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.

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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.