No-till Corn Field Research Articles

Preventive insecticide use affects arthropod decomposers and decomposition in field crops

Insecticides use in field crops has grown increasingly prophylactic, which poses a potentially unnecessary risk to arthropod decomposers. These decomposers — including millipedes (Diplopoda), soil mites (Acari, mostly Oribatida), and Collembola — act as alternative prey for generalist predators, facilitate crop-residue breakdown, and can influence nutrient cycling. However, the abundance and activity of arthropod decomposers may be reduced by extensive prophylactic pesticide use. We conducted a three-year field experiment in no-till corn and soybean fields to assess how neonicotinoid seed coatings or broadcast applications of a pyrethroid insecticide affect arthropod decomposers and litter decomposition. Both insecticides reduced densities of arthropod decomposers and reduced decomposition of plant litter by over 10%. Neonicotinoid seed coatings reduced collembolan densities by 34% and millipede densities by 52%, while the pyrethroid significantly reduced oribatid mite densities by 24% and millipede densities by 82%. Lower mite and millipede densities correlated with slower litter loss, and decomposition was slower under neonicotinoid seed coatings and broadcast pyrethroid applications. These results indicate that perennial, widespread use of prophylactic insecticides is likely to have concerning negative effects on the availability of alternative prey, plant residue breakdown, and nutrient cycling in field crops.

Characterizing mass–volume–density–porosity relationships in a sandy loam soil amended with compost

Although compost is widely used as an organic soil amendment or conditioner, little is known of how it affects the characteristics or interactions among soil constituents. To address this, mixture theory was used to describe the mass–volume–density–porosity attributes and interactions among bulk soil, the mineral constituent, and the organic matter constituent of a sandy loam soil in a no-till corn field that had received one-time additions of yard waste compost at rates of 0 (control), 64, 154, and 380 dry t ha−1. Bulk density (BD, 0–10 cm depth) decreased consistently and near-linearly with increasing soil organic matter (SOM) mass fraction (FOM) for all six growing seasons (2012–2017) after compost addition. Fitting mixture theory expressions to BD vs. FOMdata and to soil particle density vs. FOMdata for 2013–2017 yielded constant mineral and SOM self-packing densities of DM = 1.673 Mg m−3and DO = 0.335 Mg m−3, respectively, and constant mineral and SOM particle densities of ρM = 2.760 Mg m−3and ρO = 1.409 Mg m−3, respectively. On a self-packing basis, soil mineral and SOM domain porosities were constants at nM = 0.39 and nO = 0.76, respectively. On a bulk soil volume basis, soil mineral and SOM porosities and volume ratios were linear functions of FOM. The porosity and volume characteristics of the SOM domain differed substantially from those of bulk soil and the mineral domain, and may therefore control the agri-environmental performance of soil, given that organic matter influences soil functioning more than mineral matter.

Soil Health of Recently Converted No-till Corn Fields in Maine

ABSTRACTNo-till (NT) forage production in Northeast United States is growing due to farmers’ desire to reduce costs. Soil samples (15cm deep), soil penetrometer values (depth to 300 psi), and earthworm midden counts were collected from 59 fields on 14 dairy farms in Maine planted to corn. Of the 59 fields sampled, 13 fields received light tillage in the sampling year, 40 had not been tilled within 5 years, and 6 fields had not been tilled for a minimum of 12 years. Median soil health scores (SHS) varied among farms, from 23 to 43 based on the 0 to 50 Woods End SHS scale, based more on past soil management. Most soil quality attributes were significantly correlated indicating that they were useful predictors of soil quality. Among fields not tilled in 5 years, we found no relationship of SHS to time in NT. Fields with greater earthworm activity had higher SHS indicating increased biological activity and potentially improved productivity resulting from better drainage and aeration. Farmers were asked to identify their highest and lowest soil quality fields, but according to the SHS, they were 56 percent successful. Three cornfields on three different farms were NT planted into herbicide killed long-term perennial hay fields; each of these had the highest SHS, but no farmer recognized that. More education on rotating perennial forage crops with NT corn is needed. No-till forage production can improve soil health, reduce fuel and labor costs by more than $50/acre, and residue cover can reduce soil erosion impacts.

Control of glyphosate-resistant giant ragweed (Ambrosia trifida L.) with premix of iodosulfuron/thiencarbazone applied alone or in tank mixtures in no-till corn (Zea mays L.)

The objectives of this study were to evaluate the efficacy of a new premix of iodosulfuron (6%)/thiencarbazone (45%) applied alone or tank-mixed with 2,4-D, dicamba, glyphosate, or metribuzin in the fall and (or) early spring followed by preemergence (PRE) and postemergence (POST) herbicide applications for control of glyphosate-resistant giant ragweed and their effect on corn yield. Field experiments were conducted in no-till corn fields infested with glyphosate-resistant giant ragweed (20–30 plants m−2) near Clay Center and McCool Junction, NE, in 2013 and 2014, respectively. A premix of iodosulfuron/thiencarbazone applied alone or in split applications in the fall and early spring controlled glyphosate-resistant giant ragweed <60% and resulted in a density of 14 giant ragweed plants m−2, which was comparable to the untreated control at 28 d after early spring treatment (DAEST). Metribuzin or 2,4-D applied alone resulted in <75% giant ragweed control at 28 DAEST; however, 2,4-D or dicamba tank-mixed with iodosulfuron/thiencarbazone provided ≥92% control. Treatments including 2,4-D or dicamba led to 85%–98% reduction in giant ragweed biomass at 28 DAEST. A follow-up application of a premix of isoxaflutole/thiencarbazone tank-mixed with atrazine applied PRE was not effective, although a POST application of tembotrione + atrazine resulted in >91% control at 28 d after postemergence treatment. The premix applied alone did not provide effective control of giant ragweed in corn primarily because lack of residual activity.

A Bioassay Evaluation of Field-Aged and Fresh Molluscicide Baits for Control of Dusky Slug, 2015: Table 1

The purpose of this bioassay was to assess the effectiveness of fresh and field-aged molluscicide baits for control of dusky slug, which is a common slug pest in Virginia. All slug baits (Iron Fist and Deadline) were commercially formulated and obtained from AMVAC Chemical Corporation. Samples of 100 g of each bait product were applied to a no-till cornfield located near Blacksburg, VA on 29 May 2015. After 2 weeks in the field, and approximately 1 cm of precipitation, the baits were retrieved from the field and brought to …

Genetic variability of Aspergillus flavus isolates from a Mississippi corn field.

A nontoxigenic Aspergillus flavus strain, K49, is currently being tested as a biological control agent in corn fields in the Mississippi Delta. However, little is known about the overall genetic diversity of A. flavus from year to year in corn fields and specifically in Mississippi. Our objective was to assess the genetic variability of A. flavus isolates from different seasons, inoculum sources, and years, from a no-till corn field. Of the 175 A. flavus isolates examined, 74 and 97 had the typical norB-cypA type I (1.5 kb) and type II (1.0 kb) deletion patterns, respectively. Variability in the sequence of the omtA gene of the majority of the field isolates (n = 118) was compared to strain K49. High levels of haplotypic diversity (24 omtA haplotypes; Hd = 0.61 ± 0.04) were found. Among the 24 haplotypes, two were predominant, H1 (n = 71), which consists of mostly toxigenic isolates, and H49 (n = 18), which consists of mostly atoxigenic isolates including K49. Toxigenic isolates were prevalent (60%) in this natural population. Nonetheless, about 15% of the population likely shared the same ancestral origin with K49. This study provides valuable information on the diversity of A. flavus. This knowledge can be further used to develop additional biological control strains.

Silicate weathering and CO<sub>2</sub> consumption within agricultural landscapes, the Ohio-Tennessee River Basin, USA

Abstract. Myriad studies have shown the extent of human alteration to global biogeochemical cycles. Yet, there is only a limited understanding of the influence that humans have over silicate weathering fluxes; fluxes that have regulated atmospheric carbon dioxide concentrations and global climate over geologic timescales. Natural landscapes have been reshaped into agricultural ones to meet food needs for growing world populations. These processes modify soil properties, alter hydrology, affect erosion, and consequently impact water-soil-rock interactions such as chemical weathering. Dissolved silica (DSi), Ca2+, Mg2+, NO3–, and total alkalinity were measured in water samples collected from five small (0.0065 to 0.383 km2) gauged watersheds at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio, USA. The sampled watersheds in this unglaciated region include: a forested site (70+ year stand), mixed agricultural use (corn, forest, pasture), an unimproved pasture, tilled corn, and a recently (<3 yr) converted no-till corn field. The first three watersheds had perennial streams, but the two corn watersheds only produced runoff during storms and snowmelt. For the perennial streams, total discharge was an important control of dissolved silicate transport. Median DSi yields (2210–3080 kg km−2 yr–1) were similar to the median of annual averages between 1979–2009 for the much larger Ohio-Tennessee River Basin (2560 kg km−2 yr–1). Corn watersheds, which only had surface runoff, had substantially lower DSi yields (<530 kg km−2 yr–1) than the perennial-flow watersheds. The lack of contributions from Si-enriched groundwater largely explained their much lower DSi yields with respect to sites having baseflow. A significant positive correlation between the molar ratio of (Ca2++Mg2+)/alkalinity to DSi in the tilled corn and the forested site suggested, however, that silicate minerals weathered as alkalinity was lost via enhanced nitrification resulting from fertilizer additions to the corn watershed and from leaf litter decomposition in the forest. This same relation was observed in the Ohio-Tennessee River Basin where dominant landuse types include both agricultural lands receiving nitrogenous fertilizers and forests. Greater gains in DSi with respect to alkalinity losses in the Ohio-Tennessee River Basin than in the NAEW sites suggested that soils derived from younger Pleistocene glacial-till may yield more DSi relative to nitrogenous fertilizer applications than the older NAEW soils. Because silicate weathering occurs via acids released from nitrification, CO2 consumption estimates based on the assumption that silicate weathers via carbonic acid alone may be especially over-estimated in fertilized agricultural watersheds with little baseflow (i.e. 67 % overestimated in the corn till watershed). CO2 consumption estimates based on silicate weathering may be as much as 20 % lower than estimates derived from carbonic acid weathering alone for the Ohio-Tennessee River Basin between 1979–2009. Globally, this may mean that younger landscapes with soils favorable for agriculture are susceptible to fertilizer-enhanced silicate weathering. Increases in silicate weathering, however, may be offset by shifts in hydrology resulting from agricultural land management practices or even from soil silica losses in response to repeated acidification.

SPATIAL VARIABILITY IN THE UPPER SOIL LAYER OF A NO-TILL FIELD USING A SMALL-SCALE DYE EXPERIMENT

Small-scale (33 cm by 33 cm) dye experiments were performed to evaluate the spatial variation of infiltration by evaluating dye distribution within the upper 10-cm soil depth of a well-established no-till corn field. The variation of infiltration was estimated by measuring the dye concentrations in the soil samples obtained from the 0- to 3-cm, 3- to 6-cm, and 6- to 10-cm depths of the infiltration test volume (10,890 cm 3 ). Contour maps of dye concentrations were prepared for each soil layer and used to estimate the percentage of the infiltration area that had a higher than average dye concentrations. Results indicate that (1) statistically, the dye concentration in the upper soil layers (0 to 3 cm) have a higher average dye concentration with less variability than the middle and lower soil layers; (2) the majority of the infiltration solution appeared to pass through 23% of the infiltration area; and (3) the spatial distribution of the dye concentrations are highly heterogeneous. The statistically and spatially heterogeneous dye distribution suggests that under ponded infiltration conditions in no-till systems, preferential flow may be the primary mechanism affecting the distribution of infiltrating water throughout the 0- to 10-cm depth. The heterogeneous dye distribution suggests preferential flow was established in the 0- to 3-cm layer for most of the tests.

Landscape level variation in soil resources and microbial properties in a no-till corn field

Soil microbial properties are known to exhibit high spatial and temporal variability, which can hinder our understanding of the effects of agricultural management on soil microbial activities, populations and communities. However, if this variability is explicitly considered in soil sampling schemes, experimental results can help us better understand soil microbial properties. In this initial assessment of soil resources and microbial properties in a 16-ha landscape planted to corn, we hypothesized that soil microbial properties will vary by soil type. We defined soil type based on drainage class (4 levels), series (7 levels), map unit (11 levels), and texture of the Ap horizon (3 levels). We took soil samples from 16 map units in April, June, August, and October and measured 12 physical and chemical properties, and 27 microbial properties on at least one of these dates. Soil physical and chemical properties generally varied with soil type and canonical discriminant analyses showed that soil drainage classes, series, and map units were delineated by a similar set of soil properties (total C, total N, moisture, pH, equivalent CEC (CEC e), and available P). Ap texture classes were delineated by a different set of soil properties (available K, Mg, and Ca and CEC e). A number of soil microbial properties varied by soil type, but, in general, a smaller proportion of measured soil microbial properties showed soil type effects compared to the proportion of soil physical and chemical properties that showed soil type effects. Method of soil classification strongly influenced which soil microbial properties varied by soil type. However, soil microbial activities, population sizes, and community structures were generally greater or most unique in mid-range soils regardless of how soils were classified, possibly because soil moisture was optimal for microbiological activity and growth in these soils. Except at the level of drainage class, there was little consistency between patterns of variation in soil physical and chemical properties and patterns of variation in soil microbial properties among soil types. Thus, different soil sampling strategies may be required when accounting for variation in soil physical and chemical properties than when accounting for soil microbial properties at the landscape level. While sampling soils according to soil survey-defined map units indicated that some soil microbial properties vary by soil type, a number of limitations to this approach are discussed. To improve upon results presented here, future efforts to quantify landscape level variation of soil microbial properties should probably be sampled at a finer scale that explicitly accounts for soil properties that vary at the sub-map unit level, including terrain attributes, microtopography, soil texture, soil bulk density, and other factors that impact soil temperature and moisture dynamics.

Impact of hairy vetch cover crop on herbicide transport under field and laboratory conditions

This study was conducted to evaluate the effect of hairy vetch cover crop residue on runoff losses of atrazine and metolachlor under both no-till corn field plots and from a laboratory runoff system. A 2-year field study was conducted in which losses of atrazine and metolachlor from vetch and non-vetch field plots were determined from the first runoff event after application (5 and 25 days after application in 1997 and 1998, respectively). A laboratory study was conducted using soil chambers, designed to simulate field soil, water, vegetation, and herbicide treatment conditions, subjected to simulated rain events of 5, 6, 20 and 21 days after application, similar to the rainfall pattern observed in the field study. Atrazine losses ranged from 1.2 to 7.2% and 0.01 to 0.08% and metolachlor losses ranged from 0.7 to 3.1% and 0.01 to 0.1% of the amount applied for the 1997 and 1998 runoff events, respectively. In the laboratory study, atrazine runoff losses ranged from 6.7 to 22.7% and 4.2 to 8.5% and metolachlor losses ranged from 3.6 to 9.8% and 1.1 to 4.7% of the amount applied for the 5–6 and 20–21 day events, respectively. The lower losses from the field study were due to smaller rainfall amounts and a series of small rains prior to the runoff event that likely washed herbicides off crop residue and into soil where adsorption could occur. Runoff losses of both herbicides were slightly higher from non-vetch than vetch field plots. Losses from the laboratory study were related to runoff volume rather than vegetation type.

Evaluation of site-specific weed management using a direct-injection sprayer

Abstract Targeting weed patches for site-specific herbicide applications potentially represents cost savings for operators, reduction in environmental herbicide effects, and increased efficiency of weed control. An experiment was initiated in a no-till corn field in Ontario, Canada, in 1998 and was continued in rotation with no-till soybeans in 1999. Weeds were intensively scouted, and distribution maps of the most common weeds (field horsetail, spiny sowthistle, dandelion, and common lambsquarters) were generated for both years. A prescription map for each plot was made using the weed density maps. Treatment decisions were based on a weed threshold value of 1 shoot m−2. Four herbicide treatments were compared: a conventional broadcast, a site-specific application targeting weed patches only, and two combinations of broadcast and site-specific applications. Treatments were applied using a direct-injection sprayer. Efficacy of weed control and yield were compared among treatments. In 1998 and 1999 there we...

Efficacy of in-furrow zinc phosphide pellets for controlling rodent damage in no-till corn

Plagues of rodents in field crops have been a problem of human societies for centuries. These problems diminished with the onset of effective herbicides and clean farming practices in the 1960s, but there has been a resurgence of rodent irruptions in cropfields since the advent of conservation tillage systems. We examined the efficacy of in-furrow applications of 2% zinc phosphide (Zn 3P 2) pellets (27.5 kg ha −1 [5 lb acre −1]) at planting for the control of rodent damage in no-till corn. Three independent field studies were conducted in northeastern NE, southern IL, and southern IN. Vole populations in the most severely damaged fields (IL) ranged from 104 to 138 active colonies ha −1. Zn 3P 2 reduced yield loss in the three study areas by 7–34%. Projected economic returns ranged from US$1044 to US$5360, based on representative 64-ha fields and a net profit of US$250 ha −1. Benefit:cost ratios ranged from 1.1 to 5.6:1 and were directly related to vole population levels. To prevent rodent damage in no-till cornfields, we recommend an integrated pest management approach that incorporates the use of a combination of the following techniques: rodent population monitoring, economic thresholds, mowing, early pre-plant herbicides, broadcast whole-kernel corn, and in-furrow applications of Zn 3P 2 pellets.

Precision Farming Protocols: Part 1. Grid Distance and Soil Nutrient Impact on the Reproducibility of Spatial Variability Measurements

To determine temporal changes in soil nutrient status, reproducible results must be obtained at each time step. The objective of this paper was to determine the impact of grid distance on the reproducibility of spatial variability measurements. Soil samples from the 0 to 15 cm depth were collected from a 30 by 30 m grid in May 1995 in a 65 ha notill corn (Zea mays L.) field. Each bulk sample contained 15 individual cores, collected at sample points located every 11.4 cm along a transect that transversed 3 corn rows (57 cm). At each sampling point latitude, longitude, elevation, landscape position, and soil series were determined. The 30 m grid was used to develop 4 and 9 independent data sets having a 60 and 90 m, grids, respectively. Semivariograms, nugget to sill ratios, and mean squared errors were calculated for each data set. At 60 m: (i) the total N, total C, and pH semivariograms, of different start points, were similar, while semivariograms for Olsen P, K, and Zn were different; (ii) the spatial dependence ratings, based on the nugget to sill ratio, for total N, total C, and pH semivariograms were consistent and suggested moderate spatial dependence; (iii) the spatial dependence rating for Olsen P, K, and Zn for the 4 semivariograms were not consistent and ranged from weak to moderate spatial dependence. At 90 m all soil nutrients had different semivariograms for each start point, while the spatial dependence rating for each total N, total C, and pH start point were consistent and showed moderate spatial dependence. The total C, P, K, Zn, and pH MSE values at 60 m, were 30, 30, 41, 28, and 72% lower than the variance, respectively. This study showed that semivariogram, semivariance, MSE, and nugget to sill ratios reproducibility were dependent on soil nutrient and grid distance.

Measurement of Field Soil Hydraulic and Solute Transport Parameters

AbstractAgricultural chemical presence in groundwater has drawn attention toward transport processes occurring in soil. Hydraulic conductivity (K) and water‐holding capacity of a soil have great influence on water flow and solute transport. However, much of the chemical transport to groundwater can occur through preferential flow pathways. The simplified, preferential flow, mobile‐immobile model partitions the water content (θ) into mobile (θm) and immobile (θim) domains, with solute exchange between the domains characterized by the mass‐exchange coefficient (α). In this study a sequential tracer application technique was used and K, θ, θim, and α were estimated for a series of pressure heads (H = 10, −30, −60, and −150 mm). This method uses a tension infiltrometer to measure both hydraulic and solute transport parameters in situ. The study took place in a no‐till corn (Zea mays L.) field mapped as a Harps series soil (fine‐loamy, mixed, mesic Typic Calciaquoll). Unsaturated values of θ and K were distinct from the saturated values. Similarly, though less clear cut, distinctions between saturated and unsaturated values of θim, immobile water fraction (θim/θ), and α were observed. The medians of θ for the sequence of decreasing H values were 0.40, 0.34, 0.34, and 0.33 m3 m‐3. The median K values for the same sequence of H were 108, 1.69, 1.51, and 0.72 µm s‐1. The median θim/θ values for the H sequence were 0.40, 0.28, 0.25, and 0.39. The median values of α for the H sequence were 0.59, 0.015, 0.0028, and 0.0029 h‐1. A strong correlation between α and H suggests a velocity dependence of α.

Spring dynamics of soil carbon, nitrogen, and microbial activity in earthworm middens in a no-till cornfield

Earthworm activity may be an important cause of spatial and temporal heterogeneity of soil properties in agroecosystems. Structures known as “earthworm middens,” formed at the soil surface by the feeding and casting activities of some earthworms, may contribute significantly to this heterogeneity. We compared the temporal dynamics of carbon (C), nitrogen (N), and microbial acitivity in Lumbricus terrestris middens and in surrounding non-midden (bulk) soil during the spring, when seasonal earthworm activity was high. We sampled soil from middens and bulk soil in a no-till cornfield on four dates during May and June 1995. Soil water content and the weight of coarse organic litter (>2mm) were consistently higher in middens than in bulk soil. Total C and N concentrations, C:N ratios, and microbial activity also were greatest in midden soil. Concentrations of ammonium-nitrogen and dissolved organic N were greater in middens than in bulk soil on most dates, suggesting accelerated decomposition and mineralization in middens. However, concentrations of nitrate were usually lower in middens, indicating reduced nitrification or increased leaching and denitrification losses from middens, relative to bulk soil. Fungal activity, as well as total microbial activity, was consistently greater in middens. The contribution of fungae to overall microbial activity differed significantly between middens and bulk soil only on one date when both soils were very dry; the contribution of fungae to microbial activity was lower in the middens on this date. We conclude that the midden-forming activity of L. terrestris can be a major determinant of spatial heterogeneity in some agricultural soils, and that this can potentially affect overall rates of soil processes such as organic matter decomposition, N mineralization, denitrification, and leaching.

Efficacy of Granular Insecticides Against Western Corn Rootworm Larvae, 1997

Abstract An experiment was conducted at the Virginia Tech Kentland Farm (Hilltop field) in Montgomery Co., VA to determine the effectiveness of several granular insecticides, applied in-furrow or T-band at planting, against WCR larvae on ‘ MA9171’ corn. The experiment was conducted near the center of a 10-acre, no-till cornfield with a predominant Unison-Braddock silt loam soil. The field had been in continuous corn production since 1994, and had been treated with granular insecticides at planting every year since 1995. Plots of 40 X 10 ft (four rows wide) were arranged in a 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 1 May at the rate of 26,100 seeds/acre. 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 device which 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 granules was inverted and placed in each of the wooden holders. This method helped minimize soil compaction because the tractor made only one pass per plot. The roots of five consecutive corn plants were dug from each plot on 12 Jul and washed of excess soil before damage ratings were made. WCR 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 not made because of inconsistencies in the stand resulting from planter error and weed pressure. A two-way ANOVA and LSD were used to analyze differences in root ratings among treatments.

Surface alfalfa residue removal by earthworms Lumbricus terrestris L. in a no-till agroecosystem

Earthworm ( Lumbricus terrestris L.) populations increase in alfalfa ( Medicago sativa L.) and in no-till corn ( Zea mays L.) fields compared to conventionally-tilled fields. The effects of earthworm activity on surface crop residue removal in no-till corn following alfalfa have not been studied. The main objective of this research was to measure earthworm effects on crop residue removal from the soil surface. Soils were Saybrook silt loams (fine-loamy, mixed, mesic Typic Argiudolls) on 2–9% slopes in south-central Wisconsin. We used a mesh-bag method to measure earthworm removal of alfalfa residue and the influence of forage quality on removal of residue from the soil surface. Coarse-mesh bags, with mesh openings 20 × 20 mm 2, which allowed earthworms to remove alfalfa residues from the bags, had significantly greater alfalfa surface residue loss than fine-mesh bags with mesh openings 1 × 1 mm 2, which prevented worms from removing residues. Forage quality of residues did not affect quantity of residue removed. We calculated that the observed populations of 40 to 60 L. terrestris m −2 could remove surface alfalfa residues at a rate that could account for the measured 122 g m −2 October to May biomass losses, given 60 days of suitable feeding weather and based on the measured loss rate of 69 g residue lost m −2 in 30 days. Potential residue removal by earthworms should be addressed in residue management strategies, especially where populations of L. terrestris are large and where crop residues are palatable to earthworms.

Efficacy of Soil Insecticides Against Western Corn Rootworm, 1995

Abstract Two experiments were conducted in Mont-gomery Co., VA, to determine the effectiveness of several granular insecticides applied in-furrow or t-band at planting and a liquid formulation applied postemergence against western corn rootworm larvae on ‘Pioneer 3140’ corn. The experiments were conducted in 2 no-till cornfields consisting of a predominant Duffield-Ernest silt loam soil. Experiment I was in a 20-acre field (‘Back’ field) and Experiment II was in an 8-acre field (‘Machine Shed’ field). The fields had been in continuous corn production since 1988 (Back field) and 1985 (Machine Shed field), and had been treated with granular insecticides at planting every year since 1989 (Back field) and 1990 (Machine Shed field). Plots of 40 X 10 ft (i.e., 4 rows wide) were arranged in a RCB design with all insecticide treatments and an untreated check replicated 4 times. An Almaco, 2-row Max-Emerge planter was used to plant the plots on 12 May at a population density of 26,100 seeds/acre. For the granular insecticide treatments, insecticide granules were applied in front of the press wheels either directly in the seed furrow or in a 5-inch wide T-barid over the furrow, depending on the treatment. The standard granular insecticide applicator was removed from each row unit and replaced with a wooden device which held a pt mason jar 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 insecticides 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 granules was inverted and placed into each of the wooden holders. This method helped minimize soil compaction because the tractor made only 1 pass per plot. The postemergence application of the liquid formulation of Furadan 4F was made on 9 Jun using a backpack sprayer with a boom equipped with foui stainless steel 8002VS spray tips spaced 19 inches apart. Material was applied at 20 gpa 30 psi. Root ratings (20 Jul) and stand counts (13 Jun) were made. The roots of 5 consecutive corn plants were dug from each plot and washed of excess soil before 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 consisted of counting all cornstalks along a 40 row-ft section in each plot. A 2-way ANOVA with Fisher’s protected LSD was used to analyze differences among treatments.

Distribution and transport of atrazine as influenced by surface cultivation, earthworm population and rainfall pattern

Several laboratory studies were conducted to evaluate the effects of soil surface cultivation, earthworm ( Allolobophora caliginosa L) population, and rainfall pattern on 14C-atrazine (2-chloro-4-ethylamino-6-isopropylanunos-triazine) leaching through intact soil cores. Soil cores (16 cm dia x 20 cm deep) were collected from a seven year no-till (NT) corn field. Earthworms (0, 4, or 8 core −1) were introduced into the cores. Half of the cores were cultivated (2.5 cm depth) and the rest of the cores were left uncultivated prior to 14C-atrazine treatment (2.74 mg core −1). Cores were subjected to a rainfall pattern in which a low intensity rain (16 mm of rain in 2.5 h) was followed 48 h later by a high intensity rain (27 mm of rain in 1.5 h). The saturated hydraulic conductivities (Ksat) of cores with 0, 4, and 8 worms core −1 were 0.8, 3.4, and 5.3 cm h −1, respectively. Increasing the number of earthworms in each core from 0 to 8 worms, increases the amount of atrazine (% of applied) leached through untitled cores from 8.5 to 13.5% and for tilled cores from 1.0 to 5.0%. Much more atrazine was leached through untitled soil cores than tilled cores at both low and high rainfall intensities. The results of thus study suggest that herbicide transport is dependent on a combination of rainfall parameters, soil macroporosity, and disruptive surface cultivation.

Estimation of adult carabid absolute densities in a no-till corn field by removal sampling

A removal sampling technique was used and evaluated according to its assumptions for estimating the absolute densities of adult ground beetles (Carabidae). Removal sampling is a method of absolute density estimation based on the decline in successive catch numbers as individuals are removed from a population. Field arenas were used to isolate sampling areas in a no-till corn field, and pitfall traps were installed within the arenas to remove the carabids. A linear regression method was used to calculate the density estimate using the removal sampling data. Although the technique provided estimates which are relatively similar to those of mark-release-recapture studies, violations of the assumptions were observed, and suggestions are made which may improve the accuracy of the estimates and the applicability of the technique.