Farm Progress

Here are tips to send the best soil sample to the lab for testing.

August 24, 2017

3 Min Read
DO IT RIGHT: The small amount of soil in the sample bag you send to a testing lab must represent the entire area to be fertilized. Sample soil before lime, fertilizer or manure is applied; avoid unusual areas; and use clean equipment for collecting samples.

Soil sampling is one of the most economical management practices for crop production. As fall approaches, farmers are preparing nutrient recommendations for the next crop. Soil sampling determines nutrient concentrations already in the soil, so that application rates for nutrients such as phosphorus, potassium and lime can be determined for fall and spring applications.

Soil sampling can be a delicate process, which begins with making sure soil samples are collected the right way. According to Robert Mullen, director of agronomy at PotashCorp, there are four simple tips growers can try to ensure they get a good representative sample:

1. Use clean tools. The first step before collecting a sample is making sure all testing tools are clean and free of any prior contamination, such as rust, old fertilizer or previous soil samples. This is especially true when conducting micronutrient analyses. Using contaminated equipment can alter the soil test information and may provide inaccurate results.

“To best gauge correct crop nutrient status, this simple step is crucial to not miss,” says Mullen. “Taking time to ensure that soil probes and plastic buckets are clean before you go to the field can help ensure more accurate results.”

2. Collect enough cores. Soil is not uniform, and this variability can play a significant role in crop performance, crop nutrient removal and consequently soil nutrient status. Not only does soil have natural variability, but also crop production practices contribute to variability. Less-than-precise fertilizer application techniques and harvesting operations don’t evenly apply or return nutrients to the soil. Not collecting enough core samples to accurately represent an area may result in providing you with misleading soil test information.

“It is advised to collect a minimum of 15 random soil samples from a representative area to create a composite sample,” says Mullen. “Collecting too few samples may result in inaccurate information and poor repeatability in future years, and ultimately, misinforming you about soil nutrient status and fertilizer need.”

3. Sample at consistent depths. It’s recommended to collect core samples at a consistent depth. Some guidelines recommend 6 inches, some 8 inches. Either of these approaches is appropriate, farmers should just be consistent about the depth of collection. Collecting samples at too shallow of a depth may cause nutrient concentrations to appear higher than what they really are. Also, sampling too deeply can cause nutrient concentrations to appear less than what they really are. If you have questions, consult your local agronomist or the soil testing laboratory being used.

“There can be large variances within a few inches along the depth of your soil,” says Mullen. “So making sure each sample is collected from the same depth helps avoid any misconceptions about your soil’s nutrient concentrations.”

4. Thoroughly mix cores. Adequately preparing the sample to submit to a lab is equally important. After thoroughly mixing the core samples in a clean plastic bucket, place the sample into soil sampling bags and send out for testing.

“The total amount of soil that is sent to be analyzed is small, so a poorly mixed sample may cause significant variability,” notes Mullen. “Not rushing through this last step can help ensure that no matter how small your sample, it accurately reflects your soil’s nutrient status.”

All in all, the first step in making wise fertilizer application decisions is soil sampling and testing. It may require time and effort, but implementing proper nutrient management techniques can help support yields and maximize profits. For more information on soil sampling, watch this video from eKonomics.

Source: PotashCorp


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