Introduction chemicals Nicholls et al., 1982; Villeneuve et al.,

European Journal of Agronomy 11 1999 217–225 www.elsevier.comlocateeja Reducing atrazine leaching by integrating reduced herbicide use with mechanical weeding in corn Zea mays L. Heydel a,b, M. Benoit a,, M. Schiavon b a INRA Station SAD, Domaine du Joly, BP 29, Mirecourt Cedex, France b Ecole Nationale Supe´rieure d’Agronomie et des Industries Alimentaires, B.P. 172, 54505, Vandoeuvre-Le`s-Nancy, France Accepted 10 May 1999 Abstract Concern about the effects of pesticides on the environment and the desire to reduce purchased inputs are stimuli to reduce herbicide use. Field research was conducted for three growing seasons to compare the chemical contamination and effectiveness of three weed management practices. Weed control treatments included application of a herbicide mixture of 1.5 kg ai ha−1 of atrazine plus 0.9 kg ai ha−1 of pyridate, this mixture being broadcast alone or band- applied in combination with mechanical weeding, and mechanical weeding alone. The results show that it is possible to decrease the amount of atrazine residue in soil with the band-applied treatment. Such a method is very attractive because crop yields were not decreased, at least in the short run. However, we do not yet know the long-term efficiency of this method regarding groundwater quality, weed population dynamic and crop yield. Further work is therefore needed to assess the long-term impact of this weeding method. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Alternative weeding practices; Atrazine leaching; Corn weeds; Corn yields

1. Introduction chemicals Nicholls et al., 1982; Villeneuve et al.,

1990; Barriuso et al., 1993. Two factors influence the amount of atrazine Atrazine is a widely used, soil applied herbicide leaching into a watershed: the leaching per field that provides excellent weed control in corn Zea and the area of corn in the watershed. The area mays L.. Perhaps due to its persistence in soil and of corn is linked to the total area of corn in the extensive use for the past 30 years, atrazine has farms and to its location in the farm territory. been detected in groundwater Babut et al, 1992, Modifications in farm management are very 1996; Adamski and Pugh, 1996; Heydel, 1998. difficult if the farmer practices have to be changed. In France during the last 30 years, the pro- Therefore, we evaluated the potential reduction of duction of corn has increased by a factor of 16, atrazine leaching by decreasing the atrazine residue due to increases in areas planted and the yields concentration per field. per unit area. There are relatively few published In the studied area, the area of corn has reports on field studies of herbicide residue in increased rapidly from 1970 to 1985, and the groundwater despite the widespread use of these amount of applied atrazine per hectare was stable until 1992 Heydel, et al., 1997. Since 1992, the Corresponding author. Tel.: +33-3-2938-5500; amount of applied atrazine decreased from 2.5 to fax: +33-3-2938-5519. E-mail address: benoitmirecourt.inra.fr M. Benoit 1.5 lha. Thus, two questions have to be solved: 1161-030199 – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S 1 1 6 1 -0 3 0 1 9 9 0 0 03 3 - 7 218 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 1 what level of contamination is created by these Four replications were carried out for the broad- cast and the band treatment, but only three carried agricultural methods, and 2 how can we decrease the atrazine residue concentration per field with out done for the mechanical weeding alone. Treatments were randomly assigned to each plot. innovative methods? The objective of this research was to compare The experiment ran from 1995 to 1997 for the broadcast and the band treatment, but only in the effects of three weed control strategies on soil water contamination, yields, weed population and 1995 and 1996 for the mechanical weeding alone. The amount of weeds was so high in the mechan- weed control cost. Control strategies included: 1 herbicide alone, 2 mechanical weeding alone ical weeding treatment that we could not execute this treatment in 1997. between-row cultivation, and 3 band herbicide applications plus mechanical weeding. 2.2. Corn culture and treatment Each year, the plots were planted with corn 2. Materials and methods Zea mays L. in May. Corn was sown with a row spacing of 75 cm. Corn residue was left on all 2.1. Site description plots during the winter. They were soil-incorpo- rated each year in the early spring when the plots The research field was located at the INRA’s National Institute of Agricultural Research had been chisel-ploughed. Pesticide treatments were surface-applied, as a Mirecourt station about 50 km south of Nancy Meurthe et Moselle, France. commercial formulation, on the same date for each treatment. After emergence, herbicides were The field, with no slope, is a brown soil. Table 1lists the soil’s physico-chemical characteris- applied in 145 lha of water. For the broadcast treatment, a 12 m sprayer with 8003 flat fan nozzles tics. This soil type is one of the predominant agricultural soils in north-easthern France. TeeJet was used. For the band herbicide applica- tions associated with mechanical weeding, a six- Precipitation data were recorded at a meteoro- logical station near about 100 m the research row Schmotzer hoe with flat fan nozzles 8003E TeeJet spaced at 75 cm was used. Herbicides were field. The annual rainfall is 980 mm 30 years average, and the water surplus, i.e. rainfall minus applied within a 20 cm band centered on the corn row. The normal rate of herbicide consisted of evapotranspiration, is 275 mm per year 30 years average. 1.5 kg aiha of atrazine and 0.9 kg aiha of pyri- date. Herbicide use was reduced by 73 with the The field had a 5 year history of alfalfa Medicago sativa L. without any atrazine applica- band application. The mechanical weeding treat- ment was done with the same six-row Schmotzer tion. In 1995, the field site was chisel-ploughed in early spring and divided into 11 small plots, each hoe. Hoeing was scheduled by weed populations and corn heights two or three harrowings were 12 m wide by 20 m long. Grass alleyways 2 m wide were established around each plot. necessary. Table 1 Soil characteristics: particle size and organic carbon C Depth cm Partical-size distribution gkg Clay Fine silt Coarse silt Fine sand Coarse sand C 0–30 206 403 227 80 41 13.3 30–40 244 391 211 74 48 7 40–90 385 338 167 53 35 1.8 219 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 2.3. Soil water solution sampling and analysis added to the microplate wells coated with the anti- triazine antibody. After incubation for 30 min at room temperature while being shaken, the solid Each plot was equiped with three porous ceramic cups. Each comprised a ceramic cup residue was washed five times with distilled water. Then, 50 ml of substrate urea peroxide and 50 ml 63 mm in diameter, 90 mm long and 6 mm in thickness, extended with a PVC tube Nardeux of chromogen tetramethylbenzydine solution were added to each sample and left for 30 min at Company, France. Samplers were installed verti- cally with their ceramic parts at 80 cm depth. The room temperature while being shaken. The color- ation development was stopped by adding 50 mL device was completed by two tubes used to apply vacuum and to collect water samples on the field of sulfuric acid solution. The yellow color intensity was evaluated at 450 nm with a microplate reader. border. The porous ceramic cups were installed in the row after the sowing Fig. 1. Atrazine sample concentrations were determined to within 0.02–1 mgl by comparing the absor- After each rainfall event, the porous cups were purged, and a 0.7 bar vacuum was applied. Suction bances of samples to a linear regression log–logit standard curve prepared from atrazine standard was achieved within 48 h with decreasing vacuum. Soil water samples were then extracted, and the solution. Duplicates were made for each sample. volume of extracted water was measured. Samples smaller than 250 ml were discarded to avoid con- 2.4. Corn yields centration disturbance by the ceramic Perrin- Ganier et al., 1994, 1996. Water samples were Corn was hand-harvested and weighed. For each plot, ten corn plants and whole ear samples collected, and those obtained on the same plot were brought together and mixed. Then, they were were weighed, shelled and the grain reweighed to determine the shelling percentage. Moisture was transported to the laboratory and immediately frozen until analysis. The lack of soil moisture determined for plant and grain samples from each plot and yield adjusted for 30 moisture. prevented sample collection in some periods. Samples were analysed by the triazine immuno- assay developed by Transia-Diffchamb S.A. 2.5. Weed populations Ref. PE 0727. One hundred microliters of the enzyme–atrazine conjugate, either 100 ml of atra- Weed populations were estimated before ploughing, harvesting and before and after each zine standards or 100 ml of water samples, were Fig. 1. Recharge area of a suction cup. 220 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 weed treatment. Weeds were recorded by species tive in limiting pesticide transfer from one plot to and were further identified by location within the the others; 3 no other molecule interfered during plot. Those that fell within a 20 cm band centered atrazine residue dosage. on the corn-row were recorded as ‘in-row’ and all Atrazine residue concentrations measured in others as ‘between-row’. Three measurements were broadcast and band treatments using a porous taken per plot for each weed estimation. cup, throughout the 3 year study, are presented in Fig. 2. For each treatment, the concentrations were extremely variable. Indeed, they ranged from 0.02 2.6. Weeding control cost detection limit to 18 mgl; the highest values being observed 2–6 weeks after atrazine applications. Weeding costs were determined using a machinery costs work sheet Table 2 provided by These results are consistent with those of other the Bureau Commun du Machinisme Agricole researchers Jayachandran et al., 1994, who Krebs, 1997. Weeding time requirements were reported similar concentrations of atrazine residue evaluated by using the average speed observed on found in shallow groundwater systems. large fields. Despite the concentration variability, the gene- ral shapes of the two curves were similar: in June, after atrazine application, the concentrations of 2.7. Statistical analysis atrazine residue observed in the water samples Data were subjected to analysis of variance reached a peak. Then, they decreased gradually using the SAS glm procedure, which tested treat- until October or November. After that, they lev- ment effects and interaction of years. Means were eled off until the next atrazine application. compared by Fisher’s protected LSD at the 0.05 Therefore, two levels of atrazine residue concen- probabilty level. tration could be distinguished: 1 a higher level between June and October–November and 2 a lower level from November to the next atrazine application. These results agree with those of Tasli

3. Results and discussion