Multi-electrode 3D resistivity survey on soil structure in

Multi-electrode 3D resistivity survey on soil structure in conservation agriculture I. Piccoli a, N. Dal Ferro a, B. Lazzaro b, L. Furlan c, S. Macolino a, A. Berti a, F. Morari a a DAFNAEDept., Universityof Padova, Viale Dell Università 16, 35020 Legnaro (PD), Italy b DirezioneAgro-Ambiente, Politiche Agro-Ambientali, Regione Veneto, Via Torino 110, Mestre (VE), Italy c VenetoAgricoltura, Viale dell Università 14, 35020 Legnaro (PD), Italy Corresponding author, ilaria.piccoli@studenti.unipd.it ESSC2015 Moscow, May 18-22 2015

INTRODUCTION No-tillage (NT) practices affect soil physical-chemical properties: Soil compaction ( BD) is observed in NT systems, especially during transitional period from conventional tillage (CT) to NT (Chassotet al. 2001, Dal Ferro et al., 2014) Root apparatus suffer soil compaction Agronomic effect: Reduction in yield in NT systems (Lipiec et al. 2012) Environmental effect: Root-derived Carbon is retained in soils more efficiently than other inputs (Schmidt et al., 2011) Changes in root C could have an impact on soil C stock

INTRODUCTION Traditional methods to study soil structure and roots distribution are time-consuming, expensive and disruptive Modern geophysical techniques, like Electrical Resistivity Tomography (ERT), are cost-effective, rapid and non disruptive methods to study 3D soil properties Other studies highlight the potential of using ERT on root system spatial distribution (Amato et al., 2008)

STUDY AIMS To study the soil structure and roots distribution in NT systems combining: 1. Geophysical methods: multi-electrodes ERT 3D surveys 2. Traditional physical methods for soil studies

MATERIALS AND METHODS 4 farms in North-eastern Italy: F2 Silty clay loam F3 Silty clay loam F1 Sandy loam F4 Silty clay loam from 2010, 2 different management systems were established: 1. Conventional Tillage(CT) 2. No-tillage (NT) 4-yrs crop rotation (wheat, rapeseed, maize, soybean) 35-cm depth ploughing in autumn (residues incorporation) Seedbed preparation in spring Monitoring in August 2014 (maize) 4-yrs crop rotation (wheat, rapeseed, maize, soybean) Sod-seeding Residues retention Cover crops Monitoring in August 2014 (maize)

MATERIALS AND METHODS 3 monitoring areas 5m 2, soil volume 4.5 m 3 (5 m x 1 m x 0.9 m) 3D ERT (total 24 ERT) 9 penetration resistances (PR) (total 216 PR) 3 undisturbed sampling for bulk density (BD) and volumetric water content (VWC) analyses (total 648 samples) 2 undisturbed sampling for roots analyses (total 240 samples) -0.9 m

MATERIALS AND METHODS PHYSICAL ANALYSES: PR: digital cone-penetrometer (Eijkelkamp), 1 measure/cm BD and VWC: sampling 0-90 cm (hydraulic sampler), cores cut in 9 layers 10 cm high ROOTS ANALYSES: Undisturbed samples 0-90 cm (5 layers: 0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm and 60-90 cm) Root length density (RLD) and average mean diameter (AMD): images analyses (WinRhizo, Regent Instrument) Root biomass: root materials weighed after drying at 70 C until constant weight

MATERIALS AND METHODS GEOPHYSICAL ANALYSES: 3D ERT (Syscal-Pro Junior switch 72, Iris Instrument) 3 multichannel cables connected with 24 electrodes each Dipole-dipole configuration 0.4 m inter-cables spacing, 0.2 m inter-electrodes spacing Investigated soil volume 2.9 m 3 (4.6 m x 0.8 m x 0.8 m) 3D data inversion with ERTLab software (Multiphase Technologies and Geostudi Astier)

MATERIALS AND METHODS STATISTICAL ANALYSES: Mixed Model differences between treatments random effect: farm fixed effects: categorical pred: tillage continous pred: sand and clay content Principal Component Analysis (PCA) VWC, BD, PR, Res, Sand, Clay, RLD, AMD

RESULTS: PHYSICAL ANALYSES BD (g/cm 3 ) 1,6 1,5 1,4 NT CT Bulk Density (BD): Variability between farms 1,3 F1 F2 F3 F4 PR (MPa) 2,4 2,2 2,0 1,8 1,6 1,4 1,2 1,0 Penetration Resistance (PR): Reflects BD values F1 F2 F3 F4 PR affected by treatment in F3 and F4

RESULTS: PHYSICAL ANALYSES BD (g/cm 3 ) 1,6 1,5 1,4 NT CT Bulk Density (BD): Variability between farms 1,3 F1 F2 F3 F4 p=0.03 PR (MPa) 2,4 2,2 2,0 1,8 1,6 1,4 1,2 1,0 Penetration Resistance (PR): Reflects BD values F1 F2 F3 F4 PR affected by treatment in F3 and F4

RESULTS: PHYSICAL ANALYSES BD (g/cm 3 ) 1,6 1,5 1,4 NT CT Bulk Density (BD): Variability between farms 1,3 F1 F2 F3 F4 p=0.03 PR (MPa) 2,4 2,2 2,0 1,8 1,6 1,4 1,2 1,0 Depth (cm) PR (MPa) 0 1 2 3 4 5 0 10 20 30 40 F1 50F2 F3 F4 60 p<0.01 p=0.05 70 80 Penetration Resistance (PR): Reflects BD values PR affected by treatment in F3 and F4 In CT of F1 PR not performed below 40 cm (extreme resistance)

RESULTS: ROOTS ANALYSES RLD (mm) AMD (mm) 20 a NT 15 CT 10 b 5 c cd cd de ef ef f ef 0 0-10 10-20 20-40 Layer (cm) 40-60 60-90 0,55 0,50 0,45 0,40 0,35 0,30 F1 F2 F3 F4 Root Length Density (RLD): NT > CT in F1, F2, F3 and F4 (p=0.03) average: 5.5 cm/cm 3 in NT 4.1 cm/cm 3 in CT Average Mean Diameter (AMD): Differences between the farms (p=0.01) NT > CT in F1 and F3 CT > NT in F2 and F4 AMD affected by treatment in F1 (p=0.01): average: 0.48 mm in NT 0.39 mm in CT

RESULTS: ROOTS ANALYSES RLD (mm) AMD (mm) 20 15 10 5 0 0,55 0,50 0,45 0,40 0,35 0,30 a b c cd cd 0-10 10-20 20-40 40-60 60-90 de ef ef f NT CT ef Root Length Density (RLD): NT > CT in F1, F2, F3 and F4 (p=0.03) average: 5.5 cm/cm 3 in NT 4.1 cm/cm 3 in CT Layer (cm) Average Mean Diameter (AMD): F1 F2 F3 F4 Differences between the farms (p=0.01) NT > CT in F1 and F3 CT > NT in F2 and F4 AMD affected by treatment in F1 (p=0.01): average: 0.48 mm in NT 0.39 mm in CT

RESULTS: ROOTS ANALYSES RLD (mm) AMD (mm) 20 15 10 5 0 0,55 0,50 0,45 0,40 0,35 0,30 a b c cd cd 0-10 10-20 20-40 40-60 60-90 de ef ef f NT CT ef Root Length Density (RLD): NT > CT in F1, F2, F3 and F4 (p=0.03) average: 5.5 cm/cm 3 in NT 4.1 cm/cm 3 in CT Layer (cm) Average Mean Diameter (AMD): F1 F2 F3 F4 p=0.01 Differences between the farms (p=0.01) NT > CT in F1 and F3 CT > NT in F2 and F4 AMD affected by treatment in F1 (p=0.01): average: 0.48 mm in NT 0.39 mm in CT

RESULTS: ERT No-Tillage Conventional Tillage F2 F3 F4 No differences between treatments in F2, F3 and F4 Very conductive foreground Few visible resistive contrasts

RESULTS: focus on F1 site Lay yer mean depth (cm) 0 10 20 30 40 50 60 70 80 90 BD (g/cm 3 ) 1,0 1,2 1,4 1,6 1,8 p<0.01 NT CT mean depth (cm) Layer 0 10 20 30 40 50 60 70 80 ERT: NT CT in F1 high resistivity layer (>110 Ωm) in CT RLD (cm/cm 3 ) 0 5 10 15 20 25 0-10 cm p<0.01 NT CT BD: compact layer (1.78 g/cm 3 ) in CT (confirmed by PR) Plough sole in CT Roots seem not to be affected by this hardpan: RLD: NT > CT first layer

RESULTS: focus on F1 site Lay yer mean depth (cm) 0 10 20 30 40 50 60 70 80 90 BD (g/cm 3 ) 1,0 1,2 1,4 1,6 1,8 p<0.01 NT CT Depth (cm) 0 10 20 30 40 50 60 70 80 ERT: NT CT in F1 high resistivity layer (>110 Ωm) in CT PR (MPa) 0 1 2 3 4 5 NT CT BD: compact layer (1.78 g/cm 3 ) in CT (confirmed by PR) Plough sole in CT Roots seem not to be affected by this hardpan: RLD: NT > CT first layer

RESULTS: focus on F1 site Lay yer mean depth (cm) 0 10 20 30 40 50 60 70 80 90 BD (g/cm 3 ) 1,0 1,2 1,4 1,6 1,8 p<0.01 NT CT Layer mean depth (cm) 0 10 20 30 40 50 60 70 80 ERT: NT CT in F1 high resistivity layer (>110 Ωm) in CT RLD (cm/cm 3 ) 0 5 10 15 20 25 0-10 cm p<0.01 NT CT BD: compact layer (1.78 g/cm 3 ) in CT (confirmed by PR) Plough sole in CT Roots seem not to be affected by this hardpan: RLD: NT > CT first layer

RESULTS: PCA analysis PC2 (Explain ned Variance: 21%) 1 0 PR AMD BD VWC Sand Res Clay RLD -1-1 0 1 PC1 (Explained Variance: 44%) PCA analysis found two PC which explained 44% and 21% of variance respectively Resistivity signal was influenced by texture (directly from sand content and inversely from clay content) The high conductivity of soil resistivity profile is related to the high VWC which masked ERT survey Roots parameters are affected by soil physical properties: AMD increase with BD and PR high RLD are inversely correlated with BD and PR

RESULTS: PCA analysis PC2 (Explain ned Variance: 21%) 1 0-1 PR AMD BD VWC Sand Res Clay RLD -1 0 1 PC1 (Explained Variance: 44%) PCA analysis found two PC which explained 44% and 21% of variance respectively Resistivity signal was influenced by texture (directly from sand content and inversely from clay content) The high conductivity of soil resistivity profile is related to the high VWC which masked ERT survey Roots parameters are affected by soil physical properties: AMD increase with BD and PR high RLD are inversely correlated with BD and PR

CONCLUSIONS Roots affected by management and soil physical parameters Root Length Density: NT > CT superficial layers Average Mean Diameter: with BD and PR High moisture condition smoothed the contrast between treatments in ERT survey Exception: F1 site (sandy texture) plough sole in CT confirm the potential of using geophysical techniques as a rapid survey method for soil structure studies when resistivity signal is not masked by other properties The lack of consistent differences between treatments are probably due to the transitional period from CT to NT and high soil variability

http://www.lifehelpsoil.eu/en/ Acknowledgements: Research funded by HELPSOIL project ( Helping enhanced soil functions and adaptation to climate change by sustainable conservation agriculture techniques ), LIFE12ENV/IT/000578 We are grateful to Mr Efrem Destro of Miana Serraglia farm (F1) for the technical support during experimentation ESSC2015 Moscow, May 18-22 2015

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Variable PC1 PC2 AMD (mm) 0.17 0.54 RLD (cm/cm3) 0.37-0.77 VWC (%) -0.84 0.20 BD (kg/m3) 0.40 0.67 PR (MPa) 0.29 0.71 Res (Om) 0.81-0.01 Sand % 0.91 0.17 Clay % Explained variance (%) -0.91-0.17 44 21