Soil Testing in a Tough Ag Economy

Anyone who has worked in the agricultural industry in the last few years has heard someone say, “the days of $7 corn and $17 beans are gone.” You may have even seen “In memory of…” decals on truck windows commemorating those commodity prices. The truth is prices are down and most agricultural economists predict that lower prices are going to be the norm for several more years. In these tight times, producers must critically evaluate every crop input from seed selection to herbicide program to fertility program. However, these decisions cannot be made with a short-sighted mentality of getting though the current season and hoping for better prices next year. These decisions have to be made with consideration of how it will impact their operation for the next three, five, or even ten years, especially if commodity prices remain low.

When selecting which seed to plant, it can be tempting to simply go with the highest yielding variety from the previous year’s variety trials. Yield is obviously important, but be sure to purchase a variety appropriate for your operation. For example, do not pay extra for traits to protect against diseases or pests that are not an issue in your region. On the other hand, when selecting an herbicide program, glyphosate alone has a very attractive price tag, but it is necessary to utilize herbicides with other modes of action occasionally to prevent glyphosate resistant weeds from taking over. It may cost a few more dollars per acre at the time, but will certainly be worth it in future years when glyphosate is still an affordable option for most of your weed control.

Soil fertility inputs can represent one of the highest costs in row crop production. In addition to the cost of the fertilizers, there are additional costs for soil sample collection, laboratory analysis, soil mapping and prescription software, and variable rate application. To help reduce costs, some producers may choose to reduce the intensity of soil sampling by using larger grids, fewer management zones, or only collecting a single composite sample from each field. Others may choose to reduce the frequency of sampling or completely abandon sampling all together. While these decisions will initially reduce input costs, how will they impact the productivity and profitability of the operation in the future?

The goal of any fertility program should be produce the greatest yield with the least amount of fertilizer. The most effective way to reduce fertilizer inputs is to identify the areas that require additional inputs and those that do not need any. Soil fertility levels and soil pH can vary greatly in a single field whether it is from natural soil variation or past fertility practices. Collecting a single sample from a field and making a flat rate application of fertilizer or lime based on that single sample is likely to result in an over application in some areas and under application in others. The smaller the area that a soil sample represents, the more confident you can be that the laboratory results accurately represent the area. Maintaining an intensive sampling program, whether grid or zone, is essential to assure the greatest return on your fertilizer investment. 

Too often soil test results are used to make a fertilizer prescription and then discarded. There is a lot to be learned from reviewing previous soil test results. By evaluating the impact of a fertilizer or lime application on the soil test levels, future application rates and timing can be adjusted to better suit your soil type. For example, lime applications are intended to last for three to four years, but on some soils a lime application may only last one to two years and others soils it may last six or seven years. Soils that do not respond to fertilizer or lime applications as expected can only be identified with routine sampling frequency. It takes at least three sampling cycles to begin to identify trends such as this. If a field is sampled on a 4-year cycle, it will take eight years before any adjustments to the soil fertility program can be made with any confidence. By sampling more frequently, every two or three years, these trends can be more quickly identified and addressed.

Managing a successful farming operation means minimizing risk whenever possible. Maintaining a routine intensive soil sampling program is the best option for minimizing the possibility of excessive fertilizer application or losing yield from under application.