Resultados

GBZs have been studied and used since 1965, mostly in the U.S., to reduce erosion and nutrient transfer in runoff. Historical data show that buffer strips increase water infiltration, reduce nutrient transport from feedlots and trap suspended solids via filtration and sedimentation in the strips. As pesticides in runoff are both in a soluble form and a particulate form (adsorbed to fine clay particles and organic matter), it was not obvious that GBZs would reduce pesticide transfer in runoff in addition to limiting erosion. Asmussen et al. (1977) and Rhode et al. (1980) reported that a 24.4 m grassed waterway reduced 2,4 D (soluble) and trifluralin (strongly adsorbed particulate) losses in runoff by an average 70 and 94%, respectively.

In France, studies have been conducted since 1992 by ITCF and Cemagref (in collaboration with Rhône-Poulenc Agro and the Ministry of Agriculture) to evaluate the effectiveness of GBZs in restricting pesticide transfer in runoff. Pesticides with different environmental behaviours were selected (Table 1).

Table 1. Physico-chemical properties of pesticides applied

IPU DFF lindane atrazine

Water solubility 65 0.05 7 33

(mg litre-1₎a

Koc (cm3 g-1)a 120 1990 1100 100

half-life (days)a _{12-32 175-294 100-120 60-70}

a _{: from Rhône-Poulenc Agro}

Koc : Organic carbon partition coefficient

The first study, started in 1992 at ITCF’s La Jaillière experimental farm in Brittany, aimed to determine the effectiveness of a 5.7 m and a 11.1 m GBZ in reducing isoproturon (IPU) and diflufenican (DFF) transfer in runoff generated on small plots (125 m2_{). Since 1993, additional experimental sites were}

implemented at ITCF’s La Jaillière, Bignan and Plélo research farms in Brittany for two purposes: to assess the effectiveness of 6, 12 and 18 m grassed strips at reducing lindane, atrazine and its metabolites and to confirm preliminary results obtained with IPU and DFF in a range of soil and cropping conditions. Runoff in these experiments was generated from larger cultivated plots (250 m2_).

Variations in runoff volume and residue concentration observed in the different experimental conditions provide an overview of GBZ effectiveness (Pattyet al., 1995a). Runoff volume was reduced by 8 to 99.9% within the GBZs and 69 to 100% of suspended solids were retained. Lindane and

atrazine were reduced by 72 to 100% and by 44 to 100% respectively. The atrazine metabolites were reduced by 45 to 100% within the GBZs. Finally, IPU and DFF were reduced by 75 to 99% and by 68 to 97% respectively. GBZs were shown to be effective in reducing pesticide transfer in runoff under various experimental conditions, during the whole cropping period, including the first runoff events following pesticide application (Figure 1). GBZs effectiveness seems to be independent of rainfall intensity – at least, in these particular experimental conditions. Moreover, in spite of experimental limitations, rainfall simulation results obtained in 1995 at La Jaillière showed that the strips were still effective in conditions of intense runoff (Figure 2).

Figure 1. IPU (a) and DFF (b) losses in runoff at Plélo (1994-95 cropping period)

[B6: Strip width = 6 m; B12: Strip width = 12 m, etc.]

Figure 2. IPU and DFF concentrations in runoff at La Jaillière (1995 rainfall simulation)

J.J. Gril, B. Real, L. Patty, M. Fagot and I. Perret

0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 30 40 50 60 70

Time after application (days) (b) 0 1 2 3 4 5 6 0 10 20 30 40 50 60 70

Time after application (days)

B0 B6 B12 B18 (a) IPU (mg) DFF (mg) 0 2 4 6 8 10 12 14 16 18 IPU DFF -57% -69% -59% -68% B0 B6 B12 Herbicide in r unoff ( µ g/L)

73

Limiting pesticide contamination in France

It is clear that a number of hydrological, physical and chemical processes are involved in the functioning of GBZs including infiltration of water and soluble pollutants within the strips and the retention of sediment-bound pollutants due to filtration and sedimentation. Preliminary results obtained at La Jaillière showed that IPU and DFF concentrations in runoff were depleted within the strips. As infiltration and sedimentation are not likely to induce the large reductions observed in herbicide concentrations, we assume that sorption of pesticides onto organic matter and vegetation in the GBZ is a significant factor in their effectiveness. But this assumption has to be verified with further experiments.

Our results are in agreement with recent literature (Bakeret al., 1995) and show that GBZs provide a way to improve surface water quality in agricultural areas. But there are still many questions to be answered. For example, do residues accumulate in the strip or leach through the soil and reach groundwater? Baker et al. (1995) reported that atrazine and cyanazine concentrations declined in a buffer strip as the season progressed, presumably due to degradation.

These experiments demonstrate the effectiveness of GBZs. However, work should continue to evaluate the long term effects under various conditions. Current results are not yet sufficient to make conclusions about adequate GBZ widths. In particular, there is a need for more data on the interception of concentrated runoff within GBZs.

Runoff simulation experiments have also been undertaken by Cemagref and ITCF as a tool to test a variety of situations (inlet flow rates, density of grass coverage, GBZ slope, etc.). The influence of the amount of grass residue on the GBZ is also being observed. These experiments are still in progress. Note

CORPEN – “Comité d’orientation pour la réduction de la pollution des eaux par les nitrates, les phosphates et les produits phytosanitaires provenant de l’activité agricole” : committee working on the reduction of water pollution caused by nitrates, phosphates and pesticides: this collaborative organisation gathers specialists from public authorities and private organisations involved in agriculture and water protection. The CORPEN has already published general guidelines to optimise chemical treatments for crop protection and methodological guidelines to diagnose causes of contamination in a watershed. Documents concerning GBZs and good spraying methods will be published in the near future.

REFERENCES

Asmussen, L.E., White, A.W., Hauser, E.W. and Sheridan, J.M. (1977) Reduction of 2,4 D load in surface runoff down a grassed waterway.J. Environ. Qual., 6, 159-162.

Baker, J.L., Mickelson, S.K., Hatfield, J.L., Fawcett, R.S., Hoffman, D.W., Franti, T.G., Peter, C.J. and Tierney, D.P. (1995) Reducing herbicide runoff: role of best management practices. Brighton Crop Protection Conference – Weeds, 479-487.

Patty, L., Gril, J.J., Réal, B. and Guyot, C., (1995a) Grassed buffer strips to reduce herbicide concentration in runoff –

Preliminary study in western France. Symposium at the University of Warwick (U.K), Coventry 3-5 April 1995,

BCPC Monograph 62: Pesticide movement to water, 397-406.

Patty, L., Réal, B. and Masson, E. (1995b) Limitation du transfert de l’atrazine et du lindane par ruissellement – Efficacité

des bandes enherbées. ANPP – Sixteenth COLUMA conference – International meeting on weed control, Reims,

6-7-8 December, I/III , 75-82.

Rhode, W.A., Asmussen, L.E., Hauser, E.W., Wauchope, R.D. and Allison, H.D. (1980) Trifluralin movement in runoff from a small agricultural watershed.J. Environ. Qual., 9, 37-42.

The relationship between land use, river bank quality