In a tight economic year where every dollar counts, why should you spend the money on soil sampling?
There are a variety of reasons.
You need several years of soil samples, that way you can look at trends. It’s best when soil sampling occurs every year. It will pay for itself even when commodity prices aren’t favorable.
Soil test results can be variable from year to year, some years testing very high and some testing very low. Making nutrient recommendations based on a single year’s soil test results can be flawed because the soil results could be one of those outlier years. The most accurate method we implement is to take several years’ worth of soil results and look at the trends to try to eliminate the “outlier” results.
For example, say soil samples have been taken the past four years for phosphorus levels. The levels read 20, 24, 65, and 35 parts per million in chronological order. I would deduce from these results that over the past four years the phosphorus levels are definitely going up. The 65 PPM reading is an outlier and not factored into my fertilizer recommendations. These results tell us that the fertilizer rate being applied the past four years is more than the crop use rate, so in this case the fertilizer rate could be reduced.
The main benefit of soil sampling is to know if you’re fertilizing too little or too much. By soil sampling for multiple years in a row, you can create more accurate fertilizer recommendations.
The producer should want to do that every year. He can get a powerful recommendation to build off that information.
The more samples taken per field the better. A minimum of one “composite” sample per 40 acres with 15 to 20 cores per sample is generally where we start and recommend “grid” sampling every 2.5 acres for the most accurate results.
Fertilizer recommendations can be made without soil sampling. But at an annual cost of about $2 per acre, you could save $10, $15 or $20 per acre because you will only be applying what the soil requires for the crop. You can improve revenue from the higher yields due to the improved fertility. That’s a good return on investment by anybody’s standards.
Editor’s note: Mark Morten is director of education and training at Servi-Tech. To send a question to Ask the Agronomist, send an email to [email protected] with the subject line “Ask the Agronomist” or tweet @ServiTechInc or @HighPlainsJrnl with the hashtag #AsktheAgronomist.
