32 Story Idea? Email Paul.Nolan@Farms.com Better Farming | May 2024 crops: yield matter$ SOIL SAMPLING REVISITED Reviewing your fields is time well spent. By Dale Cowan Data management systems that incorporate artificial intelligence, technology, and algorithms to interpret data keep improving. We need to stay mindful that the output is only as good as the input and assumptions that are made. The goal remains to derive actionable insights from collected data to support effective decision-making. Soil sampling and soil testing have been around commercially since the 1950s. In today’s view of technology, soil sampling may seem rather traditional and, dare I say, represent the old way of doing things. We want our new measurement technologies to be descriptive, predictive, and prescriptive. I propose that soil samples and test results contain elements of a high-tech service. The results of a soil test certainly describe the soil conditions, such as whether a soil is acidic or basic, for example. Lab technicians can measure soil organic matter (SOM) content, and farmers and agronomists can use this data as a surrogate measure of soil health. Details on primary, secondary, 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 too. We can use pH, SOM and CEC values to select appropriate herbicides to minimize crop response and optimize weed control. Soil test results are prescriptive since we have calibration data to turn soil test values, such as phosphorus and potassium, into nutrient recommendations, and use them to amend the soil in very precise ways. We can examine 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 into how zinc, manganese, copper, and boron will behave in the soil. We can use SOM tests over time to assess crop rotation impacts on soil health. As we embrace sustainability, soil sampling is a cornerstone activity for 4R nutrient stewardship compliance. No substitute exists. 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 than four years. Proper soil sampling technique is important. Taking enough cores to represent the area in question is essential. In bulk, composite sampling usually averaging a core every two acres is sufficient, but as we move to more site-specific sampling, fewer cores in a smaller area is sufficient, offset by more samples being collected. In soil scanning with technology like SoilOptix’s, the onboard software chooses the sample sites that best represent the field based on the data just collected. Above all else, proper sample depth done consistently is likely the most important aspect of gathering soil samples for nutrient analysis. The chart on Page 33 indicates how nutrient levels vary by depth, often a bigger factor in minimum tilled fields Low soil pH of 5.3 in winter wheat. Dale Cowan photo
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