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Back to the basics – soil sampling

08/19/2019

While this technology has existed for decades, it should still serve as a cornerstone of your operation. We have seen the emergence and continued development of data management systems that incorporate artificial intelligence and algorithms to interpret captured data.

The aim is to derive actionable insights for production agriculture. These systems should provide a descriptive, predictive and prescriptive capacity to support meaningful management insights that extend beyond the obvious approach.

A 1950’s technology fits the descriptive, predictive and prescriptive mode of a high-tech service. This tool is soil testing. Soil sampling may not always be viewed as a high-end technology – especially when compared to today’s site-specific technologies and cloud-based data analytics.  

But soil test results contain all three elements of a high-tech service. The results of a soil test certainly describe the soil conditions. Test results show whether a soil is acidic or basic, for example. Lab technicians can measure soil organic matter (SOM) content.

Farmers and agronomists can use this data as a surrogate measure of soil health. Details on primary, secondary and micronutrients and cation exchange capacity (CEC) can all offer insights into the soil’s productive capacity.

Soil test results are predictive of crop performance based on the values reported. A low soil pH will limit crop growth of most broad-acre crops we grow. If essential nutrients test low, they will be yield limiting. We can use pH, SOM and CEC values to select appropriate herbicides to minimize crop response and optimize weed control.

These results are prescriptive since we have calibration data to turn soil test values, such as phosphorus and potassium, into nutrient recommendations. We can use these recommendations to amend the soil in very precise ways. We can examine pH and buffer pH to determine the precise rate of limestone we must apply to adjust the soil pH. We can use SOM to assess nitrogen contribution and offer insights on how zinc, manganese, copper and boron will behave in the soil.

As we embrace sustainability, soil sampling is a cornerstone activity for 4R Nutrient Stewardship compliance. No substitute exists for soil testing. We have no other way to assess the soil’s productive capacity and determine what amendments, if any, are needed to optimize crop performance. To have your acres count as 4R certified, your soil tests must be no older the four years.

Soil test results, much like a balance sheet, indicate the health of the operation. Just like you would not make financial decisions today from a balance sheet from 2010, you should not make nutrient plans with soil test results of that vintage either.

For farmers who simply opt to apply nutrients at a crop removal rate each year, this approach is not without risk. If soil nutrient ratings are low and producers are not aware of these deficiencies, simply fertilizing to replenish crop removal rate will not optimize yields.

On the flip side, if soil nutrient ratings are excessive, fertilizing at the crop removal rate means producers are increasing the size of their environmental footprints. In the process, farmers may not be optimizing harvested yield and most likely are not maximizing nutrient use.

If, simply by good luck, soil nutrient levels happen to be where they should be, the use of a fertilizer program to replace the nutrients removed by crops maintains soil fertility. Producers won’t know this information, however, if they don’t conduct soil testing.  

Often, growers base their crop removal rate calculations on last year’s crop. By taking this approach, we are looking in the rear-view mirror to make management decisions. But we should look toward the much bigger windshield of opportunity by using soil test results to guide our rates and types of nutrient applications. 

Most programs based on crop removal calculations tend to apply the same fertilizer to all fields. One thing I have learned over 40 years, however, is that not all fields are the same.

Usually, producers rationalize the use of a nutrient program that simply accounts for crop removal without the benefit of soil test results by saying “I am happy with my yields.”

A single soil report can provide good information. A series of reports over the years is better.

We can look at multiple years’ worth of reports to find trends in soil fertility and allow for adjustments in amendments.

If soil nutrient levels are increasing, then our applications of nutrients exceed what our crops are removing from the soil. If nutrient levels are declining, the opposite is true. If the values remain constant, we have a balance in our cropping system.

In years when net returns to cropping are marginalized, we can prioritize our nutrient applications. In the fields with high fertility, we can reduce the amendment rates there in the short term. We can reallocate amendments to fields that will need the most help to maintain yields.

When we face years with marginal returns, yield maintenance is vital. The higher our yields, the more yield we have available to sell at any price. The economic and agronomic risks of cutting back nutrients on all farms are unacceptably high.

Without soil tests, we will not know which fields are in most need of amendments. With all the technology we have available today, including soil sampling, keeping records and sorting fields by productive capacity, it is easy for us to custom-blend nutrient programs targeted to address field variability.

What does it cost to soil sample?

What does it cost if we don’t? It all depends. Are we talking about the soil sampling activity by itself and what it costs? Or are we integrating soil sampling data into a comprehensive forward-looking crop production system tied to farm profitability?  

Producers who soil sample on regular basis are better managing their risks and helping to optimize profits. These farmers are also gaining competitive advantages with more efficient production systems.

The below photo is from an area of a field that the producer soil tested in the fall. The area had a pH of 5.3. The winter wheat in this area is performing poorly, as the crop grows best at a soil pH of 6 .9 to 7.0. The soil test results predicted that the wheat would grow poorly well ahead of planting.

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The producer did apply limestone prior to planting but it must be applied a year ahead to have enough time to react and raise the soil pH.

Our crop specialist can walk you through a customized and personalized soil sampling, production solution that works on your fields and cropping system.

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