Brent Jaenisch

Early Summer Grid Soil Sampling

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The interest in early summer topsoil grid sampling (1.0- to 2.5-acres per grid) continues to increase, especially in traditional corn-soybean growing areas. In Minnesota alone, 30-40% of all grid soil samples are now collected in the summer months. The early summer period (late May to late June) is an excellent period of time to collect grid soil samples, instead of waiting until after soybean harvest when workload and time constraints are heavier.

These early summer soil samples are collected from unfertilized soybean fields, and the soil samples are collected when the soybean plants are in early vegetative growth stages while you can travel across soybean fields with ATVs or UTVs without causing unnecessary damage. These are fields that would have been fertilized two years prior ahead of corn planting, and the fertilizer rates were high enough to cover the following soybean crop as well.

The early summer timeframe works well for 0-6 inch soil sampling and analyzing non-mobile nutrients and soil properties. The commonly tested nutrients and soil properties are P, K, Ca, Mg, Na, B, Cu, Fe, Mn, Zn, pH, buffer pH, salts, organic matter, carbonate (CCE), CEC, and base saturation. It is not applicable for 2-ft residual nitrate-N testing, which must wait until after the crop has been harvested. The mobile soil nutrients like nitrate-N, sulfate-S, and chloride should wait for fall soil sampling.

Advantages to early summer grid soil sampling

  • High-quality soil cores with consistent depth (moist and firm soil profile)
  • No more chasing around in the fall trying to soil sample fields that have been harvested and before any fall tillage occurs
  • More time in summer to develop fertilizer management plans with growers
  • Fields can be fertilized immediately after harvest
  • Avoid post-harvest soil sampling rush in the fall
  • More available labor (interns) in the summer timeframe compared to the fall season
  • On-ground assessment of soybean stands, especially if iron deficiency chlorosis (IDC) is observed

You will want to avoid soybean fields that have been fertilized or manured in the fall or spring prior, as the recent fertilizer or manure application can skew soil test results. In these situations, it is best to wait until after the soybean crop has been harvested to collect soil samples in the fall. In small grain production areas, if soybean or pulses will be planted next year (both crops not requiring nitrogen fertilizer), the early summer timeframe can also offer another opportunity to accomplish grid/zone sampling in the early vegetative growth stages of the small grain crop (barley, oat, wheat), just make sure to avoid any fertilizer bands (seed-row or mid-row fertilizer bands).