Charles White, Assistant Professor of Soil Fertility and Nutrient Management
Penn State University
Routine soil testing is the foundation of any successful soil fertility program. Without knowing the nutrient levels and soil pH in your crop fields, it is impossible to manage nutrients and lime applications for peak crop production and the most profitable economics. Soil testing is the only way to know how much of each nutrient is needed and where. Trying to manage soil fertility without soil testing is like trying to drive with your eyes closed.
There are several reasons why collecting soil samples for soil testing in the fall is a preferred time period. First, soil sampling in the fall after crops have been harvested lets you walk or drive a buggy through the field to collect soil cores without going over a standing crop.
Next, the soil has usually moistened up a bit, so it’s easier to get a soil probe in and out of the ground. Finally, you will receive the results from the soil testing with enough time to make a game plan for lime, fertilizer, and manure applications for the coming year.
If you end up needing lime, winter can be a good time to spread lime on frozen ground to avoid soil compaction and allow enough time for the lime to react and raise soil pH before the next year’s crops. You’ll only be able to know if lime is needed, and how much, if you have a soil test taken in the fall.
If you need P and K fertility, you can calculate how much you’ll need for your different fields and place an order with your fertility dealer and figure out an application strategy well in advance of the next crop year. If you are importing manure onto the farm, results of soil testing can help you determine which fields will benefit the most from the N, P, and K contained in the manure, and may help you strategically locate manure stacking areas for the most efficient spreading on the fields that will be receiving manure.
The Penn State Agricultural Analytical Services Lab website for soil fertility testing has links to sampling instructions and submission forms.
There is also a video that explains the basics of soil sampling. Many people are accustomed to purchasing “pre-paid” soil testing kits from county Extension offices, which is essentially a special sample bag with a sticker on it indicating the analysis cost has been paid already.
Soil tests are usually good for making fertilizer recommendations for the following 3 years of the rotation. When you factor in the acreage that the soil test represents and the frequency of testing once every 3 years, the costs of soil sampling only amount to a dollar or two per acre per year, even including the labor of obtaining the soil sample.
Given that the cost of fertilizer and lime inputs each year can easily run up to and over a hundred dollars per acre, the cost of soil testing is negligible relative to the value derived from it in being able to make informed and economical decisions about nutrient applications.