The 1st Step: Building a Crop Nutrition Program
John Leif, Field Agronomy Manager
Every grower has a budget for fertilizer - where should the first crop nutrition dollar be spent? The first, most important tool for developing a plant nutrition program is a good soil test. Unless a grower knows the condition of their soil, any fertilizer program will be based on averages and generalities. Significant nutrient deficiencies cannot be adequately addressed without soil test information. In today's economic environment, it is vital to understand what the soil has, and what it doesn't have, in order to make a well-thought-out fertilizer program.
The first step is, of course, collecting a sample. While not complicated, there are a few things to keep in mind when collecting a soil sample.
Use Clean Equipment
Make sure you don't have any sources of contamination that could influence the results of a soil test. For instance, use plastic containers that are dedicated to soil testing and not sued for other purposes. The soil samples in Table 1 were taken using a standard soil probe, and the samples were placed in either a plastic bucket or in a galvanized bucket. Soil cores were mixed thoroughly in their respective container before being placed in a soil sample bag and sent to Midwest Labs for analysis. Obviously, the sample placed in the galvanized container had P, K, S and Fe values similar to the sample placed in the plastic bucket. The Zn level, however was substantially higher in the sample placed in the galvanized bucket.
Know Your Fields
Soil sampling can be done in a grid sampling pattern if nutrients are being applied using precision application and variable rate technology equipment. If variable rate applications are not intended, fields can be separated into similar areas (zones). Often the similar areas can be grouped by soil type. Knowledge of the field is critical, so that distinct areas of the field can be sampled separately. A composite soil sample should represent an area no larger than 20 acres. Larger areas can be split into multiple samples. Sampling should be done in a zig-zag pattern throughout the zone, making sure to stay away from the outside boundaries of each area. Make sure the zone is well represented in the soil sample. Remember that up to 20 acres are to be represented by less than 1 pint of soil in the sample bag, and the lab uses just a small portion of that to do their analysis.
Order the Proper Tests
There are many good soil analysis laboratories across the country. It is important that the laboratory conduct tests on cation-exchange capacity (CEC), pH, organic matter, base saturations, and all nutrient levels, including micronutrients. Most laboratories offer several test packages that offer various nutrient tests. Individual tests can be requested in addition to those included in a test package.
Be Aware of Seasonal Effects
Consistency is key when comparing multi-year soils tests. There can be considerable seasonal influence on soil test values, especially on potassium and pH. According to Midwest Labs, clay soils, like those in much of the northern corn belt, have a tendency to have a higher potassium level during winter months. Soil pH values can vary, as well, depending on rainfall or irrigation, nitrogen or sulfur inputs, and soil buffering capacity. It may be wise to take soil samples during periods when these variations hit average values. These periods are generally in the early fall (September-November) and again in the late March-April time frames. However, the ideal timeframe for taking soil samples should be based on ease of field access, so that differences in soil type, slope, drainage and cropping pattern can be most easily accounted for.
Effects of Cultural Practices
Reduced tillage, ridge tillage, and zero tillage can cause layered, stratification of organic matter, pH and soil nutrients. According to Midwest Labs, soil samples in areas where these practices are used should include samples that are split into 0"-3" and 3"-7" increments, to assess to what extent stratification is occurring. This is important in getting an informed fertilizer recommendation for the area.
The Next Step
While properly collecting and submitting soil samples is a critical first step, interpreting the results is another challenge. Upon first glance, a complete soil sample report can look like something a nuclear engineer carries in his briefcase. [In our spring newsletter, we will take a closer look at each component of a soil analysis report and use the data to build a crop nutrition program.]
*This article was in AgroLiquid's Winter 2017 Quarterly Newsletter