Assessing soil crack dynamics during dryings from reduced tillage and

conventional tillage fields Njaka Ralaizafisoloarivony1, A. Degré1, B.Mercatoris1, A. Léonard3, D. Toye3, and R. Charlier2

BACKGROUND

Cracks were mostly studied in: high clayed soil (Vertisol). This study used agricultural soil found in Gembloux-Belgium (Silt-loam). Aims: Insight on crack dynamics during dryings and re-drying of conventional and reduced tillage soil.

Water evaporation : Disturbed soil Reduced-tillage > Conventional tillage

- Cracks increased the surface of evaporation(Figure 2).

- Cracks exposed water to atmosphere (without passing the soil matrix).

- The soil temperature was stabilised at 25°C for all experiments.

CONCLUSIONS

-Cracks in disturbed soil > reduced-tillage > conventional tillage. Due to no soil cohesion, soil OC, soil aggregation, biological activities, and soil porosity.

- The opening increased the soil desiccation rate in disturbed soil reduced-tillage > conventional tillage.

-Re-drying process increased the size of the previous cracks. X-ray scan is necessary to observe the presence of pre- (micro) cracks in soil.

Special thanks to FNRS-FRIA Belgium, for sponsoring the research and the conference

REFERENCES 1. DeCarlo, K. F., and Kylor K. (2019). Biophysical effects on soil crack morphology....

Geoderma 334: 134-145 2. Schlüter S., Großmann C. et al. (2018). Long-term effects of ... reduced tillage.

Geoderma, 332:10-19 3. Shit P.K., Bhunia G.S. and Maiti R. (2015). Soil crack morphology analysis... Earth Syst.

Environ., 1: (35) :1-7. 4. Tang C., Cui Y., Shi B., Tang A. and Liu C. (2011). Desiccation and cracking.....

Geoderma, 166 (1):111-118.

1University of Liège, Gembloux Agro-Bio Tech, Gembloux, Belgium 2University of Liège, Department ArGEnCo, Liège, Belgium 3University of Liège, Chemical Engineering, Liège, Belgium

RESULTS FROM SMALL SAMPLES Re-drying process: increased cracks length and width for the deeper dense small samples (Figure 3). Some pre-existing cracks could be present in the soil and they widened with repetitive wetting-drying.

Very few cracks for the porous upper soils (Figure 4). The increase in soil shrinkage (tensile stress) could be absorbed by homogenous pores, while it burst to cracks for heterogeneous soil .

Drying chamber

heater

RH sens.

Soil sample

Temp° sensor

Heat camera

Camera

Light

Balance

Soil cracks

soil aeration, root penetration etc.

accelerate soil desiccation

Pathway for pesticides/pollutants

Pollute soil, ground water etc.

Samples

25cm

20

cm

5 c

m

1cm from above and bellow big sample

a)- Big sample : 1.6cm thick (from 4-6cm depth) b)- Small sample : 1 cm thick

Drying chamber :

- Surface temp°= 25°C - Temp° & humidity : PT1000 & DHT22

Image collection and analysis: -Digital camera: 12 Mpixel - Image analysis : Matlab + ImageJ - Cracks properties : size, shape, etc.

Soil hydraulic properties: -Evaporation rate

Consecutive drying

Tillage based treatments - Reduced Tillage - Convetional Tillage - Disturbed soil

MATERIALS AND METHODS

Cracks percentage : Disturbed soil > Reduced-tillage > Conventional tillage

- Disturbed soil: less soil cohesion, high shrinkage .

- Reduced tillage: high bio activities (worm, micro.) + more soil aggregates. Bioturbation: made heterogeneous soil. Soil heterogeneity created big

differences in heat/water absorption, and shrinkage direction.

Space between aggregates: weak area during drying. Cracks started from the area where the ratio, soil stress over soil weakness, was the highest.

- Conv. Tillage: has fresh organic matter (roots, stems and leaves), destroyed

soil structures and soil aggregate, reduced porosity, increased bulk density. All that circumvented crack formation and development.

RESULTS FROM BIG SAMPLES

Figure 4: Percentage of cracks (a) and soil bulk density (b) of small samples

0

2

4

6

8

RT-1 RT-2 CT-1 CT-2 CT-3

Reduced tillage Convetional tillage

Tota

l cra

cks

(%) a)-Surface craks on small samples

1st drying 2nd drying

1 1,1 1,2 1,3 1,4 1,5 1,6

RT-1 RT-2 CT-1 CT-2 CT-3

Reduced tillage Conv. Tillage

Bu

lk d

en

sity

(g

/cm

3)

b)-Bulk density

Surface Bottom avg-Surf. avg-Bot.

Figure 2: Cracks percentage (a), and soil evaporation rate (b) of big samples

0

2

4

6

8

10

12

RT1

RT2

RT3

T1

T2

T3

D-R

T-G

1

D-T

1-G

1

D-R

T-G

2

Reduced tillage Conv Tillage Disturbed soil

Tota

l cra

cks

(%)

a)-Surface cracks on big samples

Constant Rate Period

(CRP)

Falling Rate

Period (FRP1)

FRP2

b)-Reduced tillage a)-Conventional tillage c)-Disturbed soil + friction

Figure 1: Cracks from Conventional tillage (a), Reduced tillage (b), and Disturbed soil (c)

25 cm

20

cm

I- BIG SAMPLES

a)-Wet b)- After 1st drying c)- After 2nd drying

5 cm

Figure 3: Cracks formation from wet (a), to first (b) and second (c) dryings of small samples

New cracks II- SMALL SAMPLES