Fate of isoxaflutole and its diketonitrile metabolite under conventional and conservation tillage in an irrigated continuous-maize field

Transcription

1 Fate of isoxaflutole and its diketonitrile metabolite under conventional and conservation tillage in an irrigated continuous-maize field L. Alletto,, Y. Coquet & C. Labat École d ingénieurs de Purpan, Agronomy department, Toulouse, France. UMR INRA/INA PG Environment and Arable Crops, Thiverval-Grignon, France. Diffuse Inputs into the Groundwater January 9-3 Th, 7 - Graz Outline Introduction Context of the study The cropping systems Objectives of the study Materials and methods The experimental site: localisation and soil characteristics Isoxaflutole (IFT) properties Sampling procedure: soil Sampling procedure: water Results and discussion Conclusion General data Persistence of isoxaflutole Water and herbicide leaching

2 Context National context: generalization of water resources pollution by pesticides Economic context: Midi-Pyrénées region = nd region for maize production in France Agronomic context: Typical maize production management in the region: - 8 % of the production is in continuous maize with more than 6 % irrigated. - Tillage usually included a mouldboard ploughing (3-cm depth) at the end of the winter - Soils are unprotected during the inter-crop (from November to May) Environmental context: In the region, this system of production has generated several environmental problems (nitrate, atrazine) Now atrazine is forbidden: there is a need for development of new strategies to control weeds in continuous maize systems 3 Context Scientific Conventional tillage (CT) / Conservation tillage (MT) vs. Pesticide? Organic carbon content surface pesticides sorption (Locke et al., 997) Desorption: very few studies tend to increase under MT (Ding et al., ) Degradation: highly contrasted results! Runoff and erosion: MT are efficient to reduce erosion, but runoff depends on climatic conditions (Fawcett et al. 99) Leaching: contrasted results but for no-tillage systems leaching of pesticides increases (Watts & Hall, 996) There is a need to evaluate and/or design new cropping systems to both maintain weed control efficiency and limit environmental impacts

3 Inter-crop (7months) Cropping cycle (5 months) October November December January February March April May June July August September October Conventional tillage (a) CT bare soil maize residues in surface cm 3.5 h ha - Cover-crop sowing - Disk harrow + fertilizer spreader - depth: 5-6 cm h ha - h ha - Plowing maize sowing: seedbed preparation - Moldboard plow - depth: 8-3 cm - cultivator + harrow + roller - depth:. 6- cm Harvest (b) CT cover-crop Cover-crop inside the maize residues Conservation tillage (c) MT bare soil mulch = maize residues in surface mixed with mineral compounds (d) MT cover-crop.75 h ha -.5 h ha -.5 h ha - Disking - Disk harrow - depth: 8- cm Cover-crop sowing - Disk harrow + fertilizer spreader - depth: 5-6 cm Cover-crop inside the maize residues Destruction of the crust (and of the cover-crop) - cultivator - depth: 7-9 cm h ha - maize sowing: seedbed preparation - harrow + roller - depth: 6- cm Mulch = maize + oat residues Harvest 5 The cropping systems < 5 Decomposition of the mulch (% of soil covered) The cropping systems: soil surface differences + + Conventional 6 tillage (CT) Conservation tillage (MT) 3

4 The cropping systems: subsurface differences Conventional tillage (CT) clod Γ clod Plough pan Conservation tillage (MT) Crop residues Inter-furrow (Manichon, 98; Roger-Estrade et al.,) No visible limit of the previously ploughed layer Undulations created by the disc harrowing Root development > 7 cm Vertical cracks Consequences on water dynamics and solutes transport 7 Objectives of the study Evaluate the effects of tillage practices (conventional vs. conservation tillage ; intercrop with or without cover-crop) on: - Isoxaflutole degradation and formation of diketonitrile - Leaching potential of isoxaflutole and its diketonitrile metabolite 8

5 The experimental site: localisation and soil characteristics Legend Garden house Instrumented soil profiles CT without cover-crop CT with cover-crop Agricultural field of 5 ha Continuous maize production «Boulbènes» soils (Gleyic Luvisol) Irrigation with a centre pivot Conservation 9 tillage (MT) on 3 ha since MT without cover-crop MT with cover-crop The experimental site: localisation and soil characteristics Main features of the Boulbènes soil types: -8cm - Loamy soils with unstable structure - Low organic matter level - High sensitivity to crusting - Hydromorphic profile 8-55cm Horizon Prof. ph Clay Silt Sand OC CaCO 3 (m) (g kg - ) CT LA LA Btg cm Btg MT LA LA Btg Btg cm 5

6 Isoxaflutole (IFT) properties Proherbicide, isoxazoles Annual grasses and broadleaves weeds, roots uptake Pre-emergence of maize (75 g ha - ) Inhibitor of the biosynthesis of carotenoids IFT: low solubility in water (6. mg L - ), rapidly degraded (DT 5 :.-3 j), good retention on organic compounds (K OC : L kg - ) Degradation: formation of the diketonitrile (DKN) with a higher solubility (3 mg L - ), a lower retention (K OC : 9 L kg - ) and a higher persistence (DT 5 : 8- j) Sampling procedure: soil Before treatment: sampling of soil from surface to 8-cm depth to control initial concentration of IFT and DKN Treatment day: control of the variability of the treatment with fibreglass paper Sampling of soil from surface to a maximum of 3-cm depth Sampling time: t ini, t, t, t 3, t 5, t 7, t, t, t, t 8 Storage of frozen samples (-8 C) until analysis Control of the herbicide distribution Analysis by HPLC-MS/MS 6

7 Sampling procedure: water Ceramic cups: by soil pit at and 7 cm-depth Fibreglass wick lysimeters: by soil pit at cm (5x5 cm). Fibreglass wick length: 7 cm Sampling of soil water with ceramic cups and fibreglass wick lysimeters Storage of frozen samples (-8 C) until analysis Analysis by HPLC-MS/MS 3 General data In soil samples: Limit of quantification (LOQ). mg a.i. kg - soil In water samples: LOQ depends on collected volumes (V) If V < 5 ml LOQ =. µg L - If V > ml LOQ =. µg L - In 5: soil samples were analysed from treatment day to 8 DAT 73 water samples: ( from the ceramic cups and 59 from the fibreglass wick lysimeters Rainfall data during the cropping season Total precipitation: 599 mm 5 Total : 599 mm - rainfall : 55 mm - irrigation : 33 mm Irrigation Irrigation Irrigation Irrigation 5 Irrigation 6 Irrigation 7 Irrigation Irrigation 3 Irrigation 8 Irrigation 9 First rainfall: DAT 7.6 mm in 6 h Precipitation (mm) 3 Col /5 /6 /7 /8 /9 / 7

8 % of applied IFT Persistence of isoxaflutole Conventional tillage_bare soil 8 DT 5 (IFT) =.9 d ( h) Conservation tillage_bare soil 8 DT 5 (IFT) =.7 d ( h) :IFT in soil samples : DKN (in % of applied IFT) IFT DT 5 was short (< d) No detection of IFT 7 DAT % of applied IFT Conventional tillage_cover crop 8 6 DT 5 (IFT) =.95 d (3 h) Col DAT Conservation tillage_cover crop 8 6 DT 5 (IFT) =. d ( h) Sorption of IFT on organic matter was found to increase DT 5 (Rouchaud et al,, ) DAT Increase of DKN with rainfall events DAT Precipitation (mm) No effect of tillage on IFT DT 5 But a longer persistence under MT with cover crop: Sorption? IFT hydrolysis was catalysed by retention on solid phase (Rice et al., ) But Water and herbicide leaching Drainage (ml) Drainage (ml) Conventional tillage+bare soil Cumulative water drainage 7 L under MT_Bare soil and < 7 L under MT_Cover-crop 5 5 Cumulative leaching DAT of DKN reached about 8 % of applied dose under MT_Bare soil Conventional tillage+cover-crop and < % under MT_Cover-crop 6 5 Lower initial water content in the soil profile under cover-crop increase sorption 3 8 Quantity and/or nature of the residues vs. 6 sorption and degradation of DKN 5 5 DAT % of applied IFT % of applied IFT Conservation tillage+bare soil 6 Water drainage (ml) 5 3 : DKN concentration in water 8 (in % of applied IFT) 6 : Cumulative loss of herbicide 5 5 % applied IFT Conservation tillage+cover-crop 6 Cumulative water drainage L under CT_Bare soil & CT_Cover-crop 5 3 Cumulative leaching of DKN reached 8 about 5 % of applied dose at the end 6 of the growing season 5 5 Maximum DKN concentration was 3 µg L 3 DAT - 6 DAT (but in a low volume) % applied IFT 8

9 Tillage practices had no effect on the in-field degradation of isoxaflutole Residues on soil surface seemed to slow down degradation rate of IFT Effect of interception and retention? Migration in soil was faster and more important under conventional technique (data not shown) Water drainage was two times higher under conventional technique Herbicide leaching was between and 7 times lower under conservation technique, with the lowest leaching under the cover-crop plot Retention processes and/or degradation were modified by tillage and residues management? 7 Thank you. 8 9