INTRODUCTION
The 282 Act of the Ecuadorian Constitution reads ¨The State will Regulate Irrigation Water Use and Management for Food Production, under Equity, Efficiency and Environmental Sustainability. ¨
Though Ecuador is a country with a huge irrigation potential (more than 3 million hectares), total surface under irrigation is 942 thousand hectares. This means less than third part of the potential surface to be irrigated. The Irrigation & Drainage National Plan 2012-2026 stated that ¨…during these years, problems have been accumulated: the shortage of water availability, the increase of pollution influencing water quality, inequities in water access, low level of technology modernization and efficiency, barriers in water management coming from the responsible institutions, weakness in systems of management, operation and maintenance organizations, among others¨. (MAGAP, quoted by Pérez et al. (2018).
There are studies on irrigation regime on cotton done in Center and South America (Méndez et al., 2001), sugar cane (Avalos and Pacheco, 2012),banana (Toro et al., 2016) and potato (Sifuentes et al., 2018). In Ecuador irrigation regime researches have been developed on a variety of crops associated to pre and postgraduate papers, however, few scientific publications have been found about the theme. One of the most interesting papers is the one developed by Caicedo et al. (2015), where three schemes of irrigation scheduling for banana (Musa paradisiaca). One of the most popular computing tools for determine irrigation scheduling is CROPWAT version 8.0 (Swennenhuis, quoted by Caicedo et al. (2015), This version can be used for estimating crops´ water requirements based on climate, phenological and edafological data (Toro et al., 2016). Other authors such as Sosa et al. (2019), use this tool to search for relationships between Evapotranspiration of the Reference (Eto) and rainfall and predict the increase of the irrigation dose as climate changes (Duarte et al., 2017).
However, the program continues been limited because it considers Penman-Monteith method proposed by FAO for estimating Eto. One of the main limitations of this method is that it requires of precise measurements of air temperature, relative moisture, solar radiation and wind speed (Popova et al., qouted by Pinto et al., 2016).
In the proposal of an Irrigation Integral Management Model in Ecuador (Secretaría del Agua, 2016), it is stated ¨there is lack of programs complementary to the construction of the physical work, such as training and technical assistance programs, …¨. In the updating of Irrigation and Drainage National Plan 2018-2021, carried out by the Irrigation and Drainage Division (2018), it is recognized there is a negative water balance in some basins of Manabí province and it is proposed as an strategic objective ¨To improve efficiency and enlarge public and community heritage of irrigation and drainage in a sustainable management¨. Simultaneously to these policies, since January 2018, the University Lay Eloy Alfaro of Manabí developed the Research Project ¨Edaphoclimatic Study for Designing and Operation of Irrigation Systems in Manabí¨.
The present paper is a continuity of studies published by Pérez et al. (2018a, 2018b), focused on the study of climate variables and hydrophysical soil properties in agricultural areas of Manabí Province. The objective of this study was to define the Irrigation Regime of five crops of economic interest from the water balance developed in different sceneries in the province.
METHODS
To develop this survey, three agroproductive areas of interest were chosen at Manabí province: Northern part of Chone Province, San Ramón at Sucre Province and Mapasinge at Portoviejo Province. A spatial representation of the three zones is shown in Figure 1.
(Source: Elaboration of the Authors)
FIGURE 1.
Location of the three survey areas at Manabí Province.
Definition of Climate and Soil Features
This paper is based on the statistical analysis of the 23 years observing series in 49 meteorological stations in Manabí developed by Pérez et al. (2018a), to define rainfalls at 75% of probability and Crop Reference Evapotranspiration (Eto) of 25% occurrence probability. For water balance Eto values were taken, through Hargreaves-Samani method, due to the observations by De Figueredo et al. (2016), confirmed by Pérez et al. (2018a), who obtained more reliable results because of the lack of data at Manabí, Ecuador for applying Penman-Monteith method, considered by Sousa et al. (2016).
The hydrophysical properties of soils have been defined from trials ¨in situ¨ established by Pérez et al. (2018b) in the surveyed areas.
Definition of Crops´ Features for Irrigation Schedule
In this study, five crops of economic interest in the Province were considered: orange (Citrus sinensis), cocoa (Theobroma cacao), banana (Musa paradisiaca), papaya (Carica papaya) and passion fruit (Passiflora edulis).
Root depth data (H), crop coefficients (Kc) for calculating Evapotranspiration (Eto) for every phase of development and life cycle of each crop are shown on Table 1, taking into account authors´ considerations and the soil water depletion fraction for no stress (p) as defined by Allen et al. (2006).
TABLE 1.
Values of crop coefficient (KC) and depth to be moisture (H) for development stages for each crop, according to authors´ recommendations
| Crop | Development stage | p | Source | ||||
|---|---|---|---|---|---|---|---|
| Orange | Days | 60 | 90 | 120 | 95 | 50 % | Allen et al. (2006) Calderón (2014) |
| Kc | 0.70 | 0.70 | 0.65 | 0.70 | |||
| Days | 365 | ||||||
| H (m) | 0.80 | ||||||
| Cocoa | Days | 365 | 30 % | Allen et al. (2006) | |||
| Kc | 0.90 | ||||||
| Days | 365 | ||||||
| H (m) | 0.70 | ||||||
| Banana | Days | 120 | 75 | 45 | 35 % | Allen et al. (2006) Toro et al. (2016) | |
| Kc | 1.0 | 1.2 | 1.1 | ||||
| Days | 240 | ||||||
| H (m) | 0.60 | ||||||
| Papaya | Days | 60 | 90 | 60 | 155 | 35 % | Allen et al. (2006) Chaterlán (2012) |
| Kc | 0.90 | 1.00 | 1.10 | 0.90 | |||
| Days | 365 | ||||||
| H (m) | 0.60 | ||||||
| Passion fruit | Days | 60 | 210 | 95 | 50 % | Allen et al. (2006) Vinuesa (2009) Calderón (2014) | |
| Kc | 0.70 | 0.65 | 0.70 | ||||
| Days | 365 | ||||||
| H (m) | 0.60 | ||||||
For estimating Water Schedule of the Project of each crop, four sceneries were analyzed starting from the results obtained by Pérez et al. (2018b):
Chone with fine texture soil (CH -TF)
Chone with medium texture soil (CH -TM)
Mapasingue with medium texture soil (MP-TM)
San Ramón with medium texture soil (SR-TM)
At the same time, irrigation for each scenery was analyzed for three p values (minimum recommended for each crop, a decrease of 25% of this value from considering hot and dry atmosphere conditions of Manabí, both values taking into account recommendations of Allen et al. (2006) and a steady value p= 15% for all crops). This fact generated 60 irrigation variants (five crops x four sceneries x three-soil water depletion fraction for no stress).
For estimating Project´ s Irrigation Schedule the proceedings described in the Cuban standard 48-46, cited by Duarte et al. (2015) were used. In that document, Kb values were replaced for the Kc ones of each crop shown at Table 1.
Once Project´ s Irrigation Schedule was defined, determining maximum Evapotranspiration of each crop and the fictitious flow rate were the following steps. These elements were the basement for hydraulic design of pressure irrigation systems (localized irrigation system or sprinkler irrigation system).
Critical Crop Evapotranspiration was obtained dividing monthly evapotranspiration of highest consumption (critical month) by the amount of days of the month.
Fictitious net flow rate: Obtained for critical condition by the following expression:
RESULTS AND DISCUSSION
Water requirement calculations corresponding to each crop in the four sceneries were done. The results obtained for orange crop are summarized in Table 2.
TABLE 2.
Summary of the Annual Orange Irrigation Regime in Four Scenarios, expressed from Evapotranspiration, Effective Rainfall, Total Dose and Number of Irrigations
* Extreme value of p= 50% is defined according to Allen et al. (2006).
As it can be appreciated, there was a trend to increase dose and number of irrigation as value p decreased. Higher irrigation requirement was evident in San Ramón area (SR) due to the existing evapotranspiration and effective rainfall conditions. The annual doses to apply to orange crop were from 349 mm-743 mm. These results were lower to the annual 800 mm obtained by CEBAS and CSIC (2014) at southern Spain in an arid climate with rainfalls lower than 300 mm a year. They were also inferior to the results reported by Santos et al. (2018),which were between 1270 mm and 1306 mm per year. However, there is a coincidence with values reported by Wiegand and Swason (cited by Levy & Boman (2003), in Texas.
The annual irrigation regime for cocoa tree cultivation, summarized in Table 3, showed irrigation values from 641 mm to 1062.2 mm a year. It was corroborated, Chone zone with less water requirements and irrigation amount during the year goes between 7 and 26 according to the soil water depletion fraction for no stress (p) selected to manage water regime.
TABLE 3.
Summary of the Annual Cocoa Irrigation Regime in Four Scenarios, expressed from Evapotranspiration, Effective Rainfall, Total Dose and Number of Irrigations
*Extreme value of p= 30% is defined according to Allen et al. (2006).
The results were very similar to those recommended by Rodríguez et al. (2010), for Manabí with values from 500 to 1200 mm a year. There was also similarity with the results obtained by Romero & Proaño (2008) in their study developed in Santa Elena Peninsula, in Ecuador. In that paper, annual irrigation doses were obtained for cocoa tree between 1023.93 and 1535.9 mm for different drip management conditions.
Nevertheless, some authors like Motato & Pincay (2015), make emphasis in paying close attention to water quality more than the quantity of water for irrigation of this crop due to salinity problems found in Manabí ´s subsurface water.
For the cultivation of banana, figures of greater magnitude were obtained, as shown in Table 4.
TABLE 4.
Summary of the Annual Banana Irrigation Regime in Four Scenarios, expressed from Evapotranspiration, Effective Rainfall, Total Dose and Number of Irrigations
*Extreme value of p= 35% is defined according to Allen et al., (2006).
These results were similar to the ones obtained by Caicedo et al. (2015) into their programs through CROPWAT for irrigate banana in Babahoyo, Ecuador. The authors obtained values of Eto between 990.5 mm and 1340.7 mm a year. Though the annual amount of irrigations was between 20 and 23, total sheet to be applied was slightly lower because rainfall conditions in Babahoyo are less arid than in Manabí.
Annual Eto values also coincide with those reported by Toro et al. (2016) through simulations made with CROPWAT in Urabá, Colombia. These values were between 1188 mm and 1315 mm annually.
The summary of irrigation regime for papaya crop is shown in Table 5.
TABLE 5.
Summary of the Annual Papaya Irrigation Regime in Four Scenarios, expressed from Evapotranspiration, Effective Rainfall, Total Dose and Number of Irrigations
*Extreme value of p= 35% is defined according to Allen et al., (2006) considerations.
Bogantes et al. (2011) consider annual water consumption for this crop between 1200 and 1800 mm. However, Chaterlán (2012) obtains lower Eto values (931 mm) for papaya at southern Havana, in Cuba, under higher rainfall conditions for a p value of 40%.
A similar result was reported by Mellado et al. (2005) in Michoacán, Mexico. The authors developed a survey with the objective of evaluating the response of papaya, Marigold variety, in terms of yield, efficiency of water use, economical productivity to fertilizing and drip irrigation systems. For conditions of rainfall of 569 mm annually (similar to those in Manabí), they obtained annual irrigation sheets between 1050 mm and 1385 mm.
Passion fruit crop required an irrigation regime for each scenery, summarized in Table 6.
The consumptions obtained for this crop are very close to the ones reported by Guzmán (cited by Guerra et al., 2013) between 650 mm and 950 mm annually. However, they are lower to the ones obtained by Guerra et al. (2013) in their studies covering magnitudes between 1351.1 mm and 2303.7 mm annually.
TABLE 6.
Summary of the Annual Passion Fruit Irrigation Regime in Four Scenarios, expressed from Evapotranspiration, Effective Rainfall, Total Dose and Number of Irrigations
*Extreme value of p= 50% is defined according to Allen et al., (2006) considerations.
Equally, in Perú Chacón (2016), in a study that registered passion fruit´s consumptions during 5 successive years in La Libertad, Perú, obtained values fluctuating between 601.5 mm and 977.5 mm a year. These values are very close to the Eto ones obtained in the four sceneries analyzed in this study. Da Araujo et al., (2006), also obtained passion fruit´s consumptions in Piracicaba, Brazil of 781.01 mm in a year.
Basic Elements for Designing and Operation of Irrigation Systems
The results of maximum Evapotransporation estimation (Etm) obtained for each crop at different conditions, as well as the higher fictitious flow rate are summarized in Table 7. The Etm values of orange coincide with the records of Toledo et al. (quoted by Levy & Boman, 2003), who define an interval of 2-3 mm/day in Cuban conditions. However, they are considerably lower than the 4.5 mm/day reported by Shalhevet et al. (quoted by Levy & Boman, 2003), for Israel conditions.
TABLE 7.
Values of Maximum Evapotranspiration and Fictitious Flow Rate (q) obtained for each crop at the Different Edaphoclimatic Conditions
An important issue to be considered to analyze water consumptions and irrigation needs of permanent crops, besides specific edaphoclimatic conditions of the province, is plantation density. It is confirmed that plantation frames of these crops are not identical in all irrigation research surveyed, which has a direct influence on magnitude of moisture available, taken by plant on the soil.
It is necessary to clear up, in all cases; fictitious net flow rate for designing irrigation in each crop should be increase according to estimated efficiency and the irrigation technique to be used. It was evident for all crops that Chone´s edaphoclimatic conditions are the best for cropping, compare with San Ramón and Mapasinge.
CONCLUSIONS
In this study, 12 scenarios of irrigation management were analyzed for orange, cocoa, banana, papaya and passion fruit crops in Ecuador (60 variants in total). That allowed defining water needs taking into account the edaphoclimatic zone and the soil water-depletion fraction defined for irrigation management without causing stress in the plant.
The possibility of defining Irrigation Regime of permanent crops from the statistical analysis of the climatic variables of the region and the determination “in situ” of the soil hydrophysical properties, give the result of these studies higher reliability than studies developed before about this data.
Crops with higher irrigation demand were banana, papaya and cocoa tree with annual dose between 641.7 mm and 1329.2 mm, according of shortage level defined for irrigation management.
Edaphoclimatic conditions in Chone are the best for the development of crops opposite to San Ramón area, where higher irrigation doses were required.
Water demand definition and irrigation regime for different conditions of management on studied crops is the base for designing new irrigation systems or for scheduling the one existing in the province, hence, its use can be immediate.
