September 5, 2019
This is the sixth year Greg Whitmore has participated in the Soil Health Partnership, a National Corn Growers Association initiative led by farmers such as Whitmore to evaluate how different management practices affect soil health and the bottom line using quantifiable measurements.
As a participating farmer in the Soil Health Partnership, Whitmore has planted cover crops on a 27-acre plot on his farm near Shelby, Neb., for the past six years — but he has grown cover crops on his farm for the past 13 years and has used minimum tillage for nearly 20 years.
Over the years, he's seen plenty of anecdotal evidence of the benefits of soil health practices, but being a part of the partnership has given him a means of quantifying those benefits.
Farmers in the Soil Health Partnership are asked to enroll a 20- to 80-acre field and set up test strips with two separate treatments — a farmer control compared with an adapted management system — replicated four times.
The program involves collecting soil samples to interpret the economic and environmental benefits of different practices. In addition to nutrient and chemical attributes, the partnership is using tools such as USDA Agricultural Research Service's soil health nutrient tool and Cornell University's Comprehensive Assessment of Soil Health to analyze physical attributes and biological attributes.
For his plot, Whitmore has three replications of cover crops and four without. The cover crop mixes typically include forage radish and cereal rye. On the rest of his acres, he's planted everything from radishes, turnips, cereal rye, hairy vetch and rapeseed.
"We're still not seeing a significant difference in yield, but we are seeing an improvement in soil structure and aggregate stability," Whitmore says. "There are other measurements than just yield — that's not the only economic measurement we should be going by. I may not always see all the benefits I can possibly reap, but I'm trying to bring real-world information to other producers."
In a Cornell soil aggregate stability test conducted in spring 2016, Whitmore noticed one area of the field with a much higher aggregate stability than other areas. This test is measured by the fraction of dried aggregates that disintegrate under a simulated rain event.
Since then, he's been working to bring the rest of the field up. And at least anecdotally, he's noticed an improved aggregate stability translate into about a 5% to 10% increase in water infiltration rate across the field.
In years' past, Whitmore has aerially interseeded cover crops on this 27-acre plot. Recently, however, he's moved to what he sees as a more reliable approach: planting after harvest using a twin-row planter.
He originally switched to twin-row to increase his silage harvest yield, but as a ridge-tiller, twin-row planting gives Whitmore a chance to establish covers on the shoulders of ridges and leave the ridges established — without having to buy a new planter or drill.
"I was trying to interseed by flying on, but I wasn't satisfied with the stand I was getting," Whitmore says. "We used a high-clearance machine, and it worked well for interseeding on our seed corn acres, but on higher-density stands for our irrigated regular corn, we don't have enough light interception for interseeded cover crops to take off."
In Nebraska, getting cover crops established at the right time to get adequate biomass growth can be a challenge. Whitmore notes one of his goals for his entire farm is either getting covers such as cereal rye seeded earlier or letting them grow longer to get more biomass growth in spring.
On the other hand, timing of termination has been a critical factor for Whitmore.
"It's a matter of hitting that window 10 days to two weeks ahead of planting," he says. "If you miss that window, do you want to plant green and spray right away? In my continuous silage acres, I have a drop-dead date to spray by April 15. That gives a two-week window to plant corn for silage."
Of course, growing seed corn and silage affords different opportunities for establishment — including the chance to seed winter-sensitive brassicas and other cover crops for fall grazing.
"I'm working with a farmer with cows — he's grazing cover crops and cornstalks and that's been a really big plus," Whitmore says. "Those cover crops are planted behind seed corn and silage acres. We wouldn't have enough growth on November-planted cover crops for fall grazing."
Working with a local dairy, Whitmore also has the opportunity to redistribute nutrients in the form of manure back on his silage acres.
"It really stood out last year, yield-wise. I had a farm last year with 40% green snap, and it still produced 34 tons per acre," Whitmore says. "It was a phenomenal yield. That was a manured field. Even when we're doing silage, our organic matter levels are stable — not declining. I attribute that to manure and having a cover crop out there to keep the ground stable."
"Especially with cattle and with silage where you're cycling the crop off and putting nutrients back on, cover crops are a natural fit," he says. "Now that we're getting better soil health measurements, I think we can address certain soil health issues."
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