Overwinter Changes in Dry Aggregate Size Distribution Influencing Wind Erodibility in a Spring Wheat-Summerfallow Cropping System

A long-term study of the wind erodibility properties of a two-year spring wheat-summerfallow cropping systems was started in 1988 in south-central North Dakota as part of an USDA-ARS led effort to construct a process-oriented soil erosion predictive model. Observations were conducted on a conservation tillage experiment established in 1984 on soil classified in the U.S. as Typic-Pachic Haploborolls and in Canada as Brown to Dark Brown Chenozemic. The experiment included four residue-management treatments defined by targeted residue coverages: no-till, \u3e 60% cover; minimal-till, 30% to 60% cover and undercutter dominated; conventional-till, \u3c 30% cover and disk dominated; low-residue, \u3c 5 % cover. Fall and spring measurements of dry aggregate size distribution (ASD) of surface soil (0 to 4 cm depth), and overwinter changes in ASD are reported here. A rotary sieve produced six size fractions ranging from \u3c 0.42 mm to \u3e 19.2 mm diameter. Measurements of ASD are expressed as geometric mean diameter (GMD) or erodible fraction (EF: fraction \u3c 0.84 mm). Two major influences on overwinter changes in ASD were observed: (i) During the drier part of a multiyear weather cycle (1988 to 1990), disaggregative changes were observed, with a lowering of GMDs and an increase in EFs. Wetter years (1991 to 1993) brought mixed to aggregative ASD changes. (ii) The phase of the 21-month fallow period strongly affected overwinter ASD change, with large, aggregative changes (GMD up, EF down) observed over the first winter of the fallow period (stubble phase) and mixed aggregative to disaggregative changes observed in the second winter of fallow (residue phase). Tillage treatments had little apparent effect on overwinter ASD changes. Single and multiple regressions indicate that various factors would associate with significant fractions of variance in overwinter GMD change: (i) weather factors - (a) number of days with snowcover, (b) number of freeze-thaw cycles, and (c) precipitation in the fall; (ii) crop growth in years before the year of fallow; (iii) phase of the fallow period; and (iv) GMD level in the fall

Dryland cropping systems influence the microbial biomass and enzyme activities in a semiarid sandy soil

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

Desert RHex Technical Report: Jornada and White Sands Trip

Researchers in a variety of fields, including aeolian science, biology, and environmental science, have already made use of stationary and mobile remote sensing equipment to increase their variety of data collection opportunities. However, due to mobility challenges, remote sensing opportunities relevant to desert environments and in particular dune fields have been limited to stationary equipment. We describe here an investigative trip to two well-studied experimental deserts in New Mexico with D-RHex, a mobile remote sensing platform oriented towards desert research. D-RHex is the latest iteration of the RHex family of robots, which are six-legged, biologically inspired, small (10kg) platforms with good mobility in a variety of rough terrains, including on inclines and over obstacles of higher than robot hip height. For more information: Kod*La

Microbiology of wind-eroded sediments: current knowledge and future research directions

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

Total vertical sediment flux and PM10 emissions from disturbed Chihuahuan Desert surfaces

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, 6 m × 0.6 m, 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 6 months 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 12.6 m s−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

Ground robotic measurement of aeolian processes

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. For more information: Kod*lab (http://kodlab.seas.upenn.edu/