Crop Wealth Through Soil Health
The summer season is here! For my host site, the Cottonwood Soil and Water Conservation district, the summer season means getting outside and conducting assessments! One of the projects we’ve been working on is cropland in-field soil health assessments. These soil health assessments consist of a combination of diagnostic tests to help document soil health concerns. The goal of testing soil health is to give farmers an idea of what is going on in their fields. The Cottonwood SWCD has started a Soil Health Task Force that consists of SWCD staff and local farmers. The Task Force meetings are for exchanging ideas on how to better assist farmers with their soil health journey. One of those ideas was soil health evaluations!
In agriculture, soil health is the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans. Healthy soil helps us by providing food, reducing flooding, reducing erosion, improving nutrient cycling, increasing air quality, and providing stability and support. On the other hand, soil health concerns include decreasing plant health, erosion, runoff, reducing water and air quality, aggregate instability, and compaction. Soil health evaluations allow us to recognize soil health concerns and provide suggestions for conservation management. There are five principles to improve soil health determined by the Natural Resources Conservation Service. These principles include integrating livestock, minimizing soil disturbance, and maximizing diversity, soil cover, and living roots. Examples of these principles in practice are reduced till or no-till, cover crops, leaving surface residue, and diversifying crop rotations. By adding soil health principles to farming practices, we are keeping our soil healthy and productive!
For this blog, I would like to discuss all that goes into conducting cropland in-field soil health assessments! Here’s the process that SWCD Program Technicians and I follow for each field:
The first test we start with is penetration resistance. Compaction is a result of putting weight on the soil through repeat traffic, such as agricultural equipment. Compaction can be an issue for soil health because it decreases soil aeration and creates restriction layers that are too hard for crops to properly grow through. To assess penetration resistance, we use a penetrometer to determine subsurface pressure at increasing depths. A pressure gauge at the top of the penetrometer tells us the level of compaction as the probe is pressed into the ground. Fields that are meeting assessment criteria have a lower psi and therefore less compaction!
Next, we collect infiltration rates. To do this, we bring 6-inch diameter rings, a hammer, a wooden plank, water, a liquid measuring cup, and a timer. The metal rings are pounded three inches into the ground using the wooden plank and hammer. The water is measured out to equate to an inch of rainfall within the diameter of the ring. We record the amount of time it takes for an inch of water to fully infiltrate into the ground. This process is repeated for three inches over three rings. To meet assessment criteria, an inch of water must infiltrate in 30 minutes or less. Slow infiltration rates indicate poor infiltration which may be caused by crusting, erosion, lack of cover, poor aggregate stability, and/or compaction. We then compare the field’s soil to nearby undisturbed soil by taking an infiltration rate test in a nearby ditch.
This test gives us an idea of the infiltration rates with and without human intervention.
Structure, Biological Diversity, and Plant Roots
From there, we dig up the metal rings to look at the soil profile and take soil observations.
Holding the soil in our hands provides us with information on structure, biology, and plant roots. Healthy soils have a granular structure which is associated with rich organic matter and good aggregation. The structure of healthy soil looks like cottage cheese or spongy cake! Healthy soil smells earthy and keeps a consistent structure when wet. Conversely, poor soil structure looks cracked, crusty, and crumbly. There is very little pore space. It will break apart into blocky layers when dry and become goopy and mushy when wet. Good soil structure is important as it affects water infiltration, flooding, gas exchange, plant rooting, nutrient cycling, and biology.
Biological diversity refers to the variety of living organisms within the soil. Soil organisms are an indicator of healthy soil as they are important for soil functionality through aggregation, water infiltration, nutrient cycling, and pest suppression. To assess biological diversity, we observe and count soil organisms in the crop residue and soil. Examples of visible soil organisms include earthworms, mites, millipedes, beetles, ants, and more. We observe signs of soil organisms as well. For example, earthworms leave behind channels within the soil called biopores. Finding biopores in the soil profile is a good sign for soil health.
Plant roots can tell us a lot about soil health as they provide food and habitat to microbial communities. In turn, these microbial communities help to build soil structure by forming soil aggregates. The biopores left behind by plant roots function as areas of carbon concentration and biological activity that improve infiltration, contribute to the ability of water storage, and create pathways for gas exchange. When assessing plant roots, we look for healthy roots that are abundant, deep, and well-branched. The roots should not be inhibited by restrictive layers, balled up, or growing sideways. Roots growing in that constricted way would indicate compaction within the field.
The final task of our soil health assessments in the field is to collect soil samples. To do this, we use a soil probe, a bucket, an ice cooler, and the SoilWeb app. We collect soil samples in every field from the same soil type. We use the maps on the SoilWeb app to determine where the soil types are in the field. For example, the soil type most prevalent for agriculture in Cottonwood County is 85A Nicollet Clay Loam so that is the soil type that we target for sample collection. To collect samples, the soil probe is placed within the ground at a depth of five to six inches. The probe produces a soil core that we collect into a bucket. Around fifteen samples are collected from various spots within the field. We keep them in a freezer until they can be sealed, labeled, and shipped to a laboratory for testing. The lab will analyze the soil and provide information on nutrient levels, pH, organic matter, contaminants, and more.
Now that the summer season is here, we have an entire list of soil health assessments to finish!
I’m excited to check out all these fields and give the farmers of the Soil Health Task Force an idea of what’s going on with their soil. Healthy soil is the foundation of sustainable agriculture. With an increasing human population and changing climate, resilient soil is imperative to ensure we provide a food system for future generations. Hopefully the work we do today will live beyond us. As the Conservation Corps slogan says, “Restoring Resources. Changing Lives.”