Loam Soil Type Research Articles

Predicting pasture and sheep production in the Victorian Mallee with the decision support tool, GrassGro

The GrassGro decision support tool was designed to quantify sheep and pasture production in response to management and climate variability in temperate Australia, and has been tested in temperate but not low-rainfall Australian conditions. Data from field experiments and from on-farm monitoring was used to test GrassGro predictions of annual and perennial pasture production, and sheep production at 4 locations throughout the Victorian Mallee, which is a low-rainfall area (275–375 mm annually). Predictions of long-term pasture production were then made. Predictions of the herbage biomass of annual pastures closely matched observed data for both a sandy loam (1991–2002 data) and a whole paddock (combining sandy loam and loam and sand) (2001–2002 data) soil type, at several locations across the Victorian Mallee. Linear regression between observed and simulated (April to September) data produced coefficients, significance and root mean square error of r2 = 0.81, P<0.001, 217 kg DM/ha, respectively, for sandy loam soil types and r2 = 0.94, P<0.001, 72 kg DM/ha, respectively, for whole paddock soil types. A series of simulations for individual years from 1970 to 2002 quantified the large impact of climate variability and demonstrated that seedbank and location, but not soil fertility, had a large influence on annual pasture production. However, GrassGro underestimated the production of the perennial pasture, lucerne (r2 = 0.2). GrassGro was also unable to adequately predict sheep production because it failed to take into account the sparse, clumpy structure of the low biomass pastures typical of this region. Methods to improve GrassGro were identified and included: (i) the need to adjust sheep intake from low biomass, sparse pastures, (ii) the ability to predict summer growing and autumn growing plant species, (iii) the ability to graze crop stubbles and (iv) refinements to the coefficients of equations used to model lucerne growth.

Agronomic Response of Cool‐Season Grasses to Low‐Intensity Harvest Management and Low Potassium Fertility

Species selection, fertilization, and harvest management can have a major impact on forage K concentration, and low K is critical for nonlactating dairy cow forage. Our objective was to determine if selection of grass species, along with appropriate fertilization and harvest management, will result in minimizing forage K concentration for nonlactating dairy cows while maintaining stand persistence. Three K fertilizer treatments were applied to reed canarygrass (Phalaris arundinaceae L.), timothy (Phleum pratense L.), orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and tall fescue (Festuca arundinacea Schreb.) for 6 yr on a Williamson silt loam (coarse‐silty, mixed, active, mesic Typic Fragiudepts) soil type in Ithaca, NY. All grass species persisted through the completion of the experiment, without visible K deficiency symptoms. Yield of dry matter (DM) was 5.6% higher (P < 0.05) under split applications of K fertilizer compared with the 0 K fertilizer treatment. Annual K uptake was increased 17.2% with split application of K fertilizer although apparent recovery of K averaged less than 20%. Forage quality was not greatly impacted by K fertilization although the K concentration of forage increased by 12% due to K fertilization. Fertilization with K tended to reduce the forage concentration of P, Ca, Mg, B, and Na. Application of K fertilizer to 0 K fertilizer plots at the conclusion of the experiment overcame any negative effects on DM yield due to prolonged absence of K fertilization. It was possible to achieve sufficiently low forage K concentrations for nonlactating dairy cow forage in all five cool‐season grasses and maintain stand persistence, with lowest forage K concentrations in timothy.

Saturated Hydraulic Conductivity and Porosity within Macroaggregates Modified by Tillage

Greater knowledge of intraaggregate porosity modifications by tillage conveys new information for identifying additional hydrologic, ion retention, and aggregate stability responses to specific management practices. Macroaggregates, 2 to 4, 4 to 6.3, and 6.3 to 9.5 mm across, were separated into multiple concentric layers and their porosities were determined. Saturated hydraulic conductivity (K{sub s}) of multiple aggregate fractions from two soil types subjected to conventional tillage (CT), no tillage (NT), and native forest (NF) soils were measured individually to identify the effects of tillage on aggregate structure, porosity, and K{sub s}. Intraaggregate porosities were the highest in NF aggregates. Greater porosities were identified in exterior layers of soil aggregates from all treatments. Lowest intraaggregate porosities were observed in the central regions of CT aggregates. Soil aggregates, 6.3 to 9.5 mm across, had the greatest total porosities, averaging 37.5% for both soil types. Long-term CT reduced intraaggregate porosities and K, within macroaggregates, of the same size fraction, from both the Hoytville silty clay loam and Wooster silt loam soil types. Values for K, of NF aggregates, 5.0 x 10{sup -5} cm s{sup -1}, were reduced 50-fold by long-term CT treatments of the Hoytville series. The K, values through Wooster aggregates frommore » NF, 16.0 x 10{sup -5} cm s{sup -1}, were reduced 80-fold by long-term CT treatments. The K{sub s} values through NF and NT aggregates were positively correlated with their intraaggregate porosities (R{sup 2} = 0.84 for NF and R{sup 2} = 0.45 for NT at P < 0.005). Additional studies are needed to identify rates at which pore geometries within macroaggregates are degraded by CT or improved by NT.« less

Plant and Soil Elemental Status as Influenced by Multi-year Nitrogen and Potassium Fertilization

Forage management of perennial grass grown under potassium (K)-limiting soil conditions is not well understood. Our objective was to evaluate the elemental status of shoots and roots of reed canarygrass (Phalaris arundinaceae L.) as well as the soil fertility profile (0–90 cm) after five years of differential nitrogen (N) and K fertilization in a two-cut management system. Three N (0, 112, or 224 kg N ha−1) and three K fertilizer treatments (0, 56, and 112 kg K ha−1) were split-applied to reed canarygrass on a Williamson silt loam (coarse-silty, mixed, active, mesic Typic Fragiudepts) soil type in central New York State. At the Fall harvest in the fifth year, plant samples from low and high K fertilized plots all at the high N fertilization rate were cut at a 10-cm stubble height and sectioned into 10 segments vertically through the canopy. In addition, forage, root and soil samples were taken from all treatments to evaluate the distribution of elements under low soil K availability. Above ground biomass samples were separated into leaf blade, stem plus sheath, and dead tissue, if present. This assessment was repeated at the first cutting in the sixth year. That same year, soil cores were taken to a depth of 90 cm, sectioned into 15 cm increments, and analyzed for soil fertility parameters. Dry matter (DM) yield and proportion of DM yield at first harvest were both significantly increased by N fertilization, but not affected by K fertilization in 2001. Elemental concentrations observed vertically through the plant canopy followed patterns controlled primarily by (leaf blade):(stem + sheath) DM ratio and the difference in concentration between leaf blade and stem + sheath. Five years of N and K fertilization of reed canarygrass resulted in an accumulation of plant available K in the top 15 cm of soil under no N and high K fertilization, while the high N/no K fertilization combination greatly depleted soil K in the top 15 cm. Decline in K availability under high N and no K fertilizer was compensated for by an increase in root biomass, particularly in the surface layer. Except for soil K, N and K fertilization did not have an effect on the availability or distribution over depth of other nutrients in the soil.

Measurement and variation of site-specific hardpans for silty upland soils in the Southeastern United States

Soil compaction in the form of a hardpan layer restricts root growth and reduces crop yield throughout the Southeastern United States. However, the depth of this compacted soil layer varies significantly over landscapes. A sampling procedure was developed and evaluated to determine the depth of the hardpan layer in upland soils of Grenada silt loam soil type in this region. Cone index profiles taken with a multiple-probe soil cone penetrometer in three fields were used to measure the hardpan depth and to predict their spatial variation. Continuous treatments of these fields for several years included conventional tillage, no-tillage, segregated traffic, and random traffic. Conventional tillage systems were found to bring the hardpan significantly closer to the soil surface as compared to no-till systems; in trafficked row middles by 0.144 m, directly beneath the rows by 0.165 m, and in no-trafficked row middles by 0.094 m. Little difference in depth of hardpan was found between a no-till field subjected to random traffic and a field where traffic was segregated. However, the effect of this random traffic was found to dramatically reduce the predicted range (which is a geo-statistical measure of field variability) from 43.2 m for the no-till field in the trafficked row middle as compared to 12.4 m for the randomly trafficked no-till field. This may indicate that the depth of the hardpan layer in these soils is brought uniformly closer to the soil surface by the effect of traffic, especially when annual tillage is not practiced which could alter this hardpan depth. This information about the variation of the hardpan layer will greatly assist researchers who are interested in developing site-specific tillage technologies to remedy this soil compaction condition.

Enhancement of clay zeta-potential by chelating agents

Significant enhancement of the zeta-potential ( ζ) in heavy loam type soil samples treated with solutions of 1-hydroxypropane-1,1-bisphosphonic acid (HEDPA), 1,2-diaminoethane- N, N, N′, N′-tetraethanoic acid (EDTA), citric acid, and succinic acid was observed for a relatively broad range of concentrations and pH. An observed increase of zeta-potential in the samples treated with varying concentrations of HEDPA (0.0001–0.1 M) revealed a well-pronounced broad maximum at 0.05 M. Data also indicates that the enhancement of zeta-potential imparted by HEDPA treatment was not very strongly dependent on the pH of the treated clay suspension, showing only a weakly pronounced maximum at pH 6. It was established that the observed significant increase of zeta-potential, from −16 up to −40 mV, qualitatively correlates with a specific complex formation ability of the studied chelating agents. The relative broadness of the maximum of the zeta-potential within a wide concentration range of HEDPA could be associated with an intensive dissolution and complex formation of background cations, such as Fe(III), Al(III), Ca(II), Zn(II), Mg(II), and Mn(II) while observed increase of zeta-potential at pH 6 could be explained by sorption of studied complexing agents on the surface of clay particles.

Low Intensity Harvest Management of Reed Canarygrass

High K grass forage increases risk of animal metabolic disorders, and forage management of perennial grass grown under K‐limiting soil conditions needs further study. Our objective was to evaluate forage nutritive value, yield, and stand persistence of reed canarygrass (Phalaris arundinaceaeL.) under two‐harvest management and low availability of soil K. Three N and three K fertilizer treatments were applied to reed canarygrass for 5 yr at two sites in central New York state with Niagara silt loam (fine‐silty, mixed, active, mesic Aeric Epiqualfs) and Williamson silt loam (coarse‐silty, mixed, active, mesic Typic Fragiudepts) soil types. Reed canarygrass persisted under all treatments throughout the experiment, although K deficiency symptoms appeared in the high N, low K fertilizer combination. At the high N fertilizer rate, dry matter (DM) yield increased linearly (P&lt; 0.05) with increased K fertilizer rate, while K fertilizer did not influence yield in the absence of N fertilizer. Recovery of K fertilizer was low and increased linearly (P&lt; 0.05) with increased N fertilizer rate from 6 to 42%. Soil test K increased to 59.9 mg kg−1with no N fertilization and decreased to 34.9 mg kg−1with 224 kg N ha−1. Under high N fertilization with no K fertilization, grass forage K concentration averaged &lt;12 g kg−1in the spring and &lt;8 g kg−1in the fall. Sufficient yields of grass forage with reasonable quality and low concentrations of K were possible through high N, low K fertility management in a two‐harvest system.

Exposure to respirable crystalline silica in eastern North Carolina farm workers.

Occupational exposure to crystalline silica has been linked to silicosis, some forms of cancer, and certain autoimmune diseases. Little information exists on exposure levels of respirable silica in the agricultural industry. This study assessed respirable silica exposure of farm workers in eastern North Carolina. Sandy soils in this region have been shown to contain high levels of respirable silica. Personal breathing zone samples (n = 37) were collected from 27 workers at seven farms during various agricultural activities. The highest respirable silica concentrations were measured during sweet potato transplanting (3.91 +/- 2.07 mg/m3). Respirable silica exposure was observed to be associated with agricultural activity, soil moisture, relative humidity, and wind speed. Most of the variation in exposure (79%) was explained by agricultural activity and soil moisture. The observed percentage of silica levels (mean 34.7%) were almost twice as high as was reported in studies of California agriculture. This may be due to the loamy sand and sandy loam soil types in the regions in this study. In agriculture, respirable silica exposure is highly variable, but the potential for exposures above the threshold limit value of 0.05 mg/m3 exists during particular agricultural activities.

EFFECT OF MESSENGER-TREATED TOMATOES ON BEET ARMYWORM

Seedlings were transplanted in a sandy loam type soil on 12 Jun at the University of California's South Coast Research and Extension Center. Experimental plots were four rows wide (5-ft centers) by 40 ft long and separated by a 5-ft buffer. The tomato transplants were drip irrigated (water pH 7.2-7.5). Treatments were replicated four times in an RCB design. A drench of Messenger at 9 oz./acre was applied to the tomatoes 1 wk before transplanting. Once the plants were in the field, the Messenger-sprayed treatments were initiated on an every-other-week basis at 4.5 oz/acre. Application dates were 26 Jun, 12 and 25 Jul, 9 and 23 Aug for a total of five post-transplant applications. A tractor-mounted boom sprayer with six nozzles per row incorporated D-3 orifice disks, #25 cores, and 50-mesh screens. Operating pressure was 100 psi delivering 100 gpa. All treatments received Activator 90 at 0.125% vol/vol as a spreader sticker. Additionally, a dechlorinator was used in the spray tank water.

Cultivation effects on soil biological properties, microfauna and organic matter dynamics in Eutric Gleysol and Gleyic Luvisol soils in New Zealand

Information on the influence of duration of cultivation on soil organic matter (SOM) dynamics is needed by researchers, policy makers and farmers for assessment of global ramifications of carbon (C) sequestration and agricultural sustainabilty. This paper examines the changes in microbial biomass carbon (MBC) and nitrogen (MBN), metabolic quotient ( qCO 2), microfaunal populations, and C and N mineralisation to assess the effect of cultivation on SOM dynamics. Cultivation, for up to 34 years, of soils previously under permanent ryegrass ( Lolium perenne L.) and clover ( Trifolium sp.) pastures, resulted in a 30–60% decline in concentration of soil organic C and N, and had a significant influence on soil biological parameters in two New Zealand (Eutric Gleysol, Kairanga silty clay loam and Gleyic Luvisol, Marton silt loam) soil types. Cultivated soils had consistently lower MBC and MBN contents, and higher qCO 2 than their counterparts in permanent pastures. Changes in the soil microfauna following cultivation were consistent with changes in microbial biomass. Both the amount and proportion of mineralisable N were also reduced with cultivation. In the pasture soils C mineralisation rates (under laboratory conditions) were twice those (ca. 15 mg (CO 2-C) kg −1 soil) in the 5–20 year cultivated soils (ca. 7 mg (CO 2-C) kg −1 soil), and were reduced to one-half (ca. 3.5 mg (CO 2-C) kg −1 soil) in the 34-year cultivated soil. Over 112 days, the soils lost approximately 2.4–5.0% of their total C, and 1.4–5.0% of total N was mineralised. The percentage C loss also differed with soil type, with Marton silt loam (260 g kg −1, clay) soil losing one and half times as much percentage C as Kairanga silty clay loam (420 g kg −1, clay) soil. Despite greater C mineralisation in soil from pasture, more C and N were conserved in it than in the cultivated soils. As annual C inputs in cultivated soils are smaller than the C decomposition, this would result in a negative soil C balance. The shifts in microbial biomass, its metabolic quotients and soil microfauna appear to be associated with differences in the quantity and ‘quality’ of inputs and SOM decomposition rates, and reflect the land-use change from pasture to continuous cultivation.

EFFICACY OF GRANULAR AND LIQUID INSECTICIDES AGAINST CORN ROOTWORM LARVAE, 2000

An experiment was conducted at the Virginia Tech Kentland Research Farm in Montgomery County, VA, to determine the effectiveness of several granular and liquid insecticides, applied in-furrow or T-band at planting, against western corn rootworm larvae on Pioneer variety ‘3394’ corn. The experiment was conducted in a 5-acre, continuous cornfield with a McGary and Purdy dark gray silt loam soil type. Plots of 30 x 10 ft (four rows wide) were arranged in an RCBD, with all insecticide treatments and an untreated check replicated four times. An Almaco, 2-row Max-Emerge planter was used to plant the plots on 12 May at the rate of 28,000 seeds/acre on 30-inch rows. Insecticide granules were applied in front of the presswheels either directly in the seed furrow or in a 5-inch wide T-band over the furrow, depending on the treatment. The standard granular insecticide applicator was removed from each row unit and replaced with a wooden holder that held an inverted pint canning jar (Mason) used to dispense the insecticide granules. Attached to the underside of the wooden holder was a plastic funnel and tube through which the insecticide granules flowed. A single opening, drilled into the lid of each jar, was calibrated in the laboratory to deliver insecticide granules accurately at a speed of 3 mph. The possibility of mixing one or more insecticides was avoided by using a separate jar and lid for each treatment. At the start of application, a jar containing the appropriate insecticide was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one up and back pass per plot. The liquid insecticide Regent 4SC was applied in-furrow at a rate of 0.13 lb (AI)/acre using a backpack sprayer calibrated to deliver 20 gpa at 40 psi. The sprayer setup involved a two-nozzle spray boom with each nozzle inserted into its own clear plastic delivery tube. Immediately before application of the liquid insecticide, the regular in-furrow tubes for the granular insecticides were replaced with the liquid delivery tubes. The roots of ten consecutive corn plants, five from each of the center two rows, were dug from each plot on 11 Jul and washed of excess soil before damage ratings were made. Corn rootworm damage ratings were based on the Iowa 1–6 scale (1 = no feeding damage, 6 = three or more root nodes completely destroyed). Stand counts were determined in each plot on 17 Jul by counting the number of stalks per 20 row-ft. A two-way ANOVA and Fisher’s protected LSD were used to analyze differences among treatments in root damage ratings and stand counts.

Soil type affects accuracy of dielectric moisture sensors

Several types of dielectric soil moisture sensors were evaluated at various locations in California. The TRASE and ThetaProbe devices were reasonably accurate over a range of soil textures. In silt loam and silty clay soil types, the Enviroscan readings were inaccurate. The Aquaterr meter, which provides a qualitative measurement of soil moisture content, responded to changes in soil moisture content for several different soils, but little response occurred in one sandy soil.

Roughness indices for estimation of depression storage capacity of tilled soil surfaces

Information on the depression storage capacity (DSC) of soil surfaces is needed for modelling surface runoff and erosion. However, time-consuming measurements of the soil surface microrelief in a two-dimensional grid are necessary to obtain accurate estimates. Therefore, estimation of DSC from roughness indices requiring fewer measurements is desirable. In this study a new simple and physically based roughness index was developed and tested. Thirty-two soil surface microreliefs were determined in Danish erosion study plots on two sandy loam soil types, Humic Acrosol and Haplic Luvisol according to the FAO soil classification. The soil treatments were: cultivated up-and-down the slope (black fallow), mouldboard ploughed up-and-down the slope, winter wheat ( Triticum aestivum L.) drilled up-and-down the slope and winter wheat drilled across the slope. The slope was ca. 10% for all plots. Data were treated initially by removing the slope after which 20 artificial slopes (1–20%) were introduced producing 640 data sets. The DSC was calculated for each data set and a number of roughness indices were related to the calculated DSC. The best correlation to DSC was obtained by the newly developed index, mean upslope depression, MUD ( R 2 = 0.86), followed by the geostatistically based limiting elevation difference, LD, and limiting slope, LS ( R 2 = 0.76), and some statistically based parameters as standard deviation adjusted for oriented roughness up-and-down the slope ( R 2 = 0.76), random roughness, RR ( R 2 = 0.67), and standard deviation adjusted for oriented roughness both up-and-down and across the slope ( R 2 = 0.62). Furthermore, MUD appeared to give less biased estimates than other indices, which overestimated small DSC-values and underestimated larger DSC-values. Calculations showed that the MUD index required relatively few measurements. MUD based on less than 200 surface elevation readings gave a good prediction ( R 2 > 0.7) of DSC of tilled soil surfaces.

Topography-Based Sampling Compared with Grid Sampling in the Northern Great Plains

A practical variable-rate fertilizer application should be based on information gathered at low cost that represents field fertility levels. The number of soil samples gathered and analyzed may limit the effectiveness of some variable-rate fertilizer applications. Topography-based soil sampling is attractive because it suggests a lower number of samples needed to characterize fertility levels and patterns in a field than some current grid sampling recommendations. A 40-acre North Dakota field consisting of Barnes loam (fine loamy, mixed, Udic Haplo-borolls), Swenoda loam (mixed, Pachic Udic Haploborolls), and Wyard clay loam (fine loamy, mixed, frigid Typic Haplaquolls) soil types was sampled in a 110 ft grid each fall from 1994 to 1996. Nitrate N, P, sulfate S, and chloride level patterns were similar in all 3 yr. Correlation of both area- (sample cores obtained from a wide area within a topography zone) and point-based (a topography zone represented by a composite taken from a point location) topography sampling with the 110 ft grid values was compared with correlation from a 220 ft, 330 ft, and 5 acre grid. Area-based topography sampling for nitrate N was superior in correlation to the 220 ft grid values in 2 of 3 yr. Area-based topography sampling with P was superior to the 220 ft grid in only 1 of 3 yr, but was superior to the 5 acre grid in all years. The 220 ft grid was superior to topography sampling for sulfate S in all years, but area-based topography sampling was better than the 330 ft grid in 2 of 3 yr and superior to the 5 acre grid in all years. Area-based topography sampling for chloride was superior to the 220 ft grid in 1 of 3 yr, but was more highly correlated with the 110 ft grid than the 330 ft and 5 acre grid in all years. Area-based topography sampling was more highly correlated than point-based topography sampling in seven of 12 comparisons. Topography-based sampling for nitrate N better represented fertility patterns than did grid sampling.

Corn Rootworm Larval Control with Counter in 15- and 30-Inch Row Centers, 1997

Abstract This experiment was designed to test the efficacy of Counter 20 CR in 15- and 30-inch row centers at both full and half labeled rates. The experimental design was a split plot with four replications. Row center was the whole-plot treatment and insecticide was the subplot. The test was planned as conventional-till on 5 May into an area that had been planted to a rootworm trap crop the previous year (silty loam soil type). Treatments in the 3-inch row centers consisted of four rows 10 ft wide by 30 ft long. Treatments in the 15-inch row centers consisted of eight rows (10 ft wide) by 30 ft in length. Fifteen-inch row centers were accomplished by splitting the 30-inch centers with a second pass of the planter. Granular insecticide formulations were applied with modified Noble meter-ing units mounted on a 4-row John Deere 7100 planter (30-inch row centers). Seeding rate was 26,100/acre for 30-inch centers and 33,200 for 15-inch centers (16,600 each pass). The Noble insecticide metering units were field calibrated at both seeding rates and set accordingly. Insecticide was applied at the same oz (AI)/1000 row-ft rate, for each row-center treatment, regardless of seeding rate. Rootworm larval feeding was evaluated on 15 Jul by digging 3 roots from the center two rows of each treatment and rating the damage on the Iowa 1-6 scale (1 = no damage or only a few minor feeding scars; 6 = 3 or more nodes of roots completely destroyed). Lodging counts were taken on 22 Oct. A plant was considered lodged if the angle between the base of the plant and the ground was 45° or less. ANOVA was used to examine treatment main effects and interactions with row spacing. Means were separated with Ryan’s Q test (REGWQ).

Distribution and dynamics of the Argentine ant Linepithema (Iridomyrmex) humile (Mayr) in relation to vegetation, soil conditions, topography and native competitor ants in Portugal

The overall distribution of Linepithema humile, introduced about a hundred years ago and now widespread in western and southern Portugal, has not notably changed in the last forty years. The ant is particularly common in sand and in clay loam soils but, inexplicably and despite otherwise favourable conditions, is largely absent in adjoining easterly mostly sandy loam soils associated with metamorphic rocks. In these circumstances there was a striking change in transition areas from exclusive dominance by L. humile to exclusive dominance by the competing native species, Crematogaster scutellaris and Pheidole pallidula, which was directly associated with the change in soil type. In a site with a particular sandy loam soil type (Vt) comprising adjoining patches colonized either by L. humile or native ants, the former occurred where there was a greater sand content. In oak planted sandy and Vt soils L. humile was present in cultivated or grazed ground but was replaced by C. scutellaris when there was well established scrub and ground vegetation. There was intense fighting at a transition line in one place with uniform tree and ground vegetation that supported large populations of L. humile and of native dominants on opposite sides of the transition. Here, the former had spread about 30 m per year between 1993 and 1996 compared with an estimated 800 m per year in the first 60 years after introduction. It is concluded that the dominant native C. scutellaris and P. pallidula in their favoured plantation habitats, and T. nigerrimum and T. hispanicum in some arable and pasture habitats can delay or prevent spread of L. humile in soils and vegetation conditions that also suit it. Although L. humile was present in most valley floors, its presence and abundance were not significantly related to valley conditions, and it was sometimes abundant at the tops of adjoining hillsides and in seasonally water-deficient sandy areas. Its association with some built-up areas was strikingly displayed by abundance in a town on inimical metamorphic-based soils that were uncolonized in immediately adjoining vegetationally favourable plantation and agricultural land. The direct and indirect effects of soil type on L. humile are analysed and discussed. Three habitats largely free of human interference – sand dunes with native trees and bare areas, a similarly patchily vegetated rocky river gorge and an eroded arete – may exemplify natural conditions exploited by L. humile in its native South America.

A unified model for infiltration and redistribution during complex rainfall patterns

A relatively simple conceptual model for infiltration during complex rainfall sequences is presented. It is a reformulation of an analytically derived model developed earlier by Smith et al. (1993) [Water Resour. Res., 29(1): 133–144] and Corradini et al. (1994) [Water Resour. Res., 30(10): 2777–2784] in a more homogeneous version suitable for hydrologic applications. The model relies on a single ordinary differential equation through which successive cycles of infiltration-redistribution can be described. The wetting profile, σ(z), is described by a single similarity curve which is stretched in both z and σ dimensions in accordance with the curve area, I, representing infiltrated water. The actual profile of soil water content after rewetting may be compound, composed two parts, each part represented by a similarity profile shape which evolves in time. The model is calibrated using a silty loam soil and is then tested on a variety of soils, from fine-textured to sandy loam soil types, by comparison with a numerical solution of the Richards equation. Like the earlier formulation, the model simulates infiltration rate particularly well, and the greater simplicity of this model sacrifices very little accuracy of the earlier, more complex model.

Impact of Insecticides on Tomato Insects 1996

Abstract Seedlings were transplanted in a sandy loam type soil on 18 June at the University of California’s South Coast Field Station in Santa Ana, California. Experimental plots were 4 rows wide (5-ft centers) by 40 ft long and separated by a 5-ft buffer. The tomato transplants were drip irrigated (water pH 7.2-7.5). Treatments were replicated 4 times in a RCB block design. Weekly applications were initiated at first fruiting. Application dates were 25 Jul, 1, 8, 15, 22, 29 Aug, and 5, 12, 19 Sep. A tractor-mounted boom sprayer with 6 nozzles per row incorporated D-3 orifice disks, #25 cores, and 50 mesh screens. Operating pressure was 100 psi delivering 100 gpa. Spreader sticker (Leaf Act 80) was included for all treatments at 0.04%, except Fortune AZA and Neemix (+0.5% crop oil) and Aphistar (+ silwet @ 2 oz./lOO gal.). Leafminer populations were evaluated by weekly counts of leafminer prepupae and pupae in four 9 by 11 inch trays/replicate from 30 Jul through 18 Sep, inclusive. On 23-25 Sep, 200 mature-green to ripe fruit were harvested from the center 2 rows of each replicate (800 per treatment) and examined for internal damage (primarily by H. zed) and external damage (primarily by S. exigua and K. lycopersicella). Leafminer populations were moderate. Some treatments increased leafminer density as compared to the control.

Irrigation planning in cotton through simulation modeling

Experiments were undertaken at CCS Haryana Agricultural University Farm, Sirsa (India) to estimate the optimum irrigation schedule for cotton resulting in minimum percolation losses. The sprinkler line source technique was adopted for creating various irrigation regimes at different crop growth stages. The SWASALT (Simulation of Water And SALT) model after calibration and validation provided water balance components. The wa-ter management response indicators (WMRI's) such as transpiration efficiency Et/(Irr + P), relative transpiration Et/Etp, evapotranspiration efficiency ET/(Irr + P), soil moisture storage change ΔW/Wint (deficit/excess) and percolation loss Perc/(Irr. + P) were evaluated using water balance components as estimated by the simulation study. Under limited water supply conditions, the optimum irrigation depth was found to be 57 mm at crop growth stages with pre-sowing and 1st irrigation of 120 mm and 80 mm respectively for sandy clay loam underlain by sandy loam soil (Type I). The corresponding values of relative transpiration, transpiration efficiency and evapotranspiration efficiency were 0.65, 0.65 and 0.89 respectively. The crop yield varied linearly with increasing irrigation depth which was evident from increase in relative transpiration with increasing depth of water application. However, increased depth of irrigation resulted in less moisture utilisation from soil storage (20% depletion at 40 mm depth and 4.4% moisture built up at 100 mm depth). The extended simulation study for sandy soil underlain by loamy sand (Type II) indicated that two pre-sowing irrigations each 40 mm and subsequent irrigations of 40 mm at an interval of 20 days depending upon rainfall were optimum. This irrigation scenario resulted in zero percolation loss accompanied by 74% relative transpiration and 14 per cent soil moisture depletion.

Draft-speed relationship of simple tillage tools at high operating speeds

Field experiments were conducted with five different blades operated vertically in sandy loam and clay soil types up to a speed of 18 m s −1 to determine the draft-speed relationships at high speeds. The soils were Calcic Chernozem and Haplic Kastanozem according to FAO classification. Mechanical properties of the soils were determined to correlate the results with model predictions. The results showed that the draft increased less above a critical speed range of 3 to 5 m s −1. This critical speed range was compared with: the propagation speed of a longitudinal pressure wave in the soil, the speed of the soil particles caused by this pressure wave in the soil, and the speed of disruption of the soil. It was shown that these speeds are related to the observed critical speed range. As previously proposed, the amount of soil deformation due to tillage would decrease above the critical speed range. It is, therefore, important to examine the dynamic effect of tillage at higher operating speeds.