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Data to Management: Using Soil Health to Inform Decisions

Written by Jay Norton

When we ask ourselves, can soil health information inform range management decisions, the answer is yes, but vegetation composition and production are sensitive indicators of soil problems in rangelands. Therefore, many issues revealed by soil analyses, such as erosion, compaction and loss of organic material, may already be obvious to managers who monitor vegetation.

Soil sampling and analysis is labor intensive and expensive. Ranchers need to know whether the investment will pay off. So, the question is, which soil indicators can either reveal production-limiting issues that are not obvious or predict production problems and guide pre-emptive management decisions?

In this column, I’ll discuss how to get a start on understanding the interplay among natural constraints and management-induced changes for setting attainable goals and devising effective strategies toward improving soil health and productivity.

We often separate soil properties into those that are inherent and, therefore, limit the productivity of a site, or dynamic and, therefore, are affected by management, to sort out which soil properties might provide useful information. There is not a sharp boundary between these two concepts, however, which makes this complicated and keeps generations of soil scientists scratching their heads.

Inherent properties are the outcome of complex interactions among five soil forming factors –  climate, parent material, topography, organisms and time.

Climate sets the speed of weathering, erosion, leaching, biological activity and other processes that determine the depth, distribution and quality of the soil. Parent material sets the ease of weathering and the physical and chemical composition of the soil. Topography affects the microclimate and erosion or deposition rates. Organisms drive decomposition and organic matter accumulation, and time affects how long the other factors interact to develop soil.

Time is a variable concept in soil science. Soil in a warm, moist environment can be deeper and appear older than one forming over the same period in a cool, dry environment.

Dynamic properties change, or can be changed, in time scales relevant to management or what humans think of as long-term. The amount and composition of soil organic matter (SOM), including soil organisms, are important dynamic properties that react to management.

SOM controls soil structure or aggregation and porosity, which create water infiltration and plant-available water holding capacity, along with facilitating root penetration and movement of soil air. Soils that lose SOM lose structure and become compacted, even if they’re not physically compressed by wheel or livestock traffic.

SOM forms as plant materials decompose and mix with surface soils, but can also be redeposited from hillslopes, forming deep, rich and productive soils in swales.

Understanding how soils are distributed across the landscape and how that is reflected in the vegetation, forms a basis for recognizing soils that are not functioning to their potential.

For example, flat-topped hills are often the oldest spots on a landscape, with the oldest and most highly developed soils, though not necessarily the deepest or most productive ones.

Hillslope soils can be well developed but often have surface horizons that are naturally on the move, slowly transporting materials down slope with rainfall events. Hillslopes can support productive vegetation but might be vulnerable, where bare soil and trailing, for example, can accelerate natural erosion processes and degrade soils.

Footslopes and swale bottoms are depositional zones where water, SOM and sediments naturally accumulate to create the most productive landscape positons, but these are also often the youngest soils on the landscape. Accelerated erosion and runoff from hillslopes can accelerate deposition on swale bottoms.

Sediments from accelerated erosion can be saline with low SOM and no soil structure, which limits water infiltration, further increasing runoff from the landscape. Ultimately, continuous gullies can form, transmitting water directly from uplands out of the landscape, truncating natural erosion and deposition processes that store water and support productivity. Livestock trails and roads can also divert runoff, cutting off important soil forming processes.

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.

In next week’s Roundup, Norton will discuss several field soil tests that can be used to help identify management strategies.

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