Conventional Tillage Field Research Articles

Effect of resource conserving technologies in the disease dynamics of rice and wheat cropping systems of the Punjab

Rice and wheat crops surveys were conducted at Muridkey and MONA (Bhalwal) in the Punjab province of Pakistan. Zero tillage and conventional tillage were practiced on an experimental basis in the farmer's field. The total mean number of wheat seedlings was more in conventional tillage as compared to the 0-tillage technology of Muridkey and MONA (Bhalwal). In 1999 at Muridkey in 0-tillage and conventional fields brown spot, bacterial leaf blight and root rot were present but blast, bakanae, sheath rot, sheath blight and insect attack were absent but at MONA (Bhalwal) brown spot, bacterial leaf blight, sheath blight, insect attack and root rot were present in both technologies while blast, bakanae and sheath rot were absent. In 1999 at the seedling stage of wheat, foliar blight was absent in 0-tillage and conventional tillage fields of wheat at Muridkey and MONA (Bhalwal) but during 2000 at the booting stage of wheat foliar spot incidence was higher in 0-tillage technology fields of Muridkey and MONA (Bhalwal). In September 2000 the incidence of root rot of rice was higher and the same in 0-tillage and conventional tillage practices of Muridkey. In 2001 wheat, foliar spot incidence was higher in 0-tillage technology fields at Muridkey and MONA (Bhalwal).

Development of effective management plan for critical subwatersheds using SWAT model

AbstractThe present investigation is an effort to develop an effective management plan for the identified critical subwatersheds of Nagwan watershed located in the eastern part of India using a precalibrated and validated Soil and Water Assessment Tool (SWAT) model. In all 60 combinations of various management treatments including crops (rice, maize, peanut and soybean), tillage (zero, conservation, field cultivator, mould board plough and conventional practices) and levels of fertilizer (existing, half of recommended and recommended) have been studied.This study revealed that crops like maize, peanut and soybean could not replace rice since they resulted in higher sediment yield compared to rice. The tillage practice with mould board plough has been found to have a more appreciable impact on the sediment and nutrient losses than conventional tillage practices for the existing level of fertilizer. Sediment yield decreased in case of zero tillage, conservation tillage and field cultivator compared to conventional tillage. On the other hand, nutrient losses increased in case of zero and conservation tillage for all levels of fertilizer compared to the other tillage treatments.In conclusion it can be stated that the sediment yield is highest in case of mould board plough followed by conventional tillage field cultivator, conservation tillage and least in zero tillage practices, whereas the nutrient losses were found to be just in the reverse order with tillage practices, indicating highest nutrient losses in mould board plough tillage practices. In view of the sediment yield and nutrient losses, the conventional tillage practice was considered to be the best as the sediment yield is less than the average soil loss and nutrient loss is within the permissible limit. Copyright © 2005 John Wiley & Sons, Ltd.

Tillage index predicts weed seedling recruitment depth

The influence of tillage on the depth of weed seedling recruitment has implications for species competitive ability, weed management strategy development, and the modeling of weed emergence; characterization of this relationship could aid in the creation of field-specific models of weed seedling recruitment. A tillage index based on the percentage of residue cover remaining on the soil surface after tillage events was assessed for 44 zero-tillage and 44 conventional-tillage fields across Manitoba, Canada. This index was related to in situ measurements of seedling recruitment depth from the same fields for five annual weed species. The modeled relationship was linear and unique for each species (R2 values ranged from 0.38 to 0.71). The relationship did not differ between pre- and post-seeding measurements, or between years, except for green foxtail. Slopes of the regression lines were greater for species such as volunteer wheat, which can recruit from a great range of depths. The results of this study show that recent tillage strongly influences mean weed seedling recruitment depth, and that the recruitment depth of summer annual weed seedlings is related in a continuous and reliable manner to a simple estimation of the relative level of tillage (including seeding) applied in one season. Key words: Recruitment depth, tillage index, weed emergence, weed seedlings

Conventional- and conservation-tillage systems influence emergence periodicity of annual weed species in canola

Variation in spring emergence periodicity (both before and after crop seeding) of summer annual weeds is a potentially exploitable attribute that may be applied to weed management in canola. Tillage intensity, which is decreasing in the Great Plains of North America, may influence emergence periodicity of summer annual weeds. Emergence periodicity of common lambsquarters, field pennycress, green foxtail, redroot pigweed, wild buckwheat, wild mustard, and wild oat were monitored during the spring of 2000 in 17 producers' canola fields across southern Manitoba, Canada. The fields represented a region of approximately 2 million ha and included a broad range of soil types, agronomic practices, environmental conditions, and seedbank distributions. Fields were grouped into one of two broad tillage classifications (conventional or conservation). For most species, except redroot pigweed and wild mustard, conservation tillage promoted earlier emergence than conventional tillage in terms of both thermal and chronological time. The differences were significant even though there was only a limited range of tillage intensity for the two tillage classes within this region. Onset of canola crop emergence preceded that of all but one weed species in the conservation-tillage fields and five weed species in the conventional-tillage fields. This suggests that canola seeded in conservation- vs. conventional-tillage systems may have a competitive advantage by way of an earlier relative time of crop emergence. The influence of tillage system on weed emergence periodicity is likely due to the influence of tillage on the vertical origin of weed seedling recruitment because measurements of soil temperature and soil moisture did not help to fully explain the differences in emergence periodicity between tillage systems. The results from this study will facilitate weed control timing decisions in canola and provide validation data for weed emergence models.

Mineralogical and organic carbon content of water-dispersible particles from conventional and no-tillage soils

Soil erosion from agricultural lands causes loss of soil productivity, as well as environmental problems down stream due to sediment and contaminants sorbed on dispersed colloids. In order to estimate the potential effects of erosion and to describe the behavior of various inorganic and organic contaminants in agro-ecosystems, quantitative characterization of soil colloid dispersion is essential. The effect of long-term tillage management (conventional-tillage and no-tillage) on mineralogical and organic carbon content in both field- and laboratory-generated water dispersible particles (WDP) were studied. Field-WDP were collected during rainfall simulation. Laboratory-WDP were obtained by shaking soil for 16 hours (soil to water ratio of 1:10). Results demonstrate that laboratory- and field-WDP differ in organic carbon content, particle size distribution, and mineralogical concentrations, and are influenced by soil management. Soils under no-tillage produced much larger amounts of laboratory-WDP and smaller amounts of field-WDP than the soils under conventional-tillage. Field-WDP from both no-tillage and conventional-tillage fields were dominated by silt-sized particles, while laboratory-WDP dominated in the clay-sized fraction. Both organic carbon and dissolved organic carbon concentration in field-WDP runoff decreased with time during simulated rainfall events. The laboratory procedure used here for generating water-dispersible particles may not be suitable for studying runoff sediments in the field.

Growth and Yield of Tomatoes in Hairy Vetch-Incorporated and -Mulched Field.

For the establishment of a tomato cropping system with hairy vetch (Vicia villosa Roth), effectiveness of incorporation and mulch (no-till) of hairy vetch and nitrogen fertilizer effect on tomato (Lycopersicon esculentum Mill.) growth and yield were examined, compared with tomatoes conventionally grown in a tilled field without hairy vetch (conventionally-tilled field), in 1997 and 1999. The NO3- concentration in the petiole sap was highest 42 days after transplanting. Though it decreased to below 1, 000ppm in tomatoes grown in conventionally-tilled field 56 days after transplanting, it remained more than 2, 000ppm in tomatoes grown in the hairy vetch-incorporated field (HV-incorporated field) and hairy vetch-mulched field (HV-mulched field). The growth index (GI) was higher in the HV-incorporated and HV-mulched fields than in the conventionally-tilled field. No difference in GI was observed among the rates of nitrogen fertilizer applied to HV-incorporated and HV-mulched fields and GI in these fields reached the recommended levels for obtaining average tomato yield at the beginning of the harvest even with no nitrogen fertilizer. The NO3- concentration in the petiole sap and GI in HV-mulched field was larger than those in HV-incorporated field in early period of tomato growth. Higher total tomato yields were shown in HV-incorporated and HV-mulched fields than conventionally-tilled field in both years, especially, HV-mulched field added 0-60kg/ha nitrogen fertilizer showed similar yield obtained in conventionally-tilled field with 120kg/ha nitrogen fertilizer. Yield-increase was recognized in early and middle harvest. Though tomato yield increased as nitrogen fertilizer added in conventionally-tilled field, there were no differences in yield among rates of nitrogen fertilizers applied in HV-incorporated and HV-mulched fields. Hairy vetch used for incorporation and dead mulch contributed to the increase in NO3- concentration in the petiole sap, and promoted tomato growth and yield, especially in HV-mulched field, compared with the conventionally-tilled field. There is a possibility to reduce the nitrogen fertilizer in the tomato cropping system with hairy vetch-incorporation and hairy vetch-mulch.

Prevalence of Sclerotinia Stem Rot of Soybeans in the North-Central United States in Relation to Tillage, Climate, and Latitudinal Positions

ABSTRACT Since the early 1990s, Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, has caused considerable damage to soybean production in the north-central United States. To determine the extent of its distribution and associated factors, investigations were conducted in 1995 and 1996 in Illinois, Iowa, Minnesota, Missouri, and Ohio. Investigations also were conducted in 1997 and 1998 in Iowa, Minnesota, and Missouri. In each state, soybean fields were randomly selected in collaboration with the National Agricultural Statistics Service. From each field, 20 soybean stems 20 cm long (from the base) in 1995 and 1996 and full-length stems in 1997 and 1998 were sampled in a zigzag pattern. During the 4-year period, stem samples were collected from 1,983 fields and assessed for the presence or absence of the disease. Of the five states, Sclerotinia stem rot was most prevalent in north-central Iowa and southern Minnesota. Sclerotinia stem rot was not detected in Missouri during the 4-year investigation period. The disease was most prevalent in 1996 and least prevalent in 1995. The prevalence of the disease was strongly related to cumulative departures from normal maximum and minimum temperatures in July and August. The disease was more prevalent when yearly temperatures were below normal than when they were above normal. In 1996, a year with a cooler-than-normal summer, the disease was detected farther south than in 1995. In both years, the prevalence of the disease was exponentially related to latitudinal positions of the fields (R(2) = 0.93 and 0.83 for 1995 and 1996, respectively) reflecting the effect of the north-south variations in temperature. During the 4-year period, there was no relationship between precipitation and the prevalence of the disease. The lack of relationship may suggest that there was no shortage of moisture since it is one of the primary factors for disease development. The prevalence of Sclerotinia stem rot was less in no-till than in minimum-till or conventional-till fields (P = 0.001 and 0.007, respectively) and greater in minimum-till than in conventional-till fields (P = 0.07). Fields that had Sclerotinia stem rot, however, did not differ in incidence of the disease regardless of the tillage system.

Depth of seedling recruitment of five weed species measured in situ in conventional- and zero-tillage fields

Differences in the depth of weed seedling recruitment due to agronomic management practices, such as reduced tillage, have implications for weed competitive ability and management strategies. Depth of seedling recruitment of Avena fatua, Triticum aestivum, Setaria viridis, Polygonum convolvulus, and Echinochloa crus-galli was measured in situ in 1997 and 1998 prior to seeding (preseeding) and before in-crop spraying (prespray) in a total of 44 zero-tillage and 44 conventional-tillage fields located across approximately 3 million ha of southern Manitoba, Canada. For the monocot species, depth of recruitment was measured from the soil surface to the intact seed coats, which marked the point of germination. For P. convolvulus, a dicot, greenhouse studies were conducted prior to sampling in the field to identify a reliable morphological marker indicating the point of germination. For all species, mean recruitment depth was found to be significantly shallower in zero- vs. conventional-tillage fields and significantly shallower in the preseeding vs. the prespray period. There were relatively few differences in mean recruitment depth among weed species. Within a sampling period and tillage system, for example, the greatest difference in mean recruitment depth between species was less than 1.2 cm, and the maximum mean recruitment depth across species, sampling times, and tillage practice was very shallow (less than 4.2 cm). Locating weed seedling recruitment depth is the first step in characterizing weed seedling recruitment microsites. Results indicate this information should be specific to tillage and sampling time.

Regional Assessment of Soybean Brown Stem Rot, Phytophthora sojae, and Heterodera glycines Using Area-Frame Sampling: Prevalence and Effects of Tillage

ABSTRACT The prevalence of brown stem rot (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae in the north central United States was investigated during the fall of 1995 and 1996. Soybean fields were randomly selected using an area-frame sampling design in collaboration with the National Agricultural Statistics Service. Soil and soybean stem samples, along with tillage information, were collected from 1,462 fields in Illinois, Iowa, Minnesota, Missouri, and Ohio. An additional 275 soil samples collected from Indiana were assessed for H. glycines. For each field, the incidence and prevalence of brown stem rot was assessed in 20 soybean stem pieces. The prevalence and recovery (expressed as the percentage of leaf disks colonized) of P. sojae and the prevalence and population densities of H. glycines were determined from the soil samples. The prevalence of brown stem rot ranged from 28% in Missouri to 73% in Illinois; 68 and 72% of the fields in Minnesota and Iowa, respectively, showed symptomatic samples. The incidence of brown stem rot was greater in conservation-till than in conventional-till fields in all states except Minnesota, which had few no-till fields. P. sojae was detected in two-thirds of the soybean fields in Ohio and Minnesota, whereas 63, 55, and 41% of the fields in Iowa, Missouri, and Illinois, respectively, were infested with the pathogen. The recovery rates of P. sojae were significantly greater (P </= 0.05) in conservation-till than in conventional-till fields in all states except Iowa. H. glycines was detected in 83% of the soybean fields in Illinois, 74% in Iowa, 71% in Missouri, 60% in Ohio, 54% in Minnesota, and 47% in Indiana. Both the prevalence and population densities of H. glycines were consistently greater in tilled than in no-till fields in all states for which tillage information was available.

Effect of Tillage Practices on Vertical Distribution of Phytophthora sojae.

The vertical distribution of Phytophthora sojae was investigated in soil samples collected in the spring of 1994 from soybean fields at 62 locations in Illinois, Indiana, Iowa, and Minnesota. In the fall of 1995, soil samples were collected from 18 additional locations in Illinois and Iowa. Each location consisted of a pair of no-till and conventional-till fields, and soil samples were collected from arbitrarily selected locations in each field at 0- to 7.5-cm and 7.5- to 15-cm depths. Separate intensive sampling was made in the spring of 1995 from two pairs of adjacent no-till and conventional-till fields at the Iowa State University Northeast Research Farm, in which samples were collected from 0- to 30-cm depth in increments of 5 cm. Samples were assayed for P. sojae with the use of a leaf-disk bioassay. In the 1994 regional samples, there was greater recovery of P. sojae (P ≤ 0.05) at 0- to 7.5-cm depth in the no-till samples than in the conventional-till samples for all states except Minnesota. The fall 1995 samples from Illinois followed a similar trend (P = 0.05); whereas samples from Iowa showed no significant difference between tillage systems. At depths greater than 7.5 cm, there was generally no difference in detection frequency of P. sojae between tillage systems. Samples from the Northeast Research Farm followed patterns of vertical distribution similar to those of the regional samples. In no-till fields, the detection frequency of P. sojae was greatest near the soil surface; two to three times greater than that of the conventional-till fields at this depth. In the conventional-till fields, however, the frequency of recovery peaked at 20 cm and was comparable at these depths to those of no-till fields. There was a positive correlation between the percentage of leaf disks colonized and residue dry weights in the no-till fields (r = 0.84, P = 0.04; and r = 0.86, P = 0.03) but not in the conventional-till fields (r = -0.06, P = 0.90; and r = -0.60, P = 0.17). The recovery of P. sojae in greater frequency near the soil surface in no-till fields than in conventional-till fields suggests that the potential for damping-off may be greater in no-till fields than in conventional-till fields.

Number of Samples Required for the Estimation of Residual Soil Nitrate-Nitrogen: a Risk Based Analysis

A field experiment was conducted to determine the number of soil samples required to estimate the average residual soil nitrate (NO3 -) in a given field under no-till and conventional tillage conditions. Four soil sampling devices (a 20.3-cm power earth auger, a 5.1-cm hand earth auger, a 3.2-cm soil probe, and a 1.9-cm soil probe) were used to collect soil samples from 35 locations each within the conventionally tilled and no-till fields. Soil samples were analyzed for soil water contents and NO3 - concentrations in the soil for various depths. Simple graphs and tables were constructed which could be used by farmers and other professionals for estimating the average residual soil NO3 - contents at a given confidence level or with a certain degree of risk. The confidence interval was taken as the difference between the highest and lowest value of the quartile range of the observed data. The results of this study indicated that the number of soil samples required to estimate the average residual soil NO3 - contents increased as the degree of risk decreased. This study also indicated that the number of soil samples required for making a reasonable estimate of the residual soil NO3 - contents were greater for a no-till field compared with the conventional tillage field.

Population dynamics of Enchytraeidae (Oligochaeta) in different agricultural systems

Organic matter and abiotic conditions seem to influence distribution patterns of Enchytraeidae. In this study effects of changes in management practices on population dynamics of enchytraeids were determined. At two sites (in Athens and Griffin, GA) parts of a fescue (FE) field were converted into conventional tillage (CT) and no-tillage (NT) plots and changes in densities and depth distribution of enchytraeids were followed for 3 years. A site at Watkinsville, containing various soil textures and characterised by very low organic carbon content, which was converted into no-tillage 4 years earlier, was also sampled. Significant reductions in enchytraeid densities, after conversion of fescue into CT, were only found at Griffin. The management practices affected the vertical distribution of enchytraeids. In fescue and NT more enchytraeids were found in the 0–5cm than in the 5–15cm layer. In conventional tillage fields enchytraeids were more evenly distributed over the profile or more abundant in the 5–15cm layer. Management also affected the timing of population dynamics in the different plots. At two sample dates high abundances were found in CT plots only, not in any of the other plots. Enchytraeids were larger at Athens than at Griffin and Watkinsville and contained more soil particles in their gut. At Athens enchytraeids will presumably contribute more to the development of soil structure than at the other sites. We conclude that management affects vertical enchytraeid distributions in soil and changes the timing of population dynamics.

Earthworm populations and species distributions under no-till and conventional tillage in Indiana and Illinois

Earthworms often play an important role in maintaining or improving soil physical conditions, and earthworm populations often increase under reduced tillage systems. The objective of our study was to determine earthworm populations and species distributions under long-term no-till vs conventional tillage on a variety of soil types in the states of Indiana and Illinois, U.S.A. Fourteen paired sites were located on farmers' fields. Each paired site consisted of a no-till and conventional tillage field on the same soil type, located as close together as possible. Fields were in corn ( Zea mays L.)-soybean ( Glycine max) rotation, and earthworm counts were made in the spring following a soybean crop. Populations of shallow-dwelling earthworms (endogees) ranged from 2 to 343 earthworms per m −2. Of the 14 paired sites, eight sites had higher earthworm populations in no-till than conventional, four sites had roughly equal populations in both systems, and two sites had slightly lower populations in no-till than conventional. At most sites, shallow-dwelling species were dominated by Apporectodea tuberculata and A. trapezoides. Some of the sites also had significant populations of Lumbricus rubellus. The presence or absence of significant L. terrestris populations was noted by observing middens. Nine no-till and three conventional sites showed significant activity of L. terrestris. Implications for tillage management and the need for additional applied research are discussed.

EVALUATION OF A LABORATORY INVERSE METHOD FOR DETERMINING UNSATURATED HYDRAULIC PROPERTIES OF A SOIL UNDER DIFFERENT TILLAGE PRACTICES

Information about soil hydraulic properties and changes in the brought about by agricultural practices is essential in the development and use of models of catchment hydrology. The objectives of this study were to examine the extent to which different tillage practices affect the magnitude and variability of the hydraulic properties of a clay loam and to evaluate the effectiveness of a laboratory inverse method employed for characterizing the soil from the hydraulic point of view. The field work was conducted at an experimental farm located in the Agri River basin (Italy), selected as a target area for application of recently developed distributed models at basin scale. Undisturbed vertical soil samples (cores) were collected from the top layer of no-till and conventional-till field plots. The laboratory inverse method simultaneously determined relationships of water retention, θ (h), and hydraulic conductivity, k (θ), from an evaporation experiment using a parameter estimation technique. This method was developed with the aim of reducing experimental efforts without significantly lowering accuracy in parameter estimates. A Crank-Nicolson type finite-difference solution of Richards' equation was coupled with a nonlinear optimization problem to estimate unknown parameters in the closed-form analytical relations employed in this study for describing soil hydraulic properties. Comparisons with laboratory-measured saturated hydraulic conductivity and soil water retention data obtained for a group of soil cores by a sand-kaolin box apparatus demonstrate the applicability and accuracy of the proposed inverse method. Overall, the results of hydraulic-property characterization for the soil at the experimental farm reveal no significant differences among tillage treatments. In addition, as a general rule, a progressive annulment of tillage effects on structure and hydraulic properties of soil is observed with time.

Species and abundance of cutworms (Noctuidae) and their parasitoids in conservation and conventional tillage fields

The density of cutworm larvae (Noctuidae) was determined in fields under minimum and conventional tillage practices in Manitoba, Canada. Larval densities were based on area samples taken in the fields every spring from 1983 to 1990. During this period cutworm densities were well below the level of economic damage to crops. The results of the study provided information on the effects of tillage practices on cutworm abundance and species diversity during a period of endemic populations. Larvae were more abundant in fields under minimum tillage than conventional tillage practices. The most damaging pest cutworm in Manitoba, Euxoa ochrogaster (Gn.) (redbacked cutworm), two species often associated with this species in outbreaks, Euxoa messoria (Harr.) (darksided cutworm), and Feltia jaculifera (Gn.), and a non-pest species, Lacinipolia renigera (Steph.) (bristly cutworm), made up 63% of the larvae from minimum- and 51% of those from conventional-tillage fields. There are significantly more cutworm larvae in minimum-tillage fields, owing to larger numbers of L. renigera and other non-pest species, than in conventional-tillage fields. The percentage parasitism of cutworm larvae was not significantly different between tillage practices. Cutworm abundance in a field was related to the crop of the previous year, with larger numbers of larvae associated with broadleaf crops than with cereal crops. Different species had different patterns of abundance during the 8-year study and different relationships to tillage and crop. Minimum-tillage practices were not related to increased crop loss from cutworms during the study period, but were associated with greater species diversity of both cutworms and their parasitoids. This greater diversity was accompanied by less interfield variability in cutworm numbers, suggesting a more stable ecosystem in which outbreaks would be less common.

Relationships between soil porosity, root development and soil enzyme activity in cultivated soils

Porosity and pore size distribution from thin sections, prepared from undisturbed Ap horizon samples taken from a zero- versus conventional-tillage field experiment, were analysed by means of a Quantimet 720 image analysing computer. The length and the size distribution of plant roots were determined using the same image analyzer. Soil urease and phosphatase activity in soil samples from the plots of this field experiment was also determined. Total porosity was significantly higher in conventionally tilled plots, but the proportion of pores ranging from 30 to 500 μm in equivalent pore diameter, which are considered the most important both in soil-water-plant relationships and in the maintenance of a good soil structure, was higher in no-tilled plots. Root development showed a strict relationship with the presence of smaller pores which were more numerous in no-tilled plots. Enzyme activity was also higher in these plots than in the conventionally tilled plots. The relationships of such enzyme activities and the various pore size classes in each type of soil showed a positive common trend between the two enzyme activities and the percentage area of pores ranging from 30 to 200 μm in equivalent pore diameter. A significant correlation was observed between the degree of porosity in this range and urease activity.

Preferential Solute Transport through Macropores in Large Undisturbed Saturated Soil Columns

AbstractSix large undisturbed soil columns (61 cm in length, 15 cm in diameter) were collected from three no‐till and three conventional tillage field plots. The side walls of these columns were sealed with either plaster of paris or paraffin wax to eliminate wall effects. After these columns were saturated with CaSO4 (0.005 M), CaCl2 (0.005 M) was applied at the surface and the effluent was collected at the bottom. Effluent samples were later analyzed for Cl (chloride) concentrations. The Cl breakthrough‐curves (relative Cl concentration vs. relative pore volume) were developed and the degree of preferential flow analyzed. Shape and other breakthrough‐curve parameters, such as immobile pore‐water fraction and initial breakthrough, indicated the occurrence of preferential flow through all columns. The degree of preferential flow, however, was greater in no‐till than in conventional tillage columns (average immobile pore‐water fraction was 56% for no‐till and 49% for conventional tillage columns).

PLIERS: Pesticide Losses in Erosion and Runoff Simulator

ABSTRACT A field scale model for predicting surface losses of pesticides (Pesticide Losses In Erosion and Runoff Simulator, PLIERS) is described. PLIERS accounts for pesticide losses by degradation and volatization, washoff from vegetative soil cover, and adorption and desorption to and from soil particles, and is dissolved and adsorbed forms in surface runoff. Hydrologic data are generated by the comprehensive watershed model, FESHM, which contains an enhanced sediment detachment and transport algorithm. PLIERS uses first order rate equations to describe pesticide washoff and degradation and volatilization. The adsorption of pesticides to individual particle size classes is estimated using the Freundlich equation. PLIERS was validated using atrazine and 2,4-D losses from no-till and conventionally-tilled field plots. These plots were located on a Groseclose silt loam soil and had either 0 or 750 kg/ha crop residue. Agreement between the predicted and observed data was satisfactory for both pesticides. PLIERS shows potential for use as a planning tool since it can be used with any comprehensive hydrologic model and is able to predict pesticide losses under various field conditions.

Control of Two Spotted Mite in Soybeans, 1985

Abstract Forrest variety soybeans were planted into a conventional tillage field on the grounds of the University of Delaware experiment station near Georgetown, DE on 27 Jun. Plots consisted of a single row, 25 ft long on 30 inch centers bordered on both sides by guard rows. Six insecticide treatments replicated 5 times each were arranged in a randomized complete block design. Pre- and post-treatment mite populations were assessed by randomly picking 5 leaves from each plot and processing these through a Leedom engineering� mite brushing machine. Mite counts were then made using a binocular dissecting microscope set at 6x. All treatments were applied 23 Jul with a CO2 propelled backpack sprayer using two R and D Sprayer Inc. HC 12 hollow cone nozzles delivering a total of 37 gal per acre at 40 psi.

Field Corn, Pre-Emergence Treatments for Northern and Western Corn Rootworm Control, 1986

Abstract Six granular insecticides were evaluated in Washington Co, VA, for control of the northern and western corn rootworm in conventional-till field corn when applied as a preemergence treatment at planting. Pioneer 3147 field corn was planted conventional-till in 32 inch rows on 28 Apr. Plots were established in a randomized complete block design 4 rows × 50 ft × 4 replicates per treatment. The insecticides were applied with a hand held granular applicator over the tops of the rows. The insecticides were applied 28 Apr, at planting. One application was made over each row to assure uniform coverage. The corn rootworm damage per plot was estimated by digging and washing the roots and rating the amount of damage (from 1 to 6) for 10 plants taken from the 2 center rows of each plot on 29 Jul. Yield data was collected for ensilage by whole stalk harvest, of 40 row ft from the 2 center rows on 14 Sep. Damage and yield data were subjected to analysis of variance.