Effects of Stocking Rate on the Variability of Peak Standing Crop in a Desert Steppe of Eurasia Grassland

Proper grazing management practices can generate corresponding compensatory effects on plant community production, which may reduce inter-annual variability of productivity in some grassland ecosystems. However, it remains unclear how grazing influences plant community attributes and the variability of standing crop. We examined the effects of sheep grazing at four stocking rate treatments [control, 0 sheep ha^?1 month^?1; light (LG), 0.15 sheep ha^?1 month^?1; moderate (MG), 0.30 sheep ha^?1 month^?1; and heavy (HG), 0.45 sheep ha^?1 month^?1] on standing crop at the community level and partitioned by species and functional groups, in the desert steppe of Inner Mongolia, China. The treatments were arranged in a completely randomized block design over a 9-year period. Standing crop was measured every August from 2004 to 2012. Peak standing crop decreased (P < 0.05) with increasing stocking rate; peak standing crop in the HG treatment decreased 40 % compared to the control. May–July precipitation explained at least 76 % of the variation in peak standing crop. MG and HG treatments resulted in a decrease (P < 0.05) in shrubs, semi-shrubs, and perennials forbs, and an increase (P < 0.05) in perennial bunchgrasses compared to the control. The coefficients of variation at plant functional group and species level in the LG and MG treatments were lower (P < 0.05) than in the control and HG treatments. Peak standing crop variability of the control and HG community were greatest, which suggested that LG and MG have greater ecosystem stability.     

Seasonal dynamics in earthworm density, casting activity and soil nutrient cycling under Bermuda grass (Cynodon dactylon) in semiarid tropics, India

This work illustrates the result of a study on earthworm abundance, seasonal population dynamics and casting activities under Bermuda grass cover in a semiarid tropical part of Rajasthan, India. The earthworm abundance and their casting activities showed the drastic variation during different seasons. The maximum density (individual m^?2) of earthworms was recorded in autumn (87.0?±?7.2) and minimum in winter (5.3?±?3.2) season in grassland. There was also variation in temperature and moisture of canopy soil in different seasons of the experimental year. The casting activities of earthworm also showed variations among different seasons. The maximum cast production rate was recorded during autumn (690.0?±?78.0?g?m^?2) while in winter (17.3?±?5.1?g?m^?2), earthworms showed the lowest cast production rate. The chemical composition of worm casts and parental soil layers (topsoil: 0?C10?cm depth and subsoil: 10?C25?cm depth) in grassland ecosystem was also monitored. The earthworm casts collected during winter showed the maximum level of total N (0.890?g?kg^?1), available P (0.373?g?kg^?1), exchangeable K (0.835?g?kg^?1), exchangeable Ca (7.10?g?kg^?1) and exchangeable Mg level (5.93?g?kg^?1) while the maximum organic C content (5.27?g?kg^?1) was recorded in surface casts deposited in rainy season. The level of major soil nutrients was also high in worm casts than parental soil and indicates the earthworm-mediated nutrient mineralization and organic matter transformation. Results thus clearly suggest the major role of earthworm in soil nutrient transformation in semiarid ecosystem.     

Field-Level Financial Assessment of Contour Prairie Strips for Enhancement of Environmental Quality

The impacts of strategically located contour prairie strips on sediment and nutrient runoff export from watersheds maintained under an annual row crop production system have been studied at a long-term research site in central Iowa. Data from 2007 to 2011 indicate that the contour prairie strips utilized within row crop-dominated landscapes have greater than proportionate and positive effects on the functioning of biophysical systems. Crop producers and land management agencies require comprehensive information about the Best Management Practices with regard to performance efficacy, operational/management parameters, and the full range of financial parameters. Here, a farm-level financial model assesses the establishment, management, and opportunity costs of contour prairie strips within cropped fields. Annualized, depending on variable opportunity costs the 15-year present value cost of utilizing contour prairie strips ranges from $590 to $865 ha^?1 year^?1 ($240–$350 ac^?1 year^?1). Expressed in the context of “treatment area” (e.g., in this study 1 ha of prairie treats 10 ha of crops), the costs of contour prairie strips can also be viewed as $59 to about $87 per treated hectare ($24–$35 ac^?1). If prairie strips were under a 15-year CRP contract, total per acre cost to farmers would be reduced by over 85 %. Based on sediment, phosphorus, and nitrogen export data from the related field studies and across low, medium, and high land rent scenarios, a megagram (Mg) of soil retained within the watershed costs between $7.79 and $11.46 mg^?1, phosphorus retained costs between $6.97 and $10.25 kg^?1, and nitrogen retained costs between $1.59 and $2.34 kg^?1. Based on overall project results, contour prairie strips may well become one of the key conservation practices used to sustain US Corn Belt agriculture in the decades to come.     

Soil Changes Induced by Rubber and Tea Plantation Establishment: Comparison with Tropical Rain Forest Soil in Xishuangbanna, SW China

Over the past thirty years, Xishuangbanna in Southwestern China has seen dramatic changes in land use where large areas of tropical forest and fallow land have been converted to rubber and tea plantations. In this study we evaluated the effects of land use and slope on soil properties in seven common disturbed and undisturbed land-types. Results indicated that all soils were acidic, with pH values significantly higher in the 3- and 28-year-old rubber plantations. The tropical forests had the lowest bulk densities, especially significantly lower from the top 10?cm of soil, and highest soil organic matter concentrations. Soil moisture content at topsoil was highest in the mature rubber plantation. Soils in the tropical forests and abandoned cultivated land had inorganic N (IN) concentrations approximately equal in NH₄ ⁺-N and NO₃ ^?-N. However, soil IN pools were dominated by NH₄ ⁺-N in the rubber and tea plantations. This trend suggests that conversion of tropical forest to rubber and tea plantations increases NH₄ ⁺-N concentration and decreases NO₃ ^?-N concentration, with the most pronounced effect in plantations that are more frequently fertilized. Soil moisture content, IN, NH₄ ⁺-N and NO₃ ^?-N concentrations within all sites were higher in the rainy season than in the dry season. Significant differences in the soil moisture content, and IN, NH₄ ⁺-N and NO₃ ^?-N concentration was detected for both land uses and sampling season effects, as well as interactions. Higher concentrations of NH₄ ⁺-N were measured at the upper slopes of all sites, but NO₃ ^?-N concentrations were highest at the lower slope in the rubber plantations and lowest at the lower slopes at all other. Thus, the conversion of tropical forests to rubber and tea plantations can have a profound effect on soil NH₄ ⁺-N and NO₃ ^?-N concentrations. Options for improved soil management in plantations are discussed.     

Recovery Trajectories After In Situ Burning of an Oiled Wetland in Coastal Louisiana,USA

The high degree of physical disturbance associated with conventional response options to oil spills in wetlands is driving the investigation of alternative cleanup methodologies. In March 1995, a spill of gas condensate in a brackish marsh at Rockefeller Wildlife Refuge in southwestern Louisiana was remediated through the use of in situ burning. An assessment of vegetation recovery was initiated in three treatment marshes: (1) oil-impacted and burned, (2) oil impacted and unburned, and (3) a nonoiled unburned reference. We compared percent cover, stem density, and biomass in the treatment marshes to define ecological recovery of the marsh vegetation and soil hydrocarbon content to determine the efficacy of in situ burning as a cleanup technique. Burning led to a rapid decrease in soil hydrocarbon concentrations in the impacted-and-burned marsh to background levels by the end of the first growing season. Although a management fire accidentally burned the oil-impacted-and-unburned and reference marshes in December 1995, stem density, live biomass, and total percent cover values in the oil-impacted-and-burned marsh were equivalent to those in the other treatment marshes after three years. In addition, plant community composition within the oil-impacted-and-burned marsh was similar to the codominant mix of the grasses Distichlis spicata (salt grass) and Spartina patens (wire grass) characteristic of the surrounding marsh after the same time period. Rapid recovery of the oil-impacted-and-unburned marsh was likely due to lower initial hydrocarbon exposure. Water levels inundating the soil surface of this grass-dominated marsh and the timing of the in situ burn early in the growing season were important factors contributing to the rapid recovery of this wetland. The results of this in situ burn evaluation support the conclusion that burning, under the proper conditions, can be relied upon as an effective cleanup response to hydrocarbon spills in herbaceous wetlands.     

The convective hot air drying of Lactuca sativa slices

The storage of fresh agricultural products is not easy because of its high moisture. Dehydration is an efficient preservation method. The investigation of drying modeling and transfer characteristics are important for selecting operating conditions and equipment design. The drying behavior of Lactuca sativa slices, with the thickness of 2 mm, was investigated at 60.0–80.0°C and 0.60–1.04 m sec^?1 velocity in a convective hot air drier. The mass transfer during the drying process was described using six thin drying models. The convective heat transfer coefficient α and mass transfer coefficient k_H were finally calculated. The results showed that the drying process could be separated into three stages including accelerating rate, constant rate, and falling rate period, which was influenced by hot air temperature and velocity, and the Modi?ed Page model agreed well with the experimental data. When the operating temperature was increased from 60.0°C to 80.0°C, α was found increased from 88.07 to 107.93 W·m^?2·K^?1, and k_H increased from 46.32 × 10^–3 to 68.04 × 10^–3 kg·m^?2·sec^?1·ΔH^?1. With the increase of air velocity from 0.60 to 1.04 m·sec^?1, α was increased from 78.85 to 101.35 W·m^?2·K^?1, and k_H was enhanced from 51.78 × 10^–3 to 65.85 × 10^–3 kg·m^?2·sec^?1·ΔH^?1.     

Soil Organic Carbon Stock and Distribution in Cultivated Land Converted to Grassland in a Subtropical Region of China

Land-use change from one type to another affects soil carbon (C) stocks which is associated with fluxes of CO₂ to the atmosphere. The 10-years converted land selected from previously cultivated land in hilly areas of Sichuan, China was studied to understand the effects of land-use conversion on soil organic casrbon (SOC) sequestration under landscape position influences in a subtropical region of China. The SOC concentrations of the surface soil were greater (P < 0.001) for converted soils than those for cultivated soils but lower (P < 0.001) than those for original uncultivated soils. The SOC inventories (1.90–1.95 kg m^?2) in the 0–15 cm surface soils were similar among upper, middle, and lower slope positions on the converted land, while the SOC inventories (1.41–1.65 kg m^?2) in this soil layer tended to increase from upper to lower slope positions on the cultivated slope. On the whole, SOC inventories in this soil layer significantly increased following the conversion from cultivated land to grassland (P < 0.001). In the upper slope positions, converted soils (especially in 0–5 cm surface soil) exhibited a higher C/N ratio than cultivated soils (P = 0.012), implying that strong SOC sequestration characteristics exist in upper slope areas where severe soil erosion occurred before land conversion. It is suggested that landscape position impacts on the SOC spatial distribution become insignificant after the conversion of cultivated land to grassland, which is conducive to the immobilization of organic C. We speculate that the conversion of cultivated land to grassland would markedly increase SOC stocks in soil and would especially improve the potential for SOC sequestration in the surface soil over a moderate period of time (10 years).     

Net Carbon Sequestration Potential and Emissions in Home Lawn Turfgrasses of the United States

Soil analyses were conducted on home lawns across diverse ecoregions of the U.S. to determine the soil organic carbon (SOC) sink capacity of turfgrass soils. Establishment of lawns sequestered SOC over time. Due to variations in ecoregions, sequestration rates varied among sites from 0.9 Mg carbon (C) ha^?1 year^?1 to 5.4 Mg C ha^?1 year^?1. Potential SOC sink capacity also varied among sites ranging from 20.8 ± 1.0–96.3 ± 6.0 Mg C ha^?1. Average sequestration rate and sink capacity for all sites sampled were 2.8 ± 0.3 Mg C ha^?1 year^?1 and 45.8 ± 3.5 Mg C ha^?1, respectively. Additionally, the hidden carbon costs (HCC) due to lawn mowing (189.7 kg Ce (carbon equivalent) ha^?1 year^?1) and fertilizer use (63.6 kg Ce ha^?1 year^?1) for all sites totaled 254.3 kg Ce ha^?1 year^?1. Considering home lawn SOC sink capacity and HCC, mean home lawn sequestration was completely negated 184 years post establishment. The potential SOC sink capacity of home lawns in the U.S. was estimated at 496.3 Tg C, with HCC of between 2,504.1 Gg Ce year^?1 under low management regimes and 7551.4 Gg Ce year^?1 under high management. This leads to a carbon-positive system for between 66 and 199 years in U.S. home lawns. More efficient and reduction of C-intensive maintenance practices could increase the overall sequestration longevity of home lawns and improve their climate change mitigation potential.     

Recovery of big sagebrush communities after burning in south-western Montana

Prescribed burning of big sagebrush (Artemisia tridentata Nutt.) communities is conducted with the intention of increasing either the productivity of the understory plants or the big sagebrush. It was our objective to compare the recovery of big sagebrush communities from prescribed fire at as many sites as we could locate in south-western Montana with environmentally paired unburned portions. We located and sampled 13 sites that had been burned over a span of two to 32 growing seasons earlier. Big sagebrush canopy cover, density, and production of winter forage were significantly greater (P < or = 0.05) in the unburned portions in 34 of 38 comparisons. Canopy coverage of Idaho fescue (Festuca idahoensis Elmer), the dominant herbaceous species, was greater in the burned portion at only one site while it was less (P < or = 0.05) at four sites. Total perennial grass canopy coverage was not different (P < or = 0.05) between treatments over the 13 sites. Managers considering prescribed burning of big sagebrush communities should be aware that herbaceous plant responses may be minimal while shrub values will likely be lost for many years. The loss of the dominant shrubs in any ecosystem will affect many other organisms and severely impact species that have an obligate habit with the shrubs.     

Infrequent composted biosolids applications affect semi-arid grassland soils and vegetation

Monitoring of repeated composted biosolids applications is necessary for improving beneficial reuse program management strategies, because materials will likely be reapplied to the same site at a future point in time. A field trial evaluated a single and a repeated composted biosolids application in terms of long-term (13–14 years) and short-term (2–3 years) effects, respectively, on soil chemistry and plant community in a Colorado semi-arid grassland. Six composted biosolids rates (0, 2.5, 5, 10, 21, 30 Mg ha^?1) were surface applied in a split-plot design study with treatment (increasing compost rates) as the main factor and co-application time (1991, or 1991 and 2002) as the split factor applications. Short- and long-term treatment effects were evident in 2004 and 2005 for soil 0–8 cm depth pH, EC, NO₃-N, NH₄-N, total N, and AB-DTPA soil Cd, Cu, Mo, Zn, P, and Ba. Soil organic matter increases were still evident 13 and 14 years following composted biosolids application. The repeated composted biosolids application increased soil NO₃-N and NH₄-N and decreased AB-DTPA extractable Ba as compared to the single composted biosolids application in 2004; differences between short- and long-term applications were less evident in 2005. Increasing biosolids rates resulted in increased native perennial grass cover in 2005. Plant tissue Cu, Mo, Zn, and P concentrations increased, while Ba content decreased depending on specific plant species and year. Overall, the lack of many significant negative effects suggests that short- or long-term composted biosolids application at the rates studied did not adversely affect this semi-arid grassland ecosystem.     

Nitrogen critical loads and management alternatives for N-impacted ecosystems in California

Empirical critical loads for N deposition effects and maps showing areas projected to be in exceedance of the critical load (CL) are given for seven major vegetation types in California. Thirty-five percent of the land area for these vegetation types (99,639 km²) is estimated to be in excess of the N CL. Low CL values (3–8 kg N ha^?1 yr^?1) were determined for mixed conifer forests, chaparral and oak woodlands due to highly N-sensitive biota (lichens) and N-poor or low biomass vegetation in the case of coastal sage scrub (CSS), annual grassland, and desert scrub vegetation. At these N deposition critical loads the latter three ecosystem types are at risk of major vegetation type change because N enrichment favors invasion by exotic annual grasses. Fifty-four and forty-four percent of the area for CSS and grasslands are in exceedance of the CL for invasive grasses, while 53 and 41% of the chaparral and oak woodland areas are in exceedance of the CL for impacts on epiphytic lichen communities. Approximately 30% of the desert (based on invasive grasses and increased fire risk) and mixed conifer forest (based on lichen community changes) areas are in exceedance of the CL. These ecosystems are generally located further from emissions sources than many grasslands or CSS areas. By comparison, only 3–15% of the forested and chaparral land areas are estimated to be in exceedance of the NO₃^? leaching CL. The CL for incipient N saturation in mixed conifer forest catchments was 17 kg N ha^?1 yr^?1. In 10% of the CL exceedance areas for all seven vegetation types combined, the CL is exceeded by at least 10 kg N ha^?1 yr^?1, and in 27% of the exceedance areas the CL is exceeded by at least 5 kg N ha^?1 yr^?1. Management strategies for mitigating the effects of excess N are based on reducing N emissions and reducing site N capital through approaches such as biomass removal and prescribed fire or control of invasive grasses by mowing, selective herbicides, weeding or domestic animal grazing. Ultimately, decreases in N deposition are needed for long-term ecosystem protection and sustainability, and this is the only strategy that will protect epiphytic lichen communities.     

Modeling Nutrient Release in the Tai Lake Basin of China: Source Identification and Policy Implications

Because nutrient enrichment has become increasingly severe in the Tai Lake Basin of China, identifying sources and loads is crucial for watershed nutrient management. This paper develops an empirical framework to estimate nutrient release from five major sectors, which requires fewer input parameters and produces acceptable accuracy. Sectors included are industrial manufacturing, livestock breeding (industrial and family scale), crop agriculture, household consumption (urban and rural), and atmospheric deposition. Results show that in the basin (only the five sectors above), total nutrient loads of nitrogen (N) and phosphorus (P) into aquatic systems in 2008 were 33043.2 tons N a^?1 and 5254.4 tons P a^?1, and annual area-specific nutrient loads were 1.94 tons N km^?2 and 0.31 tons P km^?2. Household consumption was the major sector having the greatest impact (46 % in N load, 47 % in P load), whereas atmospheric deposition (18 %) and crop agriculture (15 %) sectors represented other significant proportions of N load. The load estimates also indicate that 32 % of total P came from the livestock breeding sector, making it the second largest phosphorus contributor. According to the nutrient pollution sectors, six best management practices are selected for cost-effectiveness analysis, and feasible options are recommended. Overall, biogas digester construction on industrial-scale farms is proven the most cost-effective, whereas the building of rural decentralized facilities is the best alternative under extreme financial constraint. However, the reduction potential, average monetary cost, and other factors such as risk tolerance of policy makers should all be considered in the actual decision-making process.     

Changes in a reach of a northern California stream following wildfire

One reach of a northern California stream, burned by intense wildfire in 1979, was studied to monitor changes and recovery from the fire. Benthic macroinvertebrates collected three weeks and one to four, six, eight, and 11 years following the wildfire were used to assess stream condition and compared to samples from a reach of a nearby unburned stream. Transportable sediment was measured 11 years following the fire. The fire was also used as a worst case example to compare results with a standard cumulative watershed effects assessment methodology. Benthic invertebrate density and taxa richness of the burned reach were both low compared to the unburned reach three weeks after the fire. Mean density was significantly higher in the burned reach in the three years following the fire, while taxa richness was significantly lower in the burned reach over the same time period. Higher density and lower richness in the burned reaches persisted throughout the study period but were not significant after three years. Mean Shannon diversity of the burned reach was significantly lower than that of the unburned reach for each year of the study, although absolute differences diminished throughout the 11-year study period. Transportable sediment was significantly higher in the burned reach than the unburned comparison. Pearson correlations between sediment and biological metrics were weak. Although the correlation between invertebrate diversity and a measure of watershed disturbance (equivalent roaded acres) was high (r=0.95) for the burned watershed, the measure appeared to be a poor indicator of cumulative effects on stream condition. The measure (ERA) was poorly correlated with invertebrate diversity in the unburned reach and, while the ERA calculations indicated substantial recovery, biological and physical measures indicated recovery of the burned stream reach was incomplete.     

Seasonality of Soil Erosion Under Mediterranean Conditions at the Alqueva Dam Watershed

The Alqueva reservoir created the largest artificial lake of Western Europe in 2010. Since then, the region has faced challenges due to land-use changes that may increase the risk of erosion and shorten the lifetime of the reservoir, increasing the need to promote land management sustainability. This paper investigates the aspect of seasonality of soil erosion using a comprehensive methodology that integrates the Revised Universal Soil Loss Equation (RUSLE) approach, geographic information systems, geostatistics, and remote-sensing. An experimental agro-silvo pastoral area (typical land-use) was used for the RUSLE factors update. The study confirmed the effect of seasonality on soil erosion rates under Mediterranean conditions. The highest rainfall erosivity values occurred during the autumn season (433.6 MJ mm ha^?1 h^?1), when vegetation cover is reduced after the long dry season. As a result, the autumn season showed the highest predicted erosion (9.9 t ha^?1), contributing 65 % of the total annual erosion. The predicted soil erosion for winter was low (1.1 t ha^?1) despite the high rainfall erosivity during that season (196.6 MJ mm ha^?1 h^?1). The predicted annual soil loss was 15.1 t ha^?1, and the sediment amount delivery was 4,314 × 10³ kg. Knowledge of seasonal variation would be essential to outline sustainable land management practices. This model will be integrated with World Overview of Conservation Approaches and Technologies methods to support decision-making in that watershed, and it will involve collaboration with both local people and governmental institutions.     

WATER QUALITY AFTER LOGGING SMALL WATERSHEDS WITHIN THE BULL RUN WATERSHED,OREGON1

ABSTRACT: Road building, clearcutting 25 percent of the watershed, and slash disposal by broadcast burning or by natural decomposition caused changes in water quality of two small streams in the Bull Run Watershed in Oregon, which supplies water to the Portland, Oregon, metropolitan area. Concentrations of suspended sediment increased slightly, primarily owing to construction of a permanent logging road that crossed streams. Changes in nutrient cycling occurred due to logging and slash disposal in both watersheds where cutting was done. NO₃-N concentrations, which increased most where logging residue was left to decompose naturally, increased more than sixfold and commonly exceeded 100 pg/i during the October-June high-flow season for seven years after logging. Where logging slash was broadcast burned, NO₃-N concentrations increased roughly fourfold, but rarely exceeded 50 μg/l, and increases had mostly disappeared six years after slash burning. Changes in outflows of cations and other anions were not apparent. Annual maximum stream temperatures increased 2–3°C after logging, but temperature increases had mostly disappeared within three years as vegetation regrowth shaded the streams.     

Nitrate transport in shallow groundwater at the stream–riparian interface in an urbanizing catchment

Drive point peizometers were installed at the stream–riparian interface in a small urbanizing southern Ontario catchment to measure the effect of buffers (presence/ absence) and land use (urban/agricultural) on the movement of NO^? ₃-N in shallow groundwater from the riparian area to the stream. Mean NO^? ₃-N concentrations ranged from 1.0 to 1.3 mg L^?1 with maximum values of 9.4 mg L^?1. Holding land use constant, there was no significant difference (p>0.05) in NO^? ₃3-N concentration between buffered and unbuffered sites. Nitrate-N levels were not significantly different (p>0.05) as a function of land use. The lack of difference between sites as a function of buffer absence/presence and land use is probably due to the placement of some peizometers in low conductivity materials that limited groundwater flow from the riparian zone to the stream. Subsurface factors controlling the hydraulic gradient are important in defining buffer effectiveness and buffer zones should not be used indiscrim inately as a management tool in urban and agricultural landscapes to control nitrate-N loading in shallow groundwater to streams without detailed knowledge of the hydrogeo logic environment.     

Application of polyacrylamide to reduce phosphorus losses from a Chinese purple soil: A laboratory and field investigation

Use of anionic polyacrylamide (PAM) to control phosphorus (P) losses from a Chinese purple soil was studied in both a laboratory soil column experiment and a field plot experiment on a steep slope (27%). Treatments in the column study were a control, and PAM mixed uniformly into the soil at rates of 0.02, 0.05, 0.08, 0.10, and 0.20%. We found that PAM had an important inhibitory effect on vertical P transport in the soil columns, with the 0.20% PAM treatment having the greatest significant reduction in leachate soluble P concentrations and losses resulting from nine leaching periods. Field experiments were conducted on 5 m wide by 21 m long natural rainfall plots, that allowed collection of both surface runoff and subsurface drainage water. Wheat was planted and grown on all plots with typical fertilizer applied. Treatments included a control, dry PAM at 3.9 kg ha^?1, dry PAM at 3.9 kg ha^?1 applied together with lime (CaCO₃ at 4.9 t ha^?1), and dry PAM at 3.9 kg ha^?1 applied together with gypsum (CaSO₄·2H₂O at 4 t ha^?1). Results from the field plot experiment in which 5 rainfall events resulted in measurable runoff and leachate showed that all PAM treatments significantly reduced runoff volume and total P losses in surface runoff compared to the control. The PAM treatments also all significantly reduced water volume leached to the tile drain. However, total P losses in the leachate water were not significantly different due to the treatments, perhaps due to the low PAM soil surface application rate and/or high experimental variability. The PAM alone treatment resulted in the greatest wheat growth as indicated by the plant growth indexes of wheat plant height, leaf length, leaf width, grain number per head, and dried grain mass. Growth indexes of the PAM with Calcium treatments were significantly lesser. These results indicate that the selection and use of soil amendments need to be carefully determined based upon the most important management goal at a particular site (runoff/nutrient loss control, enhanced plant growth, or a combination).     

Experimental study on microalgae cultivation in novel photobioreactor of concentric double tubes with aeration pores along tube length direction

Microalgae have been identified as a superior feedstock for biodiesel production and varied tubular photobioreactors are developed for high efficient and scale-up microalgae cultivation. This article presented a novel concentric double tubes using aeration through radial pores along the length direction of inner tube. Experiments on microalgae cultivation were carried out in the novel photobioreactor, and two control groups including concentric double tubes with axial aeration at both ends and common tubular. The biomass productivity of novel photobioreactor increased by 43.6% and 107.4%, respectively, compared with concentric double tubes with axial aeration at both ends and common tubular without aeration. The values of pH shifted from 7.5 to 9.0 for novel photobioreactor, but 7.5 to 8.8 for common tubular, and 7.5 to 9.6 for concentric double tubes with axial aeration. The dissolved oxygen concentration fluctuated between 6.0 and 7.0 mg·L^?1 for novel photobioreactor, but rose from 6.6 to 10.2 mg·L^?1 for the common tubular, and 6.9 to 8.1 mg·L^?1 for the concentric with axial aeration. Results show that the aeration style of novel photobioreactor can make efficient local mixing and maintain smaller range of pH and lower level of dissolved oxygen in case of higher biomass concentration. Moreover, compared with the two control groups, the novel concentric double tubes have advantages on the light/dark cycle frequency, which may be benefit for microalgae cultivation. The novel concentric double tubes presented in this work can give some inspiration for high efficiency microalgae cultivation.     

Temporal and spatial variation of episodic wind erosion in unburned and burned semiarid shrubland

Redistribution of soil, nutrients, and contaminants is often driven by wind erosion in semiarid shrublands. Wind erosion depends on wind velocity (particularly during episodic, high-velocity winds) and on vegetation, which is generally sparse and spatially heterogeneous in semiarid ecosystems. Further, the vegetation cover can be rapidly and greatly altered due to disturbances, particularly fire. Few studies, however, have evaluated key temporal and spatial components of wind erosion with respect to (i) erosion rates on the scale of weeks as a function of episodic high-velocity winds, (ii) rates at unburned and burned sites, and (iii) within-site spatial heterogeneity in erosion. Measuring wind erosion in unburned and recently burned Chihuahuan desert shrubland, we found (i) weekly wind erosion was related more to daily peak wind velocities than to daily average velocities as consistent with our findings of a threshold wind velocity at approximately 7 m s(-1); (ii) greater erodibility in burned vs. unburned shrubland as indicated by erosion thresholds, aerodynamic roughness, and nearground soil movement; and (iii) burned shrubland lost soil from intercanopy and especially canopy patches in contrast to unburned shrubland, where soil accumulated in canopy patches. Our results are among the first to quantify post-fire wind erosion and highlight the importance of accounting for finer temporal and spatial variation in shrubland wind erosion. This finer-scale variation relates to semiarid land degradation, and is particularly relevant for predictions of contaminant resuspension and redistribution, both of which historically ignore finer-scale temporal and spatial variation in wind erosion.     

Comparing Burned and Mowed Treatments in Mountain Big Sagebrush Steppe

Fires in mountain big sagebrush [Artemisia tridentata spp. vaseyana (Rydb.) Beetle] plant communities historically shifted dominance from woody to herbaceous vegetation. However, fire return intervals have lengthened with European settlement, and sagebrush dominance has increased at the expense of herbaceous vegetation in some plant communities. Management actions may be needed to decrease sagebrush in dense sagebrush stands to increase herbaceous vegetation. Prescribed fire is often used to remove sagebrush; however, mechanical treatments, such as mowing, are increasingly used because they are more controllable and do not pose an inherent risk of escape compared with fire. However, information on the effects of burned and mowed treatments on herbaceous vegetation and whether fire and mowed applications elicit similar vegetation responses are limited. We evaluated the effects of prescribed burning and mowing for 3?years after treatment in mountain big sagebrush plant communities. The burned and mowed treatments generally increased herbaceous cover, density, and production compared with untreated controls (P??0.05). In contrast, annual forb (predominately natives) cover, density, and biomass increased with mowing and burning (P?相似文献