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Sod to Soybean Considerations

March 10, 2012
By: John Buckner, Farm Journal Executive Editor
pC22 Sod to Soybean Considerations  1
Planting in former Conservation Reserve Program fields should be delayed until the soil temperature is above 55°F to avoid Pythium damping off disease and blight.  

Don’t be fooled for top yields

With tight hay markets, a raging beef market, $12 soybeans and corn futures near $6, the decision to convert more pasture to grain crops has not been a no-brainer this year. Solid grain demand, expiring Conservation Reserve Program (CRP) contracts and the high cost of herd replacements, however, might have tipped the balance toward more row crop acreage on your farm.

Farmers have always taken advantage of a fertilization bump on fallow land coming back into grain crops, but it’s no slam-dunk to achieve top yields the first year. CRP ground or pasture is typically not the best ground for farming, due to soil types and topography.

It takes fertilization management to match the history of that ground to a proper seedbed for grain crops, but will it be soybeans or corn? Soybeans are the probable first crop choice,

researchers say, in spite of the fact that corn nets more than beans on a per-acre basis.

"Going with soybeans the first year out of CRP is probably a good idea," says Peter Scharf, a University of Missouri (MU) research agronomist.

As one of the authors of an MU research paper comparing no-till corn yield response to nitrogen (N) fertilizer following CRP and following soybeans after sod conversion, Scharf says the choice is clear. The researchers found that it took approximately 205 lb. of N per acre to optimize profit on corn after CRP, but only about 110 lb. of N for corn after soybeans following CRP.

University of Kentucky (UK) research on converted CRP fields shows a 0.5% to 1% increase in soil organic matter. "Organic matter contains about 5% nitrogen, which is equivalent to 1,000 lb. of nitrogen per acre for each 1% of organic matter in the top 6" of soil," says Lloyd Murdock, a UK research agronomist.

The decomposing vegetation the first year might tie up some of that residual N in the soil. "The second year after sod, where soybeans were the first crop, more nitrogen is available, which aids in the decomposition of organic matter and the release of even more nitrogen," Murdock adds.

Andrew Cummins, an east central Missouri grain crop farmer, agrees with the bean choice.

Besides having a more flexible planting period with soybeans, he likes taking advantage of the soybean’s N fixing ability while the carbon to N ratio becomes more balanced throughout the first year from sod decomposition. He will be planting an additional 240 acres of prepared sod ground this year, with only 10 acres going into corn "for experimental purposes" and the remainder in soybeans, he says.

Impacting many agronomic considerations is the choice between a no-till seedbed and plowing/disking. "I’ve been on both sides of the fence on this one," Cummins says. Though aware of the benefits of no-till, he continues, "Plowing has always worked better for me—I’ve always had a much better stand the first year out of sod."

Soil secrets. The first weapon in Cummins’ sod-to-soy arsenal is a proper soil test with 20 probes to the acre. "That’s a $20 investment on ground that could gross $500. Everybody thinks you don’t need fertilizer on this ground the first year because it’s already got plenty of reserves [from decomposing sod], and they’re finding that’s completely wrong," says the Santa Fe, Mo., farmer. "For example, some farmers are finding they need 80 lb. to 100 lb. of monoammonium phosphate [or the equivalent] just to get caught up to where they need to be."

pC22 Sod to Soybean Considerations  2
High pH, like low pH, can affect yields. A pH of 7 to 7.3 in the lower right field yielded

30 bu. beans. The field on top yielded 65 bu.

Phosphorus (P) is not the only limiting fertilization factor to consider. "Most hay and pasture fields are potassium [K] deficient," says Chad Lee, UK researcher and Extension agronomist. "Hay removes a lot of K2O from the soil. Without even conducting a soil test, the odds are good that you will need 60 lb. of K2O per acre."

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FEATURED IN: Farm Journal - March 2012
RELATED TOPICS: Soybeans, Production



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