Can Soil Health Management Get You Into the Field Earlier?

Field workability. It’s difficult to quantify, because whether it’s a good time for field work depends on the work you’re trying to do, your equipment, your soil type, as well as maybe your tolerance for compaction and the other time-sensitive elements of the farm system. But lots of growers using soil health practices describe being able to do the work they needed to in more diverse conditions.

For example, Vance Johnson, a farmer in Wilkin County, MN, described in a recent talk how he was able to finish planting in a light rain in a reduced-till field with lots of residue, while in a conventionally tilled plot he could barely make it to the end of the field to get out, and still had a lot of clean up to do.

Many may recall the difficulties associated with field wet spring and fall field seasons in 2016 or 2019. In Minnesota, precipitation between the 1950’s and 2018 has increased by 10-25% across the state, with the most dramatic differences happening in southern MN. Extreme precipitation events of 2 inches or more have also increased in frequency over time. Annual precipitation is expected to continue to increase over time, with the largest seasonal increases likely during fall and spring. With a shortening window of conditions favorable for getting in the field, building soil structure using soil health practices and opting for precision ag equipment may help you get into the field sooner rather than later.

These timely operations can sometimes make a big difference to agronomic outcomes. Corn and soybean yield goes down with delayed planting in the spring. Spraying herbicide in the critical weed control window can also protect yield. Just as importantly, getting field work done when you’re ready can reduce stress and improve quality of life on the farm. If you’re able to follow through on a plan more often, that makes it easier to attend family events, and feel more in control of the farm/life balance.

So how many days do we have? The best source of field workability data is from the USDA National Agricultural Statistics Service. This is based on a county level expert who reports a number of days suitable for field work each week April-November in Minnesota. This shows up right on top of the weekly MN Crop Progress Reports (you can subscribe from the USDA) as a statewide average.

More locally, the staff at the University of Minnesota’s Southwest Research and Outreach Center (SWROC) at Lamberton have been recording field working days daily between April and November since 1974. They also record soil moisture every two weeks. Dr. Bill Lazarus, a UMN Ag Economist, has used that data to build a simple model that predicts field workability based on soil moisture for that location.

You can also calculate field workability using a “50-50” rule , which states that “at water contents around field capacity, traffic on agricultural soil should not exert vertical stresses in excess of 50 kPa at depths >50 cm.” By using soil moisture readings and calculating the vertical stress for a particular implement, you can identify a threshold for days when you should not traffic your field. Using this rule, a study from Katie Black and Samantha Wells found that even relatively light implements, like a high clearance tractor, could only operate for a third of the days in a fall cover crop sowing window (late July - late October) without risk of damage to soils in a very wet fall season.

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