Now is the time to fix your soil!

(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.

Integrating livestock into sugarbeet-barley rotations: Barley after barley for soil health and profit

(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.

Cheatgrass effects on soil health

(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:

Cheatgrass Invasion Alters Soil Morphology and Organic Matter Dynamics in Big Sagebrush Steppe Rangelands. Wildland Shrub Conference Proceedings.

Soil morphology and organic matter dynamics under cheatgrass and sagebrush-steppe plant communities. Journal of Arid Environments.

Mediterranean annual grasses in western North America: Kids in a candy store. Plant and Soil.

Occasional tillage: How persistent are soil health benefits of no till?

(This first appeared in the Wyoming Livestock Roundup in June, 2015)

No-till crop production slows decomposition of crop residues, allowing redevelopment of soil aggregates and increasing the nutrient and water supplying potential of the soil. More moisture and nutrients reduce the need for fallow and often allow more diverse crop rotations. Even perennial forage production for hay and pasture benefit from minimizing or eliminating tillage when stands are renewed.

Such benefits make true-believer no-till practitioners steadfastly committed to keeping steel out of the ground. But sometimes there are good reasons for dusting off the tillage equipment. No till can cause low-mobility nutrients like phosphorous to accumulate near soil surface; without careful traffic management it can cause soil compaction; weeds can get away; or high-yield years can create excess crop residue that is difficult to plant into. The question is how much soil health, recovered after years of no till, is lost with occasional tillage?

Even a single tillage operation can increase soil aeration and accelerate loss of carbon and nitrogen, resulting in immediate bursts of carbon dioxide (CO2) and nitrous oxide (N2O), which are very sensitive indicators of soil disturbance and organic matter loss. Carbon dioxide and N2O are greenhouse gases that drive global warming, and agricultural practices that include frequent tillage are important contributors. Soils under no till tend to store more carbon and nitrogen so that losses as CO2 and N2O are reduced.

So, would a single tillage event in a long-term no-till field create huge bursts of CO2 and N2O when stored organic matter is exposed to air? To find out, we conducted an experiment at the University of Wyoming Sustainable Agriculture Research and Extension Center (SAREC) near Lingle.

We collected and compared soil air samples and surface soil samples from winter wheat-fallow systems that have been under no-till and frequent tillage management since UW bought the research station 11 years earlier. Small plots in each of the study fields were established to create three treatments: 1) no-till; 2) one-time till in no-till; and 3) summer tillage (typical) fallows. Air and soil samples were collected before and immediately after a one-time pass with a tandem disk that loosened the dry soil to 4-inch depth in the one-time till in no-till and the frequently tilled plots, and concurrently without tillage in the no-till plots. Carbon dioxide and N2O emissions, as well as concentrations of easily decomposed forms of organic matter were determined 0, 1, 5, 25, and 50 hours after tillage. To collect soil air, we drove a sharpened six-inch long piece of eight-inch diameter PVC pipe about three inches into the soil and left it there throughout the experiment. At each sampling time we placed a PVC cap fitted with a septum onto the base and sealed it with a rubber gasket. We used a syringe to collect soil air samples from the canister three times, at 0, 15, and 30 minutes, placing each sample in to a glass vacuum vial. The samples were analyzed by gas chromatography, and emissions calculated in micrograms per square meter of each gas.

Results indicate that CO2 emissions from one-time tillage in no-till were 30 to 40% lower than from the frequently tilled soils. The one-time tilled soils also had less soluble organic carbon and mineral nitrogen, indicating less disruption of organic matter. Surprisingly, the values from one-time tilled no-till soils were much closer to those from the no-till plots that we didn’t till than to the frequently tilled plots. This suggests that soil organic matter stored in the long-term no-till soil was resistant to the single summer tillage operation. Importantly, tillage did not affect the magnitude of N2O emissions in any of the treatments, suggesting that if performed during dry summer, this operation did not contribute to nitrogen loss as gas.

The results suggest that the 11 years of no till facilitated formation of stable soil aggregates that protected organic matter and were not destroyed by the tillage operation, and also formation of resistant organic compounds, like humus, that are not easily decomposed. Experience shows that repeated tillage would breakdown those materials, compromising the resilience gained during the years of no till. But occasional summer tillage to accomplish particular management objectives may not destroy the benefits of long-term no till, at least on the silt-loam soils at SAREC.

A more in-depth article about this research can be found here:

Greenhouse Gas Fluxes and Soil Carbon and Nitrogen Following Single Summer Tillage Event, International Journal of Plant and Soil Sciences

Don’t Volatilize your bank account: Avoid N fertilizer losses

(This first appeared in the Wyoming Livestock Roundup in April, 2015)

Ah springtime! Birds are singing, days are longer, even in Laramie it’s warming up, and our thoughts turn to…. fertilizer. Well, if it’s not the first thing on your mind, it’s probably close. That’s because if you’re an ag producer you have to lay out a lot of money for plant food. Here’s some food for thought: half or more of the nitrogen you apply can escape from the soil as ammonia gas; a process called volatilization. Nitrogen has many forms during its journey through the nitrogen cycle, including organic forms in plants and microbes, soluble mineral forms (nitrate and ammonium) used by plants, and gases like di-nitrogen (most of our air) and ammonia – many opportunities for loss. Cycling of our other big fertilizer investment – phosphorus – is less complicated. With no gaseous form, it transforms among organic, fixed, and plant-available forms. Phosphorus fixation in calcareous soils is another source of heartburn for growers, but that’s a different story. This article describes factors that cause ammonia volatilization of nitrogen fertilizer, and how to minimize those losses.

Nitrogen in any type of fertilizer can be lost to volatilization, but the problem is most prominent, and most studied, in urea and urea-containing fertilizers (like UAN 28 and 32 solution). Each transformation in the nitrogen cycle is mediated by soil microbes, so conditions that favor microbial activity – the same optimum temperature and moisture as for plant growth – accelerate nitrogen cycling, including ammonia volatilization. When urea hits the soil it must go through a process called “hydrolysis” to become available to plants as ammonium . This process is catalyzed by a natural enzyme from soil microbes called urease. Hydrolysis raises pH in the immediate microsite around the urea, which favors ammonia gas over ammonium. Thus volatilization is a bigger problem for alkaline soils (like yours!) than for acidic soils in higher rainfall regions.

If warm temperatures speed volatilization, then putting down urea on cool days in fall or early spring, or on the snow, should be a safe practice, right? Wrong. For many years that was assumed to be so, but recent research in Montana shows that as much as 44 percent of nitrogen applied as urea between October and April was lost to volatilization, and the average loss across 23 study sites was 16 percent. This is enough to really hurt yields and represents money drifting up off your field and out of site in the Wyoming wind. Even though the cool temperatures slow down volatilization, all the other transformations, including plant and microbial uptake, are slowed down too, so ammonium is left exposed to the volatilization pathway for a long period. Surface crop residues also increase potential ammonia volatilization because they keep the soil surface moist, reduce the amount of urea diffusing into the soil, and have high urease activity.

Minimizing nitrogen volatilization

Choosing a nitrogen source with lower risk of volatilization is one way to minimize losses, but of the two with low risk factors, one (liquid anhydrous ammonia) is not widely used in Wyoming, and the other (ammonium nitrate) has limited availability because of explosive properties. Other alternatives to urea, like 28 or 32 solution, ammonium sulfate, and others each have lower volatilization potential, but in alkaline soils under the wrong environmental conditions the potential is still high. The Montana study showed that urease inhibitors like NBPT, the active ingredient in Agrotain®, slowed volatilization, especially under cold dry conditions. Other enhanced-efficiency urea fertilizers can slow volatilization and can work well for no-till or perennial crops under the right conditions, but proper placement and timing of fertilizer is the best route.

Broadcasting without incorporating to at least two inches should be avoided. The best alternative to incorporating fertilizer is to broadcast it just before a single rain or irrigation event of at least ½ inch; enough to dissolve and carry the fertilizer into the soil. Subsurface banding to at least two inches can be effective, but the slit produced by banding needs to be closed tight to avoid loss of ammonia from the concentrated band of urea. In conservation tillage or no-till systems fertilizers should be knifed into the soil below the residue and the slit closed tightly. That also goes for fertilizing perennial pastures or hayfields. Applying liquid nitrogen with a spoke-wheel injector has been effective for these situations.

Montana State University has produced some excellent guides on managing nitrogen fertilizers to minimize volatilization. You can access them by going to http://www.uwyo.edu/soilfert/ and clicking on Soil Links> Montana State University Soil Fertility Program>Ammonia Volatilization.

Soil quality and the benefits of crop rotation, reduced tillage, and manure application

(This first appeared in the Wyoming Livestock Roundup in February, 2015)

Two underlying strategies toward improving soil quality include conserving soil organic matter by reducing tillage and adding organic material by applying composted manure or other amendments. Crop rotation also builds soil quality by supplying diverse crop residues, especially if perennial nitrogen-fixing legume crops, such as alfalfa, are included. Starting in 2009 we conducted a four-year experiment on irrigated fields at the University of Wyoming Sustainable Agriculture Research and Extension center near Lingle to evaluate how rapidly combining crop rotations, reduced tillage, and manure application would improve soil quality on depleted soils that had been under intensively tilled continuous corn for many years.

We divided the area into 12 one-acre plots and converted four plots to a conventionally managed rotation of dry beans-corn-sugarbeet-corn, four plots to reduced-tillage under the same rotation, and four plots to an organically managed rotation of alfalfa-alfalfa-corn-dry beans. Tillage was similar among the conventional and organic plots, and fertility management was similar among the conventional and reduced-tillage plots. Tillage on the conventional and organic plots included moldboard plow, disk, and harrow for seedbed preparation and cultivation as needed for weed control. The reduced-tillage plots were tilled once with a Landstar machine (Kuhn Krause, Inc., Hutchinson, KS). Conventional and reduced-tillage plots were fertilized with commercial fertilizers based on soil-test-based recommendations, while the organic plots were fertilized with composted and fresh cattle manure applied based on crop needs for soil N (about 5 tons per acre). Yields were comparable among the three systems, and economic analysis indicates that the organic rotation is more profitable than the other two if premiums for organic-certified crops are considered. To assess effects on soil quality, we measured properties that respond rapidly to management changes, including soil microbial populations and functional groups like fungi and bacteria, soluble organic carbon and nitrogen compounds, and easily decomposed organic materials.

Results indicate that converting from monocropped corn to crop rotations had the largest positive impacts of the three strategies, regardless how they were managed, and that reduced tillage, manure, and alfalfa in rotations added to the positive effects. At the end of the four-year study total microbial biomass in the soil had tripled or quadrupled in all three systems, with the largest increase in the organic system. The most striking increases in microbes were among fungal species that break down crop residues, with five- to eight-fold increases in that group. Mycorrhizal fungi also increased in all three systems by factors of two to four. Mycorrhizal fungi form symbiotic relationships with plants and support improved uptake of water and nutrients, especially phosphorus. Both types of fungi form extensive networks of microscopic hyphae that hold soil particles together and improve soil structure, porosity, and water infiltration. Their presence indicates more stable and resilient soils. Overall microbial diversity also increased by 50 to 70% over the four years, indicating establishment of a rich soil biological system with abundant beneficial organisms.

These increases in microbial numbers and diversity correspond to increases in decomposable organic material that serves as substrate – or food – for microbes. Dissolved organic carbon, which is essentially sugar derived from initial decomposition of plant residues, increased six-fold by the end of the fourth year, with larger increases under organic and reduced-tillage than conventional management. Dissolved organic nitrogen, however, did not increase appreciably, meaning that the carbon-to-nitrogen ratio of the most microbially available substrates doubled or tripled in the three systems. This favors beneficial fungi over bacteria, and probably results from diverse types of crop residues. The amount of easily decomposable organic material more than doubled in the organic system but stayed relatively stable in the reduced-tillage and conventional systems, indicating that the combination of manure and alfalfa in rotation began to build soil organic matter more rapidly than either the crop rotations alone or reduced tillage.

Results of this four-year study emphasize the importance of rotating crops for maintaining soil quality and productivity. Even with two years of corn and one of sugarbeet – both highly consumptive crops – in the four-year rotation, soil microbial activity and organic matter components increased significantly compared with conditions after years of continuous corn. Combining rotation with reduced tillage further boosted microbial activity, as did including alfalfa and manure applications in the rotation, but rotation itself had the largest impact on soil quality.

Results of this study were published in the open access scientific journal PLoS ONE and can be found on line by searching on PLoS ONE 9(8): e103901. Parts of this article were published previously in the on-line Western Nutrient Digest Newsletter.

Conservation in furrow-irrigated cropping systems.

(This first appeared in the Wyoming Livestock Roundup in January, 2015)

Farmers are aware of low organic matter levels that hamper productivity and become lower each time the soil is disturbed. Under furrow-irrigation, declining soil organic matter (SOM) leads to loss of soil structure that causes sealing and erosion, as well as loss of nutrients and increasing fertilizer needs. Reversing those trends is difficult because furrow irrigation requires tillage to level and furrow the soil, and root crops require soil disturbance for harvest. Conserving surface residues can impede water flow and reduce irrigation efficiency. Research is sparse but shows that there are ways to improve soil quality in furrow-irrigated cropping systems. Recent research in Latin America, Australia, and Asia emphasizes advantages of permanent raised beds in furrow irrigated production. This article summarizes information from several key studies about different approaches to soil conservation under furrow irrigation.

Reduced tillage. While disturbance is necessary for making clean furrows and harvesting root crops, tillage operations can be strategically reduced to conserve SOM. A study in Montana showed that strip till yielded better than conventional tillage and no till in furrow-irrigated sugarbeet. No till yielded the same as conventional till. A similar Nebraska panhandle study showed that sugarbeet was the weak link for soil erosion control: the soil had almost no cover for over a year and a half from early spring furrowing for the beet crop to harvest of the following corn crop. They recommend an alternative beet harvesting technique that would place residues on the soil surface.

Other studies on fine-textured soils suggest that no till can lead to decreased porosity and increased runoff compared with conventional and reduced tillage. In a long-term study of a sugarbeet-wheat rotation in Germany, no till resulted in much denser soil,  4% lower wheat yields, and 15% lower beet yields than conventional tillage. Lower production costs made up for the lower yields in wheat, but not in sugarbeet. Their conservation tillage treatment (loosening and mulching), however, produced equivalent yields, and higher profits, compared with conventional plowing.

None of these authors discuss problems with residue blocking water flow, and farmers report mixed results using reduced- or no-till systems with furrow irrigation. The scale of this problem may be related to individual farmers’ tolerance of trash in their furrows, and their willingness to occasionally walk the furrows, but generally, residue-conservation is not embraced by furrow irrigators.

Cover crops. Some producers in western Wyoming use cover crops after barley and dry beans. There is not a great deal of information in the scientific literature about cover crops in furrow-irrigated systems, but one study reported much less runoff and greater infiltration when they combined a wheat cover crop with standard tillage (including several 8-inch-deep passes with a disk plow) compared with no cover crop and with no till in a California sunflower-Sudan grass-corn rotation. Fast-growing grain, grass, legume, and other crops can be planted following small grains and dry beans to create winter soil cover, contribute nutrients, and add considerable organic matter to the soil. A University of Wyoming team is currently studying cover crops following barley at our Powell Research & Extension Center.

Longer rotations. A study in the Big Horn Basin showed that the longer the rotation, the more soil organic matter and the higher the sugarbeet yields, with four-year alfalfa-alfalfa-sugarbeet-sugarbeet rotations outperforming sugarbeet-bean-barley and sugarbeet-barley rotations. Long-term studies in Nebraska, Montana, and South Dakota established that sugarbeet production improved when alfalfa was in the rotation, and kept improving with longer rotations up to one beet crop every six years.

Combining principles: Permanent raised beds. In this practice two or three rows of crops between furrows are managed with zero or minimum tillage, and furrows are maintained as needed (Figure 1). This has received a great deal of attention in recent research in Asia and Australia. Furrows double as wheel tracks for cultivating, spraying, and other operations. Studies that compare permanent-raised-bed furrow systems with typical furrow irrigation and with no till management report marked improvements in soil quality, including lower density, warmer soil temperatures, better water productivity, and increased corn and wheat yields by 5 to 42%. Root crops like sugarbeet would require destruction and rebedding each time beets are harvested, but four- to six-year rotations with grain or forage crops would allow recovery of soil quality as observed in other regions. Perennial crops like alfalfa in the rotations, and cover crops following early-harvested crops like barley and dry beans would speed soil quality improvements.

Soil degradation and erosion are causing heartburn for furrow-irrigators concerned about soil quality and sustainability. We hope to begin some research and demonstration projects on the practice of permanent raised beds in Wyoming conditions during the next growing season. I would like to hear what producers think about the practice.

furrow irrigated conservation pics

Figure 1. Bed planting with two and three rows spaced ‘a’ inches apart and furrow gaps ‘b’ inches wide (left), and direct-seeded wheat on permanent beds. From Roth et al. (2005) Evaluation and performance of permanent raised bed cropping systems in Asia, Australia and Mexico. ACIAR Proceedings No. 21, Canberra.

Careful planning can lead to successful reclamation after oil and gas development

(This first appeared in the Wyoming Livestock Roundup in November, 2014)

Oil and gas production is on the rise in eastern Wyoming. Technological advances in exploration and extraction, like fracking and horizontal drilling are opening up large new reservoirs in places that haven’t boomed in over 20 years, or that never boomed before. A large part of my job as the University of Wyoming soils extension specialist involves research and education on the best ways to restore soils disturbed during extraction activities. In much of Wyoming that involves working with federal agencies and energy companies to develop new and better ways to restore the fragile productivity of arid rangelands.

But most of the land surface in eastern Wyoming is privately owned, and landowners can profit from leasing surface rights to drilling companies. But without careful planning for reclamation, long-term sustainability of farms and ranches can be threatened. Disturbance that comes with well pads, access roads, and pipelines is often difficult to repair, and recovering forage production, wildlife habitat, and soil water storage can be a long and difficult process that, if not done correctly, is too often unsuccessful.

Lease agreements should contain clear and complete final reclamation standards, but that is not always enough. Successful reclamation results from carrying out several steps, starting before a blade ever hits the ground. Stipulating proper procedures before, during, and after construction can prevent failure. This article discusses critical components that should be clearly described in reclamation plans and included in oil and gas development lease agreements.

A predisturbance or baseline inventory provides information on general characteristics of a site from both existing information like the soil survey, and on-site evaluation of wildlife habitat and use, forage production, water quality protection, aesthetics, and other qualities, as well as specific soil, vegetation, and landscape characteristics. The inventory establishes a framework for post-reclamation monitoring and evaluation.

Topsoil stripping should carefully follow the predisturbance plan, with operators carefully salvaging only the best soil, which is often very shallow in Wyoming. Stripping too deeply mixes topsoil with salty, clayey, or rocky subsoils and reduces the reclamation potential. Stripping depth should vary with the depth of the soil across a site as indicated in the predisturbance inventory. This requires a skilled equipment operator trained to visually recognize the correct depth. Stripping depth should be marked with stakes. Lower slopes and swales usually have deeper soils while upper slopes, knolls, and ridge tops have shallower soils. Eroded sites may have no salvageable topsoil.

In the cool, dry environment of Wyoming, stockpiling topsoil deeply and for relatively long periods is not as detrimental to the quality of the soil as moving it. While the initial disturbance accelerates decomposition and causes loss of soil organic matter, once in a pile, dry soils are essentially in cold storage and don’t change much until moved again.  Stockpiles should be seeded and protected from erosion by constructing silt fences or using straw bales, trenches, or other erosion-control practices around them as soon as possible.

Backfilling with subsoil and underlying materials and grading to the original topography, along with reestablishing drainage properties, set the stage for successful reclamationKeeping slopes less than 3:1, or 33-percent gradient, minimizes erosion after reclamation. Surface drainage patterns should be rebuilt to reestablish essential hydrologic functions and minimize erosion.

Before topsoil is respread on the graded surface, sites should be deep ripped to reduce compaction of the subsoil/ underlying material to appropriate rooting depth (at least 12 to 18 inches deep). Ripping soils allows for greater water infiltration, greater aeration of the soil. The most common primary tillage practices prior to spreading topsoil are deep ripping, deep chisel plowing, deep disking, and scarifying on the contour to control erosion.

After working the graded area, topsoil should be respread to depths consistent with the original depths. Topsoil should be chiseled, disked, and firmed with, a roller harrow on the contour to control erosion and prepare a proper seedbed. If results of predisturbance soil analyses are not available, test soils for nutrient content and salinity after spreading and use the typical productivity as the yield goal. This prevents unnecessary amendment application or over-fertilization.

Seeding technique and equipment depends upon seed size, which determines the proper depth of seeding and the seeding rate for each. When seeding grasses with a seed drill, 20 seeds per square foot is a sufficient rate; however, when the mix contains grasses, shrubs, and forbs, a better rate is 50-100 seeds per square foot (usually 10-16 pounds per acre). Large-seeded species are typically planted with a grass-seed drill while small-seeded, fluffy species should be planted with a broadcast seeder. Ideally, one seed mix should be designed for drilling and another for broadcasting.

Seeding time is crucial and, for Wyoming, reclamation seed mixes should usually be seeded in the fall after the soil temperature is around 40°F but before ground freezes (typically after October 15). Most native species need to be planted in the fall to break dormancy. Seeding times may vary by year and region within Wyoming. A spring seeding prior to April 15 may work in eastern Wyoming, where annual rainfall is over 15 inches and spring and early summer precipitation is fairly reliable.

Developing and following a long-term monitoring plan is crucial so problems can be identified and controlled early. Close attention should be paid to seeding success, noxious weeds, and erosion. Establishing a seeded plant community in Wyoming often takes three to four years and some shrubs may take that long just to germinate.

For more detailed information on key components for successful reclamation that should be included in oil and gas lease agreements, please see the University of Wyoming reclamation extension bulletin series on line at http://www.uwyo.edu/wrrc/bulletins.html, especially bulletin number B-1242, Reclamation Considerations for Oil and Gas Lease Contracts on Private Land.

Soil organic matter: what you don’t know

This article first appeared in the Wyoming Livestock Roundup in September, 2014

In one of my first talks as extension soils specialist at the University of Wyoming I began to describe the importance of soil organic matter and how, unlike many soil properties, it is a component of soil quality we can really affect with management. Then a farmer in the front row said loudly, “Yeah, Yeah, soil organic matter is important. Tell us something we don’t already know.” While the audience voted for me to continue through my introduction, it made me realize how important, and often difficult, it is to provide new information to producers.

The goal of this article is to describe the research view of soil organic matter in order to provide food for thought about management practices that improve soil quality. We’ve long known the importance of soil organic matter for regulating nutrient and water supplying potential of soils. But an ever increasing number of researchers continue to discover and publish new knowledge about this old subject. Much of it is very interesting and some even impacts the way we manage soils and design cropping or grazing systems.

The deep black soils of the corn belt are typically over five percent organic matter, and sometimes 10 percent or more. Wetter soils have higher contents because of greater plant production and slower decomposition in seasonally saturated, oxygen-deprived conditions. It may seem that organic matter is not as important in the west, with less than two percent in soils of the western fringes of the Great Plains and often less than one percent in soils of intermountain basins and deserts. But, as we’ve learned in reclamation, it is crucial for maintaining or restoring sustainable production of crops or forage, even at those low levels.

Soil organic matter is formed through decomposition of above- and below-ground plant residues along with compounds secreted by roots, as well as manure and animal residues. Components of any organic (carbon-based) material cover a spectrum of decomposability, from soft tissues and intracellular materials that break down rapidly, to woody materials that breakdown very slowly. Scientists have categorized the materials into active, slow, and passive fractions that perform different functions in the soil. The fractions are quantified in different ways, including simple sieving into different sizes, floating in dense liquid to separate density fractions, and treating with strong acids to identify chemical fractions. But generally they behave similarly, whether differentiated by size, density, or chemistry.

Active soil organic matter typically turns over, or completely decomposes, on an annual basis. It consists metabolic tissues and soluble carbon and nitrogen compounds that are rapidly consumed by soil microbes that cycle nutrients and make them available to plants. This fraction is important for meeting immediate plant nutrient needs, but much of it is converted to gases including carbon dioxide and nitrous oxide during microbial respiration. Disturbance like tillage accelerates turnover of active organic matter and loss as gases.

Slow organic matter turns over on the order of decades and  is made up of less decomposable plant parts, secondary compounds created by rapid decomposition of active materials, and active materials that are protected from microbial activity. Protection from decomposition occurs with materials are locked inside soil structural units, or peds, or because soils are wet, cold, or otherwise poor  environments for microbial activity. Soils of wetlands or alpine meadows often have higher proportions of slow organic matter because environmental conditions suppress decomposition. Undisturbed grassland and rangeland soils have much higher proportions of both active and slow fractions than cultivated soils because disturbance breaks up soil peds, destroying structure and exposing protected organic matter to oxygen and rapid decomposition.

Passive soil organic matter is often known as humus turns over and on order of centuries or longer. It consists mainly of stable compounds made up of large, complex organic molecules that are distilled from plant and animal residues during microbial decomposition of active and slow organic materials. Humus does not directly supply plant nutrients like active and slow fractions, but has huge impacts on soil quality by sticking soil particles together to form strong structure, porosity, and water holding capacity, and by providing many negatively charged broken ionic bonds that hold and release plant nutrients.

This graph, modified from one in an introductory soil science text by Nyle Brady and Ray Weil, shows how cultivation affects the proportions of organic matter (OM) in the active, slow, and passive fractions. It indicates that before cultivation begins over half the total soil organic matter consists of active and slow OM, along with plant residues decomposing on the soil surface. Disturbance has a drastic effect on those fractions, especially in the first 10 years after cultivation begins. After 50 years passive OM declines by a small amount, but the proportion of total organic matter made up of fractions that actively supply plant nutrients drops to approximately 13 percent.

Organic matter history graph

This graph has two strong implications for sustainable management practices, whether for farming or grazing: first, reducing disturbance can drastically improve the nutrient-supplying power of soils by preserving active and slow organic matter. Cultivation and other forms of disturbance cause brief surges of decomposition that use up much of the organic matter without making released nutrients available to plants. Second, returning as much plant residue to the soil as possible builds the active and slow fractions. This can have rapid impacts on soil quality.

In research on Wyoming dryland wheat production, we concluded that years of wheat-fallow rotations with intensive tillage resulted in loss of nearly 70 percent of the original soil organic matter. Modern farming practices over the last two or three decades have restored much of that through combinations of reduced tillage and increased biomass production, along with diverse plant residues from more complex crop rotations.

Growing Soil and Livestock Go Together

This article first appeared in the Wyoming Livestock Roundup in July, 2014

Overgrazing – repeatedly removing most or all of the vegetation – causes loss of roots, which leads to soil compaction, runoff,  erosion, and ultimately huge reductions in productivity. But this article isn’t about overgrazing. It’s about how proper management affects soil health and productivity.

Healthy rangeland soils have thick, dark surface horizons that absorb water and supply nutrients to diverse and productive vegetation. Where does that black soil come from? It comes from diverse and productive vegetation! Virtually all the aboveground plant material produced each year and about a quarter of the roots turn over – or decompose – to build soil organic matter and provide nutrients to the next crop. Over thousands of years, this feedback loop created soils resilient to all kinds of disturbance, and the farther east you go in the prairie region, the more resilient they are. But they have their limits. Over the past century, repeated plowing caused loss of around two-thirds of the original organic matter under Great Plains grasslands.

The cycle of growth and decay that sustains productive grazing land hinges on return of adequate amounts of diverse plant residues to the soil. Plant communities with rich mixtures of bunchgrasses, rhizomatous grasses, tap-rooted forbs, nitrogen fixers, and shrubs of many species contribute a wide variety of residues to the soil that decompose at different rates and times. This supports a huge diversity of soil microbes that cycle plant materials over the entire year, providing nutrients to growing plants. Plant residues that decompose rapidly provide nutrients, while those that are more resistant to decomposition tend to become stable soil organic matter – humus – that gives the soil a dark color and sponge-like qualities that enhance moisture holding potential and resilience to disturbance.

The amount of residue left uneaten by livestock to return to the soil is one important part of maintaining soil health. This part of the equation became starkly clear to me in my previous job in the California annual grasslands, where all the plants die each summer and regenerate from seed each winter and spring. Removing too much of the plant material has immediate effects on productivity by causing erosion, poor germination, and shifts toward less desirable species (like ripgut brome!). Livestock producers there are very aware of their RDM – Residual Dry Matter. In Wyoming most of our rangeland plants are perennial so the effect is not as immediate; plants regrow from their roots so germination conditions are less important. But removing too much plant material, even when plants are dormant in the mid-summer or winter, will have the same effects, leaving soil exposed to erosion and depleting soil organic matter.

The number of species and types of plants – the diversity – is another important part of soil health in grazing lands. A great deal of research in many types of plant communities has shown that more species lead to more fertile soil, more productivity, and less weed invasion. Mixtures of plants that grow at different rates, mature at different times, and have different root structures improve animal performance, and also increase soil microbial activity. Pastures that are all one species, either from conversion to introduced grasses like crested wheatgrass or invasion of weeds like cheatgrass, tend to end up with more shallow, less productive soils with limited biological activity.

In a study of native-plant-dominated, crested-wheatgrass-converted, and cheatgrass-invaded sagebrush grassland soils in Utah, I found that soil under the native plants had a wide variety of roots, the most organic material, especially the type that turns over rapidly, and also the most microbial activity. In that soil, lack of disturbance protects easily decomposed material and regulates the availability of nutrients to plants. The soil under cheatgrass had lost organic material because the dense mass of very fine roots dies each year, leaving thousands of pores that aerate the soil and accelerate decomposition of organic materials. This causes pulses of nutrient availability that favor annual weedy vegetation; almost like tillage. The soil under the 50-year old crested wheatgrass stands was intermediate in soil organic matter content and microbial activity, probably because the presence of only one type of plant residue and roots, that all grow and turnover the same way, limits microbial diversity and causes distinct pulses alternating with periods of little microbial activity.

So how do we manage grazing to improve soil health and productivity? Proper management to maintain and enhance plant production is also the best way to maintain and enhance soil health. In native rangelands, proper rest and grazing at different times of the year can maintain or enhance diversity. In improved pastures and management-intensive situations, interseeding, especially with nitrogen-fixing legumes, and then managing to maintain them, can improve both productivity and soil health. Keeping animals off wet soils, and avoiding prolonged concentration (trying not to create sacrifice areas) are other important ways to maintain the soil that sustains productive grazing lands and healthy, growing animals.

Please contact me for more information and reading materials on this subject.