Fertility: the right source, rate, time and location

Soils in the southeast are very sandy. So any fertilizer that is mobile, like nitrogen, sulfur and boron, can really get away from you. What about foliar feeding cotton nitrogen, potassium and boron or other nutrients?

More doesn’t necessarily mean higher yields when it comes to crop fertility, but less can leave profit on the table. Farmers need sound guidance on fertility strategies to capture optimal yields. Hitting the right source, rate, time and location can be tricky.

“Our soils in the southeast are very sandy. So any fertilizer that is mobile, like nitrogen, sulfur and boron, can really get away from you. And we saw that a lot in corn this spring. We had farmers who put out the right amount of nitrogen and sulfur, but with all of the rain in the sandier areas of fields it just leached down out of the root zone. So they had to put some back to get it going again,” said Glen Harris, University of Georgia Extension soil fertility specialist.

Unlike phosphorus and potassium, which are much less leachable in soil, testing soils for nitrogen and sulfur is difficult if done at all because of the mobility of N and S in the soil profile. “A lot of times as soon as we get a big rain like we got this spring, everybody says ‘Oh, no, all my fertilizer is gone,’ which is not necessarily the case but some things are more likely than others to get away from you.”

Corn fertility was a problem in Georgia this spring due to heavy rains, mainly nitrogen and sulfur leaching, but also magnesium issues, Harris said. Higher rates of nitrogen and potassium together are going out on corn in some cases and that is forcing some magnesium issues, too, which need to be addressed by growers.

Southeast growers who deal with sandy, loamy soils, he said, often use split nitrogen applications, opting not to put it all out at planting, assuming some of it will leach through before plants can take it up. For corn, some put it out at planting, then as side-dressing and then putting some out through irrigation right up to tassel, or “kind of spoon feed it,” he said.

What about foliar feeding cotton nitrogen, potassium and boron or other nutrients? Some people think the practice doesn’t work and some think it works wonders. Harris said the truth is somewhere in between. In recent years, he has looked at how much nitrogen and potassium can be put over the foliage in-season, either by rig or plane, and when is too late to get any benefit from it. Also, what can be tank mixed with foliar fertilizer.

One thing that applies to all agronomic crops and fertility is soil pH. “It is so important because pH affects the uptake of all our nutrients,” he said. “And that is what I get the most questions about, or most varying questions about it each year.”

Trials at Sunbelt Expo Field Day

Fertility will be a top topic at the Sunbelt Expo Field Day July 10 in Moultrie, Ga. More than 200 research trials take place on the Sunbelt Expo farm site, ranging from variety trials to irrigation to weed and pest management to fertility.

“Fertility is always important to us as farmers because it is a large part of our investment in a crop. We always want to know what is new or coming to the market place. But most important, what is the minimum we can have, and what are we going to have to put into this crop to get the yields we need for the crop?” said Michael Chafin, farm manager of the Sunbelt Ag Expo Darrell Williams Research Farm.

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“There are so many fertility products and ideas out there it can get a bit confusing are hard to decide what will work best. From starter fertilizers to a lot of work now looking at in-furrow applications or what’s safe and what is not safe to put in furrow or what can we come back with in-season to really pull a crop through, especially when you think about this year with all of the rain we’ve had and what that has done to leach nutrients out of the root zone,” Chafin said.

For the Expo farm this year and last, winter and spring weather was wet and caused problems for preplant fertility applications and land preparation. But with established and historic grid sampling for the farm, Chafin says he knows what his fields need.

“It’s good to know what your farm is starting with, or what your baseline is so you can manage that crop in-season,” he said. “For example, I grid sampled last year and put out a maintenance level on my P and K. I grid sampled again this year and I didn’t need a whole lot of fertilizer. Really all I needed was a maintenance level, and some of the stuff we have in the ground didn’t get a preplant fertilizer at all. All it’s going to get is an in-season fertilizer.”

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