Results and discussion Directory UMM :Data Elmu:jurnal:E:European Journal of Agronomy:Vol11.Issue3-4.Nov1999:

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

et al. 1996, who reported the highest concen- trations in June after atrazine application and 3.1. Atrazine residue concentrations: general trend lowest concentrations after November. The rapid increase in atrazine residue in June Atrazine residues were never detected in the probably resulted from preferential flow through samples analysed for the mechanical weeding treat- macropores. Once transported, atrazine residue ment. This result indicated that: 1 no atrazine applied as a spray may be concentrated on or near residue remained in the soil solution before the field investigations; 2 grass alley ways were effec- the surfaces of the large pores where they are again Table 2 Machinery costs work sheet Commercial value Use Cost F Euros F Euros Work short 60 9.1h Tractor 75 HP 2 wheel drive 170 000 25875 700 hyear 64 9.7h Six-row hoe with band sprayer 1.5 hah 65 000 9900 150 hayear 70 10.7ha 12 m sprayer 3 hah 70 000 10650 150 hayear 75 11.4ha Atraphyt 50 atrazine 20.9 3.2l 3 lha 63 9.6ha Lentagran 45 pyridate 156 23.7l 2 lha 312 47.5ha 221 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 Fig. 2. Dynamics of atrazine residue concentrations mgl in porous cups according to the method of atrazine application [average atrazine residue concentrations mgl : broadcast application: 1.95; band application+mechanical weeding: 0.52]. susceptible to transport by additional rainfall cup, was larger than the 20 cm band over the corn row which received atrazine. Consequently, suction Isensee et al., 1990. This assumption seemed relevant because we observed numerous macro- cup sampled water came from with in-row and between-row which did not receive atrazine, 3 pores due to earthworms and clay desiccation. Such rapid leaching through macropores has also the atrazine residue movement in the soil was not vertical and only a part of the residues could be been observed by Baer et al. 1992 and Graham et al. 1992. sampled by the suction cup. This hypothesis is consistent with Sadeghi and Isensee 1992 who Atrazine residue identifications several months after atrazine aplication may be explained by studied the spatial distribution of atrazine in soil and found that the atrazine movement in soil is migration through the microporous structure and by adsorptiondesorption on soil particles. Such not vertical. The spatial distribution of atrazine is extremely variable and depends on tillage practice, slow leaching has also been observed by Buhler et al. 1993. rainfall timing and rainfall distribution. This hypothesis also agree with Heddadj 1996 who reported atrazine movement from with in-row to 3.2. Atrazine residue concentrations: comparison between broadcast and band treatment between with row after a band treatment. Large differences appeared between the data for the two weed treatments for concentration levels. 3.3. Corn yield Average concentration of atrazine from band treat- ment was about 73 less than from broadcast There were no differences between treatments at harvest in 1995, but differences were observed treatment Fig. 2. Factors that may have contrib- uted to the lower concentration of atrazine residue in 1996 Table 3. Corn yields were lower in mechanical weeding alone compared with the two in the band treatment are: 1 the lower amount of applied atrazine due to the banded application other treatments. Differences between those treat- ments were entirely attributable to the weed pop- only a 20 cm band over the corn row received atrazine, 2 the recharge area of the suction cup, ulation for the mechanical weeding treatment. Those results were similar to other studies Mulder i.e. the space in which the water flows towards the 222 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 Table 3 Corn yield according to weeding method tha a Year Weeding method Broadcast application Band application+mechanical weeding Mechanical weeding Average yield and standard deviation 1995 13.16 0.99 a 13.68 1.02 a 13.19 0.37 a 1996 16.75 1.34 a 16.15 1.79 a 7.03 0.88 a 1997 14.41 1.22 a 13.60 1.26 a – a Means followed by the same letter do not differ P=0.05, as deduced from the Newman–Keuls least difference test. Yields were not measured in the mechanical weeding treatment in 1997. and Doll, 1993; Pleasant et al., 1994; Seconda, combined herbicide plus mechanical weeding. The weed cover ranged from 16 to 20 . 1994; Imgraben and Juncker-Schwing, 1995. 3.4. Weed control 3.4.3. Weed cover distribution In 1995 and 1996, the in-row weed cover was higher, compared with the between-row cover, in 3.4.1. Composition of the weed population Before the experiment, the weed population was the mechanical weeding alone Table 5. This emphasized the difficulty of controlling weeds in essentially composed of Poa annua L., Poa trivialis L., Alopecurus myosuroides Huds., Medicago sativa the corn row with conventional cultivation equip- ment. Band application of herbicide over the row L., Taraxacum officinalis L., Capsella bursa pastoris Moench., Veronica hederifolia L., Veronica persica eliminated this problem as there were no differ- ences in the distribution of weed cover in any plots Poir., Lamium purpureum L. and Rumex crispus L. There were no differences in composition of the of the band treatment. These results agree with those of Pleasant et al. 1994, who reported the weed population among plots. Throughout the 3 years of the experiment, the weed population has efficiency of combining cultivation with banded herbicides to control weeds in corn. changed Table 4, but there were no differences in composition in the weed population between treatments. 3.5. Weeding control cost Armstrong et al. 1968 indicated that if only 3.4.2. Weed cover Weed cover in 1995 ranged from 14 to 58 yield and costs were considered and mechanical weeding was timely, mechanical weeding methods with differences between weed control treatments. Weed cover was much higher in the plot with were more profitable than chemical weeding. When the risk of untimely mechanical weeding was con- mechanical weeding alone compared with the two other treatments. Among those two treaments, sidered, banded atrazine with one cultivation gave the highest return Mulder and Doll, 1993. In there were no differences in weed cover. The weed pressure in 1996 was higher than that our research, corn yields were equivalent for the chemical weeding method and for the banded of the previous year, ranging from 16 to 73 cover. Plots with cultivation alone averaged more atrazine with one cultivation, and the weeding cost was lower for the combined method Table 6. than 70 cover, compared with less than 21 in the treatment with herbicide or a combination of This suggested that the combined weeding method gave higher economic returns than the broadcast herbicides plus mechanical weeding. In 1997, there were no differences in weed cover method. However, with the combined weeding method, the in-field time requirements increase. between plots with herbicide alone or those that 223 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 Table 4 Weed changes among years on mechanical weeding plots a Weed 1995 1996 1997 Spring Autumn Spring Autumn Spring Autumn Alopecurus myosuroides Huds. ++ + ++ + ++ + Anagallis arvensis L ++ + ++ + ++ + Capsella bursa pastoris Moench. ++ + + + + + Chenopodium album L. + +++ +++ +++ +++ +++ Fumaria officinalis L. + +++ ++ +++ +++ +++ Lamium purpureum L. + + ++ + ++ + Matricaria recutita L. + ++ ++ +++ ++ +++ Medicago sativa L. +++ + + + Poa annua L. +++ + + + + + Poa trivialis L. + + + + + + Rumex cripus L. ++ + + + + + Stellaria media L. + + +++ + ++ + Taraxacum officinalis L. + + + Veronica hederifolia L. ++ ++ ++ + ++ + Veronica persica Poir. ++ ++ ++ + ++ + a Relative abundance: 0, none; +, some; ++, presence; +++, coverage. Table 5 Visual in-row, between-row and plot weed cover between weeding methods a Localisation Weeding method Broadcast application Band application+mechanical weeding percentage weed cover Mechanical weeding 1995 1996 1997 1995 1996 1997 1995 1996 In-row 14 a 15 a 13 a 14 a 15 a 18 a 67 c 73 c Between row 14 a 16 a 16 a 24 a 24 a 22 a 43 b 70 c Plot 14 a 16 a 16 a 20 a 21 a 20 a 58 bc 73 c a Means followed by the same letter do not differ P=0.05, as deduced by the Newman–Keuls least difference test. Table 6 Operational costs estimated for the three weeding methods Broadcast application Band application+mechanical weeding Mechanical weeding Field time 20 minha 90 minha 60 minha Number of runs Two broadcast applications One band application+one mechanical weeding Two mechanical weeding Work force 40 F 6 Eurosha 150 F 23 Eurosha 120 F 18 Eurosha Draught 43 F 6.5 Eurosha 160 F 24 Eurosha 128 F 19 Eurosha Herbicide application 150 F 23 Eurosha 70 F 11 Eurosha 0 Fha Herbicides 372 F 57 Eurosha 99 F 15 Eurosha 0 Fha Mechanical weeding 0 Fha 70 F 11 Eurosha 140 F 21 Eurosha Total 605 F 92.5 Eurosha 549 F 84 Eurosha 388 F 58 Eurosha 224 L. Heydel et al. European Journal of Agronomy 11 1999 217–225 sons of mechanical and chemical weed control. Weed Sci.

4. Conclusions