MSU Extension

Editor’s note: This information was originally published in 1985 and is largely relevant today. It has been lightly updated, and some information that was not relevant has been removed.

The present economic situation for agriculture is causing many farmers to reassess all of their production costs to maximize their returns on each dollar spent. Current Michigan State University Extension cost of production budgets for corn list fertilizer costs as one-third of variable costs. Many farmers are tempted to cut fertilizer use and thereby reduce costs, but are concerned about the reduction in yield that might occur. In some situations, the decision to cut fertilizer costs without regard to some knowledge of the soil’s ability to supply nutrients can be a costly mistake.

Basic economics

Before dealing with the fertility status of the soil and the ramifications of soil testing, be aware of these basic economic principles:

• When prices are high, most farmers will survive.
• When prices are low relative to expenses, only the efficient will survive.
• Profits are greatest when the last input is paid for.
• The first bushel produced is more costly than the last.
• Primary concerns should be costs per unit of production ($/bushel, $/ton or $/cwt), not cost per acre.
• Lime and build-up fertilizer are long-term investments. They should be considered as capital investments and amortized over several years.
• Although surpluses of grain exist, it is disastrous to try to set national policy by personally limiting production per acre as opposed to limiting acreage.

Soil testing

Soil testing is the key to successfully determining the proper amount and kind of fertilizer to apply. There is little debate over soil testing procedures, but the interpretation of soil test information has long been debated and in some cases is being misused. Some have used it to increase their business or sales. Some soil test laboratories do the soil testing, but let other consultants or fertilizer dealers make the recommendations. Some of these recommendations are made with little or no soil test calibration data to support them.

Be aware that fertilizer recommendations are highly variable and some labs or companies that make fertilizer recommendations do not have good soil test calibration data to support their recommendations. Many dollars can be saved on fertilizer purchases by following recommendations that are based on good research data. Because the soil test procedures used by different labs in this region of the country are somewhat standardized, compare your recommendations with those of MSU or other universities in the north-central region. Such a comparison may be very revealing and money saving.

Lime adequately or don’t rent land that needs lime

The benefits and profitability of liming have been well-documented. The influence of lime on the utilization and uptake of other nutrients such as phosphorus is especially important when fertilizer dollars are short. The dollars spent on fertilizer may be wasted if the soil pH is not adjusted for optimum growth.

If land is owned, liming is essential for profitable crop production. If rented land needs lime and the owner is unwilling to make the capital investment of adding lime, or unwilling to enter into a long-term rental agreement, the land may not be worth renting.

Choose a realistic yield goal

Too many farmers are fertilizing for yield goals that are unrealistic, which they never have achieved. Since most fertilizer recommendations are based on yield goal, more fertilizer is recommended for higher yield goals. A realistic yield goal is one that can be achieved at least two out of five years or nearly 50 percent of the time.

Take credit for manure, legumes and organic matter for corn fertilization

Since a reliable pre-plant soil test for nitrogen has not been developed for this region of the U.S., most nitrogen recommendations are based on a yield goal. Most laboratories will reduce the nitrogen recommendation if the previous crop is a legume. Quite often the reduction is minimal because of inadequate information regarding the kind of legume, the percent stand when it is plowed under and how long it has been established.

As a general rule, allow 40 pounds of nitrogen per acre where sod is all grass and add six-tenths (0.6) of a pound of nitrogen per acre for each 1 percent increase in alfalfa stand. For example, if you plow under a 50 percent stand of alfalfa (two to three plants per square foot), subtract [40 + (0.6 X 50%)] = (40 + 30) or 70 pounds of nitrogen from the standard recommendation where no previous legume has been grown.

For red clover and other clovers, credit 40 – 60 pounds of nitrogen to the recommendation depending on the stand when plowed under or killed by herbicides for no-till production.

Credit for nutrients in manure should also be taken whenever it is applied. If the composition of solid manure is unknown, credit 4 pounds of nitrogen, 2 pounds of phosphate and 8 pounds of potash for each ton of manure applied. For liquid manure of unknown composition, credit 10 pounds of nitrogen, 5 pounds of phosphate and 18 pounds of potash per 1,000 gallons of manure applied. If the manure has been analyzed, figure 40 – 50 percent of the nitrogen, 50 – 60 percent of the phosphate and 70 – 80 percent of the potash will be available in the first year following the application.

Don’t forget to credit half of the remaining nutrients for the second year crop. Method and time of application will also have some bearing on the efficiency of nutrient utilization by the crop. The kind of livestock, the feed ration, the manure handling and storage system will also influence the amount of nutrients in the manure at the time of application. A pre-sidedress soil nitrate test just prior to sidedress application when the corn is up can be used to fine-tune how much of the nitrogen from previous legumes or manure applications is available to the crop at that time.

Apply nutrients efficiently

Nitrogen efficiency is generally greatest when applied just prior to the greatest demand. For corn, this occurs during rapid growth and dry matter accumulation. In Michigan, this period usually starts in mid-June and continues throughout July and August. To achieve maximum efficiency, this usually implies sidedressing nitrogen when the corn is 6 to 12 inches tall or applying nitrogen through the irrigation system. Nitrogen management practices, however, will be different for each farmer and previous cultural practice. Each farmer must also evaluate efficiency in terms of tillage practices, fertilizer sources, available equipment, time constraints and what is economically feasible.

Phosphorus efficiency, if phosphorus is needed according to a soil test, and potassium to a lesser extent is most efficiently utilized if banded near the seed at planting time. Broadcast applications of phosphorus for row crops is very inefficient because phosphorus will not move very far from the point of application.

When soil tests for potassium are low, band applications of at least a portion of the potash will be most efficient. Nitrogen plus potash in a 2-by-2 band should not exceed 70 pounds per acre to avoid salt injury to the seed from the fertilizer. When soil tests are medium, broadcasting may be just as efficient as banding at planting time. Potassium will move farther in the soil than phosphorus and it is not as important as phosphorus for early plant growth.

Choose fertilizers carefully

The important factors to consider when selecting fertilizers are convenience, ease of handling, availability, adaptability to the overall fertility plan and cost per unit of the fertilizer. Individual farmers must determine which of these factors are most important for their operation. Agronomically, there are no differences between sources of fertilizer if they are applied in an efficient manner.

Grow the best crop possible

There is plenty of evidence that higher profits are directly correlated with higher yields. Fixed costs represent approximately 50 – 60 percent of the total costs of production and there is little that can be done to reduce some of these costs. Certain variable costs such as herbicide, fuel and oil for tillage, and machinery repairs are also unrelated to yield. For example, it costs just as much to plow for 150 bushels of corn per acre as it does for 180 or 210 bushels per acre.

Every phase of production from seed-bed preparation to harvest and storage needs to be evaluated. Only after a thorough analysis of all phases of production can you determine those inputs that will give the greatest return. Because fertilizer costs represent a significant portion of the total production costs and often have a significant effect on yield, it is vitally important to assess the need for fertility correctly.