three-fourths of an inch of rainfall per hour, “if we’re lucky,” Robertson noted.

“If the farmers I work with set their center pivots to apply much more than a half-inch of water per hour, what do they do?” he asked. “They do a fine job of filling the ditches at the end of their fields with water because that’s about all we can get in.”

Cover crops

But if they plant cover crops in those fields for a couple of years, the average water infiltration rate increases to 6 to 8 inches an hour.

“I visited with Adam Chappell (farmer from Cotton Plant, Ark.) the other day,” he said. “One of the soil scientists from the University of Arkansas campus at Fayetteville was down measuring water infiltration rates: 12 inches an hour.

“I thought ‘that can’t be right,’ but that’s what they measured,” said Robertson. “That’s unbelievable. On most of our silt loam soils, half inch an hour is all we got, so it’s no wonder that when we get the big rain the water runs off. It won’t go down in those soils.”

Some of the fields he works with have soil moisture sensors at different levels beginning at 6 inches, he said. “We can irrigate, and sometimes the 6-inch sensor knows that we watered, and sometimes it doesn’t. I go to fields where we’ve had cover crops, and the 6-inch sensor, a 12-inch sensor and an 18-inch sensor all respond to that irrigation.”

Getting water to those depths is important because that’s where the plant’s rooting zone is located. “It makes our fertility recommendations and everything else work so much better,” he said.

University of Arkansas researchers are working with growers like the members of the Arkansas Soil Health Alliance to quantify and build a data base on the benefits of planting cover crops and no-till on water infiltration.

Soil health demonstration

Dr. Mike Daniels, Extension specialist for water quality and nutrition management for Arkansas, has applied for and received a grant to place soil health demonstration in each of Arkansas’ 25 Delta region counties.

“A lot of times we’re all from Missouri — you have to show me,” he said. “So we’ll split a field and tell the grower to do what he’s been doing on one side. We’re going to work with you on the other side to try to incorporate cover crops, to reduce your tillage and do it with the equipment you have so you don’t have to buy a bunch of stuff to be able to do this.”

The winter of 2018-19 has proved challenging for cover crops. Because of the excessive amount of rainfall in the fall, some fields — including one of Robertson’s tests — hadn’t been harvested at the time of the conference at Arkansas State University (Jan. 30).

“So we don’t have a lot of cover crops planted,” he said. “We’re going to try some spring-planted cover crops — we’re just trying to do something different. The thing is that with the cover crops we have living roots in the soil as many months as we can.”

Those living roots interact with soil microbes to generate soil structure, he said. “So we’re building a house. That house gives us room for water movement and air in the soil. Then we reduce our tillage to keep us from tearing down the house. That will increase our water infiltration rates from a half-inch an hour to 6 to 8 inches. That would be wonderful if all the infiltration on our cotton ground went to 6 to 8 inches.”

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