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5AGRICULTURAL SCIENCES
JUSTIFICATION OF CROPS WATER DEMAND AT THE ARARAT CONCAVITY OF THE RA IN
CLIMATE CHANGE CONDITIONS
Yeghiazaryan G.,
Department of Water and Land Resources Management, Armenian National Agrarian University, Doctor of Science, Researcher Yeghiazaryan A.,
Department of Water and Land Resources Management, Armenian National Agrarian University, Candidate of Science, Researcher Galstyan M.,
Scientific Center of Agriculture of the Republic of Armenia
Doctor of Science, Researcher
Ghukasyan A.,
Scientific Center of Agriculture of the Republic of Armenia
Candidate of Science, director Miroyan S.
Department of Water and Land Resources Management Candidate of Science, Researcher DOI: 10.5281/zenodo.7513801
Abstract
The current research work deals with the development of estimation and projection algorithms for crops water demand in agro-climatic conditions of three soil types in the lowland and piedmont zones of the Republic of Armenia. The development phases of the plants in 9 groups cultivated in the investigated area have been studied and the Kc coefficients for the mentioned plants have been specified, and then, ETC has been determined. A new mathematical algorithm has been developed, which enables to determine the crops water demand more precisely in different soil and climatic conditions. Projection of crops water demand has been carried out for the years with 50, 75, 95% supply of evapotranspiration deficit as of T.1i=i(ETai - Pt).
Keywords: Irrigation water demand, FAO-56, Evapotranspiration deficit, Irrigation regime, Soil and climatic condition, Plants development phases.
The research has been conducted with the support of the RA Science Committee within the framework of the scientific topic coded as 21T-4C087.
Introduction: According to the international expert research, the water deficit on the globe may reach 40 % by 2030. Therefore, there is no other way left for humanity than using the current water resources efficiently. Multiple studies on the water resources of Armenia indicate that their efficient use is still far from reality [1, 2]. In particular, more than 80% of the annually stored surface flow is used for irrigation purposes in agriculture. Over the past 20 years, the availability of fresh water resources per capita has decreased by more than 20% [3]. Naturally, it is a primary task to solve the issues related to the efficient use of irrigation water in agriculture and justification of crops water demand makes 95 % of its content scope [4]. There are great deviations between the water demand set up by irrigation norms and the actual irrigation regimes. Very often the actual irrigation norms exceed the values set upon the regime in 2-5 times [5]. Such deviations are related to a number of reasons; besides, it is very important to specify the crops water demand during the vegetation period [6]. Per the current norms the crops water demand has been determined through the simplest calculation models, which doesn't consider a number of principle approaches being used in the international practice [7].
Among these principles the application of more generic and precise models in determination of the crops water demand is involved, then the climate change impact on the meliorative regime of the given area should be taken into account and the next approach implies evaluation of the effect of crops development phases and soil medium on the total water consumption rate.
Materials and methods. The research site covers lowland and piedmont areas of the Republic of Armenia, which are located at the altitude of 800-1500 m high above the sea level. The average long-term temperature fluctuates within +2,7...11,9 0C, in summer months the maximum temperature amounts to +42 0C, the average relative humidity is 60 %, the number of sunshine days is 2600 hours. The researched sites are distributed in a semi-desert zone; they are characterized with dry and drought periods, as a result of which it is impossible to manage agricultural activities without irrigation. In the researched area cucurbits crops, vineyards and orchards are developed. The study area is involved in the basin of the river Araks, wherefrom 60-65 % of the annual flow is recorded in spring months [8].
Justification of the crops water demand aims to plan the watering process in the temporal and spatial
medium in a way so as the crops could avoid the abrupt stresses related to climate change impacts and retain the optimal humidity regime in the root system [9]. The planning is usually implemented through the development of irrigation regime [4, 10]. Irrigation regime is the integration of crops watering (mt) and irrigation norms (Mi), watering number (n^) and time periods (Ti). It also enables to develop combined irrigation regime for the crops (^^l=1mi,Mi,ni,Ti), which supposes combination of irrigation regimes for different crops through graphical-analytic method [11]. Anyhow, it should be taken into consideration that in order to develop the crops irrigation regime, first it is necessary to acquire data on water consumption regime (estimated evapo-transpiration: ET0 , total crops water consumption: £Tc,)for the same crops. Anyhow, it is obvious, that water consumption value depends on soil and climatic conditions, biological characteristics of the individual crop, as well as on the land and water use technologies and organization methodology [12, 13]. In the current work the total water consumption norm is determined based on the computation of the estimated maximum evapo-transpirations (ET0), which has been calculated per the plant coefficient (Kc) according to the plants development phases. According to FAO-56 method, which is developed based on Penman-Monteith equation, it is recommended to determine the plant's daily water demand through the following formula [4 , 14]:
ETC = Kc * ET0,
(1)
N
ARAGATSOIN
ARMAVIR
where ETC is the total water consumption of the crop, ET0 is the value of maximum estimated evaporation, mm, Kc is the crop's coefficient. Initial phase of plant development:
Kc = fwK
cini(tab).
Intermediate phase of plant development:
(2)
К — jz лcmid лcmidtable
+ [0.04(U2 - 2) 0.004(RHmin
«АЗ)'
(3)
Final phase of plant development
Kcend Kcendtable + [0.04(U2 - 2)
- 0.004(RHn
(4)
where Kcini,Kcmid,Kcend are plant's coefficients in the experimental conditions, fw is the humidified soil segment against the whole territory, U2 is the average daily wind speed at 2 m height, m/s, RHmm is the daily average relative humidity, h is the plant's average height /m/ during the specific phase of the plant development [4].
Determination of the crop irrigation water demand and irrigation norms has been conducted based on the data of meteorological stations installed in the research area (Ошибка! Источник ссылки не найден.).
Legend A Meteo stations
Figure 1 Installation of meteorological stations in conditions of Ararat concavity
Results and discussion. The development of various water-saving measures and technologies can have different effects on the efficiency of water use for plant irrigation. The investigations indicate that water saving measures promote the reduction of total water consumption value and yield capacity increase [15]. Climate change can considerably affect ET0 value. It has been found out that the seasonal, monthly and yearly changes of meteorological parameters influence ET0 value, particularly during the vegetation period. Decreasing tendency in ET0 is also observed related to agro-climatic parameters [16].
Vegetation studies show that in conditions of irrigation water deficit, evapotranspiration can be regulated due to a number of agrotechnical measures (fertilization, mulching, pre-sowing treatment) [3]. The results show that in case of 70-80% FC 20-30 % waer saving can be recorded. Under such circumstance water use efficiency is highly significant [15]. The main characteristics of the new approach for crops water demand justification consists in the fact that the estimated maximum deficit (defET0) is developed based on the long-term and short-term data of hydro meteorological stations for the years with different irrigation
rates. Hereby, the above stated approach enables to possibly adjust different rates of irrigation regimes and make it more tailored to the data of meteorological stations for that specific year. The following was considered as an estimated value:
defET0 =ET0-P (5)
where ET0 is the maximum estimated evapotranspiration , the value of which is determined through FAO-56 method, P is the atmospheric precipitations during the vegetation period.
Taking into account the fact that hydrological phenomena are multi-factorial, and the final result is obtained under the influence of various and many factors, therefore, the identification of patterns for the expected result is possible only by using statistical methods. The supply rate (Qt) of hydrological specifications is determined through the following formula:
can be determined and the experimental and theoretical supply curves can be designed. Arithmetic mean:
X = ■
Relative values of the measured X variable:
K = —
x
Variation coefficient:
Cv =
N
UÎM -1)
(7)
(8)
(9)
Qi =
m - 0,3 n + 0,4
x 100%
(6)
(n-1)
To design the theoretical supply curve Foster-Rybkin table has been used with the following formula for modulus factor:
Kp = (pp Cv +1 (10)
Ordinates of theoretical supply:
where m is the number of hydrological value among the n series.
Possessing a long series of hydrological values per years the supply rate of each member in the tested series
Xp = xi
■K,
p
(11)
In the calculations we assume that [7, 14]
Cs = 2Cv^e (12)
Figure 1 Digital map of the main soil types and subtypes distribution in the Ararat valley and piedmint zones
n
2
In the researched area three main soil types are common: irrigated meadow gray, semi-desert gray and brown soils (Figure 1).
Irrigated meadow gray soils have been formed in the areas of the Ararat valley at 800-950 m altitude. Soil strength: 80-120 cm, poor humification: 1.5-2.0 %, carbonization: 3,7 %, alkaline reaction (pH=8.2-8.5). Semi-desert gray soils are distributed at the altitudes of 850-1250 m. The strength of humus horions: 25-40 cm, the profile is rocky and skeletal. They contain great amount of carbonates (in the upper soil strata up to 818 %). The humus content fluctuates within the range of 1.5-2.0 %. They are also endowed with weak and average alkaline reaction (pH=7.5-8.5). The mentioned soils are poorly provided with mobile nitrogen, poorly and averagely provided with phosphorus, whereas
potassium content is at mid and high level. The brown soils are formed at the altitudes of 1250-1950 m in the steppe zones of Ararat concavity. The soil strength makes 30-40 cm, humification makes 2.0-4.5 %, they are endowed with weakly alkaline and alkaline reaction (pH=7,4-8,5). Hydro physical properties are not favorable. These soils are poorly provided with mobile nitrogen, poorly and averagely provided with phosphorus, averagely and well provided with potassium [17, 1218, 19]. The structure of crops cultivated in the irrigated conditions of the researched area is introduced in the diagram below. The crops developmental phases and their characteristic indicators are presented in Figure 2 and Figure 3.
Days 120
1 III ill .11 ill III III III . I..
Phase 1 ■ Phase 2 ■ Phase 3
Figure 2 Duration of crops developmental phases
0,2
0,4
0,6
0,8
1,2
1,4
0
1
I Phase 3 Phase 2 Phase 1
Figure 3 Crops ' coefficient factors per developmental phases
Crop coefficient
The climatic indicators of the last 30 years provided by 11 stations were studied in the research area. Those data were subjected to statistical processing so as it would be possible to identify the years of 50 %, 70 % and 95 % moisture supply for defET0. The designed theoretical and empirical curves of moisture supply have enabled to enhance the estimated moisture supply years and to assume their climatic indicators as
an estimated baseline value. Based on the climatic indicators of the estimated year, the maximum evapotranspirations for the years of 50 %, 75 % and 95 % moisture supply has been calculated through FAO-56 method with the support of CROPWAT software application. Particularly the data of "Yeghvard" hydrometeorological station are presented in Table 1, Table 2 and Table 3, which is characteristic in the distribution areas of semi-desert gray and brown soils.
Table 1
Yeghvard (50% moisture supply ,1336 m)_
III IV V VI VII VIII IX X XI III- XI
T-max( 22.2 23.0 25.9 35.6 38.3 35.0 32.5 27.6 14.5 28
1 mm ( / -1.7 0.3 7.2 10.8 15.7 14.9 10.0 1.6 -3.0 6,2
P(mm) 45.9 19.3 94.1 60.4 28.6 16.4 5.5 55.6 34.8 361
RH (%) 62 57 66 58 47 50 48 58 73 58
V(m/s) 2.1 3.0 2.5 3.8 5.0 5.4 4.0 2.5 1.4 3.3
Table 2
Yeghvard (75% moisture supply ,1336 m)_
III IV V VI VII VIII IX X XI III- XI
T-max( C) 15.0 24.8 31.3 36.8 37.5 35.5 33.5 24.1 18.5 28.5
T (°) 1 min \ ) -5.8 0.8 4.5 9.5 15.1 16.6 6.3 -1.2 -2.8 6.8
P(mm) 73.1 38.6 68.1 1.5 22.4 2.1 19.9 19.4 28.9 274
RH (%) 70 52 52 38 48 39 48 55 74 53
V(m/s) 2.4 2.9 3.7 4.9 4.9 5.6 4 2.7 1.8 3.7
Table 3
Yeghvard (95% moisture supply ,1336 m)_
III IV V VI VII VIII IX X XI III- XI
T-max( C) 16.9 24.4 26.1 32.2 34.0 32.5 32.2 25.4 17.0 26.7
T (°) 1 min ( ) -8.9 -1.4 6.6 8.3 12.1 12.4 8.3 1.3 -1.3 4.1
P(mm) 66.2 44.0 55.8 17.3 19.5 2.8 15.9 12.6 24.1 258
RH (%) 61 57 63 54 51 48 49 53 70 56.2
V(m/s) 2.5 3.1 3.1 3.9 5.5 5.4 3.4 2.8 1.5 3.5
ET0,
mm/
day
6 7 months
10
11
12
Figure 4 Estimated maximum evapo-transpirations Yeghvard (1336m)
1
2
3
4
5
8
9
ET0, 7 mm/ day
68 months
10
12
14
0
2
4
Figure 5 Estimated maximum evapo-transpirations Armavir (868m)
Atmospheric precipitations also undergo considerable changes per years. In conditions of Ararat valley, the maximum value has made 380 mm, the minimum one- 140 mm, the decreasing amount was 63 %. In the piedmont zone it has the following indices: maximum value - 560 mm, minimum one - 350 mm,
whereas the decreasing amount made 38 %. Change dependencies of atmospheric precipitations per the data of the last 30 years are introduced in Figure 6 and Figure 7.
500
400
£ 300
p io
ai .n a
LO
a
§ ~ 200 c Q.
ti
< <J
re100
2010 2003 2006 2015 2009 2020 2018 2016 2014 1999 1996 2004 1997 1998 2017
Figure 6 Changes in atmospheric precipitations for Armavir region
P, mm
600 500 400 300 200 100 0
^-OCT><-IO(Nl000*-l^-00(NCT>L/lCr)l0L/ll^l^Cr)O CT><HO<H(NOI<H<HO<HCT><HCT><HCT>CT>CT>CT><H<HO aioooooiooooaioaioaiaiaiaiooo 122221222212121111222
Figure 7 Changes in atmospheric precipitations for Yeghvard region
ET0 (mm)
1200 1000 800 600 400 200
•Yeghvard •Armavir
2345
OlOlŒtOlŒtOlOlOl OlOiOiOlOlOlOlOl
MOOlOHNcn^mi!!
0000000 0000000
78 90 1 2 3 4 5 6
000<H<H<H<H<H<H<H 0000000000
S M Ol o 1112 0000
(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N(N
Years
Figure 8 Dynamics of crop's water demand
Considering the estimated evapotranspirations and the dynamics of atmospheric precipitations the deficits of estimated maximum evapo-transpirations have been calculated. The results are presented in Figure 8.
According to the data of piedmont zone, the maximum irrigation water demand has made 1230.4 mm, the minimum water demand - 774.5 mm, the average value has amounted to 969.5 mm. The maximum irrigation water demand in the lowland areas
has made 1046.6 mm, the minimum one -536 mm, while the average value makes 780 mm. For practical computations the years of 50 %, 75 % and 95 % moisture supply are assumed as estimated, which supposes that the obtained water demand value will be characteristic to the periods with average moisture supply (50 %), dry years (75 %) and very dry years (95 %). The results descriptions are introduced in the form of diagram in Figure 9 and Figure 10.
0
0
Q,%
120,0 100,0 80,0 60,0 40,0 20,0 0,0
J
200 400 600 800 1000 1200
def=ET0-P,mm
Figure 9 Supply curve for estimated maximum evapo-transpirations deficit (Armavir region).
Q,%
120,0 100,0 80,0 60,0 40,0 20,0 0,0
0
/
200
400
600
800
1400
1000 1200
def=ET0-PP,titi
Figure 10 Supply curve for estimated maximum evapo-transpirations deficit (Yeghvard region).
The results of irrigation water demand for different crops depending on the plant developmental phase and evapo-transpirations deficit index for the climatic conditions of lowland and piedmont zones are introduced in Figure 11.
500 400 I 300 , 200 ^ 100 0
Traditional young vineyard
iJ
50% 75% 95%
Traditional productive vineyard
500 400 I 300 200 100 0
i
50% 75% 95%
initial medium final Total
Orchard
500 400 I 300 200 " 100 0
I.I
r /
50% 75% 95%
500 400 I 300 ^ 200 100 0
Tomato, pepper,eggplant
IA
initial medium final Total
50% 75% 95%
0
600
£ 400 EE
S 200 0
Perennial vegetable crop
a.I
Tobacco
* s
^ ^
600
■ 50% E 400
E
■ 75%
200
■ 95%
50% 75% 95%
initial medium final Total
Maize
600 ! 400
200
I.I
# ^ ^
800
600
■ 50% E
E 400
■ 75% S
200
■ 95%
Leguminous crops
IA
initial medium final Total
50% 75% 95%
Figure 11 The planning results of crops' irrigation water demand 800-1000m.
Conclusion. In the result of theoretical and empirical research crops water demand computation and planning algorithm has been developed, which has been applied in conditions of three soil types in the Ararat concavity of the Republic of Armenia. Analysis of agro-climatic indices for 1991-2020 years have been conducted and the estimated maximum evapo-transpi-rations have been calculated through FAO-56 methodology. For the projection of irrigation water, the years with 50 %, 75 % and 95 % moisture supply for the maximum evapo-transpiration deficit has been considered, based on which the values for ET0 have been determined. Crops from 9 groups have been considered and their ETC per the plants developmental phases have been determined. The selected areas are located at the altitudes of 800-1500 m above sea level: the lowland area is 800-1000 m high above the sea level, whereas the piedmont zone is at 1000-1500 m altitude above the sea level. In the research sites the climatic indices of the last 30 years retrieved from 11 meteorological stations have been studied, particularly
TmaxT¡min,RH, tshP, V. A new mathematical algorithm has been developed which enables to plan the crops water demand more precisely in any soil and climatic conditions and to use it for the problem solution in the sustainable management of irrigation water. The crops water demand has been determined for the years with 50 %, 75 % and 95 % moisture supply to the evapo-transpiration deficit, which looks as follows:
Pi).
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