Soil Strip Research Articles

Effectiveness of Switchgrass Filter Strips in Removing Dissolved Atrazine and Metolachlor from Runoff

AbstractThe effectiveness of switchgrass (Panicum virgatum L.) filter strips in removing dissolved atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) and metolachlor (2‐chloro‐N‐2‐ethyl‐6‐methylphenyl‐N‐2‐methoxy‐1‐methylethyl acetamide) in runoff was investigated using aluminum‐tilted beds set at 1% slope, filled with Emporia sandy loam soil (fine‐loamy, siliceous, thermic Typic Hapludults) and planted to switchgrass. Solution containing herbicides, followed by water alone after 2 and 4 wk were applied on the up slope of beds with and without switchgrass. Water samples from surface flow, lateral, and vertical leachates as well as soil samples were analyzed for the two herbicides using a gas chromatograph. Switchgrass filter strips reduced the mass of dissolved atrazine and metolachlor by 52 and 59% from the applied runon, respectively. The bare soil strips removed 41% of atrazine and 44% of metolachlor. Less than 0.5% of the applied herbicide was released by the two water runons 2 and 4 wk after herbicide‐solution application. The average concentrations of both herbicides in surface runoff were greater than in leachate samples. Herbicides were removed by the soil as runon moved through the soil profile. The concentration of either herbicide on the top surface (0–2.5 cm) was greater than in the soil immediately below (2.5–5 cm). Degradation of both herbicides was faster in beds with switchgrass than without. Greater amounts of both herbicides were retained in the first 67‐cm section of beds with the grass than without. Switchgrass helped to remove the herbicides by slowing runoff velocity and increasing their retention by soil.

Is dispersal density‐dependent in carabid beetles? A field experiment with Harpalus rufipes (Degeer) and Pterostichus niger (Schaller) (Col., Carabidae)

In order to investigate whether density affects dispersal, carabid beetles of two species, Harpalus rufipes (Degeer) and Pterostichus niger (Schaller), were released separately in six and two field enclosures, respectively. The enclosures were 4 m2 each and located in an oat field. The former species was released in seven densities, each with 12 replicates and the latter in five densities each with four replicates. Beetles leaving the centre of the enclosures were captured in pitfall traps along a 1 m wide strip of bare soil. Logistic models were fitted to the data. There were no significant effects of the density treatment variable on P. niger. For H. rufipes the best model was obtained by specifying the density treatment as a nominal variable. The deviance accounted for by this model was highly significant. There were, however, no consistent trends for either species with respect to the density treatment. The inclusion of climatic variables, the number of new beetles introduced at the onset of each trial, or the date of the trial did not improve the fit of any of the models. It is concluded that density did not significantly increase dispersal in the two species. It thus appears that a possible increase in behavioural interactions (i.e. interference competition) did not increase the dispersal in adults of the two species examined in this experiment.

Soil as a terrestrial sink for methyl bromide fumigant: Preliminary results

Air and surface soil samples were taken at three stations downwind of a strip of soil fumigated with injected methyl bromide. Integrated horizontal flux of methyl bromide at each sampling station showed the removal of ∼46% of the methyl bromide mass from the plume by the time it reached 30–60 m downwind. Based on the U.S. EPA's dispersion model SCREEN-3, a mass loss of ∼42% was estimated. Analysis of the surface soil samples indicated the presence of methyl bromide residues that declined in concentration with distance downwind from the source. Laboratory tests confirmed the first-order rapid uptake (2–4 minutes) of methyl bromide by field soil.

Soil evaporation from tiger-bush in south-west Niger

A previous study of evaporation from an area of patterned woodland (tiger-bush) in Niger by Culf et al. (1993) has demonstrated the need to determine the contribution from the bare soil strips which occupy 67% of the surface area. They measured total evaporation from the entire land surface using eddy correlation, but not the individual contributions from the soil and vegetation components. This distinction is necessary to create accurate models of evaporation from the tiger-bush as different processes operate in the two components. The previous study in the same area relied upon untested modelling of the bare soil evaporation as no direct measurements were available. In the present study, carried out during HAPEX-Sahel, hourly fluxes of evaporation from a large patch of bare soil within the tiger-bush were measured using a Bowen ratio system. The data obtained show in detail how soil evaporation varies after rainfall as the surface dried out. Comparison is made on an hourly and daily basis of actual and potential evaporation. A two-phase model based on the Ritchie (1972) approach is calibrated using these data and the model is used to calculate the soil evaporation component of the water balance over a number of seasons with different rainfall. This analysis shows that over the entire tiger-bush area, annual soil evaporation is normally ∼28% of annual rainfall, but this percentage increases markedly in dry years. The implications are that in dry years runoff from these bare soil areas will decrease by a greater percentage than rainfall because a greater proportion of rainfall is lost as soil evaporation.

Surface temperature and soil moisture retrieval in the Sahel from airborne multifrequency microwave radiometry

Bipolarized microwave brightness temperatures of Sahel semiarid landscapes are analyzed at two frequencies: 5.05 and 36.5 GHz. These measurements were performed in Niger, West Africa, by the radiometer PORTOS in the framework of the Hydrologic Atmospheric Pilot Experiment in the Sahel (HAPEX-Sahel), during the end of the rainy season (August-September 1992). The airborne microwave data were collected simultaneously with radiosoundings of the atmosphere, and ground measurements of surface temperature, soil moisture, and biomass of several vegetation types. After estimating the soil roughness parameters, it is shown that two kinds of vegetation canopies must be considered: sparse canopies and patchy canopies including bare soil strips. The mixed soil vegetation microwave emission is analyzed using a random continuous approach. The sparse canopy emission is efficiently described by considering the vegetation layer as homogeneous. Conversely, a simple soil-vegetation mixing equation must be used for the patchy canopies. The problem with retrieving the canopy temperature and the near-surface soil moisture is addressed. For every canopy, soil moisture retrieval is possible. Soil moisture maps are proposed. The canopy temperature can also be retrieved with good accuracy provided both vertical (v) and horizontal (h) polarizations are available. It is shown that the retrieved variables can be used to separate landscape units through a classification procedure.

Native small mammals and reptiles in cropped and uncropped parts of lakebeds in semi-arid Australia

Small mammals and reptiles were surveyed by trapping in uncropped and cropped parts of two dry lakebeds in semi-arid New South Wales, Australia, in spring 1992 and 1993. Four species of native small mammals (18 individuals) were captured in uncropped parts of the lakebeds, compared with two individuals of one species in cropped parts of the lakebeds. A total of 38 reptiles (seven species) was caught at the uncropped sites compared with 10 individuals (four species) at the cropped sites. Small mammals were absent where the soil was scarified and bare between crop cycles. The habitat requirements of small mammals (particularly Planigale gilesi) and reptiles need to be provided for when cropping lakebeds. The most effective way to do this is to leave wide strips of uncropped soil at the edges of lakebeds, and patches of uncropped country that are connected to the strips, on lakebeds.

Patterned Ground Activity in a Southern New Zealand High-Alpine Cushionfield

Recent measurements confirm the current activity of some solifluction terraces in high-alpine cushionfield, under periglacial conditions on the Old Man Range in southern New Zealand. Downslope movement amounts to some 3.5 cm a decade. Extensive areas of fully vegetated earth or soil stripes on gentle slopes (3-7?) and similarly vegetated soil hummocks on adjacent flatter sites are much less obviously active and have been assumed by previous researchers to be relicts of a more glacial climate. Three years of over-winter temperature measurements at up to four depths (5, 20, 40, 60 cm) beneath an adjacent crest and hollow of welldeveloped stripes (ca. 1.5 m between crests and 30 cm high), and similar measurements over one winter from a nearby hummock site revealed consistent differential temperatures, and usually differential freezing. Crests of both stripes and hummocks remained continuously frozen at least to 20 cm depth over much of the winter while soil in the depressions remained unfrozen at 20 cm depth and only intermittently frozen at -5 cm. Differential freezing would permit water transfer along a free energy gradient from the nonfrozen to frozen regions, where expansion associated with its freezing probably is sufficient to maintain the microtopographic patterns of both stripes and hummocks.

A procedure for determining average root length density in row crops by single-site augering

A simplified procedure has been formulated and tested for determining average root length density (RLD) by auger sampling at a single site in wheat, corn and mustard. It involves the determination of horizontal root distribution in the representative half of the unit soil strip (distance from base of plant to mid-point in the rows) by excavating small monolith segments in the top soil layer. Average RLD is computed by dividing the integral of polynomial function fitted to the horizontal root distribution (in the unit soil strip) with its length. The average RLD, thus, obtained is interpolated on the curve between root length density and horizontal distance from the plant base (d) in the representative half of the unit soil strip. Root length density determined by centering 5 cm diameter auger at the interpolated d gave minimum deviation from the average RLD of that layer compared to the other possible single site sampling schemes with same-sized auger. These results indicate that for row crops, the best centre for single-site augering is about one-third of distance from the plant base to mid-way between the two rows.

Ecotone Dependent Recruitment of a Desert Shrub, Flourensia cernua, in Vegetation Stripes

In tropical semi-arid areas, a local concentration of water on sheet wash surfaces allows the persistence of densely vegetated stripes parallel to the contour lines, alternating with almost bare soil stripes. The boundaries of the vegetated stripes are, upslope, a colonization ecotone, and, downslope, a regressive ecotone, thus inducing a slow upwards displacement. This formation, recently described in the Chihuahuan Desert (Mexico), is known from Africa and Australia. Flourensia cernua is a dominant shrub species of the stripes whose distribution suggests that its population dynamics is strongly dependent on the upslope ecotone. The spatial restrictions to recruitment were determined analyzing the location of seedlings, young individuals and adults, and the grass cover (Hilaria mutica), in 10 two-meter-wide belts perpendicular to 5 stripes (...)

Mapping of soil degradation by using remote sensing on alluvial plain, Rajasthan, India

Abstract Identification and mapping of areas affected by various soil degradation processes in medium textured alluvial plain of arid region of India was performed. Impact of degradation on physicochemical properties of soils was evaluated. Soil degradation processes were identified by using Landsat TM FCC subscene and ground truth verification. The kind, extent, and severity of degradations were mapped. Soil stripping, sheet wash, gully erosion, and natural or man‐induced salinization were the major soil degradation processes. In an area of over 3563 km2, 52% of the area was degraded due to soil stripping, sheet wash, and gully erosion, and 8% due to salinity. Degradation due to combined water erosion and salinization covered 33% of the total area. Nearly 30% of the area needs urgent attention to arrest the process of soil degradation. Soil degradation processes have resulted in the loss of organic carbon, available phosphorus, and available potassium.

Determination of root distribution of wheat by auger sampling

Although the auger method has been reported to be simple and superior to other methods of determination of roots, a standard procedure of determining roots with the same is lacking. In a bid to standardize the auger method for studying wheat root distribution; we sampled roots with 5, 7.5 and 10 cm ID augers on the row and midway between rows down to 180 cm. The suitability of a sampling scheme was adjudged from bias between observed and actual root length densities (RLD). The actual density in a layer was obtained by integrating the equation fitted to the average of root density data horizontally between 0 and 11 cm, because for 22 cm apart rows of wheat the representative half of the unit soil strip was 11 cm from the row; and assumed actual RLD was the average of horizontal distribution of RLD in a particular layer. Single site sampling on the row or between rows gave the maximum bias. Average of two sites viz. on the row and midway between rows with 10 cm ID auger and 7.5 cm ID auger or at three sites with 5 cm ID auger (additional site midway between the earlier two) gave the best estimates in that order.

Transplanted seed bank response to drawdown time in a created wetland in East Texas

Sediment was transplanted from a 13-yr-old created wetland on a nonacid mine in east Texas into a constructed experimental basin to examine seed bank response to 4 drawdown regimes. The experimental basin was flooded following sediment transplantation in February, and surface water was later removed in April, June, and August. The success of the transplanted seed bank in vegetating the experimental wetland was assessed by measuring species richness, seedling density, and above-ground biomass. April drawdown produced the greatest species richness (29), stem density (1851.0 stems m−2), and above-ground biomass (769.3 g m−2), followed by the unflooded water regime. June and August drawdowns produced less emergent vegetation than the other treatments, but 3 submergent species were produced prior to drawdowns. Results indicate that use of transplanted species-rich wetland soil subjected to early spring drawdown is a very effective technique for establishing wetland vegetation on disturbed sites in east Texas. In addition, reestablishment of vegetation in the donor wetland was assessed by comparing percent cover in disturbed plots to undisturbed plots. Disturbed plots achieved 66.0 percent cover after 10 months following soil removal compared to 96.3 percent cover in undisturbed plots. Disturbed plots were dominated by vegetatively reproducing species and contained very few annuals. Excavating relatively few widely-spaced narrow strips of soil from the donor wetland caused only slight decreases in vegetative cover during the subsequent growing season.

Shear Strength Characteristics of Sand‐Polymer Interfaces

The results are summarized for an experimental program involving over 450 direct shear tests of sand‐polymer interfaces. The interface frictional strength was found to increase with soil density and decrease with the Shore D Hardness of the polymer. The shear strength characteristics were found to vary as a function of the type of sand, but were independent of repeated loading, at least insofar as polyethylene piping and linings are concerned. The shear strength characteristics of a polymer interface can be expressed conveniently as the ratio of the interface angle of friction and the direct shear angle of soil friction, δ/ϕds′. This ratio was relatively constant at 0.55–0.65 along high‐ and medium‐density polyethylene surfaces for different types of sands at various densities. A general model for interface frictional resistance is developed, in which δ/ϕds′ is related to the Shore D Hardness, HD, of the polymer. Limiting conditions for δ/ϕds′ are defined on the basis of theoretical considerations involving the critical state angle of shear resistance, ϕcv′. This model allows for rapid evaluation of interface frictional strength and applies to plastic piping, linings, soil strip reinforcement, and a variety of other soil‐polymer systems.

MEASUREMENT OF PESTICIDE TRANSPORT TO SHALLOW GROUND WATER

ABSTRACT A field study was conducted to observe the movement of the herbicides atrazine and alachlor within the soil profile and a shallow water table aquifer following a surface application. Surface-applied bromide was used as a non-adsorbed tracer of water movement. The herbicides and tracer were surface applied to a strip of soil at the top of a sloping study site with sandy soil underlain by an impermeable clay layer. Concentrations of bromide at all three monitored depths in the unsaturated zone showed a high degree of variability. The peak concentration and the time required to reach the peak concentration varied significantly between sampling locations. Atrazine moved rapidly through the sandy soil on the study site. Concentrations of atrazine in the soil water at a depth of 0.61 m reached 350 |ag/L 19 days after application. Detectable levels of atrazine reached the water table two months after application. Atrazine concentrations as high as 90 |Jg/L were observed in the shallow ground water nearly six months after application. Alachlor was not detected in the soil below a depth of 0.36 m. No trace of alachlor was detected in the ground water samples.

Mathematical Modeling of In Situ Vapor Stripping of Contaminated Soils

AbstractMathematical models are developed for evaluating the feasibility of in situ vapor stripping for the removal of volatile organics from contaminated soils. The models simulate both laboratory soil stripping columns and field‐scale vacuum extraction wells. Local equilibrium between the condensed and vapor phases is assumed for the volatile compounds; Henry's law or more complex isotherms may be used to describe this equilibrium. Methods for determining Henry's constants from lab data and for determining soil permeability from field data are presented. The models are used to predict the effects of well depth, Henry's constant, screened radius of well, and zone of influence radius. The use of impervious caps and passive vent wells to direct gas flow is discussed, and the effects of buried obstacles and evaporative cooling are examined. The possibility of recontamination from non‐aqueous phase liquid (NAPL) underlying the vadose zone is investigated, as is the ability of the vapor stripping technique to remove pools of NAPL floating on the water table below the vadose zone. An estimate of the maximum time required for cleanup at a site is made.

Effects of alley sward width, irrigation and nitrogen fertiliser on growth and yield of Cox's orange pippin apple trees

AbstractFrom 1972 to 1988 an experiment was conducted which investigated the effects of four soil management treatments in combination with two rates of fertiliser application, on the growth and components of yield of Cox's Orange Pippin/MM 106 trees.By four years after planting, trees receiving irrigation and those in uncultivated soil maintained completely bare by herbicide had substantially greater girths than trees growing in narrow and wide bare soil strips between grassed alleys. This effect persisted throughout the life of the orchard, although after 16 years the girths of trees receiving irrigation were much greater than those of trees growing in bare soil.Increasing fertiliser application rate from 63 to 189 kg N ha−1 had either negligible or inconsistent effects on tree growth, fruit yield and size.The cumulative yield of fruit over 12 cropping years was much greater for trees growing in bare soil and for those receiving irrigation than for those growing in the narrow bare‐soil strip system.The increase in tree girth and yield caused by irrigation and bare soil, particularly in dry years, together with the lack of response to the larger rate of fertiliser application, suggests than water was more of a limiting factor than nitrogen supply for this orchard. Irrigation offers an alternative method of management to herbicide for increasing tree growth and fruit yield.

Building and Testing Traffic Lanes for Controlled-Traffic Farming

ABSTRACT Atire and wheel load like those on a new wide-span research machine were used in two soil bins to compact and test simulated field traffic lanes. Soil strips with initial heights of 0, 13 and 25 cm were compacted into lanes that were recessed, level and elevated, respectively, relative to adjacent simulated crop zones. Compaction energy was highest for the elevated lanes. Water trapped on one side of an elevated lane gradually infiltrated the lane and redued its strength. Otherwise, traction and mobility were better on the level lanes compared with recessed lanes and on the elevated lanes compared with level lanes. An elevated lane allowed machine mobility one day after receiving 104 mm of water, with traction equaling that on the level lane a day later.

Control in Dryland Barley, 1987

Abstract ‘Clark’ Barley was planted 1 May in a summer fallow 300- by 2600-ft strip of clay loam soil with a 10-inch Hoe drill operating at a seeding rate of 60 lb/acre. Di-Syston 15 G (6.7 lb [AI]/acre) was applied at planting to the entire strip, except for 2 untreated plots (100 by 25 ft), which served as the control. Total BWM/linear ft of plants were counted in 2 treated areas and in 10 locations randomly chosen in each untreated plot.

In situ soil reclamation by air stripping and sludge uptake

A laboratory-scale study was conducted to evaluate the feasibility of an in situ reclamation technique for contaminated soils by combining soil stripping techniques and in situ soil surface biodegradation. By pumping air at the base of a test column, a volatile organic compound (VOC) in the soil was mobilized through the soil and trapped in a thin layer of dried activated sludge. The contaminant, once trapped in the sludge blanket, would be available for biological degradation by the sludge microorganisms. Test soil consisted of a homogeneous sand with a moisture content less than 0.5% and particle diameters smaller than 0.84 mm. Dried sludge, obtained from a municipal waste-water facility, was blended until the particle size characteristics were consistent with the sand. Experiments were initiated by passing air saturated with toluene throught the soil column until equilibrium. The initial concentration of toluene was approximately 700, μg per gram of sand. Clean air was then forced through the system to mobilize the toluene at rates which ranged between 1 and 2.7 pore volumes per minute. Over 95% of the particle-bound toluene was removed from the sand within six hours of stripping. On a mass-per-mass basis, the sludge sorbed approximately 70% of the mobilized toluene. The combination of air stripping techniques and use of a sludge blanket to reduce volatile emissions from the soils is feasible and merits further research. Studies to investigate the biodegradation potential of the sludge blanket for toluene and trichloroethylene will be the subject of investigation for future research.

Field Soil Properties Influencing the Variability of Denitrification Gas Fluxes

AbstractThe spatial variability of field denitrification gas fluxes was investigated in relation to water content, soil‐gas diffusivity, nitrate concentration, and water soluble organic C. Water was applied in a periodic fashion along a strip of Yolo soil (Typic Xerorthents) amended with chopped alfalfa hay and nitrate. Data were analyzed statistically using simple correlations and spectral and coherency analysis. Log spectrums showed that nitrate cycled at the frequency at which water content cycled and was negatively related to water content due to apparent leaching of nitrate from the high water application areas. Denitrification gas flux cycled at twice the frequency of water content with maximum fluxes occurring at the sides of the water peaks. Spectrums for water soluble organic C and gas diffusivity indicated no significant spatial cycling. Although denitrification gas flux was more highly correlated to soil‐water content than to any other variable, coherency analyses revealed no significant relationships between denitrification gas flux and water or nitrate at specific frequencies due to opposing effects related to nitrate leaching and small gas diffusivities at the soil surface. The spatial pattern of denitrification calculated from a simple equation was examined using spectral analysis and was found to be not representing measured denitrification gas flux adequately at the frequency at which water content cycled. The discrepancy between measured denitrification gas flux and calculated denitrification rates was attributed to very small gas diffusivities preventing gas transport to the surface and inadequate characterization of actual C and nitrate concentrations at microsites.