Consider Multiple Factors for Fertilizer Decisions

Consider Multiple Factors for Fertilizer Decisions

While the headlines out of Arkansas might’ve suggested otherwise, yields in both soybeans and cotton surged in 2017.

According to the USDA National Agriculture Statistics Service forecast from December, Arkansas cotton yields hit 1.06 million bales in November, averaging 1,162 pounds per harvested acre.


Those numbers would be approaching all-time record yields in the state, according to Bill Robertson, Extension cotton agronomist for the University of Arkansas System Division of Agriculture.

“I talked with a farmer in Clay County and also heard stories from others that pulled into a 48 acre field and built 48 round modules,” says Robertson. “And the thing is, it’s not just one variety they’re doing that on, it’s several varieties. We got some very timely rains through the season, so it’s great to be lucky every once in a while.”

Not everyone in the state enjoyed record-breaking yields. Cotton planted earlier in the season – predominantly those acres south of I-40 – faced challenges that suppressed yields to “about average,” according to Robertson.

One thing Robertson warns against is a sense of complacency among his growers who did post strong yield numbers in 2017. Now is not necessarily the time to draw back on fertilizer, he says. A prior season’s yield numbers shouldn’t be the only factor to consider when determining how much fertilizer to put on. And, he says, we take more than just lint out of the field each fall.

“When we haul a lot of cotton to the gin, one of the last things we need to do is back off of our fertility,” Robertson says.

“If we look at 2-and-a-quarter bales an acre, then we take 72 units of nitrogen with us to the gin. We take 32 units of phosphorus to the gin, and we take 43 units of potash to the gin. So there’s a lot of nutrients that we’re taking  out of the field.”

Of course, there are indicators growers can use to determine how much – or how little –fertilizer is needed in their fields.

“There are a lot of things to take into account when deciding what to do,” Robertson says. “I’ve got growers who say ‘I put a ton of Pix on this cotton, and I couldn’t hold it back.’ Well, if that’s the case, then you might need to scale back a little on your nitrogen.”

Conversely, other indicators might reveal that more fertilizer is needed or applications could be timed for better efficacy.

“The last few years potash deficiencies have really started showing up more and more,” Robertson says, noting that areas where leaves have fallen off the plant are generally a good indication of this. “But a lot of times we’ll see that there’s more potash in the soil in areas where the leaves fell off. So the nutrients are in the soil, it’s just that our plants aren’t getting the potash when they need it.”

The problem often lies in root depth – or rather, lack of depth.

“The soil has tremendous capacity to supply nutrients to the plant, but we also have to think ‘Where are the active roots which tells us where the plant is doing all of its work at?’ If we go out to the field after an irrigation, and we hit dry soil about six inches deep, then the plant is kind of handcuffed in terms of where it can search for nutrients. This represents a spoon feed situation.

“That’s going to be a completely different situation than if we go out there during the season, and we’ve got really good moisture and really good roots a foot-and-a-half deep.” Deeper effective rooting makes it much easier for the plant to find the moisture and nutrients it needs when it needs them, he says.

Ultimately, there is no silver bullet indicator when it comes to determining fertilizer prescriptions. Starting with an informed idea of the soil profile is important. Robertson and his counterparts at the University of Arkansas recommend that growers soil sample every three years. He also recommends that growers understand Extension recommendations in their own home states.

“There’s not an easy answer. If we could cookbook this thing, I might even be farming,” he says with a laugh. “That would make farming a lot easier, and there’s not much about farming that’s easy.”


From Cotton Grower Magazine – February 2018