Soil Health on Rangelands: Energy Flow Back »

Soil health is picking up notoriety not only in farm and ranch circles, but it’s starting to hit the mainstream. Last year, the New York Times did a feature article about Gabe Brown. I think the best way to think about soil health is actually from a holistic viewpoint. This holistic framework offers the “Big Picture” of how the ecosystem works. The NRCS has already developed a comprehensive Monitoring Guide for Rangeland Health. This is a very useful guide to help you monitor your rangeland. Charlie Orchard (Land EKG Inc.) developed monitoring protocols based on ecological processes. I borrowed ideas from both Charlie Orchard and the NRCS and incorporated them into Figure 1.

Figure 1. Color coded monitoring indicators of nutrient cycling, water cycling, the biotic state, and energy flow that are involved in ecosystem processes (modified after Pyke et al. 2002; Pellant et al. 2005; Orchard 2013).

You will notice that the ecosystem processes (energy flow, biotic state, water cycling, and nutrient cycling) are very similar to Holistic Resource Management concepts out-lined by Allan Savory. As Allan stated in his lecture at SDSU in September 2014 lands are very complex and cannot be managed, but rather we can manage the processes that affect the outcomes of these processes. It is in a holistic context (social, environment, and economic) that I wish to address the monitoring guidelines of the ecosystem processes to build toward improving soil health.

Energy Flow: An overview

Energy flow is driven by the solar input from the sun and the uptake of CO2 through photosynthesis. Energy is displayed in two forms, kinetic and potential. Kinetic energy is energy in motion. Potential energy is energy that is stored. An easy way to think about energy flow is to use the analogy of a solar panel collecting the sun’s light energy (kinetic) and converting it into electricity stored in a battery (potential). However, instead of creating electricity, plants are creating sugar (6 carbon glucose molecule) and linking them together to form complex carbohydrates that eventually become food for herbivores (potential energy). This, of course, is all controlled by available water as the equation for photosynthesis is: 6 H2O + 6 CO2 + light energy = C6H12O6 + 6 O2, where the water molecule is split and oxygen is created.

Influence of Green Plants

As managers, we cannot influence how much sun energy we receive or how much CO2 is in the atmosphere. However, we can influence the type of solar panel (green plants) we choose to keep on our land. Figure 2 is a good illustration. The picture shows big bluestem (large leaf blades) and Kentucky bluegrass (narrow leaf blades). This photo was taken in early June in an area that received repeated clipping once a week in May. Kentucky bluegrass is a cool-season, C3 plant, which uses the 3-carbon fixation pathway. Its enzyme responsible for carbon fixation works at an optimum temperature of about 65° F. Sometimes the enzyme tries to fix O2 instead of CO2 and results in wasted energy (photo respiration). Big bluestem is a warm-season, C4 plant, which uses the 4-carbon fixation pathway. Its enzyme responsible for carbon fixation works at an optimum temperature of about 90° F. It has a high affinity for CO2 and rarely (if ever) tries to fix O2 (essentially has no photo respiration).

Figure 2. Big bluestem and Kentucky bluegrass. Photo by S. Smart.

Warm-Season & Cool-Season Plants

Warm-season, C4 pathway plants are also more water-efficient (meaning for every unit of water used they fix more units of carbon than C3 plants). Thus warm-season plants have an advantage over cool-season plants during the hot, dry summer periods. Cool-season plants have an advantage in the early spring, when its cooler, and often wetter.

Ideally, it would be nice to have a mixture of both cool-season and warm-season plants to take advantage of having an even distribution of actively growing leaf material (solar panel) throughout as much of the growing season as possible. When pastures are overtaken by a single species (e.g., Kentucky bluegrass, smooth bromegrass, or cheatgrass, you pick one) the potential to harvest as much CO2 as you can diminishes. A well-managed prairie contains both C3 and C4 plants, made up of grasses (85%) and broadleaves (15%). As a manager you would like to increase the abundance of grasses with wider leaves and forbs compared with plants that have narrow leaves. This way you can maximize the leaf area of your actively growing canopy (solar panels).

Now let’s turn our attention to the monitoring diagram of the ecosystem processes (Figure 1). The yellow represents energy flow. A grassland manager would monitor live canopy cover, plant form (over rested, overgrazed, normal appearance), plant vigor (crown width, density, seed heads, leaf color, leaf width), forage production (site potential), and utilization (too much or too little). We’ve already discussed the idea of canopy cover in detail.

Plant Appearance: Gauging biomass flow

Plant form in terms of appearance (over rested, over grazed or normal) is a way to gauge if the flow of biomass of an individual plant is in the right proportion (feeding livestock, feeding itself, feeding the soil). If it is over rested it will have a greyish color to it and too much of the biomass is being oxidized (carbon going to the atmosphere) instead of getting eaten by livestock or getting trampled as litter. Sometimes bunchgrasses can build up too much material and loose vigor. We all have seen overgrazed plants. In Figure 3, the photo is of little bluestem grazed close to the ground from a patch-burn area.

From a plant vigor perspective we would look for crown width in bunchgrasses, tiller density in rhizomatous grasses, number of seed heads, leaf color, and leaf width. The denser the stand the more leaf area you will have. If leaf color is light green or yellow in color that means it is most likely deficient in nitrogen and not so much an energy flow problem (although nitrogen is limiting potential).

Figure 3. Little bluestem grazed heavily in a patch-burn graze system.
Photo by S. Smart.

Estimating Forage Production Potential

Forage production potential can be accessed from the web soil survey to get a baseline of what the climax plant community would produce or any plant community that is predicted from the state and transition model. The best method is to set up an exclusion cage (see the Land EKG™ Grazing Cage for a free grazing cage design made out of one cattle panel and uses no T-posts) and use a clipping ring to estimate forage production (Figure 4).

Figure 4. Grazing exclusion cage (top photo) and estimating forage production by the clipping method (bottom photo). Photos by S. Smart.

Estimating your own forage production and mapping it is an important first step in determining if grazing distribution is a problem (especially in large pastures). If grazing is determined as being uneven through mapping of grazing utilization (over grazing is some spots and under grazed in others), then you might gain efficiencies by cross fencing and adding livestock watering tanks. The expected increase in efficiency from a season-long continuous grazing system to a simple rotational grazing system (4 pasture once over or twice over) should be between 10-40%. Research by NDSU at research stations near Dickinson and Streeter, ND during the 1980s showed an increase in carrying capacity of short duration grazing (8 pastures) versus season-long continuous grazing. This research was summarized by Dr. Don Kirby (former Department Head of Animal and Range Sciences at NDSU) and was given as a keynote address in 1993 at the First Interprovincial Range Conference in Western Canada. It is a great paper that documents the potential grazing efficiencies of rotational grazing systems. Ultimately, we can increase the energy flow (forage produced and eaten by livestock to produce beef) through monitoring and understanding our forage resources. Next issue I will be discussing the biotic state.

Rangeland Soil Health Article Series

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