Do you know your soil?

Written by Jason Worthington, Thad Becker, D.J. Vollrath on .

Fall always brings up conversations about soil management. Typically, when we think of soil considerations, we think about fertility. “How much N, P and K should I apply?” is generally the first question that comes to mind. Soil tests and yield maps are great tools for answering that question. Recommendations for these nutrients and other soil amendments such as lime are critical management aspects and perhaps the most important to address. However, fertility levels are only a portion of the insight growers can access through MFA’s Nutri-Track program.

Understanding physical soil properties and how they fluctuate across a field can provide valuable clues to address fertility management, hybrid and variety selection, planting rates and even weed control concerns. Among key properties are soil texture—the amount of sand, silt and clay in the soil—and organic matter. Both of these soil characteristics can impact drainage, resistance to compaction, nutrient-holding capacity, behavior of residual herbicides and other factors. Soil characteristics even impact the spectrum of weed species in the field because certain soil types are more conducive to certain weeds.

How do we manage not only variable soil fertility but also variable soil properties? There are many solutions for that: variable-rate nitrogen, nitrogen modeling, comparing yield zones to soil zones, variable-rate seeding, multi-hybrid planting or even something as simple as selecting a hybrid well suited for the unique conditions of your field. But, before any of these solutions can be implemented, it is critical to understand which soil properties you have. Traditionally, to do this, we used soil maps developed by the NRCS more than 50 years ago without the level of technology we have today. Now we have innovations such as Veris toolbars that use electrical conductivity (EC) and optical sensors to more accurately identify soil zones. These values relate closely to soil texture and organic matter. The chart in Figure 1 shows examples of how these readings can be used to measure zones and the other insights they can provide.

Just below the chart, the photos of soybeans in Zone 1, left, and Zone 4, right, depict the variability of the soil properties in the field. From these images, it’s clear that the varying soil types and properties greatly impacted the growth and development of the soybean crop, especially in a dry year such as 2018. Beyond the differences in canopy and plant height, there was a significant difference in the number of pods and blooms.  

It’s not surprising that coarser soils with lower water-holding capacities should be more prone to stress, but we did not anticipate the stark difference in weed pressure based on soil type. The coarser soil had a much higher level of weed pressure, likely due to multiple factors such as reduced canopy and differing soil/herbicide interactions.

So now that we know where these soils differ and how nutrients, crops and pests respond differently to these zones, how can we more effectively manage them? Zone 1 might respond better to lower seeding populations, a more defensive corn hybrid and lower cation exchange capacity. Coarser soil texture will not hold on to nitrogen fertilizer as well as soil with higher cation exchange capacity. Zone 4 may facilitate potentially higher-yielding hybrids at higher populations, and it may not be as risky to apply high rates of N to it.

When evaluating plans for next spring, soil fertility is critical, but it is not the only soil property to consider. Advanced EC and organic mapping solutions from MFA’s Nutri-Track program can provide valuable insights and a basis for fertilizer recommendations, seeding information, aerial imagery and even pest scouting reports. It all starts with understanding the underlying soil properties and the extent of how those properties vary across the field.

For more information on EC mapping, contact your MFA precision specialist or Nutri-Track consultant.

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