Search

Models of aeolian processes rely on accurate measurements of the rates of sediment transport by wind, and careful evaluation of the environmental controls of these processes. Existing field approaches typically require intensive, event-based experiments involving dense arrays of instruments. These devices are often cumbersome and logistically difficult to set up and maintain, especially near steep or vegetated dune surfaces. Significant advances in instrumentation are needed to provide the datasets that are required to validate and improve mechanistic models of aeolian sediment transport. Recent advances in robotics show great promise for assisting and amplifying scientists’ efforts to increase the spatial and temporal resolution of many environmental measurements governing sediment transport. The emergence of cheap, agile, human-scale robotic platforms endowed with increasingly sophisticated sensor and motor suites opens up the prospect of deploying programmable, reactive sensor payloads across complex terrain in the service of aeolian science. This paper surveys the need and assesses the opportunities and challenges for amassing novel, highly resolved spatiotemporal datasets for aeolian research using partially-automated ground mobility. We review the limitations of existing measurement approaches for aeolian processes, and discuss how they may be transformed by ground-based robotic platforms, using examples from our initial field experiments. We then review how the need to traverse challenging aeolian terrains and simultaneously make high-resolution measurements of critical variables requires enhanced robotic capability. Finally, we conclude with a look to the future, in which robotic platforms may operate with increasing autonomy in harsh conditions. Besides expanding the completeness of terrestrial datasets, bringing ground-based robots to the aeolian research community may lead to unexpected discoveries that generate new hypotheses to expand the science itself.

The National Wind Erosion Research Network was established in 2014 as a collaborative effort led by the United States Department of Agriculture’s Agricultural Research Service and Natural Resources Conservation Service, and the United States Department of the Interior’s Bureau of Land Management, to address the need for a long-term research program to meet critical challenges in wind erosion research and management in the United States. The Network has three aims: (1) provide data to support understanding of basic aeolian processes across land use types, land cover types, and management practices, (2) support development and application of models to assess wind erosion and dust emission and their impacts on human and environmental systems, and (3) encourage collaboration among the aeolian research community and resource managers for the transfer of wind erosion technologies. The Network currently consists of thirteen intensively instrumented sites providing measurements of aeolian sediment transport rates, meteorological conditions, and soil and vegetation properties that influence wind erosion. Network sites are located across rangelands, croplands, and deserts of the western US. In support of Network activities, http://winderosionnetwork.org was developed as a portal for information about the Network, providing site descriptions, measurement protocols, and data visualization tools to facilitate collaboration with scientists and managers interested in the Network and accessing Network products. The Network provides a mechanism for engaging national and international partners in a wind erosion research program that addresses the need for improved understanding and prediction of aeolian processes across complex and diverse land use types and management practices.

Horizontal (saltation) mass flux is a key driver of aeolian dust emission. Estimates of the horizontal mass flux underpin assessments of the global dust budget and influence our understanding of the dust cycle and its interactions. Current equations for predicting horizontal mass flux are based on limited field data and are constrained to representing transport-limited equilibrium saltation, driven by the wind momentum flux in excess of an entrainment threshold. This can result in large overestimation of the sediment mass flux. Here we compare measurements of the soil entrainment threshold, horizontal mass flux, and their temporal variability for five undisturbed dryland soils to explore the role of threshold in controlling the magnitude of mass flux. Average and median entrainment threshold showed relatively small variability among sites and relatively small variability between seasons, despite significant differences in soil surface conditions. Physical and biological soil crusts had little effect on the threshold value, and threshold appeared to play a minor role in determining the magnitude of sediment transport. Our results suggest that horizontal mass flux was controlled more by the supply limitation and abrasion efficiency of saltators present as loose erodible material or originating from neighboring soil sources. The omission of sediment supply and explicit representation of saltation bombardment from horizontal flux equations is inconsistent with the process representation in dust emission schemes and contributes to uncertainty in model predictions. This uncertainty can be reduced by developing greater process fidelity in models to predict horizontal mass flux under both supply- and transport-limited conditions.

Numerous parameterizations have been developed for predicting wind erosion, yet the physical mechanism of dust emission is not fully understood. Sandblasting is thought to be the primary mechanism, but recent studies suggest that dust emission by direct aerodynamic entrainment can be significant under certain conditions. In this work, using wind tunnel experiments, we investigated some of the lesser understood aspects of dust emission in sandblasting and aerodynamic entrainment for three soil types, namely, clay, silty clay loam, and clay loam. First, we explored the role of erodible surface roughness on dust emitted by aerodynamic entrainment. Second, we compared the emitted dust concentration in sandblasting and aerodynamic entrainment under a range of wind friction velocities. Finally, we explored the sensitivity of emitted dust particle size distribution (PSD) to soil type and wind friction velocity in these two processes. The dust concentration in aerodynamic entrainment showed strong positive correlation, no significant correlation, and weak negative correlation, for the clay, silty clay loam, and clay loam, respectively, with the erodible soil surface roughness. The dust in aerodynamic entrainment was significant constituting up to 28.3, 41.4, and 146.4% compared to sandblasting for the clay, silty clay loam, and clay loam, respectively. PSD of emitted dust was sensitive to soil type in both sandblasting and aerodynamic entrainment. PSD was sensitive to the friction velocity in aerodynamic entrainment but not in sandblasting. Our results highlight the need to consider the details of sandblasting and direct aerodynamic entrainment processes in parameterizing dust emission in global/regional climate models.

Wind erosion is a threat to the sustainability and productivity of soils that takes place at local, regional, and global scales. Current estimates of the cost of wind erosion have not included the costs associated with the loss of soil biodiversity and reduced ecosystem functions. Microorganisms carried in dust are responsible for numerous critical ecosystem processes including biogeochemical cycling of nutrients, carbon storage, soil aggregation, and transformation of toxic compounds in the source soil. Currently, much of the information on microbial transport in dust has been collected at continental scales, with no comprehensive review regarding the microbial communities, particularly those associated with agricultural systems, redistributed by wind erosion processes at smaller scales including regional or field scales. Agricultural systems can contribute significantly to atmospheric dust loading and loss or redistribution of soil microorganisms are impacted in three interactive ways: (1) differential loss of certain microbial taxa depending on particle size and wind conditions, (2) through the destabilization of soil aggregates and reduction of available surfaces, and (3) through the reduction of organic matter and substrates for the remaining community. The purpose of this review is to provide an overview of dust sampling technologies, methods for microbial extraction from dust, and how abiotic, environmental, and management factors influence the dust microbiome within and among agroecosystems. The review also offers a perspective on important potential future research avenues with a focus on agroecosystems and the inclusion of the fungal component.

Desert surfaces are typically stable and represent some of the longest-lived landforms on Earth. For surfaces devoid of vegetation, the evolution of a desert pavement of gravel and small stones protects the surface from erosion by wind and water and vegetation further protects the surface in arid and semi-arid rangelands. The susceptibility of the land surface to wind erosion is enhanced by mechanical damage to the desert pavement or vegetation losses resulting from fire or grazing. Despite the relatively rich literature on the effects of grazing and fire on plant community composition, land degradation, and the productivity of arid landscapes, little is known about the effects of moderate grazing or fire on the erodibility of soils in desert grasslands and shrublands. Here we investigate the effects of simulated moderate grazing, simulated livestock trampling, and of fire on the resulting wind erodibility and dust emissions of the affected soil surfaces. We surveyed 24 plots of the same size, 6m×0.6m, at a research site in the northern Chihuahuan Desert including 6 plots in a shrub-grass ecotone, 12 plots in an adjacent grassland, and 6 plots in an area that had been burned by a natural wildfire 6months earlier but had no vegetation recovery due to the time of year and drought. To evaluate the various effects of disturbances on the susceptibility of the surface to wind erosion and dust entrainment, replicates of three plots underwent different treatments including clipping, trampling, fire, and tillage. We subsequently tested each of the treated plots with a portable field wind tunnel run at 12.6ms−1. We found that moderate grazing and fire did not result in great soil loss in desert grasslands but that shrublands were more seriously affected by grazing and fire. Total removal of vegetation and disturbance of the soil surface did result in greater than order of magnitude increases of vertical sediment flux and greater than three-fold increases of dust emissions.

Simulations of the dust cycle and its interactions with the changing Earth system are hindered by the empirical nature of dust emission parameterizations in weather and climate models. Here we take a step towards improving dust cycle simulations by using a combination of theory and numerical simulations to derive a physically based dust emission parameterization. Our parameterization is straightforward to implement into large-scale models, as it depends only on the wind friction velocity and the soil's threshold friction velocity. Moreover, it accounts for two processes missing from most existing parameterizations: a soil's increased ability to produce dust under saltation bombardment as it becomes more erodible, and the increased scaling of the dust flux with wind speed as a soil becomes less erodible. Our treatment of both these processes is supported by a compilation of quality-controlled vertical dust flux measurements. Furthermore, our scheme reproduces this measurement compilation with substantially less error than the existing dust flux parameterizations we were able to compare against. A critical insight from both our theory and the measurement compilation is that dust fluxes are substantially more sensitive to the soil's threshold friction velocity than most current schemes account for.

Soil organic matter (SOM) is essential for soil water holding capacity, aggregation, and biodiversity. Little information is available regarding the carbon (C) functional groups carried away in wind eroded sediments away from the source soil. Mid-infrared (MidIR) spectroscopy was used on wind tunnel-blown sediments eroded from a loam soil during the fallow period of different cropping systems and tillage managements in Akron, Colorado. The soil was managed as fallow-winter wheat ( Triticum aestivum L.) under conventional tillage (F–Wct) or no tillage (F–Wnt) and fallow–wheat–corn under no tillage (F–W–Cnt). Two wind eroded sediments were evaluated: fine dust ( −1 ), and clays (3690–3620 cm −1 ). The saltation-sized material showed higher absorbance for quartz from 2000–1800 cm −1 and reduced absorbance from 1250–1050 cm −1 . Both wind eroded sediments showed higher absorbance for –OH/NH groups and aliphatic CH from no-till soil. Finer dust sediments, which travel greater distances from the source soil than saltation size material, can carry away higher levels of aliphatic-carbon compounds and clays with potential negative impacts on SOM quantity and quality, and consequently the sustainability of these agroecosystems.

The Soil Conditioning Index (SCI) and Soil Management Assessment Framework (SMAF) are two different but complementary methods for evaluating soil quality. Both tools have been widely used, but little is known regarding how they compare and if they provide similar results when the same agricultural management practices are compared. This SCI and SMAF soil quality index (SQI) comparison was conducted on the Fort Cobb Reservoir Experimental Watershed (FCREW) in Oklahoma. Forty-one loamy and sandy surface soil sites were sampled on the FCREW under (i) annual cropping with conventional tillage (conventional), (ii) annual cropping with either conservation tillage or no-till (conservation), (iii) cropland that had been converted to perennial grass (managed grass), and (iv) native grass. The SCI and SMAF SQI gave similar assessments, indicating that soil quality within conventional and conservation systems was similar but lower than in either managed or native grassland systems. Simple comparisons of soil properties by textural class showed no significant effects on most soil quality indicator values, and although texture by management subgroups was examined, no clear relationships were detected because of the limited number of sampling sites. The SMAF and SCI indicators and scores were correlated in tilled systems with limited vegetative cover but not for no-till or forage-based pasture or grassland systems that were in place for at least 10 yr. The SMAF provided more resolution when evaluating agroecosystem management effects on soil quality, including soil organic C enrichment, especially within forage-based systems. Recognizing that the SMAF currently does not account for soil loss, we conclude with recommendations for improving the tool, particularly for tilled systems.

Soil degradation is one of the most serious ecological problems in the world. In arid and semi-arid northern China, soil degradation predominantly arises from wind erosion. Trends in soil degradation caused by wind erosion in northern China frequently change with human activities and climatic change. To decrease soil loss by wind erosion and enhance local ecosystems, the Chinese government has been encouraging residents to reduce wind-induced soil degradation through a series of national policies and several ecological projects, such as the Natural Forest Protection Program, the National Action Program to Combat Desertification, the “Three Norths” Shelter Forest System, the Beijing-Tianjin Sand Source Control Engineering Project, and the Grain for Green Project. All these were implemented a number of decades ago, and have thus created many land management practices and control techniques across different landscapes. These measures include conservation tillage, windbreak networks, checkerboard barriers, the Non-Watering and Tube-Protecting Planting Technique, afforestation, grassland enclosures, etc. As a result, the aeolian degradation of land has been controlled in many regions of arid and semiarid northern China. However, the challenge of mitigating and further reversing soil degradation caused by wind erosion still remains.

Interest in integrated crop-livestock agroecosystems (ICL) has increased due to their versatility in management options, potential to offset increasing levels of atmospheric C and enhanced agronomic and ecosystem sustainability. Identifying agroecosystems that have the greatest potential for C sequestration requires an understanding of soil organic C distribution within aggregate fractions. Six soil aggregate C pools were physically isolated to evaluate the C sequestration potential of three ICLs and two continuous cotton (CTN) agroecosystems in the Texas High Plains. The proportions of the water stable aggregate fractions were used to calculate mean weight diameter, an indicator of soil stability. The first ICL (FRG_CTN) included paddocks of dryland perennial native grasses, a foxtail millet-cotton (Setaria italica [L.] P. Beauv. and FiberMax 9058F, respectively) rotation, and WW B-Dahl – Old World Bluestem [bluestem; Bothriochloa bladhii (Retz) S.T. Blake] under deficit irrigation (replacement of approximately 30% evapotranspiration). The second ICL (OWB_BER) included paddocks of deficit irrigated bermudagrass [bermuda; Cynodon dactylon (L.) Pers.] and bluestem and the third ICL (FRG_RC) included paddocks of irrigated bluestem and row crop production. Soil samples (0–5 and 5–20 cm) were collected in July 2010. In general, ICLs increased water stable macroaggregates providing a physical protective shell for SOC and increasing C sequestration potential. A strong correlation between SOC and mean weight diameter identified a critical SOC level of 5.5 Mg ha−1 for the greatest increases in mean weight diameter. Of the five agroecosystems evaluated, FRG_RC and OWB_BER ranked the highest in terms of mean weight diameter (130% larger), whole SOC (up to 45% more), and intra-aggregate microaggregate SOC (157% greater) relative to CTN production. Increased stability and reduced exposure of intra-aggregate fractions resulted in relatively greater intra-aggregate microaggregate SOC under perennial vegetation. The potential to serve as significant SOC accumulators may aid in offsetting increasing atmospheric C levels, and while specific to these semiarid soils, the identified critical SOC level can act as a target for producers to minimize and ultimately reverse soil degradation.

Wind erosion is a soil degrading process that threatens agricultural sustainability and environmental quality globally. Protecting the soil surface with cover crops and plant residues, practices common in no-till and reduced tillage cropping systems, are highly effective methods for shielding the soil surface from the erosive forces of wind and have been credited with beneficial increases of chemical and physical soil properties including soil organic matter, water holding capacity, and wet aggregate stability. Recently, advances in biofuel technology have made crop residues valuable feed stocks for ethanol production. Relatively little is known about cropping systems effects on intrinsic soil erodibility, the ability of the soil without a protective cover to resist the erosive force of wind. We tested the bare, uniformly disturbed, surface of long-term tillage and crop rotation research plots containing silt loam soils in western Kansas and eastern Colorado with a portable field wind tunnel. Total Suspended Particulate (TSP) were measured using glass fiber filters and respirable dust, PM10 and PM2.5, were measured using optical particle counters sampling the flow to the filters. The results were highly variable and TSP emission rates varied from less than 0.5 mg m−2 s−1 to greater than 16.1 mg m−2 s−1 but all the results indicated that cropping system history had no effect on intrinsic erodibility or dust emissions from the soil surfaces. We conclude that prior best management practices will not protect the soil from the erosive forces of wind if the protective mantle of crop residues is removed.

Integrated crop-livestock (ICL) systems that utilize perennial or high-residue no-till annual forages may build soil organic matter and, thus, enhance aggregate stability, water retention, nutrient cycling, and C storage. We examined long-term effects of ICL management on soil organic C (SOC) pools compared with continuous cotton [CTN; (Gossypium hirsutum L.)] at the system and individual vegetation levels, both using limited irrigation (65 and 77% replacement of evapotranspiration, respectively). Soil samples collected in 1997 (baseline) and 2010 were fractionated into four water stable aggregate-size classes: macroaggregate (>250 μm), microaggregate (53–250 μm), and silt + clay ( 250 μm), microaggregates (53–250 μm), and silt + clay (

Fine materials emissions from severe wind-induced soil erosion have multiple impacts on land degradation and environmental pollution in the agropastoral ecotone in northern China (APEC). Assessment of wind erosion for the agricultural land management systems in APEC is needed to determine which systems are most sustainable. In this study, the Revised Wind Erosion Equation (RWEQ) with a geographic information system method has been applied to estimate alternative wind erosion control measure scenarios. Simulation results of alternative agricultural land management scenarios for the period 2000 to 2008 indicated that the most severe potential wind eroded areas were scattered in the Horqin Sands, Hunshan Dake Sands, and Mu Us Sands. The scenarios results further showed that most croplands in the APEC would suffer severe wind erosion if no effective measures were implemented. The results further indicated that conservation tillage, no-tillage after harvest, and retention of crops residues until sowing season in the following year produced the most favorable impact on reducing wind erosion. Shrub barriers reduced wind erosion effectively, but irrigation twice per year could not reduce the wind erosion level markedly in the APEC. Even though combinations of conservation tillage, wind barriers, and irrigation could greatly reduce wind erosion, most farmlands in the APEC are still at the risk of degradation.

Disturbances such as wildfires, which cause a temporary reduction in vegetation cover, can greatly accelerate soil erosion by wind and promote dust emissions. Enhanced erosion leads to a reduction in soil fertility and the post-fire mobilisation of soil and associated emissions of dust represent a significant concern for ecosystem management and risk assessment. Here we investigate the temporal change of aeolian activity following a wildfire within both a managed grassland and an adjacent shrub encroached grassland at the Cimarron National Grassland, KS, USA. Our results indicate that, even though the grassland and shrub encroached grassland sites exhibit comparable aeolian activity soon after the fire, the duration of the post-disturbance period of aeolian activity (or “window of disturbance”) is shorter in the case of grassland than in the case of shrub encroached grassland. The degree of post-fire aeolian transport and its attenuation with time is strongly affected by the antecedent vegetation type. These findings have implications for management of semi-arid grasslands under both changing vegetation types (shrub encroachment) and disturbance (fire) regimes.

Published in Agron. J. 104:1625–1642 (2012) Posted online 12 Sept. 2012 doi:10.2134/agronj2012.0121 Copyright © 2012 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. A long-term goal for any nation must be food security— the basis of a stable society and the foundation of national security. Sustainable and secure food and fi ber production and an economically and ecologically viable agriculture cannot deplete the resources nor destroy the environment on which they depend. Agriculture today faces global challenges including continued population growth with an increasing food demand, changes in composition of food demand from a grain-based diet toward one higher in meat and milk products, depletion of natural resources, dependence on irrigation, and climate change. Th ese issues, combined with unstable economics, a fossil fuel-based energy system, changing government policies and regulations, and competition for land by nonagricultural uses threaten our capacity for food security and sustainable production. Monoculture systems in the United States, with economies of scale and advantages of specialization, have been highly successful at providing an abundance of safe and healthful foods. Such monocultures can put unacceptable stress on ecosystems and natural resources and result in unstable economics (Altieri, 2000). Input costs are now such that a single unfavorable growing season can result in fi nancial collapse for the producer and the loss of future opportunities. Water scarcity and municipal and industrial competition with agriculture for water are becoming a national imperative. Population growth and economic development are projected to have greater impact on water supply by 2025 than projected global climate change (Vorosmarty et al., 2000). Nowhere is this more evident than in the semiarid West Texas High Plains where agriculture accounts for about 28% of the region’s economy (IMPLAN, 2009), but depends heavily on water for irrigation from the Ogallala aquifer at nonsustainable rates of extraction (TWDB, 2007). Once a vast grassland, today this region has about 25% of U.S. cattle on feed and produces about 30% of U.S. cotton, primarily in monoculture systems (USDA-NASS and TDA, 2009). About 70% of this is irrigated cotton. With dependence on irrigation at nonsustainable rates of use, the future of agriculture in this region will not be a continuation of traditional practices. Although crop rotations have long been known for complementary benefi ts, eff ects of irrigation and the deliberate integration of crops and livestock to achieve complementary benefi ts on system sustainability is less well known. Krall and Schuman (1996) suggested that integrated crop and livestock systems can represent an ecologically and economically ABSTRACT

The Wind Erosion Prediction System (WEPS) and Revised Wind Erosion Equation (RWEQ) are widely used for estimating wind-induced soil erosion at a field scale. Wind is the principal erosion driver in the two models. Wind erosivity, which describes the capacity of wind to cause soil erosion, is defined as erosive wind power density (WPD) in WEPS, and wind value (W) in RWEQ. In this study, the daily average WPD (AWPD) and the daily average W (Wf) were chosen to investigate the effect of averaging time on wind erosivity estimation based on observed wind data. We compare the daily AWPD and Wf calculated from 1, 5, 10, 15, 30, and 60 minute average wind speed data. The results of comparisons indicate that averaging wind speed can significantly influence estimates of wind erosivity. Compared with the daily AWPD and Wf calculated from one minute average wind speed data, all daily AWPD and Wf values calculated from 5, 10, 15, 30, and 60 minute averaged wind speeds tend to be significantly lower than values calculated from one minute values. In general, longer averaging times tend to produce smaller values of daily AWPD or Wf, which may lead to an under-estimation of wind erosion. Further studies are needed to extend and apply the findings obtained in this study to actual wind erosion predictions. Copyright © 2012 John Wiley & Sons, Ltd.

A number of scientists have named our age the Anthropocene because humanity is globally affecting Earth systems, including the soil. Global soil change raises important questions about the future of soil, the environment, and human society. Although many soil scientists strive to understand human forcings as integral to soil genesis, there remains an explicit need for a science of anthropedology to detail how humanity is a fully fledged soil-forming factor and to understand how soil change affects human well being. The development and maturation of anthropedology is critical to achieving land-use sustainability and needs to be nurtured by all soil disciplines, with inputs from allied sciences and the humanities,. The Soil Science Society of America (SSSA) has recently approved a cross-divisional Working Group on Soil Change, which aims to advance the basic and applied science of anthropedology, to facilitate networks of scientists, long-term soil field studies, and regional databases and modeling, and to engage in new modes of communications about human–soil relations. We challenge all interested parties, especially young scientists and students, to contribute to these activities and help grow soil science in the Anthropocene.

Both recent models and historical events such as the Dust Bowl and volcanic eruptions have illustrated aerosols can play a significant role in climate change through direct and indirect optical effects. Soil dust aerosols generated by Aeolian processes represent a significant fraction of the total mass burden of atmospheric particles. Central to a better understanding of the climate effects of dust aerosols is knowledge of their optical properties. This research study utilized a dust generator and several instruments to determine certain optical properties of Aeolian dust mimics created by the Amarillo and Pullman soil types native to the panhandle of Texas, USA. Values for the mass-extinction coefficient ranged between 1.74 and 2.97 m 2 g −1 at 522 nm depending on how mass concentration was determined. Single-scatter albedo (SSA) for both soil types ranged from 0.947 to 0.980 at visible wavelengths with SSA increasing at longer wavelengths. Angstrom absorption exponents were measured as 1.73 for Pullman and 2.17 for Amarillo soil. Observed Angstrom extinction exponents were 0.110 and 0.168 for the Pullman and Amarillo soil types. The optical properties reported may be of use for optical based estimates of soil erosion and aid in understanding how regional soil dusts may alter radiative transport presently and during historical events such as the Dust Bowl era.

Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of animal disturbance (one and ten cow passes) were tested. The wind tunnel generated dust emissions under controlled conditions for firstly an initial blow-off of the surface, followed by two longer runs with sand added to the flow as an abrader material. Dust was measured using a GRIMM particle monitor. For the study playa, no significant differences in PM10 concentration and emission flux were found between the untrampled surface and following a single animal pass. This was the case for both the initial blow-offs and tests on plots under a steady abrader rate. Significantly higher dust loading was only associated with the effect of 10 animal passes. In the blow-offs, the higher PM10 yield after 10 passes reflected the greater availability of easily entrainable fine particles. Under abrasion, the effect of the heaviest trampling increased the emission flux by a third and abrasion efficiency by around 50% more than values on the untrampled surface. This enhanced abrasion efficiency persisted for a 30 min period under abrasion before the positive effect of the disturbance was no longer evident. The findings highlight the role of a threshold of disturbance that determines if supply-limited surfaces will exhibit enhanced wind erosion or not after undergoing perturbation.

Indicators of soil quality, such as microbial biomass C and N (MBC, MBN) and enzyme activities (EAs), involved in C, P, N, and S cycling, as affected by dryland cropping systems under conventional (ct) and no tillage (nt) practices were evaluated for 5 years. The soil is sandy loam with an average of 16.4% clay, 67.6% sand, and 0.65 g kg−1 OM at 0–10 cm. The crops evaluated were rotations of grain sorghum (Sorghum bicolor L.) or forage sorghum (also called haygrazer), cotton (Gossypium hirsutum), and winter rye (Secale cereale): grain sorghum–cotton (Srg–Ct), cotton–winter rye–sorghum (Ct–Rye–Srg), and forage sorghum–winter rye (Srf–Rye). The tillage treatments did not affect soil MB and EAs of C cycling (i.e., β-glucosidase, β-glucosaminidase, α-galactosidase), P cycling (alkaline phosphatase, phosphodiesterase), and S cycling (arylsulfatase)—except for separation due to tillage for Srf–Rye and Ct–Rye–Srg observed in PCA plots when all EAs were evaluated together. After 3 years, rotations with a winter cover crop history (Ct–Rye–Srg and Srf–Rye) enhanced soil MBN (up to 63%) and EAs (21-37%) compared to Srg–Ct. After 5 years, Srg–Ct and Ct–Rye–Srg showed similar soil MBC, MBN, EAs, total carbon (TC), and organic carbon (OC). A comparison of Srg–Ct plots with nearby continuous cotton (Ct–Ct) research plots in the same soil revealed that it took 5 years to detect higher TC (12%), MBC (38%), and EAs (32–36%, depending on the enzyme) under Srg–Ct. The significant improvements in MB and EAs found, as affected by dryland cropping systems with a history of winter cover crops and/or higher biomass return crops than cotton, can represent changes in soil OM, nutrient cycling, and C sequestration for sandy soils in the semiarid Texas High Plains region. It is significant that these soil changes occurred despite summer crop failure (2003 and 2006) and lack of winter cover crops (2006) due to lack of precipitation in certain years.

Old world bluestems (Bothriochloa spp.) have been successfully introduced as grasses for livestock forage in the semiarid Texas High Plains. Questions remain, however, on effects of these grasses on soil resources. We tested the hypothesis that differences in grass species produce differences in soil properties important to crop growth and useful in selecting the optimum species for the Southern High Plains of Texas. Three old world bluestem (Bothriochloa) species [C.E. Hubbard ‘Caucasian’, B. caucasica (Trin.); ‘WW Spar’, B. ischaemum (L.) Keng.var ischaemum (Hack.); and S.T. Blake ‘WW-B Dahl’, B. bladhii (Retz)] were grown in a randomized complete block design, with three replications, for nine years on a clay loam soil near Lubbock, Texas. Soil samples were collected in the ninth year to determine soil texture, wet aggregate stability, bulk density (BD), soil organic carbon (SOC), particulate organic carbon (POC), and soil strength as measured by the cone pentrometer. The grass species differed in their above-ground biomass and below- ground root production. In the ninth year of production, Bothriochloa caucasica and B. bladhii produced about twice the above-ground biomass with about 25% fewer roots than B. ischaemum. Soils where B. caucasica was grown had the highest BD (1.36 Mg m–3) and B. ischaemum had the lowest (1.31 Mg m–3). The soil in which B. ischaemum was growing had a lower BD, greatest root biomass, organic matter content, and aggregate stability suggesting superior soil quality for agricultural production. The species B. bladhii, however, often exhibited soil properties that were similar to both other species tested. Since Bothriochloa bladhii had superior or similar soil properties for plant growth among the species tested and has been shown to be higher in forage quality, animal performance, and carrying capacity than the other species, it appears to be the best choice among these three species to optimize both animal performance and desirable soil properties.

Cotton (Gossypium hirsutum L.) monoculture under conventional tillage has been the predominant cropping system in the Southern High Plains region of the United States since the 1940s. This study evaluated other cropping systems and land uses for their potential to increase soil quality and enhance soil functioning compared with continuous cotton (Ct-Ct), including a mixture of grasses in the Conservation Reserve Program (CRP), a pasture monoculture [Bothriochloa bladhii (Retz) S.T. Blake] and a cotton-winter wheat (Triticum aestivum L.)-corn (Zea mays L.) rotation (Ct-W-Cr). Soil microbial communities were evaluated according to microbial biomass C (MBC) and N (MBN), fatty acid methyl ester (FAME) profiling, and molecular cloning techniques. Soil MBC was higher under the alternative systems at 0 to 5 cm (CRP > pasture = Ct-W-Cr > Ct-Ct), 5 to 10 cm (CRP = Ct-W-Cr > pasture > Ct-Ct), and 10 to 20 cm (CRP = pasture = Ct-W-Cr > Ct-Ct). Soil DNA concentration was correlated with key soil quality parameters such as microbial biomass (r > 0.52, P < 0.05), total C (r = 0.372, P < 0.1), and total N (r = 0.449, P < 0.05). The 16S rRNA gene banding patterns (0-5 cm) of undisturbed systems (CRP and pasture) were more similar to each other than to Ct-Ct and Ct-W-Cr. Fungal/bacterial FAME ratios were higher under CRP and pasture than under Ct-Ct at 0 to 5 and 5 to 10 cm. This study found increases in sensitive soil quality parameters under alternative management compared with cotton monoculture.

Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model which estimates aerodynamic roughness length (z0) using angular reflectance of a rough surface. The new model is proportional to the frontal area index, directional, and represents the geometric anisotropy of z0. The model explained most of the variation in two sets of wind tunnel measurements of aerodynamic roughness lengths (z0). Field estimates of z0 for varying wind directions were similar to predictions made by the new model. The model was used to estimate the erodible area exposed to abrasion by saltating particles. Vertically integrated horizontal flux (Fh) was calculated using the area not covered by non-erodible hemispheres; the approach embodied in dust emission models. Under the same model conditions, Fh estimated using the new model was up to 85% smaller than that using the conventional area not covered. These Fh simulations imply that wind erosion and dust emission models without geometric anisotropic sheltering of the surface, may considerably over-estimate Fh and hence the amount of dust emission. The new model provides a straightforward method to estimate aerodynamic resistance with the potential to improve the accuracy of wind erosion and dust emission models, a measure that can be retrieved using bi-directional reflectance models from angular satellite sensors, and an alternative to notoriously unreliable field estimates of z0 and their extrapolations across landform scales.

This study evaluated microbial communities of soil (0–10 cm) as affected by dryland cropping systems under different tillage practices after 5 years. The soil type was an Olton sandy loam with an average of 16.4% clay, 67.6% sand and 0.65 g kg−1 of organic matter (OM). The cropping systems evaluated were grain sorghum (Sorghum bicolor L.)—cotton (Gossypium hirsutum) (Srg-Ct), cotton-winter rye (Secale cereale)-grain sorghum (Ct-Rye-Srg), and a rotation of forage (f) sorghum (Sorghum bicolor L. and Sorghum sudanense) with winter rye (Srf-Rye), which were under no-tillage (nt) and conventional tillage (ct) practices. Soil microbial communities under cotton based cropping systems (Srg-Ct and Ct-Rye-Srg) showed lower fungal:bacterial ratios compared to the soil under Srf-Rye. Soil under Srf-Rye showed higher population densities of Bacteroidetes and Proteobacteria while lower Actinobacteria compared to Srg-Ct and Ct-Rye-Srg. Chloroflexi, Gemmatimonadetes and Verrucomicrobiae were higher in tilled soil compared to the no-tilled plots. Regardless the limited irrigation available to sustain agricultural production within these dryland cropping systems, this study demonstrated that differences in microbial communities are more affected by crop rotation than tillage management history. Although soil fungal diversity was not analyzed in this study, pyrosequencing suggests that tillage practices can affect bacterial phyla distribution in this sandy soil.

Quantitative estimation of the material transported by the wind under field conditions is essential for the study and control of wind erosion. A critical step of this calculation is the integration of the curve that relates the variation of the amount of the material carried by the wind with height. Several mathematical procedures have been proposed for this calculation, but results are scarce and controversial. One objective of this study was to assess the efficiency of three mathematical models (a rational, an exponential, and a simplified Gaussian function) for the calculation of the mass transport, as compared to the linear spline interpolation. Another objective of this study was to compare the mass transport calculated from field measurements obtained from a minimum of three discrete sampling heights with measurements of nine sampling heights. With this purpose, wind erosion was measured under low surface roughness conditions on an Entic Haplustoll during 25 events. The rational function was found to be mathematically limited for the estimation of wind eroded sediment mass flux. The simplified Gaussian model did not fit to the vertical mass flux profile data. Linear spline interpolation generally produced higher mass transport estimates than the exponential equation, and it proved to be a very flexible and robust method. Using different sampling arrangements and different mass flux models can produce differences of more than 45% in mass transport estimates, even under similar field conditions. Under the conditions of this study, at least three points between the soil surface and 1·5 m high, including one point as closest as possible to the surface, should be sampled in order to obtain accurate mass transport estimates. Additionally, the linear spline interpolation and the non-linear regression using an exponential model, proved to be mathematically reliable methods for calculating the mass transport. © 2010 John Wiley & Sons, Ltd. Fil: Panebianco, Juan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Buschiazzo, Daniel Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Zobeck, Ted M.. USDA‐ARS; Estados Unidos

Wind erosion is a natural process that has formed landscapes but threatens sustainable agriculture in many locations. Wind tunnels have been used for several decades to study wind erosion processes. Portable wind tunnels offer the advantage of testing natural surfaces in the field, but they must be carefully designed to ensure that a logarithmic boundary layer is formed and that wind erosion processes may develop without interference from the tunnel structures. Although large portable tunnels often meet the aerodynamic criteria, their size and transportation requirements often limit the locations where they may be employed. We designed and built a self-contained portable wind tunnel that is easily transported on a tandem-axle trailer and pulled with a pickup truck. The wind tunnel uses a centrifugal blower, a flow-conditioning section with optional abrader material feed, and a 1 m tall and 0.5 m wide working section that can vary in length from 2 m to 6 m. The maximum wind velocity attainable is 18.7 m s-1 although a mid-height centerline velocity of 12.6 m s-1 is normally used for field testing of natural surfaces. Based on measured wind velocity profiles in the tunnel working section, a conservative estimate of boundary layer depth within the working section is 0.5 m. Even though no wind tunnel can truly duplicate the scale and variability of the forces that drive wind erosion, tunnels such as this one with deeply developed boundary layers offer reasonable estimates of dust emissions and erodibilities of natural surfaces. This wind tunnel has been used to test rangeland and cropped surfaces in several locations and has provided reliable and useable soil erodibility and dust emission data.

Aridland ecosystems are often susceptible to degradation resulting from disturbances like fires and grazing. By exposing the soil surface to the erosive action of winds, these disturbances contribute to the redistribution of soil nutrients associated with grassland-to-shrubland conversions and to the formation of a heterogeneous landscape. Wind erosion maintains the local heterogeneities in nutrient and vegetation distribution in arid landscapes through the removal of nutrient-rich soil from the intercanopy areas and the subsequent deposition of soil onto vegetation patches. Even though wind erosion and disturbances like fires strongly interact with each other and determine vegetation patterns in arid landscapes, very few studies have addressed these interactions. Using soil samples collected after a wildfire event at the Cimarron National Grasslands in southwestern Kansas, we demonstrate through a series of wind-tunnel experiments, laboratory measurements, and theoretical analyses how wind erosion can be enhanced by fire-induced water repellency. Results from the wind-tunnel experiments show that in semiarid grasslands fires can cause a decrease in the threshold velocity of wind erosion thereby, enhancing the post-burn erosion of (hydrophobic) soils. Further, a generalized process-based theoretical equation was derived to explain the decrease in threshold friction velocity in water-repellent soil for the case of soil particles modeled as asymmetrical cones.

Various soil management or quality assessment tools have been proposed to evaluate the effects of land management practices on soil, air, and water resources. Two of them are the Soil Management Assessment Framework and the Soil Conditioning Index (SCI). This study was conducted to test the hypothesis that the Soil Quality Index (SQI) estimated by the Soil Management Assessment Framework can detect more minute changes in soil management than SCI and to test SCI response to other soil quality (SQ) indicators. These SQ indexes were tested on irrigated cropping systems near Fort Collins, Colorado, that included no-till and conventionally-tilled corn (Zea mays L.), and no-till corn with rotations including barley (Hordeum distichon L.), soybean (Glycine max (L.) Merr.), and dry bean (Phaeseolus vulgaris L.) at three levels of nitrogen varying from 0 to 224 kg N ha-1 (0 to 200 lb ac-1). Both SQ indexes clearly separated the plots with very high levels of N from plots with no N. However, for SQI the mid-level of N was statistically the same as both extreme levels. Statistical differences were observed among all N levels for the SCI. The SQI seemed to make more detailed differentiation among crop management systems than the SCI. The SCI separated the cropping systems into three groups with no overlap among groups. All no-till systems had the statistically same higher SCI than the conventionally-tilled continual corn system. The SQI separated the cropping systems into three groups with decreasing SQI as tillage intensity increased and as lower residue crops were introduced into the cropping system. The systems that included tillage and a low residue crop (soybean) had the lowest SQI. The SQI allowed overlap among cropping groups not recognized by SCI. Selection of the most appropriate SQ index seems to be a tradeoff between data requirements, resolution required, and the desired use of the evaluation tool.

Crop production on the Llano Estacado of the Texas High Plains has used precipitation and supplemental irrigation with water pumped from the Ogallala aquifer at rates that have far exceeded recharge for many years. Over 20% of the U.S. cotton (Gossypium hirsutum L.) crop is produced currently in this once vast grassland. Most of this cotton is produced in monoculture systems that are economically risky and contribute to wind-induced erosion and depletion of ground water resources. Although large numbers of cattle are found in this region, little integration of livestock and crop production exists. Integrated crop–livestock systems could improve nutrient cycling, reduce soil erosion, improve water management, interrupt pest cycles, and spread economic risk through diversification. Two whole-farm scale systems compared (1) a cotton monoculture typical of the region; and (2) an alternative integrated system that included cotton, forage, and Angus-cross stocker beef steers (initial body weight 249 kg). Steers grazed the perennial warm-season grass ‘WW-B. Dahl’ old world bluestem [Bothriochloa bladhii (Retz) S.T. Blake] in sequence with rye (Secale cereale L.) and wheat (Triticum aestivum L.) from January to mid-July when they were sent to the feedyard for finishing. Grass seed were harvested from bluestem in October. Cotton in the alternative system was grown in a two-paddock rotation with the wheat and rye. Cotton was harvested from both systems in October. At the end of 5 years, the alternative system reduced needs for supplemental irrigation by 23% and for nitrogen fertilizer by 40% compared with the conventional cotton monoculture. Fewer chemical inputs including pesticides were required by the alternative system. Soil with perennial grass pasture was lower in predicted soil erosion and was higher in soil organic carbon, aggregate stability, and microbial biomass than soil where continuous cotton was grown. Profitability was greater for the alternative system until cotton lint yields reached about 1500 kg ha−1 for the continuous cotton system. Differences between the systems became larger as depth to ground water increased. Systems that are less dependent on supplemental irrigation and less consumptive of non-renewable resources and energy-dependent chemical inputs appear possible, but further improvements are required to ensure sustainability of agricultural systems for the future in the Texas High Plains.

Wind erosion has degraded over one-half billion hectares of land worldwide. 137 Cesium ( 137 Cs) has been used as a tracer to study long-term rates of soil redistribution by water and, to a lesser extent, by wind. Early studies assumed that the decline in 137 Cs activity for a potentially eroded soil relative to that for an uneroded soil was linearly proportional to soil loss. More recently, models have emerged that consider the effects of soil cultivation and the particle surface area-dependent partitioning of 137 Cs on soils. We investigated the partitioning of 137 Cs in wind-eroded sediments and with soil surface samples sieved into contiguous ranges of particle sizes. We also compared the 137 Cs activities and stratification of several adjacent soils with known wind erosion and deposition histories. Finally, we tested 137 Cs-based soil loss models with measured data from sites with documented histories. 137 Cs activities and mean particle diameters of aeolian samples agreed well with the 137 Cs activities and respective mean diameters of the sieved surface soil samples. Good agreement between model estimations and measured data indicated that 137 Cs models developed to estimate soil redistribution by water were also applicable to soil redistribution by wind provided that the models contained an appropriate particle size correction parameter.

Wind erosion is said to be an important degradation process of soils, but little is known about the magnitude of this process and its effect on soil nutrient transport in Entic Haplustolls of the semi-arid Pampas of Argentina. The objective of this study was to measure the rate of wind erosion and the concentration of nitrogen and phosphorus in the sediment originating from different tillage systems: conventional tillage (CT), vertical tillage (VT), and no-till (NT), for two different crops of the semi-arid Pampas of Argentina. Measurements of airborne sediment were carried out in an 8 ha field using Big Spring Number Eight (BSNE) samplers, in two periods of 1998 and 1999, after seeding sunflower (Helianthus annus) and rye (Secale cerale). Losses and accumulations of material were detected. Losses varied between 4 and almost 900 kg ha−1, and accumulations between 3 and 580 kg ha−1. Wind erosion was higher in 1999 than in 1998 in all tillage systems, due to higher wind speeds and lower plant residue coverage of the first measurement period. In 1999, erosion was lower in plots with higher plant residue coverage (NT against CT), and in 1998 sediment accumulation was observed in these treatments. Nitrogen concentration in the sediment collected at greater heights increased and phosphorus concentration decreased with wind speed. This was due to the accumulation of nitrogen in the coarsest aggregates and of phosphorus in the finer aggregates. The nitrogen enrichment of the sediment varied between 2 and 5, while the phosphorus enrichment varied between 1.5 and 8. The nitrogen enrichment increased and the phosphorus enrichment decreased with wind speed. Lower wind-speed storms will erode relatively more phosphorus than nitrogen. When high wind-speed storms occur, nitrogen becomes more susceptible to erosion. Wind speed is the variable that may regulate the amounts of nutrient loss.

Deposition of suspended dust near eroding source fields can have detrimental effects on vegetation, as well as on soil and water quality. This study was undertaken to quantify dust deposition within 200 m of a source field during wind erosion events. Erosion was measured with BSNE samplers on a small field of Amarillo fine sandy loam at field at Big Spring, TX. Suspension-sized dust discharge averaged 33 ± 5 per cent of the total sediment discharge and ranged from 18·0 to 147·4 kg m−1 during eight selected storm events. Within 200 m of the source field boundary, dust collected in deposition samplers placed above a vegetated surface averaged 34 per cent of initial dust discharge. Predicted deposition, according to a line source model, was 43 per cent. Actual deposition was likely near that predicted, because of lateral diffusion of the dust and some under-sampling by the disk samplers. Thus, the line source model seems useful in estimating both the pattern and quantity of deposition. About 30 per cent of the suspended dust was deposited within the initial 50 m of vegetated surface, but only about 12–15 per cent was deposited in the initial 10 m. Published in 2006 by John Wiley & Sons, Ltd.

G efforts to identify and develop soil quality indices that can accurately and efficiently quantify effects of soil and crop management began to emerge around the world during the latter portion of the 20th century. This occurred as people became more aware that soil is a unique, nonrenewable resource that nurtures and sustains human civilizations (McNeill and Winiwater, 2004). These efforts have been further encouraged by a growing awareness of the multiple ecosystem services that soil resources provide to sustain food security, environmental quality, ecological functions, and most recently feedstock production for biofuels (Doran et al., 1996; Bouma, 2005; Lal, 2007). In addition to serving as assessment tools, soil quality indices also provide land managers with a better understanding of how their short-term, economically driven management decisions are affecting soil properties and processes over time.

To improve wind erosion model calculations across several spatial and temporal scales simultaneously, there is a requirement for a non-invasive approach that can be used rapidly to assess changes in the compositional and structural nature of a soil surface in time and space. Remote sensing allows consideration of the processes controlling erodibility on the same spatial continuum to avoid time-consuming and expensive fieldwork. Multi-angular spectral reflectance appears to provide a holistic framework for the measurement and calculation of soil surface characteristics remotely using ground-based radiometers and current and future generations of angular sensors on airborne and satellite platforms. To investigate the utility of this framework, a ground-based study was performed using three soils susceptible to wind erosion that were modified using rainfall simulation and wind tunnel abrasion experiments. Measurements of those changes were made and recorded using digital images. Multi-angular spectral measurements of reflectance were also made and inverted against a bi-directional soil spectral reflectance model. Comparison of the measurements and calculations showed good agreement with small errors in accuracy. Optimised values of the model parameters produced the single scattering albedo and a description of the reflectance scattering behaviour of the soil surfaces that included an estimate of roughness. The model parameters removed the effect of illumination and viewing geometry on the spectral reflectance. The combination of single-scattering albedo spectra and model parameters for each treatment provided information about the composition and structure of the soil surface changes. The main changes detected at the soil surface included the presence of a crust produced by rain-splash, the production of loose erodible material covering a rain crust and the selective erosion of the soil surface. Redundancy analysis showed that much of the variation in the values of the soil reflectance model parameters was explained by the scattering properties and the roughness parameter of the soil surfaces. Variation in the soil surface reflectance was not explained solely by soil type. Instead, low intensity rainfall combined with short and long duration abrasion explained a significant portion. These findings provide a source of considerable variation in experimental and operational spectral reflectance measurements that has perhaps hitherto been largely ignored. The results demonstrated the readily available information on the composition and structure of the soil surface without interfering with natural processes. The directional soil reflectance methodology appears to have potential for use in improving the understanding of erodibility and ultimately for identifying and quantifying soil erosion.

Wind erosion is a dominant geomorphological process in arid and semi-arid regions with major impacts on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. The understanding and modelling of aeolian erosion requires a better understanding of the soil erodibility associated with different moisture conditions. In arid regions during the dry season, the atmospheric humidity plays an important role in determining the surface moisture content and the threshold shear velocity. By a series of wind tunnel tests and theoretical analyses, this dependence of threshold velocity on near surface air humidity is shown for three soils of different textures: sand, sandy loam, and clay loam. The results show that the threshold shear velocity decreases with increasing values of relative humidity for values of relative humidity between about 40% and 65%, while above and below this range the threshold shear velocity increases with air humidity. A theoretical framework is developed to explain these dependencies assuming an equilibrium between the surface soil moisture and the humidity of the overlying atmosphere. The conditions under which soil-atmosphere equilibrium occurs were tested experimentally in the laboratory for different soils in order to determine the effect of grain surface area and texture on the time required to reach equilibrium starting from different initial conditions.

The surface susceptibility to erosion (erodibility) is an important component of soil erosion models. Many studies of wind erosion have shown that even relatively small changes in surface conditions can have a considerable effect on the temporal and spatial variability of dust emissions. One of the main difficulties in measuring erodibility is that it is controlled by a number of highly variable soil factors. Collection of these data is often limited in scale because in situ measurements are labour-intensive and very time-consuming. To improve wind erosion model predictions over several spatial and temporal scales simultaneously, there is a requirement for a non-invasive approach that can be used to rapidly assess changes in the compositional and structural nature of a soil surface in time and space. Spectral reflectance of the soil surface appears to meet these desirable requirements and it is controlled by properties that affect the soil erodibility. Three soil surfaces were modified using rainfall simulation and wind tunnel abrasion experiments. Observations of those changes were made and recorded using digital images and on-nadir spectral reflectance. The results showed clear evidence of the information content in the spectral domain that was otherwise difficult to interpret given the complicated interrelationships between soil composition and structure. Changes detected at the soil surface included the presence of a crust produced by rainsplash, the production of loose erodible material covering a rain crust and the selective erosion of the soil surface. The effect of rainsplash and aeolian abrasion was different for each soil tested and crust abrasion was shown to decrease as rainfall intensity increased. The relative contributions of the eroded material from each soil surface to trapped mixtures of material assisted the erodibility assessment. Ordination analyses within each of two important soil types explained significant amounts of the variation in the reflectance of all wavebands by treatments of the soil and hence changes in the soil surface. The results show that soil surface conditions within a soil type are an underestimated source of variation in the characterization of soil surface erodibility and in the remote sensing of soil. Copyright © 2005 John Wiley & Sons, Ltd.

Continuous monoculture systems can reduce soil organic matter because of low organic inputs and disturbance from tillage practices. Integrated cotton (Gossypium hirsutum) cropping and livestock production systems in West Texas may provide more sustainable alternatives to the traditional continuous cotton system and improve soil quality. Our study was conducted on a Pullman soil (Fine, mixed, thermic Torrertic Paleustolls) after 5 yr as a complete randomized block design (three replications) that compared continuous cotton and an integrated livestock-crop system with a perennial warm-season grass pasture (Bothriochloa bladhii) paddock and two paddocks (two stages) of a rotation (wheat [Triticum aestivum]-fallow-rye [Secale cereale]-cotton). Total N (average: 1.0 g kg -1 soil) remained similar among systems and soil pH was >8.1. Organic C was higher (13.5 g kg -1 soil) in perennial pasture compared with continuous cotton (9.0 g kg -1 soil) at 0 to 5 cm.[...]

Soil C and N have long been recognized as important indicators of soil productivity. The current low levels of soil C and N of cropland soils have led to interest in sequestering C with reduced tillage cropping systems and the Conservation Reserve Program (CRP). Our objective was to assess agroecosystem effects on soil C and N pools in the Southern High Plains. The agroecosystems included three cotton (Gossypium hirsutum L.) cropping systems, CRP land, and native rangeland (NR). We sampled 0- to 5-, 5- to 10-, 10- to 15-, and 15-to 30-cm soil depths at 12 farm sites in five counties in West Texas. Total soil C and N, particulate organic matter (POM) C and N, natural abundance of carbon-13 isotope (δ 13 C) of POM and of whole soil, potentially mineralizable C and N, water-extractable carbon (WEC), and extractable ammonium (NH + 4 ) and nitrate (NO - 3 ) were determined. Total C and N in the 0- to 30-cm soil profile were 34 Mg C ha -1 and 2.5 Mg N ha -1 for NR, and 23 Mg C ha -1 and 1.9 Mg N ha -1 for cropland systems, respectively. Total soil C and N in CRP land were greater in cropland soils only in the 0- to 5-cm layer, and were 24 Mg C ha -1 and 2.1 Mg N ha -1 in 0 to 30 cm. Labile C and N pools were positively correlated with each other and with total soil C and N. Low soil test P may have limited C and N sequestration in CRP land and NR. Improved management practices are needed to sequester C and N in CRP and conservation-tillage cotton systems in the Southern High Plains.

The wind erosion stochastic simulator (WESS) is a single event wind erosion model that is the core of the wind erosion submodel of the environmental policy integrated climate (EPIC) erosion model. WESS uses inputs of soil texture, erodible particle diameter, soil roughness, soil water content, crop residue, and 10 min average wind speeds to predict the erosion at several user-selected distances within a given field. The revised wind erosion equation (RWEQ) makes annual or period estimates of wind erosion based on a single event wind erosion model that includes factors for wind and rainfall, soil roughness, the erodible fraction of soil, crusting, and surface residues. In this study, we compared estimates of wind erosion at multiple points in a field for 24 events at Big Spring, Texas with the predictions of WESS and compared estimates of maximum sediment transport capacity (Qmax), critical field length at which Qmax is attained ( S ), and soil loss (SL) calculated from field measured data collected at six locations and 41 events with the predictions of RWEQ. Compared to observed estimates of erosion for the 24 events, WESS under-predicted 9 events, accurately predicted 8 events, and over-predicted 7 events. In general, RWEQ underestimated Qmax and SL and overestimated S .

The Wind Erosion Equation (WEQ) is currently used by the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) to ensure compliance with government guidelines for soil loss from agricultural land. The model uses inputs of soil texture, annual mean climate data, statistically derived wind energy apportionment tables, and field management options to predict soil loss on a management period and annual basis. In this study, we compared estimates of wind erosion derived from the sums of field measurements at seven locations, two of which had multiple years of observations (a total of 14 periods of comparison), with the predictions of WEQ. WEQ under-predicted the observed estimates of 11 of the 14 periods by as much as a factor of nine. For the three periods that WEQ over-predicted observed erosion estimates, the factor was less than 1.5. Across all sites and periods considered in this investigation, WEQ only predicted about 53% of the observed estimated erosion. Analysis of two average years at Big Spring, TX, indicated that WEQ could be locally calibrated by use of increased climatic (C′) and soil erodibility (I) values as well as combinations of the two.

Soil particle size analyses (PSA) are needed to relate soil texture to soil performance or behavior. Standard analyses of dry soils usually include dispersion of the soils followed by particle size determination by a variety of time-consuming methods. Clay- and silt-sized particles are usually measured by sedimentation using a hydrometer or pipette method. Sands are then measured by sieving. Recent advances in laser diffraction technology have led to the production of devices specifically designed to rapidly measure the particle distribution of dispersed particles. This study compares the PSAs of 43 soil samples collected from the Southern High Plains of Texas measured by the pipette method and sieving with results obtained using a laser diffraction particle size analyzer (LDPSA). No pretreatment to remove organic matter or salts was used. The LDPSA required about 300-mg soil sample and overnight dispersion while shaking in a sodium hexametaphosphate solution. Each sample was analyzed in about 10 min, including device clean up. The correlation of the laser analyses with pipette analyses varied by particle size and mineralogy. Better correlations were obtained when non-calcareous soils were separated from calcareous soils. Regression analyses relating laser with pipette methods for non-calcareous soils yielded coefficients of determinations of 0.97, 0.99, and 0.99 for the

There is limited knowledge of biochemical processes in low carbon content soils of semiarid regions under different land use and management. This study investigated several enzyme activities of C, N, P, and S transformations in semiarid soils with different clay (10–21 %) and sand (59–85 %) contents that were under conservation reserve program (CRP), native rangeland (NR), and cropland (CL) under sunflowers (Eriophyllum ambiguum (Gray)), continuous cotton (Gossypium hirsutum L.), or in rotations with wheat (Triticum aestivum L.) or sorghum (Sorghum bicolor L.) in West Texas, USA. Soils under CRP and NR showed higher total C and N contents than cultivated soils under continuous cotton, but soil pH (6.7–8.4) was not affected by the management or land use studied. The activities of β-glucosidase, β-glucosaminidase, arylamidase, acid and alkaline phosphatase, phosphodiesterase, and arylsulfatase (mg product (kg soil)–1 h–1) were lower in CL under continuous cotton compared to cotton in rotation with other crops, CRP, and NR. The enzyme activities were also lower when compared to soils from other regions. Linear regression analyses indicated positive correlations between enzyme activities and total C (r values up to 0.96, P < 0.01). There was a positive relationship between enzyme activities and total N, but soil pH showed the opposite trend. Enzyme activities were significantly intercorrelated with r values up to 0.98 (P < 0.001). The specific enzyme activities (mg product (g organic C)–1) were lower in continuous cotton in comparison to the uncultivated soils (i.e., NR and CRP) reflecting differences in organic matter quantity and quality due to cultivation. Among the enzymes studied, the specific activities of β-glucosidase and arylamidase showed a more pronounced decrease with increasing soil depth. In general, soils under CRP or wheat-cotton rotations revealed higher enzyme activities than soils under the common agricultural practice for these regions, i.e., continuous cotton under conventional tillage. Enzymaktivitaten in semiariden Boden unter konservierender Landnutzung, naturlichem Weideland und Ackerland Begrenzte Informationen liegen uber biochemische Prozesse in semiariden Boden unter verschiedenen Landnutzungssystemen vor. In dieser Studie wurden die Aktivitaten von verschiedenen Enzymen des C-, N-, P- und S-Kreislaufes in semiariden Boden mit variierenden Gehalten an Ton (10–21 %) und Sand (59–85 %) unter konservierender Landnutzung (CRP), naturlichem Weideland (NR) und Ackerland untersucht. Innerhalb des Ackerlandes wurden Boden unter Sonnenblumen (Eriophyllum ambiguum (Gray)), Baumwoll-Monokulturen (Gossypium hirsutum. L.), bzw. unter Baumwolle in Fruchtfolge mit Weizen (Triticum aestivum. L.) oder Hirse (Sorghum bicolor. L.) beprobt. Boden unter CRP and NR wiesen hohere Gesamtgehalte an C und N auf als Ackerboden unter Baumwoll-Monokultur. Die pH-Werte (pH 6.7–8.4) waren von der Landnutzung unbeeinflusst. Die Aktivitaten von β-Glukosidase, β-Glukosaminidase, Arylaminidase, saurer und alkalischer Phosphatase, Phosphodiesterase und Arylsulfatase (mg Produkt (kg Boden)–1 h–1) waren geringer unter Baumwoll-Monokulturen als unter Baumwolle in Fruchtfolge mit anderen Kulturen, CRP und NR. Im Vergleich zu Boden anderer Regionen fielen die Enzymaktivitaten in semiariden Boden geringer aus. Lineare Regressionsanalysen ergaben enge Korrelationen zwischen den Enzymaktivitaten und dem Gehalt an C (r ≤ 0.98, P < 0.001). Die Enzymaktivitaten zeigten positive Beziehungen zum Gesamtgehalt an N und negative Beziehungen zum pH-Wert. Signifikante Interkorrelationen bestanden zwischen den einzelnen Enzymaktivitaten (r ≤ 0.98, P < 0.001). Die spezifischen Enzymaktivitaten (mg Produkt (g organischem C)–1) waren geringer unter Baumwoll-Monokultur als unter CRP und NR. Diese Ergebnisse lassen auf nutzungsbedingte Unterschiede in der Quantitat und Qualitat der organischen Bodensubstanzen schliesen. Die spezifischen Aktivitaten von β-Glukosidase und Arylamidase folgten einem starkeren Tiefengradienten als die anderen Enzymaktivitaten. In der Regel wiesen Boden unter CRP oder Baumwolle in Fruchtfolge mit Weizen und Hirse hohere Enzymaktivitaten auf als Boden unter konventionellen Baumwoll-Monokulturen. Letztere stellen jedoch die ubliche landwirtschaftliche Praxis in dieser Region dar.