Soils: January 2001

You may notice that all of us soil scientists preach soil testing at every opportunity, so we are obviously sold on its benefits. Your logical question may well be, What's in it for me?

The number-one thing soil testing can do is help you make more money. For instance, a test may show that your soils have adequate levels of some nutrients and that you can make optimum yields with less fertilizer than you're using. Cutting back on fertilizer can make you money because you spend less while making the same yield.

Here's an example. Let's say you are currently using 60 pounds of phosphate and 60 pounds of potash per acre on a field. Soil test results come back saying the 60 pounds of phosphate is right, but your soil is high in potassium and you don't need the potash. Eliminating the potash can save you $9 to $12 per acre without reducing yields. Over large acreage, that amount can add up to significant savings.

Another way soil testing can help you make more profit is by identifying fields that have low fertility and need more fertilizer than you're applying. Your potential yield or carrying-capacity increase can far outweigh the cost of the fertilizer you need to apply. You actually make more profit by increasing spending.

Let's look at an example. Suppose you're using 30 pounds of phosphate and 30 pounds of potash per acre, and soil tests show you need twice the amount because your fields are deficient in these nutrients. Doubling this rate would cost you $12 to $15 per acre. However, the resultant increase in yield or carrying capacity means you make a profit.

A third way soil testing can increase your profits is by identifying acidic fields where low pH is limiting your yields by causing inefficient fertilizer use. If your budget is limited, you may increase profits by applying lime and less fertilizer in some fields instead of applying more fertilizer with no lime. You can spend the same amount of money but increase yields.

Let's assume you've been using 60 pounds of phosphate and 60 pounds of potash per acre. Your soil test results reveal that your soil is extremely acidic, causing retarded plant growth and inefficient nutrient use. The P and K you're using cost about $25 per acre. For one year, you may be better off spending the $25 on 1 ton of high-quality lime per acre rather than on P and K fertilizer. The next year you can go back to using fertilizer as recommended by soil tests, since a lime application will last three to five years.

One more way soil testing can increase your profit margin is by changing what nutrients you apply. For example, a test may show that your soil is high in one nutrient but low in another, but under your current fertilizer program, you apply equal amounts of both nutrients. By applying more of the deficient nutrient and none of the surplus nutrient, you may keep your input costs about the same but dramatically increase your fertilizer efficiency and yield.

Let's say you've been using 40 pounds of phosphate and 40 pounds of potash per acre, and soil test results show your field is high in potassium but very low in phosphate. You could eliminate the potash and raise your phosphate rate to 60 pounds per acre. The total cost would be about the same, and yields or carrying capacity would increase.

A famous football coach of yesteryear often said that when you threw the ball, three things could happen, and two were bad. He was obviously a fan of running the ball. In a similar vein, when you fertilize without a soil test, three things can happen, and two are bad:

1. you may apply more fertilizer or lime than you need, resulting in unnecessary costs and no increase in yield;
2. you may apply less fertilizer or lime than you need, resulting in reduced yield; and
3. you may get it right.

The odds of successfully fertilizing without a soil test are about one in three. We think we can greatly improve these odds with good soil testing practices. Soil testing is often touted as a tool that monitors nutrients and helps the environment, among other things, and it's true. But remember, the number-one benefit it can provide is an increase in your profits.