Soil sample reports provide the actual nutrient level information from the field in crop plan creation. You can take your own samples and analyze your own report, or hire someone to take the samples and review the results.
If you’re taking your own samples, here are a few tips:
Test annually. Nutrient levels change according to crop yields and fertilizer application. The soil sample is the account balance.
Use GPS to mark where the samples are taken so that future sampling is based on those same points within the field or the zone.
Make sure you get an accurate representation of the field. Consider using electro conductivity, yield maps, satellite imagery, vegetative index or topography to identify different management zones in the fields. Using soil sample information, you can manage those zones separately within the field boundary
Look at sample analysis from both a zero to six-inch depth and the six- to 24-inch depth. Subsoil information from the lower depth will provide good soil quality indicators.
Once you get your report results, there are several things to consider.
Soil sample reports may include the lab’s recommendations. This is good place to start, but local knowledge and field experience can make recommendations more accurate for your field.
Consider the “low”, “medium” and “high” rating for each nutrient as an indication of levels, rather than an absolute number. Think of it as eyeing the levels on a measuring stick, rather than worrying about exactly how many litres of oil are in the tank.
The soil test report will include quantity and quality values. Quantity values measure nutrients in the soil that are available to the plant. Quality values are indicators of the ability of the soil to provide those nutrients to the plants. Very high or excess nutrient values can cause problems with other nutrient availability in the soil.
We look at is the sodium and sulphur levels in the subsoil. High levels are a good indication of a solonetzic sub soil. The field will have a hardpan that may require deep ripping and or lime application to improve the soil quality and crop yields.
When I get soil sample results, I check to see if the numbers follow the same trends as other fields in the area. If there are regional similarities, I want to see if the trends are similar. Typically pH, calcium (Ca), magnesium (Mg), iron (Fe) and aluminum (Al) will be at similar levels throughout in an area. This indicates that the soil parent material and the natural makeup of the soil are alike.
Understand the lab’s calculations. For example, cation exchange capacity gives an indication of the soil’s ability to hold nutrients, water and organic matter.
I like to see the Percent Base Saturations on the soil test report and check percentages of the cations potassium (K), Mg, Ca, hydrogen (H), and sodium (Na). There are limitations to creating the ideal ratio of cations: specific product availability, application equipment and guaranteed economic return.
Consider ratios. For example, the K:Mg ratio calculation on the soil test helps you understand potassium availability. If the K:Mg ratio is out of range, availability of either nutrient may be affected.
It is worthwhile testing micronutrients regularly as a guideline, so you know what to test for when you’re doing tissue analysis. Having the lab indicate the range for the micros is important. For some micronutrients, we are looking at a very small amount. The difference between deficient and sufficient can be one or two parts per million. Crop response to micronutrients can be crop specific — certain crop show higher responses to micronutrient applications. A good level for one micronutrient on a certain crop might be too low for optimum crop potential.
When looking at micronutrients it is also important to also understand the relation of nutrients to each other. Sometimes a high level of one nutrient will affect the availability of another, leaving the plant with limited availability. Consider addressing micronutrients to fields that need them most and are likely to provide the greatest response.
When I go through soil sample reports with farmers, I like to look at all of the fields together. I place the test report values in spreadsheet columns, then look at average values for each column. We look at the highest and lowest 20 per cent of the fields, to see if anything interesting explains differences in the field productivity. It’s helpful to also have past yield information.
There can be benefits to working with an agronomist. Someone with experience who sees a lot of samples can help you appreciate the differences in values and the relevance of your own information.
The agronomist should be very familiar with the specific technique of the lab that has done the analysis — each lab presents soil results in a slightly different way. It is very common for two different labs to give different reports for samples taken from the same field.
Two agronomists may make two different recommendations when looking at the same soil test report. Each agronomist will have their own philosophy when making recommendations, and should be able to explain the theory behind the recommendations. †