Testing’s Role in Continuous Yield Improvement

Whether striving to reach 300-bushel-per-acre corn, 80-bushel-per-acre soybeans or just steady yield growth on their acreage, farmers are focused on continuous improvement. As Michael Porter’s quote suggests, this type of continuous improvement goes hand in hand with strategy. Farmers who commit to a regular soil-sampling strategy, for example, often make more-informed decisions about their farm’s ongoing productivity.

Strategy is also about making choices with one’s available resources and tools. Since every farmer’s resources (such as soil, climate and topography) are different, it’s recommended they evaluate their options and then apply what makes sense to their particular farm.

In the Corn Belt, for example, taking 2.5-acre grid samples every three to four years is common, while some farmers narrow their sampling to 1-acre grids. Others choose to sample by management zones using yield maps or their local county’s soil surveys. Some ag retailers or seed suppliers may also suggest particular methods for creating zones tied to local conditions. Zone management can be particularly helpful on fields with variable topography and different soil types that affect nutrient holding capacity and productivity, while grid sampling is cost-effective on flat land without much variability in soil type.

Whatever the method, soil scientists recommend being consistent with apples-to-apples comparisons and the ability to spot trends over time. Sampling the same locations at the same depth as previous years, and at about the same time of year, will provide better comparisons. Ideally, you will want to take samples under similar soil conditions each time, since there is temporal variability when nutrients become available.

James Schoff, who farms 2,600 acres of corn and soybeans near Walnut, Illinois, prefers early-spring sampling since soil moisture after snow cover has been fairly consistent in his fields. The northern Illinois farmer has used the soil-testing service at Ag View FS to do sampling and analysis every four years. Schoff is quick to point out how soil sampling plays a role in reaching the long-term, sustainable goal of producing 300 bushels of corn per acre.

Ag View FS does 2.5-acre grid sampling, taking 7.5-inch cores. Data is then evaluated to determine how to best manage crop nutrition.

“Fertility is a big piece of the crop management puzzle,” Schoff says. “If you’re not on top of it, it’s tough to get fertility back to levels where soils are performing at their peak.” Schoff points to soil testing conducted on his fields in 2012, when most of the Corn Belt experienced a prolonged drought. “We had a lot more variability than we thought,” Schoff explains, adding that the differences in soil type became especially apparent on yield maps.


Farmers who know their soil conditions as a result of soil testing can dramatically improve their bottom line by providing crops with the right amount of nutrients. Dan Kaiser, extension nutrient management specialist, University of Minnesota, advises farmers to calibrate soil test results against crop response.

“Without calibration, soil test results have no value,” Kaiser says. When soil test results are calibrated against crop response, the farmer gets a better idea of what is potentially at risk for not providing enough fertility. A calibrated soil test will provide a probability of response to phosphorus or potassium.


Should plant tissue testing be part of a farmer’s crop management strategy? Kaiser does not recommend it as a substitute for soil sampling, but says it can help farmers diagnose problem areas. For these areas, he recommends that farmers take a soil sample and then evaluate the rate at which nutrients are applied to hone in on what may be causing a particular issue. For example, there could be a potassium deficiency, but the problem could also have resulted from a nematode infestation.

Farmers with a history of nutrient deficiency in their fields may want to use tissue sampling as part of a planned exercise, such as regularly taking samples to monitor nitrogen levels. Tissue sampling should be part of the plan from the beginning, and not a reaction to what you’re seeing in the field. A sound nutrition program begins with soil sampling. Tissue sampling can help with foliar application. Tissue sampling can be used as a tool to make a planned or rescue application, adding that more retailers are now providing tissue-sampling services.

If a farmer decides to incorporate tissue sampling into his or her strategy, Kaiser recommends not sampling until the crop is beyond its vegetative stage. This is because various environmental stresses, and not necessarily nutrient deficiencies or imbalances, may be adversely affecting the crop. For corn, Kaiser advises testing after the V5 stage, and for soybeans, beyond the trifoliate, mid-bloom stage.

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