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Fertilization Trends: High Plains Perspective

Tuesday, February 1, 2011
filed under: Fertility

Ron Meyer is area extension agronomist with Colorado State University, based at Burlington. He has worked with High Plains sunflower producers for many years, and likewise has conducted numerous research trials on a variety of topics related to producing sunflower in east central Colorado and adjacent areas.

The Sunflower: Does any fertilization of upcoming sunflower ground in your area occur in the fall, or is it almost exclusively spring-applied?

Meyer: Fertilizer in High Plains sunflower fields is mostly applied in the spring. This season (2010), corn harvest was finished early, and a fair amount of fertilizer was applied to irrigated circles — but most of that was intended for corn production. Only a small amount of sunflower acreage is fertilized in the fall, mainly because the focus is on corn production at that time of year.

While fall fertilization finishes that activity on a field and spreads out the workload in the spring for other activities (i.e., seedbed preparation, planting, herbicide applications), the tradeoff is that this activity also ties up capital over the winter, adding interest costs to production.

How much at-planting and/or sidedressing goes on in sunflower? Are there any evolving trends in this regard?

Possibly about a third to half of the N fertility needs are placed at planting with 2x2. Most of the phosphorus needs are placed this way as well (about 20-30 lbs of P per acre). No sidedressing currently takes place in sunflower production in our region.

A small amount of fertigation takes place with nitrogen (about 30 lbs/ac

actual in some fields). Strip-till practices allow flexibility, so quite a bit of the nitrogen — and some phosphorus — is placed during the strip-till pass.

Less chemigation occurs with sunflower than with corn. Most sunflower fertilizer is placed ahead of planting and at planting — as compared to corn, where there is always some N placed in-season. That’s mostly a function of the N application amounts needed for corn.

A lot of the sunflower is produced under a minimum-till or no-till system. How has that impacted fertilizer application timing and methodology, as compared to conventional ‘flowers?

It is the reason a lot of fertilizer is placed in a strip-till application ahead of planting. The balance is applied with the planter.

Regarding nitrogen (soil plus applied), is the standard High Plains rule of “6-7 Lbs N Per 100 Lbs Yield Goal” still a good one to follow?

This still works well — mostly due to the ability of sunflower to “harvest” deep fertilizer that other crops in the rotation cannot get to.

Do most growers adequate test for and apply P and K as needed, or do these two nutrients tend to get under-emphasized?

There is a general tendency to not soil test on every field of every farm. As a result, many growers apply maintenance levels yearly.

In the High Plains region, phosphorus tends to be applied at 20-30 lbs/ac per year when yield goals are optimistic due to soil moisture levels. Our heavy soils test at over 800 lbs/ac of K, so therefore we don’t use much potash. North of Burlington about 60 miles, the soils are lighter and sandier. Potash is deficient there and applied similar to phosphorus.

Do you encounter any micronutrient deficiencies in your area? Are there

situations where including micronutrient applications would pay?

Micronutrient deficiencies are rare in sunflower in the High Plains. In a number of years of testing micronutrient applications in sunflower, I could not find economic yield increases. Sunflower has not shown responses to any micronutrients I’ve applied at the locations where I’ve tested.

I believe that in sandy, lighter-colored soils, micronutrients may be beneficial. However, I don’t have data to support that; it’s just a guess. My “elevator speech” to growers says, “Test micronutrients on your farm and let the combine tell you if they pay for themselves.”

Remember to Take Organic Matter Credits into Account

Merle Vigil, soil scientist and research leader at the USDA-ARS Central Great Plains Research Station at Akron, Colo., reminds growers of the importance of organic matter credits.

“Nitrogen can come from soil residual N from previous fertilization and from soil organic matter, and should be considered from at least the top two feet of the soil profile,” he notes.

“We have found that a grower can expect 20-40 lbs of N from mineralization for each percentage unit of soil organic matter found in his soil in the top six inches. So a farmer with 2% OM could expect 40 to 80 lbs of N from mineralization during the season (average of 60).

“If the residual inorganic N in that soil was 20 lbs, that farmer would have enough N (60-100 lbs) without adding any fertilizer N for an 850- to 1,400-lb crop of sunflower.

“If he put on, say, 30 lbs of N, he would have enough to meet the needs of a 1,285- to 1,860-lb crop of ’flowers.” - Don Lilleboe
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