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Dr. Dan Talks Agronomy
Tuesday, September 1, 2015 7:22AM CDT

By Daniel Davidson
DTN Contributing Agronomist

I really like getting reader questions because it lets me know what is on grower's minds.

Recently, a Pennsylvania grower asked me to make some specific comments about starter fertilizer and placement and foliar nutritional products for soybeans and cautions about their use. The question: "Is there any reliable information about their effectiveness?"

Yes, I know we're already past this application window for 2015, but thinking ahead and trying to determine how we change things for next year is always a good strategy. If your soybean yields seem stagnant or don't meet expectations this fall, fertility is a good place to start looking for a fix.

Applying fertilizer directly before the next soybean crop isn't yet a customary practice. The common practice is to fertilize for two crops, corn and soybeans and let beans scavenge for what remains after the first corn crop.

However, most agronomists are now telling growers to fertilizer both crops independently. Once you make sure the basic phosphorus and potassium needs are met, then you can add on enhancements such as starters at planting and foliar nutritionals as a post application.

Let's tackle the effectiveness question first because it pertains to both starters and foliar nutritionals. To be frank, these products don't work all the time. Even if you see a visual response, that doesn't mean you will measure a yield response at the end of the season. I consider it a good response if a starter or foliar nutritional works 60% to 65% of the time. Also, these products typically don't work on all acres, but on a portion of the acres in a field, which masks their overall value.

Starters provide nutrients early in the season to stimulate early growth when the soil is too cold to mineralize nutrients in the vicinity of the seed and there are no roots to capture nutrients further from the seed. Visual growth symptoms -- more vibrant color and greater vigor -- are common when starters are used, but increases in yield are less common.

Starters can be applied on soybeans, but watch salt content and keep pop-up volumes limited to two gallons per acre. Personally, I like adding in another gallon or two of water but that adds time to tender the planter. Farmers using center fill rigs generally don't want to spend time tendering their planter. In our area of Nebraska, I like to add in some chelated iron because iron chlorosis appears in our high pH calcareous soils. Soybeans can benefit from some nitrogen, phosphorus and potassium at planting just like corn and you can put in some zinc and sulfur. Again, my rule is keep the gallonage at two per acre as a pop up and don't overload with nitrogen and potassium as it adds to the salt content.

There is interest in applying nitrogen on soybeans and it makes sense to add some as a preplant or with starter or popup. Nitrogen fixation doesn't kick in fully until mid-June. If you inoculate your beans with Rhizobia bacteria, do not add molybdenum to the pop up, as it will be fatal for the bacteria.

I would not worry too much about nitrogen in starter or foliar nutritional depressing nitrogen fixation. It is true a buildup of nitrate in the soil (40 or 50 pounds) will depress nitrogen fixation. But applying 2 to 5 pounds in a starter or foliar is not a risk. Some agronomists feel that about 20 to 30 pounds preplant actually benefits soybeans during the first 30 days of growth before fixation really kicks in.

OVER THE TOP

Foliar nutritionals are flooding the scene as cocktails, specialty blends and single products. More choices are coming as stimulants and growth regulators enter the market. It is a crowded market with a lot of claims and few measurements of a response.

I think the key with foliar nutritionals is that they don't replace what the soil supplies, but can overcome short-term deficiencies. They keep the plant's metabolism humming along and stimulate the roots to do their job. Foliars make sense:

-- If there is a true deficiency, a tissue test will show and a foliar nutritional can help overcome it.

-- If the plant is experiencing stress, a foliar nutritional can stimulate the plant to overcome it.

The best strategy here is to do tissue testing to see if you soil is supplying all the nutrients the crop needs. Do that tissue testing in conjunction with soil testing to make sure soil reserves are ample.

Dan Davidson can be reached at AskDrDan@dtn.com

Follow Dan Davidson on Twitter @dandavidsondtn

(PS/SK)


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