Does the soil supply enough nutrients or can foliar feeding really help yield?

It is becoming a common practice to foliar feed crop plants when spraying herbicides, insecticides or fungicides. If you are making a pass across the field, why not throw in nutrients, sugars, biologicals or growth stimulants to give plants a boost? Foliar feeding can supply nutrients when they are lacking or unavailable in the soil, or when roots are stressed and not active.

But the question is, do you get a clear economic return or are you pouring money down the drain?

Many farmers foliar feed their crop once or twice, spraying on a cocktail of nutrients and other products like sugars, growth stimulants and pesticides. There is a wide array of products available today from your retailer and you have a lot of products to choose from. But how do you know which product to buy or how many different ingredients it should have? The marketplace is crowded, claims can be confusing and you have to rely on the salesperson for sound advice—or do your own testing.

There are a few instances where a foliar application can benefit a crop—but not always. For example, glyphosate is a chelate and is known to tie up manganese. Soybeans are more sensitive to manganese deficiencies, so adding in some manganese with glyphosate can help overcome this temporary deficiency. However, soybeans can be iron deficient (iron chlorosis) in early spring, yet foliar applications of iron aren’t always effective in overcoming this deficiency. If you experience nitrogen deficiency, a foliar application can quickly green up the plant—at least until it runs out of nitrogen again, which it will do shortly since the plant can’t meet its nitrogen needs through leaf uptake.

So how do you know if foliar feeding is effective or not if you don’t do your own strip trials or look at any data from your area? I know this is a tough question to answer and I am not against foliar feeding, I just wish it was easier to identify when nutrients are needed and to be able to measure that they are actually contributing to growth and yield. First, look for symptoms of deficiencies that occur. Second, run soil tests to see which nutrients might be lacking. Finally, run tissue tests to see if nutrient levels are deficient or sufficient.

When it comes to foliar feeding, remember that you can’t feed a crop through the foliage and meet its nutrient demands, regardless of whether it is a primary, secondary or micronutrient. The bulk of those nutrient resources have to come from the soil and through the roots. However, I also believe that foliar feeding makes a range of nutrients immediately available to the plant, which increases photosynthesis and other metabolic processes and stimulates the roots to be more active. Maybe that is just enough to get the roots pulling more nutrients out of the soil. Unfortunately, this is conjecture and I have no science to back this up—and I wish someone would study and answer this question.

For some farmers, foliar feeding is a risk management and crop health tool, so the crop isn’t deficient in any nutrients. Sure, it won’t be effective on every acre, but it will be effective on a portion of acres and that is a reason to apply. It is no different than using seed treatments to ensure seedling establishment. They aren’t needed on every acre, but they do help on some acres.

How do you decide whether to foliar feed your crop, and will depressed commodity prices influence that decision on 2015? Please leave a comment below.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.