Comparison of different lateral depths and irrigation scenarios insorghum plant using HYDRUS-2D•

Begüm Polat1, Dursun Büyüktaş1,• 1 Akdeniz University, Faculty of Agriculture, Department of Farm
Structures and Irrigation, Antalya/Turkey•*Corresponding Author: btekelioglu@akdeniz.edu.tr•

Prague, April, 2023

OUTLINE
Importance and Aim of the Study
Material and Method
Result and Discussion
Conclusion

The use of fossil fuels causes an increase in greenhouse gases andconsequently global warming. And so, scientists have tried to finddifferent energy sources.

Sweet sorghum is an energy plant.
In recent years, it is considered to be produced for the purpose ofbioethanol.

In order for the production of sweet sorghum to be sustainable, inputs
such as irrigation, fertilization, good seed should be used at an optimum
level.
Among these inputs, especially irrigation is seen as the most important
application that increases the efficiency of other agricultural inputs andensures stability in agricultural production

Why is irrigation important?
*Rapid population growth*Negative consequences of global warming andclimatechange,*Increasing water pollution as a result ofurbanization and industrialization,
It has made the optimization of water resources
compulsory.
Water used in agriculture has the largest share.
Increasing population will increase competition
for water between different sectors. Therefore,
increasing the efficiency of water use is an
important issue.
Also, it affects both agricultural production andwater resources

Subsurface drip irrigation is one of the application forms of drip irrigation, since thelaterals are buried under the ground in this method, there is no loss of evaporationand this leads to an increase in water use efficiency.

It has been reported in many studies that it has higher water use efficiency and increases
the yield of the plant compared to drip irrigation.

In the method and design of subsurface drip irrigation the installation depth of the lateral is an importantparameter that affects the moisture change around the dripper

The depth where the lateral will be laid should be preferred according to the plant, soil type, water source,
climate, tillage equipment and necessity.
Lateral depth should be at the depth where the root zone of the plant will make maximum use of irrigationwater.
On the contrary, if the lateral is close to the soil surface, evaporation on the soil surface increases, if thelaterals are placed deeper, water losses increase due to deep infiltration and the water available to the plantroots may decrease.

The aim of this study is to determine the effects of different lateral depths andwater application strategies on the moisture distribution in the soil profile, bymeans of the HYDRUS-2D model.

The research was carried out in the research area located in Aksu Campus of Akdeniz University
in 2020 and 2021. The study area located 20 km away from Antalya city center in Turkey is
between 36o 55' north latitude and 30o 53' east longitude, and its height above sea level is 15 m

Some physical properties of field soil are given in Table,
Mass based field capacity (FC) of the study area ranged from 0.23 to 0.24 g3 g-3 and permanent wilting point(PWP) ranged from 0.15 to 0.16 g3 g-3.

Some physical properties of field soil.
Soil
depth

Sand

Clay

Silt

Soil Texture

Field
capacity

Wilting point(g3 g-3)

Bulkdensity

(%)

(%)

(%)

0-30

17

41

42

Silty clay

0.23

0.16

1.38

30-60

19

40

41

Silty clay

0.23

0.16

1.51

60-90

18

35

47

Silty clay
loam

0.24

0.15

1.50

(cm)

(g3 g-3)(g cm-3)

Some chemical properties of field soil are given in Table,

Some chemical properties of field soilEC
(dS m-1)
0.4

pH
8.3

SAR

Ca +2

Mg+2

K+

Na +

C03-

HCO3-2Cl -SO4 -20.2(me l-1)
3.1(me l-1)
9.2(me l-1)
0.3(me l-1)
0.5(me l-1)
0.3(me l-1)
1.4(me l-1)
0.3(me l-1)
10.9

Where Na+ is the sodium, K+ is the potassium, Ca2+ is the calcium, Mg2+ is the magnesium, CO32− is the carbonate, HCO3− is the bicarbonate, Cl− is thechlorine, SO4 2− is the sulphate, SAR is the sodium absorption, rate and EC is the electrical conductivity

The electrical conductivity (EC) of irrigation water is 0.2 dS m-1 and the sodium adsorption rate is 0.2, which
is suitable for growing sorghum plants

Some chemical properties of irrigation water used in the study are given in Table,
Some chemical properties of irrigation water used in the studyEC(dS m-1)
0.6

pH
7.3

SAR
0.4

%Na

Ca+2

Mg+2

K+

Na+

C03-

HCO3-2

Cl-

SO4-2

10

(me l-1)
3.9(me l-1)
3.0(me l-1)
0.5(me l-1)
0.8(me l-1)
0.2(me l-1)
3.8(mel-1)
0.8(me l-1)
3.3

Where Na+ is the sodium, K+ is the potassium, Ca2+ is the calcium, Mg2+ is the magnesium, CO32− is the carbonate,
HCO3− is the bicarbonate, Cl− is the chlorine, SO4 2− is the sulphate, SAR is the sodium absorption, rate and EC is theelectrical conductivity

Sorghum plant• Sweet sorghum (Sorghum bicolor L.) variety
Uzun, registered in the name of BATEM(Western Mediterranean Agricultural ResearchInstitute), which is one of the two varieties
grown as sugar sorghum in Turkey, was used asplant material in the research, Sorghum seeds
were planted on May 15, 2020 and May 17,
2021 at 0.70×0.05 m spacings.
• The plants was harvested on September 4,2020 in the first year and August 20, 2021 in
the second year

Irrigation method, experimental design, and irrigation treatments• In the experiment, irrigation water was applied with subsurface drip irrigation system. The amount ofirrigation water applied to different treatments was measured by the water meter installed in thesystem.
• Polyethylene (PE) drip line with 16 mm diameter was laid along the plant row and in-line drippers
were placed at 40 cm intervals along the pipe with 2 L h-1 discharge at 100 kPa.
• Laterals were placed 70 cm apart, one lateral to each plant row, and placed under the soil surface at
two different depths, 25 and 50 cm. The experiment was carried out in three replications in arandomized block trial designIrrigation method, experimental design, and irrigation treatments• Combinations of three different irrigation levels and two different lateral depths were used in irrigation
applications.
• Irrigations were made when the cumulative reference crop evapotranspiration (ETo) reached 25±5 mm.
• 100%, 66% and 33% of this amount was applied as irrigation water at three different irrigation waterlevels (S100, S66, S33, respectively).
• Two different depths, 25 cm and 50 cm (D25 and D50, respectively) were used in field conditions
Details of experimental treatments

Treatment
D25S33
D25S66
D25S100
D50S33
D50S66
D50S100

Depth of drip lateral (cm)
25
25
25
50
50
50

Irrigation level(%)
33
66
100
33
66
100

Irrigation method, experimental design, and irrigation treatments• Cumulative reference crop evapotranspiration (Eto) and irrigation amount were calculated using
equations 1 and 2, respectively.

𝐸𝐸𝐸𝐸𝑜𝑜 = 𝑘𝑘𝑝𝑝𝑝𝑝𝑝𝑝 𝑥𝑥 𝐸𝐸𝑝𝑝𝑝𝑝𝑝𝑝

𝐼𝐼 = 𝐸𝐸𝐸𝐸𝑜𝑜 𝑥𝑥 𝑘𝑘𝑐𝑐 𝑥𝑥 𝑃𝑃 𝑥𝑥 𝐴𝐴

(1)
(2)

• where, ETo is reference crop evapotranspiration (mm day-1); kpan is pan coefficient; Epan is pan evaporation (mmday-1), I is amount of irrigation water applied (L); kc is crop coefficient (GTHB, 2017); P is wetted area (%) and A
is plot area (m2). The kpan coefficient was determined as 0.75 according to the environmental conditions in which
the evaporation pan was placed .In this study, the wetted area ratio was determined as 0.60.

Monitor of soil moisture
content• Before the determined irrigation days,
soil moisture content was determined(by gravimetric method) by taking soil
samples from three different depths,
0-30, 30-60, 60-90 cm in eachtreatment and at a distance of 5 cm
from the lateral.
• Gravimetric soil samples were used in
the calibration and validation phase of
the HYDRUS program.

Numerical modeling• HYDRUS-2D numerical model was used in the research. The HYDRUS-2D model wasdeveloped at the US Salinity Laboratory Agricultural Research Station, Riverside,
California.
• Only one dripper was used as a point water source, so water movement during theinfiltration and redistribution processes was considered as an axisymmetrical process.

• HYDRUS-2D (License number: 1002) numerical model was used in the
research. The HYDRUS-2D model was developed at the US Salinity
Laboratory Agricultural Research Station, Riverside, California.

Numerical
modeling• Only one dripper was used as a point water source, so water movement
during the infiltration and redistribution processes was considered as an
axisymmetrical process.

Numerical modeling• The program numerically solves the Richards equation for water flow using the finite
element method. The two-dimensional Richards equation governing water flow inhomogeneous and isotropic soils is given in Equation 3,

𝜕𝜕𝜕𝜕
𝜕𝜕
𝜕𝜕𝜕
𝜕𝜕
𝜕𝜕𝜕
=
+
+ 𝐾𝐾(ℎ)𝐾𝐾(ℎ)
𝐾𝐾 ℎ𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕

Equation 3• Where 𝜃𝜃 = volumetric water content (L3 L−3), h = soil water pressure head (L), t = time (T), z = vertical spacecoordinate (L), and K = hydraulic conductivity (L T−1)

Numerical modeling• Equation 3 turns into Equation 4 when water uptake by roots S(h) is included in theequation.
𝜕𝜕𝜕𝜕
𝜕𝜕
𝜕𝜕𝜕
𝜕𝜕
𝜕𝜕𝜕
=
+
+ 𝐾𝐾(ℎ) − 𝑆𝑆(ℎ)
𝐾𝐾(ℎ)
𝐾𝐾 ℎ
𝜕𝜕𝜕𝜕 𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕
𝜕𝜕𝜕𝜕

Equation 4• The term S(h) represents the volume of water removed per unit time from a unit
volume of soil due to plant water uptake. Feddes et al. (1978) defined S(h) as
𝑆𝑆 ℎ = 𝛼𝛼(ℎ)𝑆𝑆𝑝𝑝

Equation 5• α(ℎ) = the water stress response function of the soil-water pressure head (0≤α ≤1) (L-1), Sp = the water uptake rateduring periods of no water stress when α(ℎ) = 1.

Numerical modeling• When the potential water uptake rate is equally distributed over a two-dimensional rectangular root
domain, Sp becomes,
Equation 6

1
𝑆𝑆𝑝𝑝 =𝑆𝑆 𝑇𝑇
𝐿𝐿𝑥𝑥 𝑥𝑥 𝐿𝐿𝑧𝑧 𝑡𝑡 𝑝𝑝• where Tp = the potential transpiration rate (L T-1), Lz = the length of the root zone (L), Lx = the width of
the root zone (L), St = the width of the soil surface associated with the transpiration process (L).
• Vrugt et al (2001) defined the two-dimensional root distribution 𝑏𝑏(𝑥𝑥, 𝑧𝑧) for non-uniform cases asfollows:
𝑏𝑏 𝑟𝑟, 𝑧𝑧 =

𝑧𝑧
1−
𝑧𝑧𝑚𝑚

𝑟𝑟 − 𝑧𝑧𝑝𝑝𝑧𝑧 𝑧𝑧 ∗ −𝑧𝑧 + 𝑟𝑟𝑝𝑝𝑟𝑟 𝑟𝑟 ∗−𝑟𝑟
𝑚𝑚
𝑚𝑚
1−
𝑒𝑒
𝑟𝑟𝑚𝑚

Equation 7• Where rm = the maximum rooting length in the horizontal direction (L), zm = depth direction (L) pz, z*, pr and r* =empirical parameters that can describe non-symmetrical root geometries.

Numerical modeling• WhereIn the program,the initialwater
water content
content andsoil hydraulicparameters
be knownin, θ= volumetric(L3theL-3van), θsGenuchten= the saturated
volumetricwater (shapecontentparameters)(L3 L-3) , mustθr = theresidual-1) ,theorder tocontent
determine
Thehydraulicvolumetricconductivity
water content(L(θ)Tthatcan sizehold distribution
at different soilpressurewater(L3theL-3water), Ks flow
= thecorrectly.
saturated
l =soilpore, Swatere = effectiveisdetermined
Equation constant
11. The combinationof empiricalthe Van Genuchten–Mualem
1976;
Genuchten
water
contentwith(L3 theL-3),help
α =ofempirical(L-1) , m, n =constant with m= (Mualem
1-1/n, andh = Vanpressure
head
1980)
formulation
for
the
water
retention
curve
is
used
to
explainthehydraulicconductivity
functionunder
unsaturated(L). The empirical constants are fitting parameters that define the shape of the curveconditions, Van Genuchten functions are defined as (Van Genuchten, 1980),

𝜃𝜃𝑠𝑠 − 𝜃𝜃𝑟𝑟
+
𝑛𝑛 𝑚𝑚
𝜃𝜃𝑟𝑟
1
+
𝛼𝛼𝛼
𝜃𝜃 ℎ = �𝜃𝜃𝑠𝑠𝑙𝑙

𝐾𝐾 ℎ = 𝐾𝐾𝑠𝑠 𝑆𝑆𝑒𝑒 1 − 1 − 𝑆𝑆𝑒𝑒
𝑆𝑆𝑒𝑒 =

𝜃𝜃−𝜃𝜃𝑟𝑟1, 𝑚𝑚 = 1 −𝜃𝜃𝑠𝑠 −𝜃𝜃𝑟𝑟𝑛𝑛𝜃𝜃𝑆𝑆 − 𝜃𝜃𝑟𝑟𝜃𝜃 = 𝜃𝜃𝑟𝑟 +1 + 𝛼𝛼𝛼 𝑛𝑛 𝑚𝑚

ℎ<0
ℎ≥0

1⁄𝑚𝑚 𝑚𝑚2

Equation 8

Equation 9
Equation 10
Equation 11

Systemgeometry•

HYDRUS-2D uses the Galerkinfinite-element method to solve
thegoverningwater flow
equation.

•

Subsurface drip irrigation system
can be simulated using a planar
two-dimensional model in which
the lateral is represented as apoint source in a two-dimensional
domain.

•A small semicircle on the left sideofthetransport
domainrepresents the dripper.

•

The field geometry of the soil
section for which the numericalsolution was obtained wascreated as a 35 cm wide and 90
cm deep rectangle (except for thesemicircle
representingthedripper on the left side of thedomain).

•The position of the semicircle waschanged according to the depth ofthelateralsindifferent
experiments. A total of 30000
finite elements are defined in thedomain area.

Boundary conditions• Atmospheric boundary condition wasapplied along the upper boundary. Also, thisboundary represents the soil surface• A free drainage boundary condition wasapplied along the bottom boundary• A time-variable flux boundary condition wasused along boundary elements representing
the emitter during water application insimulations of the field experiment• All the remaining boundaries wereassigned-1
The water flux at the variable flow boundaryawas
calculated
as 318cm day . The water flux was
zero-flux
boundary
condition
calculated using the following equations,
𝑞𝑞 =

𝑄𝑄
𝑥𝑥 10
𝐿𝐿𝑑𝑑

𝐿𝐿𝑑𝑑 = 2𝜋𝜋𝜋𝜋 𝑥𝑥 𝑆𝑆𝑑𝑑

Equation 17

Equation 18

In the equations, q is water flow applied to the variable condition in the emitter zone (cm day-1), Q is dripper discharge (Lhour-1), Ld; circumference of the dripper, r; radius of the lateral (cm); Sd; eemitter spacing (cm); π is defined as the numberpi.

For this study, the r value was determined as 0.63 cm. It is calculated as Ld= 2πr = 3.96 cm. Sd= 40
cm is taken as. Q=2.1 l h-1 was determined.

Initial and boundary conditions-1), 𝐸𝐸𝐸𝐸 = crop evapotranspiration (mm day-1), k = a coefficient for solar radiation•• Where,E = daily evaporation(mm𝑐𝑐
For HYDRUS-2D
simulations,thedayupper
partof the area of the simulated soil cross-section was determined as(takenas 0.39 in thisstudy, Ritchie
1972; Feddesevaporation
et al 1978), 𝐸𝐸𝐸𝐸
= crop evapotranspiration(mmcondition
day-1), 𝐸𝐸𝐸𝐸𝑜𝑜 =the atmosphericboundary
condition.Sinceis 𝑐𝑐 definedby surface boundaryand•reference
evapotranspiration(mmterm
day-1in), 𝐸𝐸Richards
evaporation(mm day-1(Equation), 𝑘𝑘𝑝𝑝 = pan12)
coefficient(The kpan
transpiration
is defined by sink
evaporationand transpiration
𝑝𝑝 = panequation,coefficientwasvalues
determined
as 0.75separately
according andto theenvironmental
conditions
in whichthe evaporation pan(Equation 15)
are defineddaily
in atmosphericboundary
condition.Evaporation
andwasplaced (Allenal. 1998),using
𝑘𝑘𝑐𝑐 = crop
coefficienttranspiration
wereetestimatedthe following
equations (Allen, 1998):

𝐸𝐸 = 𝐸𝐸𝐸𝐸𝑐𝑐 𝑥𝑥𝑒𝑒 −𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘

Equation 12

𝐸𝐸𝐸𝐸𝑜𝑜 = 𝐸𝐸𝑝𝑝 𝑥𝑥 𝑘𝑘𝑝𝑝

Equation 14

𝐸𝐸𝐸𝐸𝑐𝑐 = 𝐸𝐸𝐸𝐸𝑜𝑜 𝑥𝑥 𝑘𝑘𝑐𝑐

𝑇𝑇 = 𝐸𝐸𝐸𝐸𝑐𝑐 − 𝐸𝐸

𝐿𝐿𝐿𝐿𝐿𝐿 𝑛𝑛𝑦𝑦
𝐿𝐿𝐿𝐿𝐿𝐿 =𝑃𝑃𝑃𝑃

Equation 13

Equation 15

Equation 16

Initial and boundary conditions• It was determined daily by interpolation of LAI values. LAI values were calculated with the help of
Equation 16. Where, LA= area of leaves in the plant (cm2) (The area found after multiplying the widthand length of each leaf is multiplied by the correction coefficient of 0.75 and the leaf area is determined(Elings 2000), PA= plant area (cm2), (PA is calculated as 70x5 cm) (Addai and Alimiyawo 2015)), 𝑛𝑛𝑦𝑦 =number of leaves.

Spatial root
distribution androot water
uptake• The maximum root
depth is 90 cm, depthof maximum intensity
is 30 cm, the maximum
rooting radius is 25 cm,
and the vertical lengthof the maximum root
density is 15 cm. The
width (L) of the soil
surface associated withthe transpiration
process wasdetermined as 30 cm.
• The same parametervalues were used in thesimulations created for
all treatments.

Parameters of van Genuchten–Mualem equation used in the simulations• For the computation of the Van Genuchten analytical model. θr, θs, α, n values need to be determined.
These values can be estimated according to the soil texture in the HYDRUS program. The parameters of
the Van Genuchten analytical model estimated by the program are given in Table,
Parameters of van Genuchten-Mualem Model for Considered Soil𝜃𝜃𝑠𝑠

(m3 m-3)
0.45

𝜃𝜃𝑟𝑟

(m3 m-3)0.067

𝛼𝛼(cm-1)
0.02

𝑛𝑛

(-)
1.41

𝐾𝐾𝑠𝑠

(cm day-1)
10.8• The initial water content pressure was determined as -100 cm (θ = 0.26 cm3 cm-3). For D50S33, all input
parameters (E, T, irrigation days and amount) were defined and a simulation was created and soil
hydraulic parameters were estimated by the program according to soil texture.

• While soil water content values in 90 cm soil profile
were determined by gravimetric method from 15,
45 and 75 cm depths in field conditions, the watercontent values calculated at the observation points
placed at the same depths in the soil section in the
HYDRUS/2D program were used. Observation points
placed in the program (points where soil watercontent changes are determined during thesimulation)• We took gravimetric soil samples from depths of 15,
45, 75 cm, we also defined observation points atthe same depths in the domain area.

Statistical Analyses• To check the performance of Hydrus-2D model, three performance indicators namely, 𝑅𝑅2 coefficient ofdetermination, Root mean square error (RMSE ), Mean Absolute Error (MAE) were used, which compared
the observed and the simulated values

𝑅𝑅2 =

𝑛𝑛
∑𝑖𝑖=1
𝑋𝑋𝑖𝑖 − 𝑋𝑋∑𝑛𝑛𝑖𝑖=1 𝑋𝑋𝑖𝑖 − 𝑋𝑋

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 =2

𝑌𝑌𝑖𝑖 − 𝑌𝑌

2∑𝑛𝑛𝑖𝑖=1 𝑌𝑌𝑖𝑖 − 𝑌𝑌

2∑𝑛𝑛𝑖𝑖=1 𝑋𝑋𝑖𝑖 − 𝑌𝑌𝑖𝑖 2
𝑛𝑛∑𝑛𝑛1 𝑋𝑋𝑖𝑖 − 𝑌𝑌𝑖𝑖
𝑀𝑀𝑀𝑀𝑀𝑀 =𝑛𝑛• where Xi and Yi are observed and simulated values, respectively, and n is the number of observations.

Simulated scenarios• In the scenarios determinedin our study, 3 different
irrigation water levels (S33,
S66, S100) and 6 different
lateral depths (10, 20, 30,
40, 50, 60) combinations
were created in the domain.

Treatments

Depth of drip lateral (cm)Irrigation level(%)

D10S3310

33

D10S66

10

66

D10S100

10100

D20S3320

33

D20S6620

66

D20S100

20100

D30S3330

33

D30S6630

66

D30S100

30

100

D40S3340

33

D40S664066

D40S100

40

100

D50S3350

33

D50S660

50

66

D50S100

50

100

D60S33

60

33

D60S66

60

66

D60S100

60

100

Simulated scenarios• In addition to lateral depth scenarios, 2different irrigation strategies were created inour study. In these strategies, the laterals
were placed at both 25 and 50 cm.
• In the first strategy, irrigation water wasapplied at the same time by dividing bothlaterals equally.
• In the second strategy, irrigation water wasapplied alternately to the laterals at 25 cm in
one irrigation and 50 cm in the otherirrigation.

Treatments(D25/50)1/2S33(D25/50)1/2S66(D25/50)1/2S100(D25//50)S33(D25//50)S66(D25//50)S100

Depth of drip
lateral (cm)both 25 and 50
both 25 and 50
both 25 and 50
25 in one
irrigation, 50 in
the otherirrigation
25 in one
irrigation, 50 in
the otherirrigation
25 in one
irrigation, 50 in
the otherirrigation

Irrigationlevel(%)
33
66
100
33

66

100

Calibration process
Statistic

Input parameters• During the calibration phase, a
total of 17 comparisons weremade by changing the van
Genuchten
soil
hydraulicparameters (α, n, Ks shapeparameters) in the model• We changed the values of Ks, αand n until the water content
obtained in field conditions
matched the water content
simulated in the program at a
depth of 0-90 cm , and then themost appropriate values were
determinedusing
certainstatistical parameters.
• Comparisons were evaluatedaccording to statistical analyzes
and α, n and Ks were determined
as 0.005 cm-1, 1.39, 9 cm day-1,
respectively. R2, RMSE and MAE
values in these determinedparameters were calculated as 1
mm, 15.86 mm, 14.06 mm,
respectively.

Simulations

Ks(cm gün1)α(cm-1)

n

R2

RMSE

MAE

1

10.8

0.02

1.41

0.96

52.26

50.40

2

10.8

0.03

1.41

0.90

62.15

58.19

3

10.8

0.05

1.41

0.70

72.53

66.06

4

10.8

0.01

1.41

0.97

38.01

37.06

5

10.8

0.009

1.41

0.97

35.97

34.98

6

10.8

0.007

1.41

0.99

30.43

29.20

7

10.8

0.006

1.41

0.99

27.12

25.69

8

10.8

0.005

1.41

1.0

24.03

22.22

9

10.8

0.005

1.40

1.0

21.62

19.84

10

10.8

0.005

1.39

0.99

19.54

17.76

11

10.8

0.005

1.38

0.99

19.54

17.76

12

10.9

0.005

1.37

1.0

15.86

14.06

13

9.0

0.005

1.37

0.95

50.00

48.17

14

8.0

0.005

1.37

0.95

49.11

46.82

15

11.0

0.005

1.37

0.96

52.42

50.66

16

15.0

0.005

1.37

0.96

55.91

54.50

17

9.0

0.005

1.39

1.0

15.86

14.06

Validation process• After the calibration process, the soil water content values determined by the gravimetric method in the first and the second year field
conditions were compared with the soil water content values obtained from the program for validation. At the end of the validaiton process,the R2, RMSE and MAE values obtained from different treatments varied between 0.80-0.92 mm, 16.76-27.91 mm, and 16.18-24.24 mm,
respectively. For the validation process, D50S100 in the first year and D50S33 in the second year was used.

• After the calibration and validation processes, it was concluded that the HYDRUS-2D program is asuitable tool to investigate the design and management of the subsurface drip irrigation system andsuccessful simulations can be created.
• In the evaluated scenarios, the amount of water uptake by the plant roots, the amount of waterdrained, the distribution of water content in the soil profile of 0-90 cm one day after the irrigation day,and the change in the water content at the depth of 0-90 cm throughout the experiment werecompared.

(D25/50)1/2 S33(D25/50)1/2 S66(D25/50)1/2 S100

(D25/50)1/2 S33 (D25/50)1/2 S66(D25/50)1/2 S100

Soil water content distribution one day after irrigation

(D25//50) S33(D25//50) S66(D25//50)S100

(D25//50) S33(D25//50) S66(D25//50)S100(D25//50) S33

Soil water content distribution one day after irrigation(D25//50) S66(D25//50)S100

D10S33

D10S66

D10S100D10S33

D10S66

D10S100

Soil water content distribution one day after irrigation

D20S33

D20S66

D20S100D20S33

D20S66

D20S100

Soil water content distribution one day after irrigation

D30S33

D30S66

D30S100D30S33

D30S66

D30S100

Soil water content distribution one day after irrigation

D40S33

D40S66

D40S100D40S33

D40S66

D40S100

Soil water content distribution one day after irrigation

D50S33

D50S66

D50S100

D50S33

D50S66

D50S100

Soil water content distribution one day after irrigation

D60S33

D60S66

D60S100

D60S33

D60S66

D60S100

Soil water content distribution one day after irrigation• It was concluded that the HYDRUS-2D
program is a suitable tool to investigate
the design and management of thesubsurface drip irrigation system andsuccessful simulations can be created• In different lateral depth scenarios, the mostsuitable lateral depth for the sorghum plant
was determined as 40 cm, and the mostsuitable irrigation water level was S66 (which

66% of the amount were applied as
irrigation water, when the cumulativereference crop evapotranspiration reached25±5 mm)• In fact, we compared 25 and 50 cm lateral
depths in field studies and found higher
bioethanol yield at 50 cm depth. Since
optimum soil water exchange wasobtained at a lateral depth of 40 cm inthe simulations, we can say that thesimulations agree with the field studies.