Presentation at the Wibaux Montana Conservation District spring workshop, January 30, 2019.
January 25, 2019. For publication in the Wyoming Livestock Roundup
Climate change is bringing more variability, less predictability, warmer overall temperatures, and drier soils. This combination creates need for resilient agricultural systems, and managing soils to supply water and nutrients is fundamental to increasing resilience. In the field of ecosystem ecology, resilience is the ability of a system to absorb shocks and continue to function, even if not exactly as before. Ecosystem stability, on the other hand, is the ability to resist change, returning to the exact previous state after temporary disturbances. The degree that ecosystems are resilient or stable depends on the predictability of the environment in which they develop. It is easy to extend those concepts to agroecosystems, and in fact, agricultural strategies almost always reflect the resilient or stable characteristics of their environment.
Resilient long-term agroecosystems
Research among pastoral cultures of semiarid grasslands indicates that where normal annual rainfall varies by one third or more from the long-term average, drought is so common that people don’t develop stable communities or sedentary lifestyles. Pastoralists are nomadic, utilizing forage resources differently depending upon the widely varying production. In good years they may stay put, but in dry years they pull up stakes and move to greener pastures, often encroaching on neighboring territories and leading to “raid-or-trade” strategies.
Long-term farming systems also adapt to variable conditions. Native American farmers of the Zuni, Hopi, and Navajo tribes produce rainfed corn and beans in semiarid Arizona and New Mexico with highly variable rainfall. They utilize wind- or water-deposited soils that rapidly soak up water. Summer thunderstorms drive crop growth but are hit-or-miss for particular fields. Complicated family- and clan-based land tenure ensures that farmers’ have small fields across broad areas, improving the chance that some of them will produce crops.
In both cases, persistent societies in dry, variable environments don’t depend on stable annual production, but on strategies to deal with variable productivity. These agroecosystems are resilient, but not stable; they absorb shocks and continue to function, but not by relying on stable production from one field or pasture. Conversely, predictable agroecosystems, where adequate rains almost always come at the right time, are stable, but not resilient; reliable productivity recovers rapidly after infrequent floods or droughts. In those situations, increasing variability, with more frequent and drastic storms and droughts, could push systems beyond their ability to recover, especially if the resistance of soils or plant communities is weakened by long-term intensive farming or livestock grazing.
Soil management practices
Modern soil management typically focuses on short-term crop needs for maximum yield. Those practices often result in a long-term spiral of soil degradation: combinations of tillage and fertilization reduce soil organic matter, leading to denser soils able hold and supply less and less water and nutrients. Then maximum yields require ever increasing tillage, fertilizer, and, in irrigated settings, water inputs, which further decrease soil organic matter, and on and on. Excessive tillage destroy soil aggregates, exposing soil organic matter to rapid decomposition; over-fertilization stimulates decomposer microbes that attack organic materials; and frequent irrigation creates many wetting-drying cycles that physically break down organic materials and make them vulnerable to rapid decomposition.
Turning around and heading back up this spiral staircase requires a long view toward soil quality that underlies the options necessary for resilient farms and ranches. Decision making that centers on restoring or maintaining soil organic matter is key to the long view, and it doesn’t always coincide with short-term maximum yields. Key practices toward that long view include:
Diversification: Longer-term rotations with many different crops, cover crops or annual forages to keep the soil covered year-round, and periods of perennial pasture or hay that integrate crop and livestock production, are practices that diversify the types of organic residues returned to the soil, the types of revenues generated by the farm, and the options available to respond to unpredictable conditions.
4R fertilizer management: Applying the right rate of the right type of fertilizer at the right time and in the right place for each crop is key to optimizing benefits of expensive nutrients. Good fertilizer management increases the amount of crop residue returned to the soil, which builds organic matter, while minimizing money spent on excess nutrients that pollute our air and water.
Minimizing soil disturbance: While totally eliminating tillage may be difficult, tilling only when absolutely necessary and using implements that leave crop residues on the surface are proven to build and conserve soil organic matter, improving water and nutrient supplying potential. Integrating perennial pasture and hay into rotations is one way to reduce tillage.
Grazing management: Careful management of stocking density, timing, and distribution with the long view of growing healthy plants with deep and dense root systems, whether on rangelands or irrigated pastures, builds organic matter and the accompanying soil quality benefits. On hay lands, leaving the last cutting on the field is a long-view approach proven to improve soils and productivity.
Organic amendments: Adding manure, compost, or biochar directly increases organic matter, while the added nutrients and water holding properties they provide increase plant biomass to add yet more organic material.
All these practices and more combine in a “long-view” approach toward building farm and ranch resilience. A focus on building and conserving soil organic matter contributes to soils with optimal water and nutrient supplying potential. Increased water and nutrient supply means more options – a bigger tool box for responding to whatever our increasingly unpredictable climate throws at us. Building healthy soils is the foundation for creating farms and ranches able to absorb climatic or economic shocks and continue to function.
While increasing soil organic matter is the goal of the long-view practices, changes are difficult to detect. Soil organic matter content represents a long-term equilibrium among climate, parent material and management factors; changing the equilibrium is like turning an aircraft carrier: difficult to detect at first. Observations of productivity, soil hardness, soil surface conditions like micro erosion and runoff, and other characteristics might provide a sense of whether you’re headed back up the spiral staircase. Many labs now offer assessments of soil health indicators, including dynamic components of soil organic matter that are more sensitive to change than total organic matter content.
Jay Norton, November 8, 2018. For publication in the Wyoming Livestock Roundup
Fertilizers generally improve soil health when used as part of sustainable agricultural systems, but degrade soil health when used to replace good management. Fertilizer can enable “quick-fix” systems with heavy tillage and without good crop rotations or inputs of organic materials.
In sustainable agricultural systems, the 4 Rs of fertilizer management (Right rate, Right placement, Right time, and Right type of fertilizer) are combined with proven conservation practices in ways that increase crop biomass and conserve soil organic matter. This enhances soil health and reduces fertilizer needs.
The right rate means correctly using soil test results to determine how much nutrient the soil can provide and how much more is required for optimal yield.
The right placement means appropriately injecting, banding, incorporating, or watering in for best root access and minimal loss.
The right time means applying nutrients as close as possible to when plants need them.
And the right source means choosing the right form of dry or liquid fertilizer for the crop and environment.
In natural, undisturbed rangeland soil systems, nitrogen in forms available for uptake by plants and soil microbes is almost always the most growth-limiting nutrient. That’s because nitrogen comes almost solely from breakdown of plant and animal residues. In an undisturbed rangeland, lack of disturbance (tillage) constrains air supply to microbial decomposers. Constrained decomposition means that most N is tied up in organic forms and not available for uptake by plants or microbes. Cycling rates of organic materials can be high, but released nutrients are quickly taken up by diverse plant and microbial communities. We often refer to such systems as “nitrogen limited” because, while there is usually abundant organic nitrogen, forms available for uptake by plants and microbes are usually in short supply. Mycorrhizal fungi, which form symbiotic relationships with plants that increase access to nutrients, are often prevalent in the soil microbial community of undisturbed rangelands.
Fertilizers create a large influx of available nitrogen and other nutrients previously in short supply. This drives huge increases in the number of soil microbes, especially when tillage increases access to air. Numbers of bacteria usually increase while mycorrhizal fungi decrease. The happy microbes rapidly decompose crop residues, converting carbon to carbon dioxide and creating a “carbon limited” system. With a limited supply of carbon, microbes attack soil organic matter that is crucial to soil health.
In a quick-fix system, continuous annual cropping and heavy tillage cause degradation of soil structure and losses organic matter, often leading to erosion. Loss of soil health causes a spiral of decreasing yields and increasing fertilizer needs. The resulting soil system has a small and opportunistic soil microbial community where nutrient availability is often out of sync with crop demands. Expensive fertilizers not taken up by plants or microbes are lost to deep leaching, runoff to surface waters, or as gases to the atmosphere.
Poor fertilizer management also damages soil health by allowing bad farming practices to continue without losing too much yield. Besides on-farm decline in soil health, the lost nutrients, sediments, and organic matter pollute water and air as they contribute to global warming.
On the other hand, good management that combines the 4Rs with conservation farming practices improves soil health, reduces fertilizer demand, removes carbon dioxide from the atmosphere, and mitigates global warming.
Sustainable agricultural systems include practices that increase soil organic matter by either conserving it (slowing decomposition) or adding it, including minimized tillage, cover and green-manure crops, compost application, rotations that include periods of perennial hay or pasture, careful grazing management, and others. In such systems, proper use of fertilizers increase plant biomass production. More plant roots and aboveground residues contribute to soil biota and increased soil organic matter content.
Higher soil organic matter contents support thriving plant and microbial communities that convert available nutrients into organic materials that are easily decomposed. Decomposing plants and microbes release nutrients in ways that coincide with crop uptake, because both plant growth and decomposition increase with increasing temperature and moisture.
With time, practices that increase soil organic matter also decrease the amount of added fertilizer needed per unit of crop yield, but as soil health improves, yields can also increase, so optimal fertilizer rates might stay the same or increase.
The 4 R’s of fertilizer management are crucial to efficient and responsible use of fertilizer as part of a sustainable agricultural production system, whether in pasture, hayland, or cropland.
For more detailed information about managing fertilizers to enhance soil health from a global perspective and about the 4 R’s of fertilizer management, go to my Web site (https://soilmanagement.wordpress.com) and click on Soil Links.
Feel free to contact me at 307-766-5082 or firstname.lastname@example.org to talk about sustainable management or the 4 R’s for your soil.
Click above to see the slides from my presentation at the Wyoming Stock Growers Association fall meeting in Casper, November 28, 2017. This presentation at the Rangeland Soil Health workshop presents a stepwise guide to soil health indicators and focuses on the first level: simple observations of surface conditions, topsoil thickness, and resistance to penetration with a knife.
1.Identify good monitoring and reference locations;
2.Observations of soil depth, structure, surface conditions, water holding capacity that only require a tape, shovel, knife, and notebook;
3.Field measurements of water infiltration, bulk density, aggregate stability, and nutrient content that provide harder numbers, but require more tools and more time, and;
4.Sampling for lab tests when the need is indicated.
First published in the Wyoming Livestock Roundup
For row-crop farmers, translating soil test results to management decisions is straightforward: subtract the soil test nutrient status from an estimate of crop needs and apply the difference as fertilizer. For ranchers, it is more like detective work: trying to uncover reasons that rangelands may not be functioning to their potential.
Ranchers could approach soil testing with this question: Is degraded soil constraining range productivity, biodiversity, or soil water properties in ways that I can address with the management tools at hand?
Productivity, biodiversity, and water properties (including infiltration, holding capacity, and resistance to erosion) are functions typically assessed to define rangeland soil health. Each soil type has its own potential for performing these functions. Assessing whether a soil is degraded or is functioning at or near its potential requires the following steps:
Identify sampling zones. Identify sampling zones based on soil type and management history. Soil type varies with topography and underlying geology. Soil survey maps can help define zones, but might be too large scale. The drawing shows how a landscape might be split into zones that each have different potential for performing functions, and different levels of vulnerability to erosion, compaction, and degradation.
From Ohio State University Extension Soil Sampling Fact Sheet.
Identify reference areas. Reference areas are performing soil functions at or near the potential for each zone. They provide benchmarks for assessing management effects. Soil survey information and ecological site descriptions can also provide this type of information. Ideal reference areas are long-term grazing exclosures, but can also be areas that receive less pressure than the sampling zone as a whole.
Field observations. Many soil properties can be assessed directly, without sending samples and your credit card number to a lab. Fast, simple techniques include: soil resistance to penetration with an old hunting knife (penetrometers are expensive and range soils are usually too hard), soil texture, structure, moisture (after a nice rain), surface horizon color and thickness, amount of bare soil, signs of rill and sheet erosion, and visible salt accumulation. Somewhat more involved techniques include ponded infiltration rate (this correlates well with penetration resistance), soil bulk density (requires precisely weighing a known volume), soil solution pH and salinity (as electrical conductivity; requires an electrode device), aggregate stability, calcium carbonate (free lime) content, plant-available nitrogen and phosphorus content, and others. These tests, what they mean, and where to order supplies are described on my Wyoming Soil Management Web site (soilmanagement.wordpress.com).
Collect composite samples. Sending samples to a lab can provide an excellent baseline for starting to understand soil health, and can help to calibrate your field observations. Some procedures can ensure lab data truly represents soil health. How and where to sample: collect at least three composite samples from each zone and associated reference site. The best way is to follow a zig-zag path, placing at least 20 samples into a bucket. In a patchy plant community, collect samples from each patch in proportion to its part of the zone. Thoroughly mix and fill at least one quart zip-lock bag. How deep to sample: the best is to sample the surface horizon, which is most impacted by management. This could vary from 2 or 3 inches on slopes or hill tops to a foot or more in swales. Note the average depth for each composite sample. Sampling at constant depth may include subsoil in some samples and not others, giving an inaccurate picture of soil properties. When to sample: mid-summer when everything is dry makes proper handling of samples easier. Disturbance from sampling stimulates decomposition and changes dynamic soil properties, especially with moisture. Variable moisture among samples can skew the results. Sample handling: air dry the samples immediately after collecting them. Set them out on a bench or shop floor with the bags rolled open if they’re nearly dry to begin with. If they’re moist, pour them out on a paper plate. They should be dry in 24 to 48 hours. Avoid letting the bags set out in the sun or in a vehicle. They get very warm and microbes become very active.
Ohio State Extension Soil Sampling Fact Sheet.
What to have the lab analyze. The standard soil fertility analysis offered by many labs would provide good information. Make sure it includes soil organic matter. The Colorado State University Soil testing lab offers a Farm & Ranch Package ($15.00) or a Routine general fertility package ($35.00)(prices appear on the lab submission forms. Other properties that indicate soil function include total nitrogen and phosphorus content, cation exchange capacity, texture, and water holding capacity. Skip or ignore the fertilizer recommendations and just compare each sample to the matched reference sample. The plant-available nutrients provided by the standard test have a very different meaning for rangelands than for croplands. For crops, they mean you can buy less fertilizer. In healthy, undisturbed soils with perennial plant communities, most plant-available nutrients come from decomposing organic material and are taken up by plants and microbes as fast as they’re released. So a healthy soil may have high total nitrogen content, for example, but little plant-available nitrogen. Higher contents of plant-available nutrients indicate disturbance where release rates are exceeding uptake rates. This can be caused by physical disturbance that accelerates decomposition, or by disruption of plant/microbe populations that slows uptake. Plant-available nutrients, especially nitrogen, are vulnerable to loss by several pathways, and they indicate a degrading soil system.
How often to sample. A subset of the field observations could be done every year and the lab work repeated every five years or so; long enough for management changes to have an effect.
The results of field observations and lab tests might point to needs for deferring grazing to allow plant establishment on vulnerable areas, fencing or herding to change traffic paths or reduce pressure on areas affected by compaction or low organic matter, or even active repair of gullies to reduce sediment deposition on low landscape positions. In future articles, I’ll describe more specifics about translating soil test data to management actions.
July 12, 2017. Published in the Wyoming Livestock Roundup
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 are 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 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. Links to Web sites that describe these tests can be found on my Wyoming Soil Management site (https://soilmanagement.wordpress.com/).
- Soil texture by feel: 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.
- Resistance to penetration: indicates soil density and porosity, and correlates to infiltration, root penetration, and 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 by feel: 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.
- Simple chemical tests:
- 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: 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.
More information, along with this and past columns, are posted at https://soilmanagement.wordpress.com/.
Rangeland Soil Health presentation given at the Wyoming Stock Growers Association’s (WSGA) Rangeland Soil Health Workshop on June 7, 2017 in Buffalo, Wyoming.
(This first appeared in the Wyoming Livestock Roundup in May, 2017)
Last January this paper printed an article that described predictions of warmer temperatures, more winter and spring precipitation, and large increases in evaporation, leading to drier soils. This should have thoroughly frightened readers who depend on sustainable soil productivity. Drier soils hold less soil organic matter (SOM), and soils with less SOM hold less water, defining a drying feedback cycle. The article summarized Wyoming-specific parts of the Third National Climate Assessment released by the National Oceanic and Atmospheric Administration (NOAA). While more precipitation should support more plant growth, increased frequency and intensity of wetting-drying cycles accelerates decomposition and loss of SOM. As quoted from NOAA in the January 14 article, “Even if precipitation amounts increase in the future, rises in temperature will increase evaporation rates, resulting in an increased rate of loss of soil moisture during dry spells.”
The Assessment analyzes past climatic trends and variability, and predicts future Wyoming climate. Models that predict future conditions use known relationships among the composition of the atmosphere, air temperature, and weather. Weather is the wildcard, because warmer air holds more moisture, which translates to more energy, and therefore increases the unpredictability of place-by-place future conditions.
The increased frequency and intensity of wetting-drying cycles sets the stage for loss of SOM. The amount of SOM is generally equivalent to soil health and productivity, since organic matter supports both soil water and nutrient supplying potential.
Soils that are at or near their potential SOM content can withstand drought, heavy rain, heavy grazing, and even climatic fluctuations and still provide forage, crops, water storage, habitat, and many other functions. Loss of SOM reduces this resilience, and with the predicted conditions, it will become more and more difficult to restore resilient soils. If you own some soil that you suspect may contain less SOM than it can hold, or is producing below what you think it should, now is the time to start the slow process of building soil health by adopting management practices that conserve SOM.
Understanding and managing for soil health
The amount of SOM a soil can hold is a reflection of interactions among the climate, landscape, and soil properties like texture, rock content, and alkalinity or acidity. Those factors control the type of plant community present and its productivity, which contributes different forms and amounts of organic materials that become SOM. These factors create complex and variable patterns, such that any particular piece of ground has optimal and sub-optimal management approaches for maintaining soil functions.
There are many approaches for assessing soil health. Some directly quantify the total and most rapidly management-affected components of SOM. Others evaluate properties affected by SOM, such as density, aggregation, water-holding capacity, nutrient content and supplying potential, pH, salinity, and others.
Given underlying variability, there are three basic principles that conserve or build SOM levels in either rangeland or cropland management:
Minimize soil disturbance. Disturbance from tillage or excessive hoof action destroys soil structure, exposes SOM to decomposition, and creates conditions for wind and water erosion. Frequent disturbance causes soil microbial communities to be dominated by opportunistic bacteria that thrive on the readily available nutrients from a deteriorating soil system. Undisturbed systems are often dominated by soil fungi that help to decompose woody materials, cycle nutrients, and form symbiotic relationships that increase plant access to moisture and nutrients. In croplands, minimizing disturbance means transitioning to minimum- or no-till systems, and especially eliminating operations that invert the soil, such as moldboard plowing. In rangelands it means avoiding over grazing, using care in wet conditions, shifting sacrifice areas around, and controlling heavy trailing.
Maintain soil cover. This means minimizing the amount of bare soil. Bare soil increases erosion, while plant residues on the surface decompose in a controlled manner to contribute to SOM. In croplands, it includes maintaining crop residues on the surface and minimizing the amount of time the soil is bare by planting cover crops. Incorporating residues with tillage accelerates decomposition such that much less is converted to SOM. In rangelands, controlling grazing to minimize bare soil, even during winter grazing of senescent plants, helps to build SOM. Some plant communities are patchy and naturally have a lot of bare ground, but they can still be managed to maximize cover and to minimize disturbance of residues and biological soil crusts.
Promote plant diversity. A diversity of different types of vegetation contributes different types of residues, some that decompose rapidly to provide nutrients, others that decompose very slowly, contributing to stable humus SOM, and the whole spectrum in between. In croplands, this means rotating crops, intercropping, and/or planting cover crops. In rangelands, it means maintaining or restoring diverse plant communities, with many species and life forms, including bunch grasses, rhizomatous grasses, forbs, shrubs, biological soil crusts, and trees in some places.
Clearly implementing these principles in croplands requires much more active management and can bring more rapid results compared with rangelands. But actively controlling grazing by fencing or herding to apply specific livestock impacts to specific sites can change conditions rapidly, especially on moist, productive sites with relatively high SOM and productivity.
Climate change predictions suggest that future conditions will increasingly favor loss of SOM that supports healthy, productive range and croplands. Therefore now is the time to build resilient soils by implementing the tried and true soil building concepts of minimum disturbance, soil cover, and plant diversity.
(This first appeared in the Wyoming Livestock Roundup in November, 2015)
Driving around and talking to producers in the Big Horn Basin this fall, I noticed an increasing trend toward replanting barley for fall and winter grazing. Some producers are also lengthening rotations and including two to three years of alfalfa for seed or forage.
Sugarbeet-barley rotations are notoriously destructive to soil health because of intensive tillage, long periods of bare soil, and the every-other-year frequency of heavily consumptive sugarbeets. Several research papers have shown that the less often sugarbeets are grown, the healthier is the soil. One of the latest reports is from our on-farm study in the Powell area, in which both soil health and sugarbeet yield improved in the order sugarbeet-barley, sugarbeet-bean-barley, sugarbeet-barley-alfalfa-alfalfa (Hurisso et al., 2015).
Farmers are realizing that the early harvest of barley creates a window of opportunity. Barley can be replanted right behind the combine to grow a tall, green forage crop before freeze up. Some farmers irrigate and fertilize to maximize forage production. Others include a mix of other cover crop species to benefit both the soil and the livestock.
The system works especially well with sprinkler irrigation because of reduced requirements for tillage, leveling, and bedding, but if those operations can wait until spring, it should benefit furrow systems as well.
We’re catching up with farmers to evaluate the benefits, but barley is known to be a great cover crop. It grows very rapidly, competes voraciously with weeds, is very salt tolerant, and has prolific fine roots that improve soil tilth and organic matter content. Barley can produce more biomass in a shorter time than any other cereal crop. It can form a deep, fine root system that improves soil structure and scavenges valuable nutrients. Grown together with a legume like field pea, barley can stimulate more nitrogen fixation and capture it in easily decomposed biomass. A USDA Sustainable Agriculture Research and Education (SARE) on-line publication provides an excellent description of barley and many other cover crops (http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition).
Several research studies have shown that grazing does not reduce soil health benefits of cover crops. To the contrary, a recent study in the southeastern US found that grazing sped turnover rates of cover crop biomass, increasing biologically active carbon and soil microbial biomass without affecting the amount of potentially available nitrogen (Franzluebbers and Stuedemann, 2015). The benefits were greater under reduced tillage, which is another growing trend under sprinkler irrigated systems in Wyoming. We’re making plans to study interactions among cover crops, tillage, and grazing in this part of the country, but we expect similar beneficial outcomes.
If grazing is not part of the picture, replanting barley could still be worth the effort, especially if other cover crops like nitrogen fixers and deep rooted radishes are included. Planting just-harvested barley seed is a very cheap way to get a cover crop in the ground, and following the combine with the planter maximizes the time for growth before frost. Simply allowing volunteer barley to thrive and provide cover during winter could result in better soil health and productivity. The cover crops capture and cycle residual soil nitrogen and phosphorus from fertilizers to reduce losses from leaching, runoff, or volatilization.
Overall, replanting barley after barley looks to be an excellent way to save soil, cycle nutrients, and integrate livestock grazing into sugarbeet production systems. The benefits might be even greater if legumes and other cover crops are mixed with the barley seed. Expanding rotations to include perennial crops like alfalfa also has clear benefits for soil health and productivity.
Contact the author for copies of literature referred to in this article:
Franzluebbers and Stuedemann, 2015, Journal of Soil and Water Conservation 70(6):365-373.
Hurisso et al., 2015, Soil Science Society of America Journal: doi:10.2136/sssaj2015.02.0073.
(This first appeared in the Wyoming Livestock Roundup in July, 2015)
Driving across the green Wyoming rangelands this June, the reddish patches that indicate cheatgrass is having a good year remind me of the summer 14 years ago I spent up to my eyeballs in the weedy annual grass. Cheatgrass grows well in Great Basin of Utah and Nevada, but not that tall; I spent much of that summer standing in five-foot deep holes with my head protruding at ground level in a sea of cheatgrass.
As a researcher at Utah State University, I was collecting data on how conversion from sage-steppe grassland to persistent monocultures of the exotic winter annual grass impacts soil health and organic matter processes. I started by working with long-time Great Basin ecologists like Neil West and Steve Monsen to locate seven long-term infestations with matched areas dominated by native range vegetation.
With help from a crew of muscle-bound Utah college students, I dug holes at each of the 14 locations and carefully described the soil to make sure the paired sites were well matched, and to look for differences attributable to the weed infestation, like porosity and root characteristics. Then I took samples back to the lab where I measured many properties that underlie soil health and productivity, such as density, texture, alkalinity, organic carbon and nitrogen, microbial activity, and easily decomposable soil organic matter.
It turned out that looking at soil under paired cheatgrass and native range in the Great Basin was almost like looking at soil under paired wheat fields and native range in eastern Wyoming. Cheatgrass grows a thick mat of shallow, very fine roots that die each summer, aerating the soil and adding carbon-rich organic material in almost the same manner as tilling to incorporate wheat straw. Soil microbes thrive on the added air and the carbon energy source, and their rate of decomposing organic material multiplies.
The initial effect of increased microbial activity is increased mineralization of soil organic matter, making more nutrients available for the crop (or the weed). But after a few years of enhanced conditions caused by disturbance, microbes start eating themselves out of house and home, depleting soil organic matter that accumulated under millennia of perennial grassland vegetation. Loss of organic matter degrades all the properties that contribute to soil health, including building soil structure, enhancing water infiltration and storage, providing a time-release nutrient supply, and supporting sustained productivity.
In cropland, organic matter loss means that more and more tillage and more and more fertilizer might be necessary to keep growing crops. In cheatgrass-infested rangelands, it means that the older and more monocultural the infestation, the more difficult it might be to restore desirable vegetation. Cheatgrass tends to convert slow, conservative nutrient cycles of native grass and shrublands to flashy, leaky nutrient cycles where mineral nutrients accumulate to create conditions for rapid cheatgrass growth (just add water), or to be lost with erosion, leaching, or volatilization. In native perennial plant communities, a diversity of plants and microbes turn mineral nutrients into more stable organic forms almost all year.
In annual cropping, a great practice is to try to keep plants growing and covering the soil all year, or especially to convert fields to perennial cover, like hay or pasture, for a few years. This minimizes disturbance (aeration) and shifts the system back toward accumulating, rather than losing, soil organic matter.
The extensive nature of cheatgrass infestation, often on hot, south slopes and rough ground, makes restoration difficult. Range managers in the Great Basin have had some success “re-perennializing” cheatgrass stands by seeding introduced cool-season bunchgrasses like pubescent wheatgrass or crested wheatgrass. After the bunchgrasses become established and reduce competition from cheatgrass, managers increase the diversity by weakening the introduced grasses with fire, heavy grazing, herbicides, mechanical treatment, or a combination, and then planting native grasses, forbs, and shrubs.
Rigorous fire prevention is crucial to restoring cheatgrass infestations to diverse, desirable plant communities. Once a seed bank is established, cheatgrass may always be there in the understory, filling the bare spaces and creating a continuous fine fuel load so that when a fire occurs, it can be much larger and more destructive, and the plant community quickly converts back to cheatgrass.
A comprehensive guide to cheatgrass management in the Rocky Mountain region can be found on the University of Wyoming Extension publications Web site (http://www.wyoextension.org/publications). Search on “cheatgrass” or bulletin number B-1246.
For more detailed information on the study discussed here, see the papers posted at: