With more Mississippi producers following a corn/soybean rotation, scrimping on crop nutrients can mean leaving money on the table at harvest time.

“Producers tell me, ‘I can’t make that fertilizer application because it’s going to cost me an extra $25 per acre,’” says Bobby Golden, assistant research professor at the Delta Extension and Research Center, Stoneville, Miss.

 “But we all know it’s yield that pays the bills — and if you don’t give the crop the gas it needs to run, you’re not going to produce maximum yields,” he said at the annual meeting of the Mississippi Agricultural Consultants Association.

“I know fertilizer is expensive. But, we’re paying high costs for land, for seed, and other production inputs. We gripe about it, but we pay. Why are we so reluctant to do it with our fertility?”

It’s important to maintain soil fertility, Golden says. “You don’t want to draw it down because it will cost you a vast amount more money to raise soil test levels than it will to maintain the current level in the field all along.”

“Corn removes more phosphate than soybeans, and soybeans remove more potash than corn — but when you put them together in a one-on-one rotation, you’re going to have somewhere between 180 and 200 units of each coming off the field in the grain cart, based on 200 bushel corn and a 60 bushel soybean yields.”

Soybeans also remove a lot of potassium from the soil, Golden says, and “there is a very tight correlation between potassium and soybean yield. For typical 60 bushel soybeans, we’re removing around 80 pounds of K20. If we’re not putting back 80 pounds, we have the potential for drawing down our soil test numbers.”

Early stage studies in Mississippi indicate a response to potash in soybeans up to about 150 parts per million soil test K, he says. “Data are limited on this, but we hope our work can nail this down a bit better, so we’ll be able to offer more precise recommendations.

“In one site we looked at in the Delta, where soil had been mined of nutrients, they were missing 10 bushels of soybean yield because they had been omitting potash and phosphorous over a period of several years.”

In the Midwest, Golden says, there is a well-established correlation between potassium and corn yield, “but we have very little work on this in the Mid-South. Do Iowa and Nebraska results hold true in the Mid-South? We feel they do, but more research is needed to establish values here. We think soil test K can predict yield in the Mid-South, just as it does in Iowa, but we need to establish those values, and we got a good start with work we did in 2012.”

On two distinctly different sites in the Delta, Golden says, yields were improved significantly by applying 80 units of K20.

“On a very sandy site, we saw a large yield increase, 75 bushels, over the untreated control. On the heavier soil site, we still got a 27 bushel increase. In both cases, a lot of money was being left on the table by not providing adequate fertility to the corn crop.”