Kinsey Agricultural Services

What would you recommend, based on the type of soil testing you do, for making the highest yield of corn possible on my field?

First of all, take the needed soil tests far enough ahead of time to be sure there is sufficient time to receive and consider fertilizer and soil amendment recommendations, locate the required materials, and apply them in a timely manner.

Timing the Soil Sampling, Fertilizer Application

For liming materials and trace elements such as iron, manganese or copper: if you intend on planting corn in the spring, plan to apply these materials during the autumn prior for best response from the crop.

Before corn is hip-high in the spring is generally considered the time to sample in order to see soil fertility levels at their best (Provided that the soil is not drought stressed, that large amounts of sulfur have not been applied in the last two to six months, and that sampling avoids areas where nitrogen has been knifed in, or recently broadcast in large amounts. Any of these situations could significantly lower the soil pH and make it appear that lime is needed when such is not the case). Otherwise, to see soils at the lowest fertility levels sample as soon after harvest as possible where drought is not a factor.

We count on each sample received as having been taken to correctly represent the area being tested. (To assure soil testing is correctly achieved please see the instructions on taking a good soil sample). That being the case, the more completely you inform us about conditions for the corn (or any other crop) you will be raising, the previous crop including yield, and the fertilizers previously applied, the better we can advise concerning needed soil amendments and fertilizers.

Considering Nitrogen

To grow corn, nitrogen is usually the biggest question in regard to fertilization, and the most difficult recommendation to correctly determine. So in order to properly consider nitrogen needs, several questions need to be answered. For example, what should be a reasonably expected yield goal? Fertilizing for each field’s average yield plus 10% is usually a prudent goal to set. Instead, too many corn growers just apply an excess of nitrogen to assure there is an ample supply, because “it requires such a small increase in yield to pay for it.”

Keep in mind that an excellent soil only requires one lb. of nitrogen (including N from humus) for each bushel of corn produced. But poorer soils will require up to one and a half pounds of nitrogen per bushel of corn. Any farmer who consistently applies more than one and a half pounds of N per bushel of corn, including N from humus, legumes, manure and carryover from the previous crop, is likely to be hurting soil fertility and nutrient uptake in relation to calcium, copper, and perhaps even sulfur.

Such overuses will most likely not result in a reduction of yield that same year, so producers that overuse nitrogen are slowly blind-sided as a result. When average corn yields begin dropping don’t just blame “the weather”, check fertility levels too! Failing to build correct soil fertility can easily cost corn growers 20-40 bushels of potential yield.

Other Information That Helps Us Provide the Best Recommendations

Yield Can vary widely due to climate, especially moisture availability, so we have to rely on those sending the soil samples to give the proper potential yield information.

Irrigation In some areas all corn is irrigated, in other areas none. We need to know if the land is irrigated because it can influence the amount of nitrogen, sulfur, and boron recommended.

Type of corn Be sure to state as clearly as possible the type of corn you intend to grow. When a sample lists the crop as “corn”, unless stated otherwise it is taken to be corn for grain, not silage corn, sweet corn, seed corn, or popcorn, which could require quite different recommendations.

It also matters whether you will be raising 90-day up to 110-120 day corn. 90-day corn needs the bulk of its nitrogen early in the season. But 110-120 day corn needs adequate nitrogen and sulfur over a longer period of time. When not specified, 110-120 day corn for grain will be the default used for making fertilizer recommendations, since it is more widely grown in the areas from which we receive the most samples.

Fertilizers available to you Be sure to list the fertilizers that are available for use in your area. Nitrogen materials are most readily available, but which types are easiest to obtain? The grower needs to tell us. The same goes for phosphate and potassium. Also list any liming that has been done in the past three years as that can affect nutrient availability – and possibly change both the amount and type of lime presently shown to be still needed for the soil.

Finally, the type of fertility program the grower wants to pursue should be stated. Most growers choose the ‘excellent’ program but, unless the corn is already producing top yields, most growers find it is too expensive when the costs to provide excellent yields and quality are calculated. It is better to begin with a ‘building’ program or ‘maintenance’ program and stick with it for at least three years. When fertilizer prices are high, commodity prices are low, and financing is limited, consider the minimum program for crop production in terms of fertility for a year or two under such circumstances.

In Conclusion…

Perhaps this will help explain why it is important for you to inform us about more than the fact that corn will be planted on the areas where soil tests have been taken and for which recommendations have been requested. Just keep in mind that the information you provide along with the soil sample is a key factor in determining the best fertilizer program to achieve the best yield of corn.