Estimating irrigation requirement and scheduling for major crops: Case study in Kampong Thom, Cambodia

The situation is the outcome of both increased water demand and climate change, the shortage of water resources is increasing in Cambodia. In this regard, efficient irrigation water management for vegetable production is a crucial need for farmers. The main crops farmed in Chroab commune, Santuk district, Kampong Thom province, Cambodia, are cabbage, potato, and tomato. This article uses the CROPWAT model to predict the water requirement. The pressure plant was used to measure the soil’s soil water capacity, and the findings ranged from 45.65 to 234.159 mm/m. The analysis showed that the overall CWR for crop water for the entire growing season for cabbage, potato, and tomato was 589.4 mm/165 days; 442.5 mm/130 days; and 585.4 mm/145 days, respectively. The findings of the study contribute to investigating the irrigation water requirements with scientific soil and climate inputs.


Introduction
A large amount of freshwater is utilized by agriculture worldwide, and 60% of crops are produced by rain-fed agriculture, which covers 80% of all cultivated area [1].his has led to an ongoing decrease in the amount of freshwater that can be used for agricultural production [2].Leaving enough water in rivers and lakes to support ecosystems, meet the expanding requirements of cities and industry, and increase agricultural water output is a critical solution to the developing water scarcity.Otherwise, attempts to improve water use efficiency should concentrate mostly on irrigation.Unlike irrigation water that is transported from a river or another body of water, during a crop's growing season, it is "the ratio of irrigation water transpired by the crops of an irrigation farm or project."The irrigation water diverted from a river or other natural source into the farm or project canal or canals during the same period is what irrigation scientists and engineers refer to when describing how effectively water is delivered to crops and when indicating the amount of water wasted at plot, farm, command, or system level.[3].The population growth and improving standards of living have made water shortages a serious problem, necessitating the development of integrated technologies and multidisciplinary water resources IOP Publishing doi:10.1088/1755-1315/1297/1/012051 2 management capabilities [4].However, because they lack a successful irrigation plan, the local farmers rely on merely irrigating their crops and waiting for rain when a severe drought has occurred [5].They simply have no notion when to irrigate their crops or how much water is needed, let alone how much the agricultural produce may be boosted.To improve the effectiveness of water consumption, it is crucial to understand how much water the crops need at various times.To improve the effectiveness of water use, it is crucial to understand how much water the crops need at various times.Therefore, this area requires an efficient and straightforward irrigation strategy [6].This study's goal is to estimate the crop water requirement of cabbage, potato, and tomato.

Study area
The study was carried out in the agricultural areas of Chroab commune, 12°36'48.71"Nlatitude and 105° 1'50.23"Elongitude, covering 40.54 ha, is located in the south of Kampong Thom province as shown in figure 1.It is important to study in this area because it is a Lowland area, where the majority of the residents grow crops to eat and sell for daily survival.Two tropical monsoons have an impact on the local climate.The first monsoon, which lasts from November to April, is the chilly, dry, and northeastern monsoon.The second monsoon, which lasts from May to October, is the humid southwestern monsoon.

Data collection
The required data for this research was acquired get from the site location at Kampong Thom.Weather data require for estimating monthly reference evapotranspiration was considered.Laboratory investigations on soil texture, hydraulic conductivity, and total accessible water were used to test the accuracy of the soil data.The crop data was proposed in the CROPWAT.The following sets of data must be present in order to run a simulation of the Cropwat model: climate data, rain data, crop data, soil data, and irrigation criteria.Evapotranspiration is determined by the climate and is computed using the Penman Monteith formula, which is used in Cropwat.Rain reduces the amount of irrigation water left on the ground, saving water.Effective precipitation, as it relates to agricultural productivity, is the amount of rain that plants can really use.That is to say, not all rain falls on crops since part is lost to deep percolation (DP) and runoff (RO).Cropwat includes four techniques for calculating effective rainfall.The FAO/AGLW formula, which is a reliable rain approach, was applied in this study.P is the amount of rain that falls each month in millimeters.

Table 2. Crop data
Because soil is an essential component of irrigation systems, it is important to understand the characteristics of the soil in rice fields.Soil texture so affects the saturation, field capacity, wilting point, infiltration, and percolation.These characteristics regulate how much water is kept in the root zone.For this study, there were used a set of typical cabbage crop coefficient data files, as provided in the program of CROPWAT (FAO).The cabbage, potato, and tomato varieties were used to do the experimentation of estimating the water requirement.The cabbage, potato, and tomato was planted on 1 December for 165 days, 130 days, and 145 days in dry season, respectively.

Figure 3. Crop water requirement of cabbage
Cabbage's evapotranspiration during its 165-day growth period is 589.4 mm.The cabbage only needs 73.3 mm per decade, in the beginning, to make up for the water needs of crops.It makes sense that the cabbage crop started to use a lot of water during the growth season.At the beginning of the decade in the growth phase, the water needs for cabbage ranges from 23.4 to 25.9 mm.Then, in January and February of the development-season stage, it rises from 23.7 mm to 41.2 mm.The decade in which the cabbage grows to its greatest height and uses the most water has an evapotranspiration range of 44.3 to 48.8 mm.Finally, the water requirement of cabbage decreases linearly from 48.2 to 16.9 mm in the late season.In the 145-day growth cycle, the tomato's evapotranspiration is equal to 519.5 mm.The tomato only requires a small amount of water in its early stages, between 20.1 and 20.6 mm per decade for yields.At the development stage of the decade in the growth phase, the water demand of the potato ranges from 22.2 to 36.9 mm.The tomato's annual evapotranspiration varies from 39.4 mm to 48.8 mm throughout this decade, when it uses the most water for growth.In the late season, cabbage's water need drops linearly from 54.4 to 14.9 mm.

Discussion
According to [8], with the estimation of cabbage's crop water demand (CWR) in Erbil being 604.1 mm and the irrigation need being 448.7 mm.The irrigation requirement in Chamchanmal is 401 mm, and the CWR for potatoes is 491.2 mm.At Zakho, the tomato CWR is 658.1 mm, and 545 mm of irrigation are needed.So, it can be concluded from the comparison of the current study to the prior research that CropWat can be used to compute crop water requirements with acceptable results and that it can also disseminate information to communities.

Conclusions
The findings of Cropwat's research, cabbage requires a crop water requirement of 589.4 mm.while 410.3 mm is needed for irrigation.The potato's irrigation water requirement is 352.3 mm, the tomato's irrigation water requirement is 519.5 mm, and the potato's irrigation water requirement is 442.6 mm.Irrigation management is really important.Water will either be conserved or not wasted.Since the water is well-managed, the irrigation system will be expanded, and when this expansion is put into place, a growing number of work opportunities occur at once.This will help Cambodia, a developing nation largely dependent on the agricultural sector, reduce poverty.We think that by strengthening the irrigation system, our farmers will be able to produce more crops for both domestic consumption and international exporting, which will lead to the sustainable development of our nation.

2. 3 .
CropWat modelBased on soil, climate, and crop data as well as current or new irrigation climatic data and crop demands, CROPWAT 8.0 is freeware for calculating agricultural water requirements.The application also enables supply system calculations for a variety of farming patterns and the creation of irrigation programs for various management scenarios.The model can provide data that are crucial for the design of the channel and actually aids irrigation engineers in analysing how an irrigation system using a different culture uses crop water.Additionally, Using CROPWAT 8.0, farmers may evaluate their irrigation practices and forecast crop yield in irrigation-and rain-fed situations.The two FAO publications from the Irrigation and Drainage Series, No. 56 "Crop Evapotranspiration -Guidelines for computing crop water requirements" and No. 33 "Yield response to water," serve as the foundation for all calculation methods in CROPWAT 8.0.

Figure 4 .
Figure 4. Crop water requirement of potato

Figure 5 .
Figure 5. Crop water requirement of tomato

Table 1 .
Data collection of this research

Table 3 . soil data Soil texture: Sandy loam
Noted: Total available water = Field capacity -Wilting point