Allan R. Isensee

INFLUENCE OF RAINFALL INTENSITY AND CROP RESIDUE ON LEACHING OF ATRAZINE THROUGH INTACT NO-TILL SOIL CORES

Pesticide leaching may be affected by rainfall parameters and the amount and type of vegetation on the soil surface. This study was conducted to determine the effect of rainfall intensity and crop residue on the movement of [ring-14C]atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and bromide (Br) through no-till (NT) cores. Undisturbed soil cores (10 cm diameter by 8 cm depth) were taken from the surface horizon of a NT corn (Zea mays L.) field. The cores were surface treated with 1.3 kg ai ha−1 atrazine and 150 kg ha−1 of Br and subjected to simulated rainfall at 3, 6, 9, or 12 mm h−1. The amount of crop residue on the surface of another set of soil cores was adjusted to 0, 2000, 4000, and 8000 kg ha−1, then treated with atrazine and subjected to 9 mm h−1 of simulated rain. Overall, the transport of atrazine and Br were significantly (P < 0.01) affected by rainfall intensity. An average of 92% (Br) and 52% (atrazine) of the total amount applied was leached through the soil cores by 2 pore volumes (520 ml) of simulated rain applied at 12 mm h−1 compared with 61% for Br and 33% for atrazine at the 3-mm h−1 rate. Covering soil cores with 2000 or 8000 kg ha−1 of crop residue reduced atrazine leaching by 26 to 37%, respectively, compared with soil cores without crop residue. Soil cores covered with recently harvested vegetation reduced atrazine leaching by 39% compared with cores covered with aged crop residue.

Long-term effect of thj.age and rainfall on herbicide leaching to shallow groundwater

The interaction of conventional tillage (CT) and no-tillage (NT) crop production practices with rainfall on the movement of three herbicides into shallow groundwater was evaluated over 4 yr. Groundwater was sampled from unconfined (< 1.5m deep) and confined (<3 m and 4.5 to 11 m deep) monitoring wells in 1989–1992 and analyzed for atrazine, alachlor, and cyanazine . Pesticide concentrations were cyclical: residues were highest soon after application, declined during the growing season, then increased during winter recharge. Alachlor and cyanazine were at nondetectable levels within 3 mo after application. Atrazine residues, present in confined groundwater all year, ranged in concentration between 0.03 to 1.9 and 0.16 to 3.7 ug L−1 for the CT and NT plots, respectively. Herbicide residues were higher in unconfined (< 1.5 m deep) than confined (< 3 m deep) groundwater. Atrazine was sporadically detected in groundwater to 4.6 m, but not deeper. Lateral transport in confined groundwater to untreated areas was evident. The rapid movement of herbicides to groundwater with the first major rain after application suggest that preferential transport may be common. Results of this study also indicate that timing, amount and intensity of rainfall relative to pesticide application may be the primary factors governing pesticide leaching.

Influence of hairy vetch residue on atrazine and metolachlor soil solution concentration and weed emergence

Abstract High levels of cover-crop residue can suppress weed emergence and also can intercept preemergence herbicides and potentially reduce their effectiveness. This research was conducted in continuous no-tillage corn to compare the effect of residue from a hairy vetch cover crop with that of background crop residue on the soil solution concentration of atrazine and metolachlor and on the emergence of weeds with and without herbicide treatment. In a 3-yr field experiment, 5-cm-deep soil samples were taken and the weed density measured in paired microplots with and without herbicide at approximately weekly intervals after application of atrazine and metolachlor. High levels of residue were present in both treatments; the percentage of soil covered by residue ranged from 91 to 99 in the no–cover-crop treatment and from 99 to 100 in the hairy vetch treatment. Initial metolachlor concentration was lower and degradation rate higher in two of the 3 yr with a hairy vetch cover crop than without a cover crop. Cover-crop treatment had little effect on atrazine concentration or degradation. Annual grass weeds (predominantly fall panicum) were the major species in this field. Hairy vetch alone reduced grass emergence by 50 to 90%, and preemergence herbicides alone reduced emergence by 72 to 93% compared with the treatment without cover crop and herbicide. The combination of preemergence herbicides with hairy vetch provided only 24 to 61% control of grass weeds compared with control by hairy vetch alone and 23 to 52% compared with control by herbicide alone, suggesting an antagonism probably resulting from reduced metolachlor concentration by hairy vetch residue. Metolachlor with hairy vetch delayed emergence of weeds and reduced the concentration of metolachlor required to prevent emergence initiation compared with metolachlor without a cover crop. Nomenclature: Atrazine; metolachlor; fall panicum, Panicum dichotomiflorum Michx. PANDI; corn, Zea mays L.; hairy vetch, Vicia villosa Roth VICVI.

Influence of soil texture and tillage on herbicide transport

Two long-term no-till corn production studies, representing different soil texture, consistently showed higher leaching of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to groundwater in a silt loam soil than in a sandy loam soil. A laboratory leaching study was initiated using intact soil cores from the two sites to determine whether the soil texture could account for the observed differences. Six intact soil cores (16 cm dia by 20 cm high) were collected from a four-year old no-till corn plots at each of the two locations (ca. 25 km apart). All cores were mounted in funnels and the saturated hydraulic conductivity (Ksat) was measured. Three cores (from each soil texture) with the lowest Ksat were mixed and repacked. All cores were surface treated with 1.7 kg ai ha(-1) [ring-14C] atrazine, subjected to simulated rainfall at a constant 12 mm h(-1) intensity until nearly 3 pore volume of leachate was collected and analyzed for a total of 14C. On an average, nearly 40% more of atrazine was leached through the intact silt loam than the sandy loam soil cores. For both the intact and repacked cores, the initial atrazine leaching rates were higher in the silt loam than the sandy loam soils, indicating that macropore flow was a more prominent mechanism for atrazine leaching in the silt loam soil. A predominance of macropore flow in the silt loam soil, possibly due to greater aggregate stability, may account for the observed leaching patterns for both field and laboratory studies.

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.

EFFECT OF TILLAGE AGE ON HERBICIDE DISSIPATION: A SIDE-BY-SIDE COMPARISON USING MICROPLOTS

This study was designed to compare rates of herbicide dissipation and leaching in side-by-side microplots that have been under no-till and plow-till practices for various time periods. Microplots were established within eight field plots (0.1 to 0.25 ha) that had been in no-till for 1 or 4 years, re

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

Abstract 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.

Effect of tillage on atrazine bioavailability

Studies were conducted to determine atrazine sorption (partitioning), bioavailability (soil solution concentrations), and dissipation in the top 0 to 1.5, 1.5 to 3, and 3 to 5 cm of soil as a function of tillage. Paired microplots (plow-till vs no-till) were established in replicated long-term tilla

Impact of burn-down herbicides on atrazine washoff from vegetation

Abstract Crop residue and living vegetation in no-till fields can intercept large amounts of the pesticides applied at the time of planting. Previous studies have shown that the type of plant tissue intercepting the pesticide can affect the amount washed off this report compares the washoff characteristics of two cover crops with dead crop residue before and after treatment with burn-down herbicides. Laboratory studies were conducted to determine the effect of burn-down herbicides, paraquat (1,1′-dimethyl-4,4′-bipyridylium dichloride) and glyphosate (N-(phosphonomethyl)glycine) on washoff of atrazine (2-chloro-4-(ethylamio)-6-(isopropylamino)-s-triazine) from ryegrass ( Lolium perenne L.) and hairy vetch ( Vicia villosa Roth.). Ryegrass and hairy vetch were treated with paraquat and glyphosate and one or five days later 14 C-atrazine was applied. Ryegrass, hairy vetch and dead crop residue not treated with paraquat and glyphosate were included as controls. One day after application of atrazine, all treatments were subjected to 4.5 to 5 cm of simulated rainfall at 9 mm h −1 , leachate was collected and analyzed for atrazine. Atrazine washoff from hairy vetch, ryegrass and crop residue not treated with glyphosate or paraquat ranged from 29–37%, 43–49% and 70–75%, respectively, of the amount applied. Paraquat was more effective than glyphosate in increasing the amount of atrazine washoff in both ryegrass and hairy vetch. Washoff was increased when the time between application of the burn-down herbicides and atrazine was increased from one to five days, especially for the ryegrass treatments. Results indicate that availability of herbicides applied to no-till cropping systems may be significantly affected by type of vegetation and bum-down herbicide treatment.

Quantification of runoff in laboratory-scale chambers

Many of the variables that control transport of agrochemicals and pathogens in the field are difficult to measure because parameters such as slope, soil and plant conditions, and rainfall cannot be adequately controlled in the natural environment. This paper describes the design, construction, operation and performance of a system useful for studying surface transport of agrochemicals and pathogens under controlled slope, rainfall and soil conditions. A turntable is used to support and rotate 4 soil chambers under oscillating dripper units capable of simulating rainfall intensities from 1 to 43 mm h-1. Chambers (35 x 100 x 18 cm i.d.) were constructed with an adjustable height discharge gate to collect runoff and three drains to collect leachate. Height adjustable platforms were constructed to support and elevate the chambers up to 20% slope. The chambers were uniformly packed with 35 to 45 kg of soil (bulk density 1.18-1.27 g cm-3) and initially saturated with two low intensity rain events. The coefficient of variation of the rainfall delivery over a range of 5 to 43 mm h-1 averaged 7.5%. An experiment to determine the variability between chambers in runoff amount and uniformity indicated that at least one runoff-equilibration cycle is needed to obtain steady state conditions for conducting runoff transport evaluations. Another experiment conducted to evaluate atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] runoff under simulated crop-residue covered vs bare soil conditions indicated six times more runoff from bare than crop residue covered soil. The system is capable of precise application of simulated rain, the simultaneous collection of runoff and leachate at slopes up to 20% and can be easily modified to meet a wide range of research parameters.