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Data to Management: Using Soil Health to Inform Decisions, Part 2

Written by Jay Norton

In the first part of this column, Jay Norton described the factors that impact soil formation and interactions within the soil. In this second part, he explains how producers can perform simple tests to assess their soil’s health.

Some simple field soil tests can help understand landscape-soil-vegetation links, recognize where the soil may not be functioning to its potential and identify places where lab tests might be useful.

First, we can assess soil texture by feel. This is an important inherent property that controls water infiltration and holding capacity. This simple test using a mud ball to estimate relative proportions of sand-, silt- and clay-sized particles in the soil takes a little practice but is very informative.

Soil texture is an important indicator of site potential. Sandy soils absorb water rapidly but do not hold it for plant uptake, while clayey soils can seal up and cause runoff. A more or less even mix of sand, silt and clay provides the ideal combination of water infiltration and holding, but this is a property that management must adjust to rather than change.

Next, producers can test for resistance to penetration, which indicates soil density and porosity and correlates to infiltration, root penetration and soil organic matter (SOM) content. You can purchase a penetrometer with a gauge on it, which requires moist soil, or you can use an old hunting knife. This is affected by moisture, so all the spots tested should be the same level of moisture – either dry or after a rain.

Simply push the knife into the soil and note how much force it requires. Start in a spot that seems like it should be functioning at or near potential. Note differences between soils under shrub canopies, under grasses and without vegetation.

It might take a while, but if you do this enough you start to see patterns emerge, along with anomalies that might correspond to less-that-optimal productivity.

Soil moisture can also be tested by feel. Soil moisture indicates relative soil water holding capacity if observed while the soil is still moist after a soaking rain. This is another mud ball test that can show interesting patterns of water storage on the landscape.

Finally, simple chemical tests can be performed.

Soil pH and salinity are important properties that correspond with nutrient and water availability. Higher than optimal numbers can indicate erosion or sediment deposition from changes to surface hydrology that may be reversible. Small hand-held meters can be purchased for around $100.

Soil calcium carbonate content causes the soil to become very hard when dry. It’s common to almost all rangeland soils, but high contents can indicate loss of surface soils or SOM. A weak acid solution is used to cause the soil to effervesce, or fizz, with more fizz indicating higher calcium carbonate content.

Nitrate and phosphate content are both important plant nutrients that can be estimated with water quality test strips or inexpensive garden kits from the hardware store. These forms of nitrogen and phosphorus are the end result of organic matter decomposition and are usually taken up by plants and micro-organisms as quickly as they are released. Therefore, we expect very low concentrations in healthy rangelands, but the tests can indicate patterns of soil fertility.

Higher concentrations can indicate disturbance, where release rates exceed uptake rates. Excess available nutrients can lead to weed invasion and loss of soil fertility.

With practice, making these observations part of range vegetation monitoring can increase an overall awareness of the productivity relative to it’s potential. Collecting some samples for lab analyses of SOM, texture and other parameters can for a good baseline and help calibrate your field observations. Select sampling areas by landscape position and management level.

While these observations may not lead directly to management decisions, they will support improved understanding of vegetation and productivity patterns on the range.

In future columns, I’ll provide more details on soil sample schemes and how lab results can inform management.

Editor’s Note: For the first half of this two-part article, see the July 15 edition of the Roundup or visit wylr.net.