Brenton Sharratt

Tillage and straw management for modifying physical properties of a subarctic soil

Conservation tillage practices are intended to minimize soil erosion. Yet little is known concerning changes in physical properties of subarctic soils subject to tillage practices. This study ascertained whether physical properties of a newly cleared subarctic soil are altered after 7 years of continuous barley (Hordeum vulgare L.) using different tillage and straw management strategies. Tillage and straw treatments were established in 1983 near Delta Junction, Alaska, and consisted of conventional fall and spring disk, fall chisel plow, spring disk, and no-tillage. Tillage plots were split by straw management practices, which included straw and stubble, stubble only, and no straw or stubble. Soil samples were collected from the upper 0.15 m of the profile in the spring of 1990 to assess water content, bulk density, saturated hydraulic conductivity, dry aggregate and mechanical stability, penetration resistance, water retention, and particle size distribution. Percent non-erodible aggregates, mechanical stability, and penetration resistance were greater for no-tillage compared to conventional tillage, chisel plow, and spring disk. No-tillage soils were also typically wetter, denser, and had a greater hydraulic conductivity. The spring disk treatment was least susceptible to erosion and also conserved soil water compared with chisel plow. Straw maintained on the surface conserved water and promoted soil stability.

A wood-strand material for wind erosion control: effects on total sediment loss, PM10 vertical flux, and PM10 loss.

Fugitive dust from eroding land poses risks to environmental quality and human health, and thus, is regulated nationally based on ambient air quality standards for particulate matter with mean aerodynamic diameter < or = 10 microm (PM10) established in the Clean Air Act. Agricultural straw has been widely used for rainfall-induced erosion control; however, its performance for wind erosion mitigation has been less studied, in part because straw is mobile at moderate wind velocities. A wood-based long-strand material has been developed for rainfall-induced erosion control and has shown operational promise for control of wind-induced erosion and dust emissions from disturbed sites. The purpose of this study was to evaluate the efficacy of both agricultural straw and wood-strand materials in controlling wind erosion and fugitive dust emissions under laboratory conditions. Wind tunnel tests were conducted to compare wood strands of several geometries to agricultural wheat straw and bare soil in terms of total sediment loss, PM10 vertical flux, and PM10 loss. Results indicate that the types of wood strands tested are stable at wind speeds of up to 18 m s(-1), while wheat straw is only stable at speeds of up to 6.5 m s(-1). Wood strands reduced total sediment loss and PM10 emissions by 90% as compared to bare soil across the range of wind speeds tested. Wheat straw did not reduce total sediment loss for the range of speeds tested, but did reduce PM10 emissions by 75% compared to a bare soil at wind speeds of up to 11 m s(-1).

Winter soil microclimate altered by corn residue management in the northern Corn Belt of the USA

Management of crop residue is important for promoting soil water recharge and early spring thaw in the northern Corn Belt of the USA. This study assessed the impact of residue management in no tillage, continuous corn (Zea mays L.) production systems on the soil thermal and water regime during winter in west central Minnesota. Residue treatments were initiated in the fall over three years and included the removal of stubble and loose residue (RR) from the soil surface, all residue lying prostrate (PR) on the soil surface, and stubble standing and loose residue lying (SR) on the soil surface. Soil (to 0.3 m depth) temperatures were recorded hourly whereas soil water content, frost depth, and snow cover were measured weekly. The SR treatment effectively trapped more snow, which resulted in warmer soil (2°C or less), shallower frost penetration (as much as 0.5 m), and earlier soil thaw (up to 20 d) as compared with the RR or PR treatments. Winter soil temperatures and depth and duration of soil freezing were the same for the RR and PR treatments. Soil water content was the same for all treatments prior to fall freezing, but was less for the PR treatment than for the SR or RR treatment during winter due to less snowmelt infiltration for the PR treatment. Corn production utilizing no tillage in the northern USA necessitates the retention of stubble on the soil surface for promoting warmer soil during the winter as well as earlier spring thaw as compared with removing or chopping stubble.

Instrumentation to Quantify Soil and PM10 Flux Using a Portable Wind Tunnel

Wind erosion threatens soil productivity and air quality in the Columbia Plateau region of the Pacific Northwest United States. Management practices are sought that will abate erosion, but limitations exist in measuring the effectiveness of these practices in reducing erosion. Portable wind tunnels are ideal tools that can be used to assess the impact of management practices on erosion. A portable wind tunnel, characterized by a 7.3-m long working section that is 1-m wide and 1.2-m high and capable of generating winds of 20 m s-1, was instrumented to measure wind speed as well as soil loss and PM10 (particulate matter =10µm in diameter) emissions in the laboratory and field. Wind speed was measured at various heights above the soil surface using pitot tubes. Creep was measured using trays while saltation and suspension were measured using an isokinetic slot sampler. PM10 concentration was measured by mounting Dustrak inlets at various heights above the soil surface both at the windward and leeward position in the wind tunnel. PM10 loss was determined by integrating horizontal PM10 flux from the soil surface to plume height and subtracting the mass flux at the windward position from that at the leeward position in the tunnel. Pitot tubes and Dustrak inlets were mounted on a sliding instrument rack. Auxiliary devices (e.g. datalogger) were mounted on the frame of the wind tunnel to enhance portability and timeliness of operations. The instrumentation package has performed well in assessing soil and PM10 flux in the laboratory and field.

Evaluation of two empirical wind erosion models in arid and semi-arid regions of China and the USA

Wind erosion models are important tools for assessing soil erodibility and identifying management practices to control erosion. The Agricultural Policy/Environmental eXtender (APEX) model and Revised Wind Erosion Equation (RWEQ) were tested using data collected from the Tarim Basin of China and Columbia Plateau of the United States of America. Adequate performance in simulating soil loss was achieved using the original APEX model and RWEQ in respectively a cotton field and desert-oasis ecotone in the Tarim Basin and winter wheat - summer fallow (WW-SF) field in the Columbia Plateau. We calibrated the APEX model and RWEQ to improve performance because both models have many empirical parameters. After calibration, both models adequately simulated soil loss from all land use types except the RWEQ from the red date orchard in the Tarim Basin. Inadequate performance of the calibrated RWEQ in the red date orchard was likely due to underestimating maximum mass transport. Performance of the APEX model and RWEQ was tested in China and USA.The wind erosion models were compared under different land cover types.Both models, when uncalibrated, inadequately simulated soil loss.Calibration improved the performance of both models.

Particulate matter emissions from biochar-amended soils as a potential tradeoff to the negative emission potential

Novel carbon sequestration strategies such as large-scale land application of biochar may provide sustainable pathways to increase the terrestrial storage of carbon. Biochar has a long residence time in the soil and hence comprehensive studies are urgently needed to quantify the environmental impacts of large-scale biochar application. In particular, black carbon emissions from soils amended with biochar may counteract the negative emission potential due to the impacts on air quality, climate, and biogeochemical cycles. We investigated, using wind tunnel experiments, the particulate matter emission potential of a sand and two agriculturally important soils amended with different concentrations of biochar, in comparison to control soils. Our results indicate that biochar application considerably increases particulate emissions possibly by two mechanisms–the accelerated emission of fine biochar particles and the generation and emission of fine biochar particles resulting from abrasion of large biochar particles by sand grains. Our study highlights the importance of considering the background soil properties (e.g., texture) and geomorphological processes (e.g., aeolian transport) for biochar-based carbon sequestration programs.

Influence of long-term tillage and crop rotations on soil hydraulic properties in the US Pacific Northwest

In the low precipitation zone (<0.3 m [11.8 in] annual precipitation) of the Inland Pacific Northwest, no-tillage continuous spring cereal and no-tillage spring cereal-chemical fallow rotations are being examined as alternatives to the traditional winter wheat–summer fallow rotation for soil conservation. There is limited information, however, regarding the long-term effects of no-tillage cropping systems on soil hydraulic properties in this semiarid region. The objective of this study was therefore to characterize infiltration, water retention, saturated hydraulic conductivity and bulk density of a silt loam that had been subject to various tillage and crop rotations in east-central Washington. Treatments examined included no-tillage spring barley–spring wheat (NTSB–SW), no-tillage spring wheat–chemical fallow (NTSW–ChF), and traditional winter wheat–summer fallow (WW–SF). Soil properties were measured in spring and late summer 2006 due to the vulnerability of the soil to rapidly dry and erode during these seasons. Saturated hydraulic conductivity was determined by the falling-head method, infiltration was measured using a double-ring infiltrometer, and water retention characteristics was assessed by examining the temporal variation of in situ soil water content. NTSB–SW resulted in higher infiltration and saturated hydraulic conductivity, lower bulk density, and larger and/or more continuous pores in the upper soil profile (<0.1 m [<3.9 in] depth) than WW–SF and NTSW–ChF. Infiltration and saturated hydraulic conductivity were lower for chemical fallow than for traditional fallow in spring whereas hydraulic conductivity was lower for summer fallow than chemical fallow in late summer. Soil hydrologic properties appeared more favorable for no-tillage continuous spring cereal rotations. These results are useful for soil and water management and conservation planning in the low precipitation zone of the Inland Pacific Northwest.

A multiscale database of soil properties for regional environmental quality modeling in the western United States

The USDA Natural Resources Conservation Service State Soil Geographic (STATSGO) database contains general soils information, but data available in STATSGO cannot be readily extracted nor parameterized to support regional environmental quality modeling. As such, each user must individually and repeatedly process data in STATSGO to obtain necessary soil properties. The objective of this study was to develop a comprehensive database, the Western States Soil Database (WSSD) (http://www.lar.wsu.edu/nw-airquest/soils_database.html), for use in modeling regional soil and water resources and environmental quality across eight western states (Washington, Oregon, California, Idaho, Nevada, Utah, Montana, and Wyoming). We aggregated existing soil properties in STATSGO from 19,681 map units of the eight states and estimated soil properties based upon quantitative relationships among existing soil properties. The WSSD comprises 3,910 map units, with each map unit defined by 10 soil layers and each layer characterized by 31 soil properties. The WSSD was gridded to 1 and 12 km (0.62 and 7.44 mi) resolution cells for application to grid-based environmental models. Data from WSSD was tested against USDA Natural Resources Conservation Service field data and indicated satisfactory agreement; for example, the Root Mean Square Error (RMSE) for sand and clay content varied between 4% and 7%. The RMSE appeared to be greatest for organic matter and was as large as 106% of the measured value. The WSSD provides information on soil properties useful for regional-scale modeling.

Fate of autumn-applied metolachlor in a clay loam in the northern U.S. Corn Belt.

Application of herbicides in autumn is of interest to land managers who seek to reduce the number of field operations during spring in the northern Corn Belt. A limited number of herbicides, however, posses the physical characteristics that are required to minimize loss from soil over winter. This study examined the fate of one of these herbicides, metolachlor, during three consecutive winters (1994–1995, 1995–1996, and 1996–1997) near Morris, MN. Metolachlor was applied to the top 5 cm of a clay loam that was packed into a 1.8‐m long plastic pipe. The pipe was then set inside a larger diameter 1.8‐m long plastic pipe that was buried vertically in the field. The gap between the pipes was insulated along the sides and sealed at the top; this configuration allowed collection of leachate and extraction of the smaller diameter pipe while the field soil was frozen. The experimental design was replicated thrice with sample date (date that the smaller diameter pipes were extracted from the field) as the main treatment. Pipes were extracted from the field at least twice during winter and sectioned into 2 cm or larger increments. The soil contained within these sections was then analyzed for metolachlor. Downward movement of metolachlor occurred in the soil profile during the autumn, but only in 1995. This movement was likely caused by exclusion during pore ice formation as the soil froze. At the time of complete soil thaw in spring, the majority of metolachlor was still detected in the zone of application (0–5 cm depth). Some metolachlor, however, was detected 1 to 3 cm below the zone of application in all three years. Downward movement during thaw was due primarily to infiltration of snowmelt and rain. Metolachlor was most vulnerable to degradation during spring, but some loss occurred in autumn prior to freeze‐up. This study suggests that autumn‐applied metolachlor moves little in a repacked clay loam profile during winter. Further studies are warranted in evaluating movement under a range of soil physical properties and management practices.

Soil properties influenced by summer fallow management in the Horse Heaven Hills of south central Washington

The Horse Heaven Hills (HHH) is the worlds driest rainfed wheat (Triticum aestivum L.) region where soils are highly susceptible to wind erosion due to use of tillage during the fallow phase of the winter wheat–summer fallow (WW-SF) cropping system. Wheat straw residue biomass and cover, surface roughness, soil water content and strength, and aggregate size distribution of no-tillage fallow (NTF), undercutter-tillage fallow (UTF), and traditional-tillage fallow (TTF) were measured after primary tillage of UTF and TTF in late April and after sowing winter wheat in late August of 2007 at two sites in the HHH. Residue cover and silhouette area index were at least two times greater and penetration resistance and shear stress were at least five times greater for NTF than TTF in spring and late summer at both sites. Random roughness was typically lower for NTF as compared with UTF in spring and late summer at both sites. Summer fallow treatments influenced soil aggregation whereby geometric mean diameter was greater and erodible fraction was lower for NTF than TTF. Based upon the Revised Wind Erosion Equation (RWEQ), sediment flux was lowest for NTF and at least 70% lower for UTF as compared with TTF. Thus, soil loss due to wind erosion can be reduced by using NTF and UTF rather than TTF for WW-SF rotations in the HHH.