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Article

Water Management in Wheat Farming in Romania: Simulating the Irrigation Requirements with the CROPWAT Model

by
Dana Maria (Oprea) Constantin
1,†,
Florentina Iuliana Mincu
2,*,
Daniel Constantin Diaconu
3,†,
Cristina Doina Burada
4 and
Elena Băltățeanu
4
1
Faculty of Geography, University of Bucharest, 1 N. Bălcescu Boulevard, 010041 Bucharest, Romania
2
National Institute of Hydrology and Water Management, 97E București-Ploiești Street, 013686 Bucharest, Romania
3
Interdisciplinary Center for Advanced Studies, University of Bucharest, Panduri 90, 050663 Bucharest, Romania
4
National Meteorological Administration—Oltenia Regional Meteorological Centre, Str. Brestei, 3A, 200581 Craiova, Dolj, Romania
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2025, 15(1), 61; https://doi.org/10.3390/agronomy15010061
Submission received: 16 November 2024 / Revised: 19 December 2024 / Accepted: 25 December 2024 / Published: 29 December 2024
(This article belongs to the Section Water Use and Irrigation)
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Abstract

:
The development of water demand analysis methodologies to maintain agricultural crops at an optimal production level, in relation to current climate changes, is a necessity for many geographical areas. The methodology used uses CROPWAT 8.0 software, in the desire to highlight for an important agricultural region in Romania the need to optimize the water requirement for winter wheat crops. The methodology used was able to highlight this fact, as major changes are needed in future technological processes in the current context of climate change. Based on the modeling of evapotranspiration, effective precipitation, and irrigation requirements, it was obtained that the winter wheat needs four additional irrigations per year (in April, May, and July). The irrigations at critical depletion led to a 100% efficiency of reducing the harvest deficit, during the middle and late vegetation stages. The irrigation required by winter wheat depends on precipitation efficiency, and it is very important for improving crop yield up to 100%. The obtained results provide a methodological framework, but also concrete information for decision-makers in the field of agriculture.

1. Introduction

In the current climate context, with average annual and extreme temperatures constantly increasing [1], with water resources in danger of exhaustion, agricultural productions are strongly affected, especially in agricultural areas with a high risk of drought and with a low potential of adaptation [2,3,4,5,6,7].
Agricultural production is determined both by natural factors (air temperature, precipitation, soil, etc.) and by social factors, such as the scientific and technological level [8,9,10,11]. Thus, there is a need to use hydro-climatic, technological cultivation (irrigation, fertilization, disease, and pest control), and economic information to be able to establish sustainable strategies for adapting to the effects of climate change [12,13,14].
Evapotranspiration (ET) is one of the hydro-climatic processes with a high impact on the water resources needed in order to obtain optimal agricultural production. ET is a combined process by which water is transferred to the atmosphere, from the soil by evaporation, and from the vegetation by transpiration [15]. These two processes are complementary and take place one after the other, so when the crop is small, water is predominately lost by soil evaporation, but once the crop is well developed and completely covers the soil, transpiration becomes the main process [16]. ET is a complex parameter that controls the exchange of energy and mass between terrestrial ecosystems and the atmosphere [17], and it plays an important role in the hydrological budget. It varies regionally and seasonally due to climatic parameters, including temperature, sunshine duration, wind speed, and air humidity, as well as soil characteristics and albedo [18,19,20,21,22,23]. ET is considered a physical phenomenon. If there were no limiting factors between soil and atmosphere, then the water supply to the atmosphere would be continuous, which would lead to a potential evapotranspiration—PET [24,25,26]. So, this one is defined as, what can evaporate from the surface of soil and vegetation, thus that atmospheric conditions at a certain point.
All over the world, many methods have been tested to estimate the PET or the reference evapotranspiration (ET0), by using some climatic parameters like temperature, humidity, wind or vapor pressure, and deficit [27,28,29,30]. In the last decade, indirect methods have also consisted of satellite products that use both in situ data and satellite data, or normalized difference vegetation index and CORINE Land Cover products at different spatial resolutions (e.g., MOD16 satellite product) [31,32,33,34]. The best method with proper results remains Penman–Monteith, which is also the key to CROPWAT 8.0 software. This one was already tested in Romania by [35,36,37,38,39,40,41,42].
Now, different software has been developed by FAO: CROPWAT, ET0 Calculator or AquaCrop in order to calculate crop evapotranspiration (ETc), irrigation requirements (Irr. Req.), and to simulate irrigation schedules for different management conditions [38,42,43,44,45,46,47]. Various researchers such as Bouraima, Tsakmakis, Vozhehova, Makar, and Soomroa have applied the CROPWAT model for major crops, e.g., rice, cotton, banana, sugarcane, berseem, and wheat, in order to obtain ETc and Irr. Req. [48,49,50,51,52].
Thus, a series of different approaches were observed in relation to the increase in air temperature and the reduction in precipitation amounts. Regarding Irr. Req., it either decreases in the case of certain crops predominant in the subtropical climate, such as rice [53], or increases as in the case of wheat, corn, and vegetables grown in desert or temperate climate regions [54,55], bringing with it higher costs in the agricultural economy. The largest crop, in Romania, is that of cereals, representing about 65% of the total cultivated agricultural area [56]. The main cultivated cereals, of strategic importance for the country’s agriculture, are autumn wheat and corn [57]. Romania placed fourth in the European Union (EU) in 2022, due to 9.18 million tons of wheat harvested from 2.1 million hectares [58]. Until now, research concerning Romania has focused on the CROPWAT model for ETc estimation for soybean and wheat crops. They indicated a higher water requirement for soybean crops from the south of Brazil (CWR—322 mm), compared to the most cultivated plant in Romania, wheat (CWR—99 mm); thus, Irr. Req. resulted clearly lower than this, due to the temperate climate [59].
The purpose of this study is to estimate the irrigation requirements for winter wheat in the southwestern part of Romania and to simulate some irrigation scenarios, but the research question is when does the plant need irrigation, precisely in which vegetation stage? More precisely, the research question is what quantities of water are required for winter wheat, and at which stage of development are they necessary, to increase the crop yield and to obtain maximum production in the southwestern part of Romania? This field crop, as a rule, is not exposed to irrigation in Romania, and as a result, the modeling is carried out for the following scenarios of critical depletion and no irrigation, by using CROPWAT 8.0 software. The irrigation at a critical depletion scenario was chosen first of all to identify the periods during the vegetation stages, in which the crop needs a greater quantity of water, in order to not reach moisture depletion, but also because the irrigation required by winter wheat crop over the southwestern part of Romania depends only by precipitation efficiency and is very important for improving crop yield. The study does not aim to present extreme values, but a general picture of the water requirement of the wheat crop, in relation to the current climatic trends. Starting from the results of this analysis, it is desired to expand the study on a national scale.

2. Materials and Methods

2.1. Study Area

The study area is represented by the SW part of Romania (Figure 1). It corresponds to the Southwest Oltenia Development Region (S.O.D.R.), representing 12.2% of the country’s surface and being an important region from the point of view of wheat cultivation [60]. The study area includes the southern and eastern S.O.D.R. and is characterized by a plain relief and a transitional temperate-continental climate with an average annual temperature of 12.4 °C (Caracal meteorological station), precipitation totaling 565.8 mm (Caracal meteorological station), and potential evapotranspiration of 753.7 mm (Caracal meteorological station) for the period 2016–2018.
Climatic data contain monthly, decennial, and daily data of minimum, maximum, and average air temperature, air humidity, precipitation, wind speed, and sunshine duration for the period 2016–2018. The years taken for analysis are three of the warmest years of the period 1900–2018, respectively. The year 2018 represents the third warmest year for the reference period, and the years 2016 and 2017 occupy the 11th and 12th positions for the warmest 15 years in Romania (Mateescu, 2019). Climatic data come from five meteorological stations (M. S.): Băileşti, Bechet, Caracal, Drăgășani, and Slatina, and belong to the Oltenia Regional Meteorological Center. Meteorological stations are located at altitudes between 36 and 280 m (Figure 1 and Table 1) and are considered representative of the study area. Also, these meteorological stations carry out agrometeorological monitoring activities. From the point of view of the variation in meteorological parameters, in the analyzed period 2016–2018, at all 5 stations, the average annual temperature exceeded the value of 12 °C (Table 1), and the precipitation represented the most variable of the elements of the climate, an aspect reflected off the difference in recorded values of the annual amounts of precipitation (Table 1).

2.2. Methodology

The methodology of this study was based on CROPWAT 8.0, which was developed by the Land and Water Development Division of FAO for planning and management of irrigation. All the information regarding the calculation and the method used by this software are described over the papers published by FAO [16,61]. The CROPWAT 8.0 software can be used in order to obtain simple results regarding the ET0 and advanced ones: ETc, Irr. Req., or even some simulation over the irrigation scheduling, yield reduction, or run flow caused by the irrigation campaigns.
The input data consist of (i) climatic and rainfall data, (ii) crop characteristics, and (iii) soil features (Table A1). The accuracy of the output data is always based on the accuracy of the climatic data which in many parts of the world are not reliable. Over this guideline, some general data can be found in CLIMWAT 8.0 software (for CROPWAT)—climatic data, or into the tables, regarding the general crop data, eq. crop coefficient, number of stage days, maximum crop height, or root depth (Table A1).
Based on this simple climatic data (air temperature and humidity, wind speed, sunshine duration, and precipitation), completed by the site location (altitude above the sea level, latitude, and longitude), the CROPWAT 8.0 software estimate the radiation and the ETo. The original Penman–Monteith equation was modified by the owner of the CROPWAT model, in order to be more applicable and simplified, and for greater use in Equation (1):
E T o = 0.408   Δ R n − G + γ 900 T + 273 U 2 e s − e a Δ + γ 1 + 0.34 U 2
where ETo—expressed the reference evapotranspiration (mm/day−1), Rn—net radiation at the crop surface (MJ/m2 day), G—soil heat flux density (MJ/m2day), U2—wind speed at a height of 2 m (m/s), es—saturated vapor pressure (kPa), ea—actual vapor pressure of the air at standard screen height (kPa), γ—psychrometer constant (kPa/°C), Δ—the slope of the vapor pressure curve between the average air temperature and dew point (kPa/°C), and T—air temperature at 2 m height (°C).
For the estimation of ETc and crop water requirement (CWR), some general crop characteristics are needed: planting date, harvest, crop coefficients values (Kc), length of crop development stages (by each stage: initial, development, mid-season, late season), crop height, rooting depth, critical depletion, and yield response. Some of them were completed by the general tables founded in the guidelines, but others we have adapted to the Romanian conditions and by the direct measurements made in situ. So, for the winter wheat crop, the Kc values varied from 0.25–0.4 at the initial stage and late season, to 1.15 during the mid-season [16]. The importance of the Kc values consist of their implication in the estimation of ETc by the Equation (2):
E T c = E T o × K c
where ETc represent the crop evapotranspiration (mm/day−1), ETo—expressed the reference evapotranspiration (mm/day−1), and Kc the crop coefficient.
The winter wheat has a different period of development from one hemisphere to another, and from one climate to another. So, for California, USA, the length of crop development stages is 180 days (the planting date is during December), while for the Mediterranean region, it is 240 days (the planting date in November). In Romania, the length of crop development stages for winter wheat is close to the Mediterranean region (planting date—late September or early October), with insignificant variation from one region to another, so for our study area, the number of days varies from 268 (Băilești MS) to 283 (Bechet MS). For the analyzed periods (agricultural years 2016–2017 and 2017–2018), the development stages took into account the actual planting date for each station (1–6 October) and the harvest date in its case (29 June–11 July) (Table 2). Also, the values regarding the crop height up to 1 m and the rooting depth of 0.4 m have been determined in situ.
The critical period for the development of autumn wheat crops in terms of air temperature and humidity in Romania is between May and June. Then, the optimal temperature for the development of the crop must have daily values between 16–20 °C for the month of May and 16–22 °C for the month of June. For these months, the thermal stress caused to the crop occurs at minimum daily temperatures of 8–10 °C and at maximum daily temperatures of 30–35 °C. The optimal requirement of autumn wheat in terms of precipitation for the critical period of May–June is 80.0 mm for each month [2].
Other data used in this study consist of the soil information on total available soil water content and the maximum infiltration rate for runoff estimates, and, in addition, the initial soil water content at the start of the season is needed [62]. All of that depends on the soil texture (Table 3), so for our study area, the soil ranges from sandy loam (Caracal, Bechet MS), to clay (Slatina MS), to clay loam texture (Drăgășani MS).
One of the most important output data is the CWR, defined as the amount of water required in order to compensate for the ET loss, from planting to harvest, for a given crop in a specific climate regime [16,63]. The difference between the CWR and effective rain (Eff. rain) represents the net irrigation water requirement (NIWR), which is basically the amount of water required to refill the root zone soil water content back up to field capacity. The NIWR is compared generally with the soil water deficit, i.e., the difference between field capacity and current soil water level [46]. The purpose of irrigation is to supply the soil water deficit, especially during dry periods, depending on the rate of loss and the duration of the stressed condition that can affect crop development.

3. Results

The productivity of the wheat crop shows significant fluctuations from one year to the next due to climatic variability.
For the Băilești meteorological station, the optimal thermal requirement is recorded for the critical period for all the analyzed years. Pluviometrically, there is a deficit in the amounts of precipitation for the months of May and June, with the exception of May 2016, in which the required threshold of 80 mm is exceeded (Figure 2A). At the meteorological station Bechet, for the same critical period, the thermal values recorded are optimal. The monthly amounts of precipitation are either surplus (May 2016 and June 2018) or deficit (May 2017 and 2018, June 2016 and 2017) (Figure 2B). For the other weather stations, Caracal (Figure 2C), Slatina (Figure 2D), and Drăgășani (Figure 2E), the recorded air temperature values are optimal for the May–June period. Pluviometrically, the same thing is observed at the weather stations Băilești and Bechet, namely, the prevailing monthly amounts that are deficient compared to the optimal amount of 80 mm. In June 2018, at the three meteorological stations, the optimal requirement was exceeded, the largest exceedance, recorded at the Drăgășani meteorological station, being 252.5% (by 122 mm compared to the threshold value of 80 mm) (Figure 2E).
The ET0 over Romania varied from 300 mm/year to 800 mm/year. The results obtained with the CROPWAT 8.0 software showed that the ET0 from southwest Romania has values between 720 and 800 mm/year (Figure 3), reaching monthly maximums in the summer season. Over the summer months, ET0 values exceeded 130 mm/month in June and July, close to values recorded directly near our study area at some evaporation stations. At daily times, ET0 exceeded 5 mm/day at the end of June, and at the beginning of July.
ETc regarding the winter wheat over the southwest part of Romania during our analyzed periods varied between 378 mm and 444.6 mm, which was dependent on climatic conditions, but also on soil conditions. Larger differences in ETc from one year to another are observed in the case of M. S., where Eff. rain was higher. This was similarly the case in Slatina M. S., where during 2016–2017, Eff. rain was 315 mm and in 2017–2018 almost doubled to 606.9 mm, which also attracted higher values of ETc (Table 4). A larger amount of water in the soil allows an intense evaporation into the atmosphere. The same thing was observed at Bechet M. S. and Drăgașani M. S., where the higher precipitations from 2017–2018 led to an ETc of over 400 mm (up to 50 mm higher than in 2016–2017) (Table 4).
Also, the higher the Eff. rain, the lower the Irr. Req. For the winter wheat over the southwest of Romania, the Irr. Req. varies between 131 mm and 225 mm (Table 5). The lowest requirement is recorded at Slatina, Bechet, and Dragasani M. S. (less than 170 mm), which are located near important watercourses of Romania, Olt and Danube, where the exchange between surface water and soil occurs rapidly. For Caracal and Băilesti M. S., the higher values of Irr. Req. (more than 200 mm) show the significance of scientific planning for irrigation.
The precipitation exceeds the ETc values (10–20 mm/decade) in the initial and development stages, so the Irr. Req. is not necessary during this period. With the intensification of the ETc in the middle and late stage (values of over 40–50 mm/decade), the water demand increases the direct proportion, so the Irr. Req. has values between 30–40 mm/decade (Figure 4). There are no major differences from one year to another concerning the distribution of ETc and Irr. Req. The only slightly different aspect is the fact that for the Bechet, Slatina, and Drăgășani stations, the precipitations that fell in 2018 during the late stage caused the need for irrigation to be reduced in that period of culture (Figure 4).
One of the main results of our study was the actual water use by crop, which varied between 231.9 mm (Slatina, 2017–2018) and 443.3 mm (Bechet, 2017–2018) (Table 5). Overall, it can be seen that the actual water use by crops has lower values for the non-irrigation scenario and for the period 2016–2017. In the case of irrigation at critical depletion, the actual water use by crops is equal to the potential one. Based on the climatic and soil conditions, it is observed that the winter wheat has a deficiency irrigation schedule of up to 43.3%, with a rainfall efficiency of over 60% (Table 5). The application of irrigations at critical depletion leads to 100% efficiency and a reduction in the harvest deficit by up to 33% (Slatina) and even 100% (Bechet).
Although the period 2017–2018 has higher precipitation compared to 2016–2017, it is distributed in the autumn and spring months (October and May/June). Without irrigation, the depletion rate would be higher, i.e., more than 50% over the development and middle stage. The water needs of winter wheat are not covered by rain or other water supply (Table 6). Irrigation at critical depletion consists of irrigation when water stress (Ks) is equal to 1, which represents the ratio between readily available moisture (RAM) and total available moisture (TAM). Knowing these aspects can greatly improve agriculture and the economy based on it, only by completing the water requirements by crop with about four watering periods per year (Figure 5 and Figure 6). According to the CROPWAT results and the irrigation schedule (Table 6), the first irrigation demand and watering is specific for all five stations during the development stage, around 195–200 days after planting, between 11 and 25 April, depending on climatic conditions (Figure 5 and Figure 6). The next two or three watering periods demanded are in May, in the middle stage, distributed at an interval of 15–20 days. Finally, in July, before harvesting, we noticed that due to the lack of precipitation and the intensification of ET, in its final stage of ripening, the wheat tends to approach drying, which justifies one last request for irrigation. For each watering period, the net irrigation supplied is about 55 mm, which leads to a maximum flow of 0.50–0.60 L/s/ha (Table 6). So, the NIWR plus losses in water application and other losses, called gross irrigation requirement, does not exceed 81 mm per watering period, for the winter wheat planted in the southwest part of Romania.

4. Discussion

The correlation between the needs of the analyzed crop and the moisture in the soil coming from the precipitations indicates that additional amounts of water are needed. This validates the study hypothesis.
The CROPWAT model has been used so far on a large scale, for regions known to have a water deficit [64,65,66,67,68] and for the purpose of identifying the irrigation needs for different agricultural crops [44,46,69], fruit crops or perennial plants [38,70]. The objective of the obtained results was to improve the management of the water used in irrigation and to obtain the highest possible yield of the crop. A series of studies have been developed in order to identify the impact of climate change on agriculture and the water requirement for plants [55,71,72].
The obtained results indicate that S.O.D.R. evapotranspiration values for the wheat crop vary between 378–444.6 mm, and the water requirement for irrigation is 131–225 mm, against the background of the effective precipitation between 309–610.6 mm. In the context of international research, the crop evapotranspiration estimated in this study is lower than the mean values estimated for the central and eastern parts of Europe (between 400–800 mm/year) [73]. However, low values of crop evapotranspiration (less than 450 mm/year) were also obtained for other cereals (maize) and oilseeds (sunflower) at experimental stations in Romania [38,47]. Due to the increase in air temperature, an increase in evapotranspiration values (about 50–200 mm/year) is expected at the level in the central and eastern parts of Europe, in the far future [73].
Some experimental studies carried out in different regions of the world (such as Canada, China, Korea, and Romania) exposed to recent climatic, pedological, and economic conditions, sustain the importance of additional watering respective of irrigation quantities, to increase the yield and the productivity of wheat. The irrigation requirement is inversely proportional to the actual rainfall; thus, it increases the lower the amount of rainfall and the less it allows the optimal development of the plant. For the analyzed region, large amounts of precipitation are specific to the initial periods and the development of the winter wheat crop. The maximum water requirement of the winter wheat crop corresponds to the middle and late development period, which makes the precipitations, regardless of their quantity, insufficient, requiring additional irrigation of up to 40 mm/decade. In China, at the level of the two-season field experiment, the effect of the sprinkler irrigation method at 2–2.5 mm of water each time was followed. Significant impact was observed on meteorological parameters, during and after watering, such as high air temperatures by over 2–4 °C and increasing air humidity by up to 10%, which led to the intensification of plant transpiration [74]. In Korea and Romania, some research has shown that due to global warming, heat events occur more frequently during the reproductive growth period of wheat crops, and mean temperatures over 25 °C or 30 °C during the ripening development stage can cause a critical reduction in the wheat yield [75,76]. This fact is also supported by experiments carried out in the last few years in Bulgaria and Romania, which indicated evapotranspiration differences between irrigated crops and non-irrigated crops, of more than 140 mm per vegetative season, especially during the months of July and August [76].
According to Harrison et al. (1996) [77], the wheat yield was predicted to increase throughout Europe, especially in the east, central, and southern parts, despite any climate change scenarios and human intervention. Positive effects were predicted for winter wheat compared to other crops, due to the lower sensitivity to increased temperature or CO concentrations. The rate of increase in winter wheat yields over Europe was estimated at 0.2 t ha−1 decade-1 up to the 2020s. At the same time, using different crop models (CROPWAT, AquaCrop, STICS) and continental crop growth monitoring systems, it was assumed that winter wheat varieties do not change over time, and that it is more an adaptation to climatic changes, as well as the farmers to the requirements of a crop, and to the variety of wheat, to ensure yield stability and performance [78]. The results obtained during the period 2016–2018, however, show considerable differences regarding the modeling of irrigation parameters (actual and potential water use by crop, deficiency irrigation schedule, yield reduction) through the prism of two scenarios, critical depletion and no-irrigation, contrary to what was estimated in previous years at the European level. Thus, in the condition in which the wheat crop is not exposed to additional irrigation, but only to the natural conditions regarding the climate and the soil, actual water use by crops has lower values, and the depletion rate is higher than 50% during the development and middle stages. Also, the yield reduction varies from 17.9 to 43.3%, and it has high values in points with high Irr. Req. more than 40 mm/decade. The application of irrigation at critical depletion leads to a 100% efficiency reduction in the harvest deficit during the vegetation stages in which the crop needs a greater quantity of water. This fact allowed us to understand and emphasize the importance of crop irrigation in order to reduce the water deficit that affects plant development and increase crop productivity. So, the irrigation required by winter wheat crops over the SV part of Romania depends on precipitation efficiency, and it is very important for improving crop yield. According to the CROPWAT results, the winter wheat needs four watering periods per year (one in April, two/three in May, and the last one in July). For each watering, the net irrigation supplied is about 55 mm, which leads to a maximum flow of 0.50–0.60 L/s/ha.
In this study, changes regarding the planted and harvesting date were observed, so a maximum of +4 days was observed around the date of planting (comparing the year 2016 and the year 2017) and up to +11 days in the case of the harvest date. Changes in winter wheat phenology in Romania were analyzed by Croitoru et al. (2011) [37] on data series longer than 30 years, and the results indicate a decrease by 1–3 days/decade in the maturity and anthesis periods, but no change in the grain filling stage. Lazăr et al. (2010) [79] conclude in their study that anthesis and maturity in winter wheat are advanced by approximately one week for each 1 °C increase in temperature.

5. Conclusions

The obtained results represent significant progress in understanding the water requirement for each agricultural crop and the moment when irrigation is necessary. This leads to optimal agricultural yield, and the water resources are not exhausted. The periodic running of the program, with the annual updating of the parameters, allows us to focus on the needs of the culture as faithfully as possible and obtain optimal production.
In order for the agricultural yield to be optimal and the water resources not to be exhausted, the periodic running of the program is recommended, with the annual updating of the parameters that allow orientation to the needs of the culture as faithfully as possible, in order to obtain optimal productions. The knowledge of this information can greatly improve agriculture, and the economy based on it, contributing to decisions in land management [80,81].
Achieving the research objectives was, however, hampered by the lack of data for a longer period of time, as detailed data on climatic factors are needed, but especially precise data on soil moisture, as well as sowing/harvesting of agricultural crops.
We propose to continue the study and apply the CROPWAT model at the national level, in order to identify the way in which irrigation requirements for winter wheat over Romania can improve the yield of the crop and implicitly the national economy.

Author Contributions

Conceptualization, D.M.C.; Data curation, C.D.B. and E.B.; Formal analysis, D.M.C., F.I.M. and D.C.D.; Funding acquisition, D.C.D.; Investigation, D.M.C. and F.I.M.; Methodology, D.M.C. and F.I.M.; Project administration, D.C.D.; Resources, D.C.D.; Supervision, F.I.M. and D.C.D.; Validation, F.I.M., C.D.B. and E.B.; Visualization, D.C.D.; Writing—original draft, D.M.C., F.I.M. and D.C.D.; Writing—review & editing, D.C.D., D.M.C. and F.I.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by a grant from the Ministry of Research, Innovation and Digitization, CNCS/CCCDI-UEFISCDI, project number COFUND-DUT-FEED4FOOD, within PNCDI IV Project title: Vulnerable communities fostering innovation and governance of sustainable building systems in European cities, through project number 50/2024.

Data Availability Statement

Data are available through a request to the corresponding author.

Acknowledgments

Special postmortem thanks to Victor Viorel Vătămanu for his constructive comments and additions that improved the overall quality of the article. This research work was carried out with the support of the Oltenia Regional Meteorological Center from the National Meteorological Administration of Romania. We also thank the two anonymous reviewers for their recommendations which improved the quality of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
ETEvapotranspiration
PETPotential evapotranspiration
ET0Reference evapotranspiration
ETcCrop evapotranspiration
Irr. Req.Irrigation requirements
S.O.D.R.Southwest Oltenia Development Region
M. S.Meteorological station
CWRCrop water requirement
KcCrop coefficients
NIWRNet irrigation water requirement
Eff. RainEffective rain
KsWater stress
RAMReadily available moisture
TAMTotal available moisture
Gr. Irr.Gross irrigation
Depl.Depletion

Appendix A

Table A1. The input and the output data provided by CROPWAT 8.0 software.
Table A1. The input and the output data provided by CROPWAT 8.0 software.
Input DataOutput Data
Climatic data:
           ➢
maximum, minimum, mean air temperature (°C);
           ➢
air humidity (%);
           ➢
wind speed (km/day);
           ➢
sunshine duration (hours);
           ➢
precipitation (mm).
✓
radiation (MJ/m2/day);
✓
reference evapotranspiration (mm/day);
✓
effective rain (mm).
Crop characteristics:
           ➢
planting date;
           ➢
harvest date;
           ➢
crop coefficients values;
           ➢
length of crop development stages (by each stage initial, development, mid-season, late season);
           ➢
crop height (m);
           ➢
rooting depth (m);
           ➢
critical depletion (fraction);
           ➢
yield response (fraction).
✓
crop evapotranspiration (mm/decade);
✓
crop irrigation requirement (mm/decade).
Soil features:
           ➢
soil name and texture;
           ➢
total available soil moisture (mm/m);
           ➢
rain infiltration rate (mm/day);
           ➢
initial moisture depletion (%);
           ➢
rooting depth (cm).
✓
net irrigation requirement (mm);
✓
deficit (mm);
✓
loss (mm);
✓
gross irrigation requirement (mm);
✓
flow (l/s);
✓
yield reduction (%).

References

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Figure 1. Study area localization and analyzed meteorological stations.
Figure 1. Study area localization and analyzed meteorological stations.
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Figure 2. The annual regime of monthly air temperature averages and monthly rainfall amounts at the Băilești (A), Bechet (B), Caracal (C), Slatina (D), and Dragășani (E) meteorological stations for the years 2016, 2017 and 2018.
Figure 2. The annual regime of monthly air temperature averages and monthly rainfall amounts at the Băilești (A), Bechet (B), Caracal (C), Slatina (D), and Dragășani (E) meteorological stations for the years 2016, 2017 and 2018.
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Figure 3. Reference evapotranspiration ETo (mm/year)—CROPWAT results for the study area and period.
Figure 3. Reference evapotranspiration ETo (mm/year)—CROPWAT results for the study area and period.
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Figure 4. CRW—CROPWAT results regarding ETc, Eff. rain, and Irr. Req. for each meteorological station Caracal (A), Băileşti (B), Bechet (C), Slatina (D), Drăgășani (E), during two agriculture periods: October 2016–June/July 2017 (left) and October 2017–June/July 2018 (right).
Figure 4. CRW—CROPWAT results regarding ETc, Eff. rain, and Irr. Req. for each meteorological station Caracal (A), Băileşti (B), Bechet (C), Slatina (D), Drăgășani (E), during two agriculture periods: October 2016–June/July 2017 (left) and October 2017–June/July 2018 (right).
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Figure 5. The variation in RAM and TAM (a) and the irrigation schedule at critical depletion (b) for Caracal M. S. during the period 2016–2017.
Figure 5. The variation in RAM and TAM (a) and the irrigation schedule at critical depletion (b) for Caracal M. S. during the period 2016–2017.
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Figure 6. The variation in RAM and TAM (a) and the irrigation schedule at critical depletion (b) for Caracal M. S., during the period 2017–2018.
Figure 6. The variation in RAM and TAM (a) and the irrigation schedule at critical depletion (b) for Caracal M. S., during the period 2017–2018.
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Table 1. Geographic location data and average annual values of meteorological parameters (2016–2018) recorded at the analyzed stations.
Table 1. Geographic location data and average annual values of meteorological parameters (2016–2018) recorded at the analyzed stations.
Nr.Meteorological Station (M. S.)Altitude (m) Latitude (°′N)Longitude (°′E)201620172018
TaerPTaerPTaerP
1.Băilești57.0044°01′23°21′12.2627.512.0495.412.4630.2
2.Bechet36.043°47′23°57′12.1662.112.1602.012.2651.4
3.Caracal106.044°06′24°22′12.3560.812.3538.412.5598.1
4.Drăgășani280.044°40′24°17′12.1683.712.3663.212.3891.8
5.Slatina172.044°26′24°21’12.0633.512.0634.512.0789.9
Taer = air temperature (°C), P—precipitation (mm).
Table 2. Planting and harvesting dates for winter wheat in southwest Romania, in 2016–2018.
Table 2. Planting and harvesting dates for winter wheat in southwest Romania, in 2016–2018.
NoMeteorological StationPlanting DateHarvesting Date
1Caracal06.X.2016
05.X.2017		01.VII.2017
01.VII.2018
2Băilești04.X.2016
06.X.2017		28.VI.2017
06.VII.2018
3Bechet03.X.2016
02.X.2017		30.VI.2017
11.VII.2018
4Slatina02.X.2016
06.X.2017		29.VI.2017
08.VII.2018
5Drăgășani01.X.2016
03.X.2017		03.VII.2017
06.VII.2018
Table 3. The CROPWAT soil input data.
Table 3. The CROPWAT soil input data.
NoMeteorological StationSoil TextureTotal Available Soil Moisture (mm/m)Rooting Depth (cm)Initial Available Soil Moisture (mm/m)
1CaracalSandy loam240.040168.0
2BăileştiSandy loam
3BechetSandy loam
4SlatinaClay
5DrăgășaniClay loam
Table 4. CROPWAT results regarding ETc, Eff. Rain, and Irr. Req. at annual scale.
Table 4. CROPWAT results regarding ETc, Eff. Rain, and Irr. Req. at annual scale.
M. S.YearETc (mm)Eff. Rain (mm)Irr. Req. (mm)
Caracal2016–2017400.6494.1196.7
2017–2018398.8496.9206.6
Băilești2016–2017378.0309.0225.0
2017–2018424.3492.7210.6
Bechet2016–2017389.5532.9141.3
2017–2018444.6581.7171.1
Slatina2016–2017370.5315.2173.3
2017–2018409.9606.9163.8
Drăgășani2016–2017385.3355.8160.1
2017–2018410.8610.6131.0
ETc = crop evapotranspiration (mm), Eff. rain = effective rain (mm), Irr. Req. = irrigation requirements (mm).
Table 5. Comparative results regarding the non-irrigation scenario no. 1 and the irrigation at critical depletion no. 2, for each meteorological station and study period.
Table 5. Comparative results regarding the non-irrigation scenario no. 1 and the irrigation at critical depletion no. 2, for each meteorological station and study period.
No.M. S.TimeType of IrrigationActual Water Uses by Crop (mm)Potential Water Uses by Crop (mm)Efficiency Irrigation Schedule (%)Deficiency Irrigation Schedule (%)Moist Deficit at Harvest (mm)Actual Irrigation Requirement (mm)Efficiency Rain (%)Yield Reduction %
1Caracal2016–2017Scenario 1278.0399.4-30.427.5120.14930.4
Scenario 2399.4399.410008.4143.6450
2017–2018Scenario 1263.5397.8-33.819.2124.74833.8
Scenario 2397.8397.810005.6141450
2Băileşti2016–2017Scenario 1250.5376.2-33.490.6187.55633.4
Scenario 2376.2376.2100055191.1550
2017–2018Scenario 1285.8432.0-32.452.6161.14732.4
Scenario 2432.0432.010003.9189.6420
3Bechet2016–2017Scenario 1318.3387.5-17.912.653.05417.9
Scenario 2387.5387.510005.986.6480
2017–2018Scenario 1347.4443.4-21.76.673.85521.7
Scenario 2443.3443.310006.6138.6450
4Slatina2016–2017Scenario 1234.6368.7-36.481.8129.67036.4
Scenario 2368.7368.7100055134.9680
2017–2018Scenario 1231.9408.6-43.376.5−41.26043.3
Scenario 2408.6408.6100036.3−26.6580
5Drăgășani2016–2017Scenario 1267.9383.9-30.275.981.27330.2
Scenario 2383.9383.9100043.999.7690
2017–2018Scenario 1285.0409.5030.463.5−41.16030.4
Scenario 2409.5409.5100031.9−8550
Table 6. Irrigation schedule at critical depletion, CROPWAT results for each M. S.
Table 6. Irrigation schedule at critical depletion, CROPWAT results for each M. S.
No.StationPeriodDateDayStageKs (Fract.)Depl (%)Net Irr. (mm)Gr. Irr. (mm)Flow (L/s/ha)
1Caracal2016–201718-Apr195Dev15552.675.20.04
06-May213Mid15855.879.80.51
22-May229Mid15855.479.20.57
01-JulEndEnd19
2017–201819-Apr197Dev15754.878.20.05
04-May212Mid15855.479.10.61
20-May228Mid15754.477.70.56
01-JulEndEnd16
2Băileşti2016–201725-Apr204Mid15754.878.20.04
18-May227Mid15653.876.90.39
04-Jun244End15956.380.50.55
28-JunEndEnd157
2017–201818-Apr195Dev1585477.20.05
02-May209Mid15552.975.50.62
25-May232Mid15553.175.90.38
11-Jun249End15754.577.90.53
06-JulEndEnd14
3Bechet2016–201721-Apr201Mid15855.779.60.05
15-May225Mid15653.876.90.37
30-JunEndEnd16
2017–201822-Apr203Dev15854.277.50.04
09-May220Mid15552.975.60.51
01-Jun243Mid15653.776.70.39
11-JulEndEnd17
4Slatina2016–201719-Apr200Mid15553.175.90.04
11-May222Mid1565477.20.41
30-May241End15855.378.90.48
29-JunEndEnd157
2017–201821-Apr198Dev15955.979.80.05
09-May216Mid15855.679.40.51
26-May233Mid15754.6780.53
09-Jun247End15855.679.40.66
08-JulEndEnd138
5Drăgășani2016–201711-Apr193Dev15651.974.10.04
20-May232Mid1555375.80.22
09-Jun252End15956.981.30.47
03-JulEndEnd146
2017–201820-Apr200Dev15753.476.30.04
10-May220Mid15653.876.90.45
01-Jun242Mid15956.881.10.43
06-JulEndEnd133
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MDPI and ACS Style

Constantin, D.M.; Mincu, F.I.; Diaconu, D.C.; Burada, C.D.; Băltățeanu, E. Water Management in Wheat Farming in Romania: Simulating the Irrigation Requirements with the CROPWAT Model. Agronomy 2025, 15, 61. https://doi.org/10.3390/agronomy15010061

AMA Style

Constantin DM, Mincu FI, Diaconu DC, Burada CD, Băltățeanu E. Water Management in Wheat Farming in Romania: Simulating the Irrigation Requirements with the CROPWAT Model. Agronomy. 2025; 15(1):61. https://doi.org/10.3390/agronomy15010061

Chicago/Turabian Style

Constantin, Dana Maria (Oprea), Florentina Iuliana Mincu, Daniel Constantin Diaconu, Cristina Doina Burada, and Elena Băltățeanu. 2025. "Water Management in Wheat Farming in Romania: Simulating the Irrigation Requirements with the CROPWAT Model" Agronomy 15, no. 1: 61. https://doi.org/10.3390/agronomy15010061

APA Style

Constantin, D. M., Mincu, F. I., Diaconu, D. C., Burada, C. D., & Băltățeanu, E. (2025). Water Management in Wheat Farming in Romania: Simulating the Irrigation Requirements with the CROPWAT Model. Agronomy, 15(1), 61. https://doi.org/10.3390/agronomy15010061

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