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Introduction
Water is a crucial element for life and productive processes, especially agriculture, which is the sector that makes the greatest use of water resources, with approximately 70 % of the total used worldwide (Organización de las Naciones Unidas para la Alimentación y la Agricultura [FAO], 2011). In Mexico, agriculture demands 76 % of water reserves (Comisión Nacional del Agua [CONAGUA], 2017), with an average efficiency of 40 % (Oswald-Spring, 2011). This sector is concentrated mainly in the central and northern part of the country where, due to the arid and semi-arid conditions prevailing in the region, groundwater is its main source of supply.
The Calera aquifer is located in the state of Zacatecas, Mexico, in an area of low surface water availability, making it the main groundwater reservoir in the region and one of the most important in the state. This aquifer supplies the largest population centers in Zacatecas, namely Fresnillo, Calera, and Zacatecas, and is home to the largest industrial and agricultural activity. However, CONAGUA (2015) reported that the aquifer has a deficit of 73 577 147 m3 per year due to the extraction volume of 163 477 147 m3, an established natural discharge value of 1 200 000 m3 and a recharge of 91 100 000 m3, so it is considered a depleted aquifer.
In the 1997-2015 period, depletion values varying from 2 to 30 m were recorded in most of the aquifer, as well as cones of depression in the central-northern and southern zones, where extractions are concentrated for agricultural use, in which the average annual depletion is in the range of 1.2 to 1.8 m, while in the remaining area there is an average depletion of 0.6 m (CONAGUA, 2015). This behavior of the static level represents the impact that irrigated agriculture has on the Calera aquifer, since 92 % of the total volume of water extracted is destined for agricultural use (CONAGUA, 2015) to irrigate 18 074 ha with an overall efficiency of 43.5 % and an average depth of 99 cm (Ingeniería y gestión hídrica, S.C. [IGH], 2011a), by means of drip (29.9 %) and gravity (70.1 %) irrigation systems, of which 35.05 % is by piping with floodgates (Vélez, Padilla, & Mojarro, 2013).
The agricultural sector, the main user of the water resource, remains, inexplicably, without the obligation to pay water use fees (CONAGUA, 2016) and with various subsidies that are not well designed or applied and that hinder the management and preservation of aquifers (Moreno-Vázquez, Marañón-Pimentel, & López-Córdova, 2010), namely: 1) the Special Field Energy Program and 2) support for the modernization of irrigation systems.
In the first case, the program includes the 9-CU and 9-N stimulus rates that apply to the electricity used in the daytime and nighttime operation, respectively, of the water pumping and re-pumping equipment for irrigation (Comisión Federal de Electricidad [CFE], 2018). Both increase annually on a linear basis by $0.02 and $0.01, respectively (Diario Oficial de la Federación [DOF], 2007), while the 9 and 9M rates, for low and medium voltage, and without stimulus for the same use, increase their cost exponentially. With the stimulus rates, electricity costs decrease by up to 90 % (Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación [SAGARPA], 2018a), which is negative for the aquifer. This is because, according to Ávila, Muñoz, Jaramillo, and Martínez (2005), when the price of electricity increases 100 %, water withdrawal decreases 15 %, although in this case water extraction increases because the cost of electricity decreases. In the second case, support for the modernization of irrigation systems has not permeated enough to reduce aquifer depletation since the release of water volumes is transformed into increases in irrigated area, so there is no real action in favor of the aquifer (IGH, 2011b).
Despite the impact on the aquifer, agriculture in the region is important since a large percentage of the state's main crops (green pepper, dry bean, corn for grain, onion, garlic and green alfalfa) are produced in an irrigation mode, which accounts for 80 % of the total value of agricultural production, even though it occupies four times less area than rainfed production (IGH, 2011a). In addition, the agricultural sector is an essential part of the Zacatecas economy, since 16.24 % of the total employed population is in the primary sector (Instituto Nacional de Estadística y Geografía [INEGI], 2015), and this activity contributed 9.3 % of the state’s gross domestic product in 2016 (INEGI, 2016).
Faced with the current water crisis and the recognition of agriculture as the activity with the greatest pressure on the aquifer, it is necessary to use water in this sector in a more productive way. It is therefore valid to measure such productivity in terms of crop production or net profits per m3 of water used.
Water productivity is the ratio of net benefits to the amount of water used to produce them (Molden et al., 2010). According to Ríos-Flores, Torres-Moreno, Castro-Franco, Torres-Moreno, and Ruiz-Torres (2015), agricultural water productivity is used as a tool to know the water use efficiency in agricultural systems, identify water savings opportunities, increase productivity, and left the decision for the allocation and redistribution of water in the basin or aquifer. In agriculture, this productivity can be improved by water management practices such as deficit irrigation, precision irrigation techniques, canal lining and reduced water allocation. On the other hand, there are indirect practices that impact on water productivity due to the interactive effects with the crop. In addition, its economic productivity can be increased in order to save water by switching from low-value to high-value crops, and reassigning water from lower-value to higher-value uses (Molden et al., 2010).
Therefore, this research was carried out with the objective of determining the productivity of irrigation water in the main crops of the central-southern zone of the Calera aquifer and identifying practices to improve the use of water from the aquifer, in addition to knowing the impact of the electricity rate subsidy on the aquifer.
This study updates and improves the results obtained in 2011 within the Plan de Manejo Integral del Acuífero Calera (Calera Aquifer Integrated Management Plan), as it considered more recent information on the characteristics of extraction wells, irrigation, planted crops, production costs and income, based on information from the Zacatecas Rural Development District (RDD), belonging to the Calera aquifer, and not with information from the Jerez RDD as was done in a previous study (IGH, 2011b).
Materials and methods
Geographic location
The Calera aquifer is located in the central zone of the state of Zacatecas, Mexico. Its central-southern zone is made up of the municipalities of Enrique Estrada, Calera and Morelos, with an area of 766,447 km2, representing 33.97 % of the total area of the aquifer. It is bordered to the north by the municipality of Fresnillo, to the east by Pánuco and Vetagrande, to the south by Zacatecas and to the west by Jerez (Figure 1). The zone has a predominantly semi-dry temperate climate with average annual temperatures of 14.6 to 16.6 °C (IGH, 2010), average annual precipitation of 425 mm and evapotranspiration of 2 263 mm per year (CONAGUA, 2015).
Study crops in the central-southern zone of the Calera aquifer
The study was carried out on irrigated crops for the 2007-2017 period. The crops were determined considering their relative importance in terms of their percentage contribution to the planted area and gross production value of the agricultural census of the municipalities of Enrique Estrada, Calera and Morelos (Sistema de Información Agroalimentaria y Pesquera [SIAP], 2018) (Table 1); for this, the drip and gravity irrigation systems reported by Vélez et al. (2013) were considered.
| Crop | Scientific name | Planted area (%) | Gross production value (%) |
|---|---|---|---|
| Garlic |
|
0.813 | 7.39 |
| Green alfalfa |
|
0.794 | 1.97 |
| Onion |
|
1.183 | 8.63 |
| Green pepper |
|
9.470 | 48.47 |
| Dry bean |
|
4.263 | 4.77 |
| Corn for grain |
|
3.674 | 6.56 |
Agricultural water productivity
Agricultural water productivity was calculated using Equation 1 (Molden, Murray-Rust, Sakthivadivel, & Makin, 2003) and expressed in physical and economic terms (Bessembinder, Leffelaar, Dhindwal, & Ponsioen, 2005).
W P = R V
Where WP is the agricultural water productivity (kg·m-3 or $·m-3), R is the production volume (kg) or production value ($), and V is the volume of water used for irrigation (m3).
Physical water productivity
The variables analyzed were planted area (ha) and production volume (t), for the period, crops and municipalities mentioned above. The values were obtained from the SIAP database (2018). The reported values for each variable were added to obtain the totals for the study area and each crop per year.
Irrigation volume was calculated with Equation 2, for which the information presented in Table 2 was used.
| Crop | Irrigation depth1 (cm) |
|---|---|
| Garlic | 80 |
| Green alfalfa | 110 |
| Onion | 70 |
| Green pepper | 60 |
| Dry bean | 50 |
| Corn for grain | 50 |
V j i = S T j i L r j 10 000
Where V ji is the total irrigation volume (hm3) of crop j (garlic, alfalfa, onion, green pepper, dry bean or corn for grain) and of year i of the period 2007 to 2017, ST is the total planted area (ha), Lr is the irrigation depth (cm) and 10 000 is a conversion factor to hm3. The production volume R of the alfalfa crop was considered to be dry product at 20 % moisture.
Economic water productivity
Gross and net economic water productivity levels were calculated. The first was determined because no information on production costs was found for the years 2007 to 2016 and it was desired to know their behavior in the period studied. On the other hand, net economic productivity was calculated only for 2017 for all crops, for which production costs with a 9-CU rate subsidy and those without a 9 rate subsidy were considered. This was done in order to have a result closer to reality and to know the impact that this stimulus has on the aquifer.
The variable average rural price (ARP) (in pesos per ton) was analyzed for the period and the municipalities studied. The values were obtained from SIAP (2018) and averaged for each municipality by crop and year.
The gross production value was obtained by multiplying the ARP by annual physical production. The valuation of gross and net economic productivity, subsidized and unsubsidized, was performed with the June 2012 base period = 100 using the National Producer Price Index reported by INEGI (2019). Results were expressed in constant Mexican pesos (MXN).
Production costs with and without subsidy
Before describing production costs, it is important to note that the cost of “irrigation” was considered as the cost of electricity consumed by pumping water for irrigation and labor for its application; this is because no water fees are paid for agricultural use. Emphasis is placed on this concept because it involves the object of study and the subsidy that impacts the aquifer.
For production costs with a 9-CU rate subsidy, those provided by SAGARPA (2018b) (Table 3) were taken into account.
| Crop | Production costs1 (MXN·ha-1) | |
|---|---|---|
| Irrigation | Total | |
| Garlic | 7 528 | 90 615 |
| Green alfalfa | 3 170z | 11 649 |
| Onion | 2 377 | 47 689 |
| Green pepper | 4 279 | 26 230 |
| Dry bean | 1 585 | 11 158 |
| Corn for grain | 2 774 | 13 876 |
Production costs without subsidy were estimated based on the costs reported by SAGARPA (2018b), for which the cost of irrigation was replaced by the one calculated with the costs of the 9 rate (CFE, 2018) and the following characteristics of an average well located in the study area were considered: flow rate of 37 L·s-1, pumping depth of 150 m, average equipment efficiency of 60 % (indicated in NOM-006-ENER-2015 as the minimum for 126 to 350 HP submersible pump motors [DOF, 2015]) and a 25-m water column to contemplate total losses in suction and discharge, as well as delivery pressure at discharge.
Electricity consumption was calculated using the following equation:
C s m o E E j = V U j 3.6 Q H P × 0.746
where:
H P = γ Q C D T 76 η m B
C D T = h s + H f + h d + v 2 2 g
Csmo EE j is the electricity consumption per unit area of crop j (kWh·ha-1), VU j is the irrigation volume per unit area of crop j (m3·ha-1), HP is the horsepower, Q is the pumped flow rate (37 L·s-1), γ is the specific weight of water (1 000 kg·m-3), CDT is the total dynamic load (m), η mB is the efficiency of the engine and pump (dimensionless), 76 is the conversion factor of kW units to HP that contemplates water temperature correction, 0.746 is the conversion factor of HP units to kW, h s is the suction height (m), Hf are the total load losses that the liquid undergoes in the suction and discharge piping (m), h d is the discharge load height (static load) (m) and v 2 2 g is the discharge velocity load (m), where v is the discharge velocity (m·s-1) and g is the gravitational acceleration (9.81 m·s-2).
Once the electricity consumption was calculated, its cost (CEE) in pesos per hectare was determined with Equation 6, for which an average rate 9 price of $9.377·kWh-1 for the months May-September 2017 (CFE, 2018) was considered.
C E E = C s m o E E R a t e 9 p r i c e
Results and discussion
Physical water productivity
Onion was the most efficient and productive crop in terms of water use. On average, this crop had a productivity 3.6 times higher than that of garlic, which was the second most efficient crop, and 18 times higher than that of dry bean, which was the least efficient crop (Table 4 and Figure 2).
| Crop | Average planted area (ha) | Physical water productivity (kg·m-3) | ||
|---|---|---|---|---|
| Minimum | Maximum | Average | ||
| Garlic | 444.81 | 1.08 | 1.98 | 1.54 |
| Alfalfa1 | 450.06 | 0.86 | 1.84 | 1.53 |
| Onion | 599.63 | 4.71 | 6.67 | 5.48 |
| Green pepper | 4 764.86 | 0.30 | 2.14 | 1.19 |
| Dry bean | 2 114.18 | 0.12 | 0.41 | 0.30 |
| Corn for grain | 1 770.27 | 1.12 | 1.70 | 1.37 |
Onion
The range of physical water productivity in onion was 4.71 to 6.67 kg·m-3, values higher than the minimum obtained by González-Robaina, Herrera-Puebla, López-Seijas, and Cid-Lazo (2014) in onion cultivated in Cuba (from 3.76 to 16.6 kg·m-3), while in India, Wakchaure et al. (2018) reported values between 7.8 and 9.6 kg·m-3 in onion cultivation with plant bioregulators and deficit irrigation, and a value of 7.36 kg·m-3 in control crops. In Mexico, Ríos-Flores, Jacinto-Soto, Torres-Moreno, and Torres-Moreno (2017a) obtained a productivity level of 4.77 kg·m-3 in a study conducted in the 005 irrigation district in Delicias, Chihuahua. This last study was the best to compare the productivity obtained in onion, since the climatic and edaphic conditions are more similar. With a physical productivity of 4.77 kg·m-3 in Delicias and from 4.71 to 6.67 kg·m-3 in the Calera aquifer, it can be concluded that in both regions the use of water for this crop was similar. However, it could be maximized if some technologies such as plant bioregulators and deficit irrigation used by Wakchaure et al. (2018) were implemented.
Garlic
Garlic was the crop with the second highest physical water productivity, with values from 1.08 to 1.98 kg·m-3, and an average of 1.54 kg·m-3 in the 11 years studied. In spite of being one of the crops that best uses water, its productivity was considered low in comparison with that obtained by Bravo (2008) in the municipality of Calera, Zacatecas, which was 2.8 kg·m-3 with drip irrigation technology and fertigation; however, it was higher than that obtained with wheel move irrigation (0.45 kg·m-3) (Bravo, 2008).
Alfalfa
Alfalfa is planted over a large part of the study area, and continues to increase year after year; however, it is the crop that demanded the most water per unit area, an aspect that makes it a possible risk to the aquifer’s permanence. The physical water productivity for alfalfa was 0.86 to 1.84 kg·m-3. The lowest value was lower than that reported by the National Institute of Forestry, Agricultural and Livestock Research (INIFAP, 2000) for the Lagunera Region under wheel move irrigation (1.07 kg·m-3), but the highest value was greater than that obtained in a sprinkler irrigation system (1.64 kg·m-3).
In a study conducted by Quiroga-Garza, and Faz-Contreras (2008) in La Laguna, Coahuila, Mexico, where gravity irrigation was used, physical productivity increased from 1.18 to 1.33 kg·m-3 after suspending two irrigations in August and September from the second year of cultivation.
Green pepper
Green pepper was the most important crop in terms of cultivated area; in 2017 it occupied 42 % of the total irrigation area in the study area (SIAP, 2018). In addition, after the municipalities of Fresnillo and Villa de Cos, the Calera aquifer zone is the one that allocates the largest area for green pepper cultivation in the state of Zacatecas, which in turn ranks third nationally in the production of this crop.
The physical water productivity for green pepper in the evaluated period varied from 0.30 to 2.14 kg·m-3. This range contemplates the productivity reported for 2006 in the Aguanaval aquifer (2.09 kg·m-3), which is located northwest of the Calera aquifer (IGH, 2010).
Corn for grain
This was the only crop that tends to decrease its planted area over time; however, it was the fourth crop in terms of area occupied, with 8.13 % of the total irrigated area. Water use efficiency in the cultivation of corn for grain resulted in a value of 1.12 to 1.7 kg·m-3; this productivity is within the range reported in 27 publications from 10 countries on 4 continents (from 1.1 to 2.7 kg·m-3) (Zwart & Bastiaanssen, 2004). In this crop, physical water productivity improved, since it went from 0.48 kg·m-3 in 2006 (IGH, 2011b) to a range of 1.12 to 1.7 kg·m-3 in the period from 2007 to 2017.
Several studies conducted in China show that regulated deficit irrigation decreases water consumption by the crop without an apparent drop in yield, which improves water use efficiency. In corn, the application of this irrigation technology increased water productivity by an average of 17 % and decreased yield per hectare by 4 % (Shaozhong et al., 2017).
Dry bean
Physical bean productivity was from 0.12 to 0.41 kg·m-3, a value that coincided with that reported by Ríos-Flores, Torres-Moreno, Torres-Moreno, and Cantú-Brito (2017b) of 0.13 kg·m-3 in the municipality of Calera, Zacatecas, and that of 0.32 kg·m-3 calculated based on information from the Plan de Manejo del Acuífero Calera (Calera Aquifer Management Plan) (IGH, 2011b).
Research has also been carried out on the impact on water productivity when deficit irrigation is applied to this crop. According to Boydston, Porter, Chaves-Córdoba, Khot, and Miklas (2018), this irrigation modality applied one month after emergence, and with conventional agricultural practices, reduced dry bean yield by 46 to 48 % in their research conducted in Washington State, USA, so they suggested combining deficit irrigation with tillage (conservation agricultural practice) to improve results. Satriani, Catalano, and Scalcione (2018), in a study conducted in southern Italy, demonstrated that the combination of deficit irrigation with the application of biodegradable superabsorbent polymers maximizes the crop’s water productivity index.
Subsidized and unsubsidized production costs
The garlic crop had the highest production cost (Table 5) due to the cultural work carried out, as well as the amount of fertilizers, insecticides and fungicides it demands. On the contrary, dry bean turned out to be the crop with the lowest cost per hectare, which may be partly why it is the crop with the largest area in the study zone, in addition to custom, as indicated by Vélez et al. (2013).
| Crop | With subsidy | Without subsidy | |||||
|---|---|---|---|---|---|---|---|
| SAGARPA (2018b) | 9-CU rate | 9 rate | |||||
| Electricity | Total | Electricity | Total | Electricity | Total | ||
| Garlic | 7 528 | 90 615 | 2 986 | 86 073 | 48 277 | 131 364 | |
| Green alfalfa | 3 170z | 11 649 | 4 106 | 12 585 | 66 381 | 77 713 | |
| Onion | 2 457 | 47 689 | 2 613 | 47 845 | 42 242 | 87 471 | |
| Green pepper | 4 279 | 26 230 | 2 239 | 24 190 | 36 208 | 58 158 | |
| Dry bean | 1 585 | 11 158 | 1 866 | 11 439 | 30 173 | 39 746 | |
| Corn for grain | 2 774 | 13 876 | 1 866 | 12 968 | 30 173 | 41 275 | |
Based on data provided by SAGARPA (2018b), it was observed that, on average, 15 % of production costs were allocated to the electricity used in pumping water for irrigation; however, if the 9-CU rate subsidy did not exist, an average of 63.5 % of total costs would be allocated to the payment of electricity. In this way, alfalfa, garlic and onion would allocate up to 85, 37 and 48 % of the total costs for this item, respectively.
Institutions such as the Organization for Economic Cooperation and Development (OECD), the World Bank, the United Nations Educational, Scientific and Cultural Organization (UNESCO) and SAGARPA agree that subsidizing electricity for pumping water for agricultural irrigation is a program that has negative effects, since it promotes incentives for inefficient production and damages the environment (Moreno-Vázquez et al., 2010), making it a determining factor in the depletation of aquifers (Secretaria de Medio Ambiente y Recursos Naturales [SEMARNAT], 2012).
This study estimated a total subsidy, approximate to the cost of electricity of 338.6 million pesos in 2017 (Table 6), which grows exponentially compared to the linear growth of the 9-CU and 9-N rates (Figure 3).
| Crop | Planted area (ha) | Electricity cost (MXN)1 | Subsidy (MXN) | |
|---|---|---|---|---|
| 9 rate | 9-CU rate | |||
| Garlic | 773.00 | 37 318 131.71 | 2 308 157.53 | 35 009 974.18 |
| Green alfalfa | 925.00 | 61 402 326.99 | 3 797 785.06 | 57 604 541.92 |
| Onion | 600.00 | 25 345 432.27 | 1 567 636.09 | 23 777 796.18 |
| Green pepper | 4 442.00 | 160 834 871.64 | 9 947 770.77 | 150 887 100.87 |
| Dry bean | 1 660.00 | 50 087 401.87 | 3 097 947.52 | 46 989 454.34 |
| Corn for grain | 860.00 | 25 948 894.95 | 1 604 960.77 | 24 343 934.18 |
| Total | 9 260.00 | 338 612 801.67 | ||
Green pepper and alfalfa were the crops that received the greatest benefit, the first due to the area it occupied, and the second due to the amount of irrigation required. According to SEMARNAT (2012), the subsidy for agricultural pumping is inequitable at the national level, since while 10 % of the largest users receive 409 thousand pesos per year, 20 % of the smallest irrigation units receive 113 pesos per year. In other words, this subsidy benefits the richest farmers, and it is to be assumed that something similar happens in the study area, since green pepper was the most benefited crop, and at the same time the one with the greatest investment per total occupied area, which indicates that the producers of this crop have greater economic resources and are favored more with the subsidy.
Economic water productivity
Gross economic productivity showed growth across all crops (Figure 4).
Without considering production costs, economic productivity was high in 2017 (Table 7), compared to the values obtained with energy subsidies (Table 8). The vegetable group had higher gross and net economic productivity, with and without electricity subsidies. This group had positive unsubsidized productivity, while alfalfa, corn and dry bean had negative productivity (Table 9).
| Crop | Volume used (hm3) | Production volume (t) | Production value (MXN) | Gross economic productivity (MXN·m-3) |
|---|---|---|---|---|
| Garlic | 6.18 | 11 260.60 | 127 376 711.80 | 20.60 |
| Alfalfaz | 10.18 | 17 682.07 | 28 797 819.57 | 2.83 |
| Onion | 4.20 | 24 050.00 | 84 976 040.46 | 20.23 |
| Green pepper | 26.65 | 42 237.20 | 392 975 700.90 | 14.74 |
| Dry bean | 8.30 | 3 187.90 | 38 825 914.55 | 4.68 |
| Corn for grain | 4.30 | 7 016.55 | 18 559 367.82 | 4.32 |
| Crop | Volume used (m3·ha-1) | Production cost (MXN·ha-1) | Production value (MXN·ha-1) | Profit (MXN·ha-1) | Net economic productivity (MXN·m-3) |
|---|---|---|---|---|---|
| Garlic | 8 000 | 90 615.30 | 164 782.29 | 74 166.99 | 9.27 |
| Alfalfaz | 11 000 | 11 648.84 | 31 132.78 | 19 483.94 | 1.77 |
| Onion | 7 000 | 47 688.93 | 141 626.73 | 93 937.81 | 13.42 |
| Green pepper | 6 000 | 26 229.70 | 88 468.19 | 62 238.49 | 10.37 |
| Dry bean | 5 000 | 11 157.53 | 23 389.11 | 12 231.58 | 2.45 |
| Corn for grain | 5 000 | 13 875.59 | 21 580.66 | 7 705.07 | 1.54 |
| Crop | Volume used (m3·ha-1) | Production cost (MXN·ha-1) | Production value (MXN·ha-1) | Net profit (MXN·ha-1) | Net economic productivity (MXN·m-3) |
|---|---|---|---|---|---|
| Garlic | 8 000 | 131 364.15 | 164 782.29 | 33 418.14 | 4.18 |
| Alfalfaz | 11 000 | 77 712.76 | 31 132.78 | -46 579.98 | -4.238 |
| Onion | 7 000 | 87 470.79 | 141 626.73 | 54 155.94 | 7.74 |
| Green pepper | 6 000 | 58 158.30 | 88 468.19 | 30 309.89 | 5.05 |
| Dry bean | 5 000 | 39 745.79 | 23 389.10 | -16 356.68 | -3.27 |
| Corn for grain | 5 000 | 41 275.19 | 21 580.66 | -19 694.53 | -3.94 |
IGH (2011b), when evaluating the Calera aquifer with production cost values of the 2005-2006 cycle, found that the economic productivity of the garlic, green pepper and corn crops was 3.35, 3.28 and 0.35 MXN·m-3, respectively, while Pedroza-Sandoval et al. (2014), in the Lagunera region, obtained for alfalfa an economic productivity level of 0.90 MXN·m-3. On the other hand, Ríos-Flores et al. (2017b) reported productivity of 3.27 MXN·m-3 in dry bean in the municipality of Calera, Zacatecas, and of 10.84 MXN·m-3 in onion in Delicias, Chihuahua (Ríos-Flores et al., 2017a), both 2015 crops. These values differ, for the most part, from the results obtained in this work (Table 8), which was to be expected because there are external factors that can directly influence the economic productivity of water, such as market access, market prices, change in the cost of inputs (fertilizers, insecticides and seed, among others), product demand and supply, and positioning in the international market (such as the vegetable group), among others. For this reason, the values most similar to those determined for 2017 belong to more recent studies, such as the case of dry bean and onion.
Production values were analyzed per hectare because many small producers do not seek to maximize profits, as is the case with business-type producers, but rather consider the total value entered at the end of the cycle. Alfalfa and dry bean are a good example of such a situation, since per hectare alfalfa had a higher yield than dry bean; however, in the latter, more profits were obtained per unit of water used (Table 9). If water were paid for, the real cost would mean that alfalfa would have a lower value in the cost-benefit ratio indicator (which would be -0.6) compared to other crops, and a lower profit per unit of water used.
Without the electricity subsidy, economic productivity was reduced in all crops, even becoming negative for alfalfa, dry bean and corn (Figure 5). The first was the least sustainable, since it was neither economically viable nor environmentally supportable, while corn and dry bean were less economically favored compared to the vegetable group.
Conclusions
In the central-southern zone of the Calera aquifer, crops are produced that have low water use efficiency, which negatively and significantly impacts the aquifer.
Dry bean, corn and alfalfa had lower physical and economic productivity. Alfalfa was less sustainable because of the amount of water it demands and the amount subsidized, without which it would be the least profitable crop.
The application of deficit irrigation, drip irrigation and agricultural conservation practices has resulted in increased water productivity in other studies.