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