Using HYDRUS-1D and 2D for assessing the impact ofdifferent root distributions on simulated root water uptake
Aleš KLEMENT, Miroslav FÉR, Šárka NOVOTNÁ, Antonín NIKODEM, Radka KODEŠOVÁ
Department of Soil Science and Soil Protection; Faculty of Agrobiology, Food and Natural Resources; Czech University of Life Sciences Prague,Czech Republic, E-mail: klement@af.czu.cz

Knowledge of the distribution of plant roots in a soil profile (i.e. root density) is needed when simulating root water uptake from soil. Therefore, this study
focused on evaluating barley and wheat root densities in a sand-vermiculite substrate. Barley and wheat were planted in a flat laboratory box undergreenhouse conditions. The box was always divided into two parts, where a single plant row and rows cross section (respectively) was simulated. Roots wereexcavated at the end of the experiment and root densities were assessed using root zone image processing and by weighing. For this purpose, the entire
area (width of 40 and height of 50 cm) of each scenario was divided into 80 segments (area of 5x5 cm). Root density in each segment was expressed as aroot percentage of the entire root cluster. Vertical root distributions (i.e. root density with respect to depth) were also calculated as a sum of root densities ineach 5 cm layer. Resulting vertical root densities, measured evaporation from the water table (used as the potential root water uptake), and the Feddes stressresponse function model were used for simulating substrate water regime and actual root water uptake for all scenarios using HYDRUS-1D. All scenarios
were also simulated using HYDRUS-2D.
2.5
7.5
A/I
A/G
B/I
B/G

Average depth (cm)

12.5
17.5
22.5
27.5
32.5
37.5
42.5

Barley47.5
05101520

Root density (% )

2.5
7.5
A/I
A/G
B/I
B/G

Average depth (cm)

12.5
17.5
22.5
27.5
32.5
37.5
42.5

Wheat

47.5
05

101520

Root density (% )Figure 1. Photos of roots of barley sown in single row (a) and 4 spots (b) and ofwheat sown in single row (c) and 4 spots (d).

Figure 2. Areal barley root density in row (A) and rows cross section (B) evaluatedusing image (I) and gravimetric (G) analysis.
Cumulative root water uptake (cm)

Root water uptake (cm hour -1)

0.016
0.014
0.012
0.010
0.008

Figure 3. Areal wheat root density in row (A) and rows cross section (B) evaluatedusing image (I) and gravimetric (G) analysis.

0.50

Table 1. Van Genuchten soil hydraulic parameters θr, θs, α, n and Ks.

0.40

Material

0.30Time (hours)
Cumulative root water uptake (cm)-1

Root water uptake (cm hour )

0.014
0.012
0.010
0.008c)PRWU
Wheat A/I
Wheat A/GWheat B/I
Wheat B/G

0.006
0.004
0.002
0.000
0102030
Time (hours)

Fine sand andvermiculite
Coarse sand

PRWU
Barley A/I
Barley A/GBarley B/I
Barley B/G
30405060Time (hours)

0.016

405060Count
A/I and A/G
B/I and B/G

0.30
0.25
0.20

0.10
0.05

1020

30

4050

Figure 8. Water contents in sand-vermiculite substrate simulated using
HYDRUS-1D for barley in row and root density evaluated using image
analysis.

α(cm3cm-3) (cm3cm-3) (cm-1)nKs-(cm hour-1)

50

0.022

0.4160.053

315.3

50.0100.4000.190

3750

Barley80 a76 b0.429*** a0.422***b0.579*** a0.514*** b

Wheat A/I

0.000θsWheat
80 a59 b0.778*** a0.643*** b0.624*** a0.369** b

Table 3. Pearson correlation coefficient and p-value exposing relationships between
evaluated root densities with respect to depth for barley and for wheat.
a all data, b data after removing low values, * p < 0.05, ** p < 0.01, *** p < 0.001.

PRWU
Wheat A/IWheat A/G
Wheat B/I
Wheat B/G0.15

θr

Table 2. The Pearson correlation coefficient and p-value exposing relationships between
evaluated areal root densities.
a all data, b data after removing zero and very low values, * p < 0.05, ** p < 0.01,*** p < 0.001.

0.35

60

Time (hours)

Figure 6. Root water uptakes and cumulative root water uptakes simulated using HYDRUS-1D for barley (a and b, respectively) and wheat(c and d respectively): PRWU - potential root water uptake, A – row, B – rows cross section, I - root density from image analysis, G - root densityfrom gravimetric analysis.
Figure 7. Barley root water uptakes simulated using HYDRUS-1D andHYDRUS-2D: PRWU - potential root water uptake, A – row,
I - root density from image analysis.

Layerthickness
(cm)

PRWU
0.20
0.006
Barley A/I
0.004
Barley A/G
0.10 to depth for barley.
Table 7. Pearson correlation coefficient and p-value exposing relationshipsBarleybetweenevaluated root densities with respect
B/I
a all data, b data after removing low values, * p < 0.05, ** p <0.0020.01, *** p Barley< 0.001.
B/G
0.00
0.000
010200102030
405060Figure 5. Relationship between root densities in depths (A - rows,
B - rows cross sections) evaluated using both techniques, i.e. image (I)and gravimetric (G) analysis.

Figure 4. Vertical root distributions in rows (A)and rows cross sections (B) obtained using image(I) or gravimetric (G) analysis.

Wheat A/I
Wheat A/G
Wheat B/I
Wheat B/G10.680 a0.627 a
Barley A/I

Barley A/I
Barley A/GBarley B/I
Barley B/G

10.430 b
0.486 b-Wheat A/G0.814** a
1-0.308 a

Wheat B/I
0.872** a10.411 aBarley A/G
0.698* a
1-0.194 b

Barley B/I0.652* a
10.883** b

Wheat B/G
0.536 a0.893** a1Barley B/G
0.511 a0.846** a
1Figure 9. Water contents (cm3 cm-3) in sand-vermiculite substrate simulated using HYDRUS-2D for barley in row and root density evaluated using image analysis 10 (a), 20 (b), 30 (c), 40 (d), 50 (e) and 60 (f) hours
from the simulation beginning.

The application of two root detecting techniques resulted in noticeably different root density distributions. Differences were mainly attributed to the fact that fineroots of high density (located mostly at the deeper part of the box) had lower weights in comparison to the weight of few large roots (at the box top). Thus, at thedeeper part, higher root density (with respect to the entire root zone) was obtained using the image analysis in comparison to that from the gravimetric analysis.
Conversely, lower root density was obtained using the image analysis at the upper part in comparison to that from the gravimetric analysis. On the other hand,fine roots overlapped each other and therefore were not visible in the image, which resulted in lower root density values from image analysis. Root water
uptakes simulated with HYDRUS-1D using diverse root densities obtained for each cereal declined differently from the potential root water uptake values
depending on water scarcity at depths of higher root density. Usually, an earlier downtrend associated with gradual root water uptake decreases and vice versa.
Similar root water uptakes were simulated for the presented scenario using the HYDRUS-1D and HYDRUS-2D models. The impact of the horizontal root
density distribution on root water uptake was, in this case, less important than the impact of the vertical root distribution resulting from different techniques andsowing scenarios. For more details see Klement et al. (2016).
Klement, R., Fér, M., Novotná, Š., Nikodem, A., Kodešová, R. (2016): Root distributions in a laboratory box evaluated using two different techniques (gravimetric and imageprocessing) and their impact on root water uptake simulated with HYDRUS. Journal of Hydrology and Hydromechanics, 64(2), 196-208.
Acknowledgment: Authors acknowledge the financial support of the Czech Science Foundation (No. 13-12477S) and the Ministry of Agriculture of the Czech Republic (QJ1230319).