Terra Latinoamericana E-ISSN: 2395-8030 [email protected] Sociedad Mexicana de la Ciencia del Suelo, A.C. México

Castellanos, J. Z.; Ortega Guerrero, A.; Grajeda, O. A.; Vázquez Alarcón, A.; Villalobos, S.; Muñoz Ramos, J. J.; Zamudio, B.; Martínez, J. G.; Hurtado, B.; Vargas, P.; Enríquez, S. A. Changes in the quality of groundwater for agricultural use in Terra Latinoamericana, vol. 20, núm. 2, abril-junio, 2002, pp. 161--170 Sociedad Mexicana de la Ciencia del Suelo, A.C. Chapingo, México

Available in: http://www.redalyc.org/articulo.oa?id=57320209

How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO Cambios en la Calidad del Agua Subterránea para Uso Agrícola en Guanajuato

J.Z. Castellanos1‡, A. Ortega-Guerrero2, O.A. Grajeda1, A. Vázquez-Alarcón3, S. Villalobos1, J.J. Muñoz-Ramos1, B. Zamudio1, J.G. Martínez4, B. Hurtado1, P. Vargas1, and S.A. Enríquez5

SUMMARY complicated problems in the management of soil fertility may arise in the near future. By the same To study changes in the quality of groundwater for token, it is necessary to carry out systematic studies agricultural use in the State of Guanajuato over the on groundwater that will allow us to identify the last 18 years, information from 1982 to 1998 geochemical processes that control increases of the produced in INIFAP’s Laboratorio de Suelos y Aguas water quality variables mentioned above, and so be del Campo Experimental Bajío (“Soil and Water able to take them into account in the planning the Laboratory of the Bajío Experimental Station”) was exploitation of the aquifer and agricultural activity in reviewed. The variables included in the analysis the region. were: CE, pH, Na, K, Ca and Mg, Cl, SO4, HCO3, CO3, SAR and CSR. Each one of these variables was Index words: Electrical conductivity, pH, sodium related to time, measured in years. These values were absorption ratio, residual sodium carbonate. then used to determine the regression equations, for which the SAS statistical package was used. This RESUMEN allowed us to analyze the tendencies of each water quality parameter over the evaluation period. It could Con el fin de estudiar los cambios que ha sufrido be observed that groundwater in Guanajuato is la calidad del agua subterránea para uso agrícola en el experiencing an increase in the concentration of estado de Guanajuato en los últimos 18 años, se revisó sodium, SAR, and pH through time, possibly as a la información generada en el Laboratorio de Suelos y result of incorrect use. On the other hand, the Aguas del Campo Experimental Bajío del Instituto concentrations of Ca, Mg, and K, that would Nacional de Investigaciones Forestales y constitute part of the cations that are beneficial to soil, Agropecuarias desde 1982 hasta 1998. Las variables have not been significantly modified in the period incluidas en el análisis fueron: CE, pH, cationes: Na, studied. The highest concentration of sodium was K, Ca y Mg, aniones: Cl, SO4, HCO3, CO3, RAS y found in water samples taken in the southeastern zone, CSR. Cada una de las variables antes mencionadas se where the negative effects on soil and on the nutrition relacionó con el tiempo en años y con esos valores se of crops, such as sorghum, have already been determinaron las ecuaciones de regresión, utilizando observed. If measures are not taken to avoid the el paquete estadístico SAS. Esto permitió analizar las indiscriminant management of the aquifer and, tendencias de cada parámetro de calidad del agua a consequently, the reduction of piezometric levels, then través del período de evaluación. Se pudo observar que las aguas subterráneas de Guanajuato están 1 Instituto Nacional de Investigaciones Forestales y incrementando significativamente la concentración de Agropecuarias. 38010 , Guanajuato, México. sodio, el RAS y el pH a través del tiempo, ‡ ([email protected]) 2 Instituto de Geología, Universidad Nacional Autónoma de posiblemente como resultado de la explotación México. Apartado Postal 70-296, Cd. Universitaria, inadecuada del agua subterránea. Por otro lado, las 04510 México, DF. concentraciones de Ca, Mg y K, que formarían parte 3 Departamento de Suelos, Universidad Autónoma Chapingo. de los cationes benéficos para el suelo, no se han Chapingo, Estado de México. modificado significativamente en dicho período. La 4 CENID-RASPA, Instituto Nacional de Investigaciones Forestales y Agropecuarias. Gómez Palacios, Durango. mayor concentración de sodio se observó en el agua 5 Instituto Tecnológico y de Estudios Superiores de Monterrey, extraída en la zona suroeste, donde ya se ven los Campus Querétaro. Querétaro, México. efectos negativos en el suelo y en las características nutricionales de los cultivos, como el sorgo. Si no se Recibido: Enero de 2001. Aceptado: Diciembre de 2001. Publicado en Terra 20: 161-170. toman las medidas para evitar el manejo

161 TERRA VOLUMEN 20 NUMERO 2, 2002 indiscriminado del acuífero con el consecuente “Adjusted SAR”) takes into account the precipitation abatimiento de los niveles piezométricos, pueden of calcium in the form of carbonates. In both cases, provocarse problemas de difícil manejo de la the cations in the equations are expressed in me/L, fertilidad del suelo en un futuro cercano. De igual while the units of SAR are adimensional. manera, es necesario realizar estudios sistemáticos del The residual sodium carbonate agua subterránea, que permitan identificar los [CSR = (CO3+HCO3)-(Ca+Mg)], expressed in me/L, procesos geoquímicos que controlan el incremento de is another indicator of the danger of the increase in the las mencionadas variables de la calidad del agua, con concentration of sodium in the soil, because it also el fin de considerarlos en la planeación del takes into account the precipitation of calcium and aprovechamiento del acuífero y de la actividad magnesium as carbonates and bicarbonates, once the agrícola regional. water comes into contact with the soil, and propitiates the reduction of the antagonistic effect of these two Palabras clave: Conductividad eléctrica, potencial divalent cations on the sodium. Aceves (1979) hidrógeno, relación de absorción de sodio, carbonato indicated that the ranges for classifying waters de sodio residual. according to this variable are < 1.25 me/L, good water; from 1.25 to 2.50 me/L, marginal water; and INTRODUCTION > 2.50 me/L, water with a great risk of causing higher concentrations of sodium in the soil. The development of a more high-tech agriculture During recent years, in the region known as “El in areas characterized by arid and semi-arid climates Bajío” in Guanajuato, the agricultural area detected as depends on the availability of water for irrigation that having problems of iron deficiencies related to crops is sufficient in terms of quantity and acceptable in such as sorghum, corn and even wheat has been terms of quality. This input is the basis for planning increasing steadily (J. Antonio González, pers. an intensive system of agricultural exploitation with comm.). Solving the nutrient problem has become sustainable characteristics. Water quality plays an more and more difficult. It has been suggested that the important role in the management of irrigation and cause of this problem is associated with an increase in leaching fraction (Ayers and Wescot, 1985), as well as the level of sodium in the soil, but this has not been in the treatment of the water itself, so as to achieve an sufficiently well documented. This possible increase optimal level of production in situations where drip in the level of sodium in the water would provoke a irrigation systems are used (Burt et al., 1995). natural increase in the sodium bicarbonate content and From an agricultural perspective, the principal in soil pH, that could cause a physiological deficiency variables to be evaluated in the classification of water of iron which —from a nutritional point of view— is quality are a) the concentration of dissolved solids and difficult to manage (Uvalle-Bueno et al., 1996). On salts (CE), b) the relative presence of sodium (SAR), the other hand, a severe decrease in the piezometric c) the carbonate and bicarbonate content (CSR), and levels of groundwater in the State of Guanajuato d) the concentration of other specific ions, such as (Chávez, 1998) has been observed as a consequence chlorine and boron (Aceves, 1979; Castellanos et al., of the irrational exploitation of the aquifer. Changes in 2000c). the quality of groundwater proportional to decreases In irrigation water, sodium propitiates the in piezometric levels have been reported for other dispersion of colloids or clays when it comes into areas of the world, such as southeastern Spain (Pulido, contact with the soil and displaces the divalent cations 2+ 2+ 1998), south Texas, and northern Chihuahua (Samani, Ca and Mg . This has a negative effect on the 1998). However, up to now no study has been structure of the soil and reduces its capacity to reported in that indicates changes in conduct water and air through its profile (Castellanos groundwater quality through time. et al., 2000b). This, in turn, damages soil fertility, The objective of our study was to examine the because in addition to affecting aeration it also increases pH and reduces the availability of Fe and changes that the quality of groundwater for Zn. The concentration of sodium is expressed as the agricultural use has been experiencing in the State of relative presence of Na+ compared to Ca2+ and Mg2+: Guanajuato over the past 18 years, on the basis of the 1/2 1/2 SAR = Na/[(Ca+Mg)/2] and SARaj = Na/[(Cax+Mg)/2] recompilation and evaluation of laboratory reports on (Suárez, 1981). This second parameter (called water analyses during this period.

162 CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

MATERIAL AND METHODS average values for each year come from a large amount of data. This research project was carried out using the At the same time as we carried out the analysis of information generated from a series of water analyses the information mentioned above and in order to done in the State of Guanajuato, at INIFAP’s observe the spatial variability of the problem, the Laboratorio de Suelos y Aguas del Campo State of Guanajuato was divided into five zones, as Experimental Bajío (“Soils and Water Laboratory of follows: 1) North, covering the municipalities of the Bajío Experimental Station”) between 1982 and Ocampo, San Felipe, San Diego de la Unión, Dolores 1998. This comprised 2916 samples taken from areas Hidalgo, Guanajato, , San Miguel throughout the State. The variables included in the de Allende, Victoria, Dr. Mora, San José Iturbide, analysis were: electrical conductivity (EC), Tierra Blanca, Santa Catarina, Xichú, and ; determined through the use of the conductivity cell 2) West, including Purísima de Bustos, San Francisco (Richards, 1990), pH, Na, K, Ca, and Mg. The last del Rincón, León, , and ; 3) Center, four determined by atomic absorption (Sumner and including the municipalities of , Salamanca, Miller, 1996), Cl, SO4, HCO3, and CO3 anions, Juventino Rosas, Villagrán, Cortazar, Jaral, determined as indicated by Rhoades (1996), the rate , Celaya, , and Apaseo El of sodium absorption (SAR) and residual sodium Alto; 4) Southeast, covering Cd. Manuel Doblado, carbonate (RSC) were determined as indicated by Cuerámaro, Pénjamo, Abasolo, Huanímaro and Valle Richards (1954). For each one of these variables, de Santiago; and, 5) South, covering , regression equations against time were determined Moroleón, , Santiago Maravatío, Salvatierra, utilizing the SAS statistical package. This allowed us Tarimoro, Acámbaro, Jerécuaro, and to analyze the tendencies of each parameter of water . This zoning was based on the existing quality through the period of evaluation. It is general knowledge of the area in terms of such important to point out that, given the high variability elements as climate, soil and the general chemical of the quality parameters in groundwater, the characteristics of groundwater (Castellanos et al., correlation of these variables with time is generally 2000a). The distribution of the zones is described low; nevertheless, it is important to remember that the in the map of the State of Guanajuato (Figure 1).

North Zone

West Zone

Center Zone

Southeast Zone

South Zone

Figure 1. Municipalities of the State of Guanajuato that form the five regions in which the State was subdivided for the study.

163 CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

Averages for each of the variables analyzed were calculated in each zone, as well as a general average (a) for the entire State for the years 1994-1998; that is, 1.0 the final five years of the evaluation period. In addition, this mean general concentration was used to 0.9 calculate ranges of concentration. Finally, the mean contributions that the elements analyzed make to the 0.8 soil were calculated through the application of an 0.7 irrigated depth of 50 cm. EC (dS/m)

0.6 y = 0.0112x + 0.651 RESULTS AND DISCUSSION r = 0.4050 0.5 Soluble Salts 0 3 6 9 12 15 18 Time (years) The variation in the contents of soluble salts in the groundwater, expressed in the form of electrical (b) conductivity, is shown in Figure 2a. Although a 7.8 tendency towards an increase is observed, it turned out to be statistically significant only at P < 0.10. In 7.7 other studies, when an increase in the salinity of water 7.6 has been found, it has been associated with a decrease pH in piezometric levels (Pulido, 1998; Samani, 1998) 7.5 that may be related to the reduction of the hydrostatic pressure in the upper aquifer, which allows the 7.4 y = 0.0161x + 7.4549 influence of older, deeper aquifers or of flow systems r = 0.6775** with greater travel distance of groundwater and, 7.3 therefore, higher salt content (Carrillo-Rivera, 2000). 0369121518 The increase in the saline concentration of the Time (years) groundwater that accompanies the decrease in piezometric levels has been reported for other regions of the world, such as southeastern Spain, south Texas Figure 2. Electrical conductivity and pH of groundwater in and northern Chihuahua (Pulido, 1998; Samani, the State of Guanajuato for the period 1982-1998. 1998). Table 1 presents the results of the division of the Wescot (1985), although there are clear tendencies State into zones, showing that the region with the towards an increase through time, with a significant lowest concentration of soluble salts is the north, with correlation coefficient of 0.68 (P < 0.01). According only 0.57 dS m-1; while the zone with the highest to projections of these data, in 18 years the pH of concentration is the southeast with 1.22 dS m-1. These water rose from 7.40 to 7.70. Taking into account that figures are relatively low when compared to those pH is a logarithmic measurement of the concentration from other agricultural regions, but it is important to of hydrogen ions [H+], an increase of one unit means a remember that the most significant goal is to conserve 10-fold reduction in the concentration of these ions. water quality in order to assure a more secure and The variation found from one region to another was sustainable agriculture for the future. minimal (Table 1), as all regions presented an average pH between 7.7 and 7.8. pH Cations A particularly important variable is the pH of water, due to its implications for the availability of Figure 3 presents the regressions through time nutrients and the management of the nutrient solution. obtained for the four cations analyzed. From the The data in Figure 2b indicate that the pH found physical and chemical points of view (Aceves, 1979), is within the normal range, reported by Ayers and calcium, considered one of the cations with the

164 CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

Table 1. Chemical characteristics of groundwater for the different zones of the State of Guanajuato, average for the period of 1994-1998.

† - - - ‡ § Zone EC pH Ca Mg Na K CO3 HCO3 Cl SO4 SAR RSC dS m-1 ------me L-1 ------me L-1 North 0.565 7.7 1.7 0.6 3.0 0.4 0.1 4.1 0.8 0.8 3.1 1.9 West 0.701 7.7 2.7 1.5 2.8 0.2 0.1 4.8 1.0 1.3 2.1 1.3 Center 0.781 7.8 2.0 1.1 4.4 0.3 0.2 5.0 1.0 1.6 4.0 2.1 Southeast 1.219 7.7 2.2 1.9 7.2 0.5 0.2 7.0 2.0 3.4 6.1 3.5 South 0.576 7.7 1.9 1.3 2.4 0.3 0.0 4.2 0.6 0.9 2.1 1.3 Average 0.770 7.7 2.1 1.2 4.2 0.3 0.1 5.0 1.1 1.6 3.8 2.1 † EC = electrical conductivity. ‡ SAR = sodium adsorption ratio. § RSC = residual sodium carbonate.

(a) (b) 2.7 2.2

y = -0.0284x + 1.6207 1.9 2.4 r = - 0.5538*

1.6 2.1 1.3 Ca (me/L)

Mg (me/L) 1.8 1.0 y = 0.0064x + 2.0285 r = 0.1035 1.5 0.7 0 3 6 9 121518 0 3 6 9 12 15 18 Time (years) Time (years)

(c) (d) 0.5 6.5

y = 0.0037x + 0.2857 y = 0.1731x + 2.1499 r = 0.3289 5.5 r = 0.5854* 0.4 4.5

3.5 K (me/L) 0.3 Na (me/L)

2.5

0.2 1.5 0 3 6 9 12 15 18 0 3 6 9 12 15 18

Time (years) Time (years)

Figure 3. Calcium, magnesium, potassium, and sodium in groundwater of the State of Guanajuato for the period 1982-1998.

greatest impact in terms of conferring beneficial of these three cations would be considered beneficial, characteristics to the soil, showed no significant as they are essential nutrients for plant growth. This change in the period studied. A similar situation was study, however, found no such change, and the found with respect to magnesium and potassium. concentrations of these substances have remained Within certain limits, an increase in the concentration stable through time. The concentration of Mg, on the

165 TERRA VOLUMEN 20 NUMERO 2, 2002 other hand, presented a tendency to decrease during Anions the last 18 years with a correlation coefficient of 0.55 (P < 0.05). The concentration of anions shows little variation With respect to sodium, a cation that can imprint through the period under study (Figure 4). undesirable physical properties upon the soil (Levy, Bicarbonate is the anion that reveals the greatest 2000), a clear upward tendency was observed through upward tendency, though this rise is only statistically time, with a correlation coefficient of 0.59 that was significant at P < 0.10. Bicarbonates are undesirable statistically significant (P < 0.05). The data in Figure because they precipitate calcium and magnesium, thus 3 indicate that the concentration of sodium in the magnifying the problem with sodium in water that waters extracted from the subsoil is increasing at an contains high concentrations of this element. As in the average rate of 0.17 me/L per year. The cause of this case of sodium, the zone most seriously affected by increase may be associated with the reduction of bicarbonates is the southeast, while the rest of the piezometric levels, as has been documented with zones show similar averages (Table 1). A useful respect to other variables of water quality in other treatment for reducing the problem of bicarbonates in regions (Pulido, 1998; Samani, 1998), though a more the case of pressurized irrigation systems, is through thorough understanding of the causes of this rise is the injection of sulfuric or nitric acid at a dosage that now the subject of more detailed hydrogeological reduces the pH of the water to 6.0 (Burt et al., 1995). studies. The elimination of bicarbonates from water prevents In terms of the division into zones that was the precipitation of calcium that would take place if established at the beginning of this study, the highest they entered the soil. This, in turn, favors the average level of sodium is located in the southeast, antagonistic effect of this element upon sodium, with a mean concentration of 7.2 me/L, followed by reducing its negative impact. This procedure, the central zone, with 4.4 me/L. All of the other however, adds an additional cost to the production regions present a mean concentration below 3 me/L. processes that the low profit margins of certain crops The municipalities with the highest levels of sodium may be unable to absorb. in their groundwater are Manuel Doblado, Cuerámaro, Pénjamo, Abasolo, Huanímaro, Pueblo Nuevo, and Sodium Adsorption Ratio (SAR) , all of which are in the southeastern zone (Table 1). The high level of sodium in the water This index has shown a clear tendency to increase from this zone has brought about a rise in the level of with a correlation coefficient of 0.66, statistically sodium in the soil, in comparison to the other zones significantly at a P < 0.01. The increase in SAR goes (Castellanos et al., 2000b). In some isolated areas this from an approximate value of 2.0 to 4.5 over the is causing problems in terms of the availability of iron period studied, which means an average rise of (J. Antonio González, pers. comm.), particularly for 0.14 units per year (Figure 5a). These data are sorghum cultivation. A high level of exchangeable congruent with the increase in the sodium content sodium in the soil is reflected in the increase in the shown earlier in Figure 3d, a situation that has been concentration of bicarbonates and pH in the soil caused by the deterioration in soil quality in many solution, a condition that reduces the availability of fields in the State (Castellanos et al., 2000b), because iron (Levy, 2000). The way to counteract the growers do not make periodic or permanent damaging effects of sodium in the soil in the applications of agricultural gypsum to counteract the southeastern zone or any other region with problems effect of sodium in irrigation water. However, the use of this kind is by adding a source of calcium, such as of gypsum to counteract the effect of sodium means agricultural gypsum (Aceves, 1979). Calcium an additional increase in production costs. Just as in substitutes the sodium in the exchange sites of the the case of sodium, the most severely affected zone is clays and temporarily returns the original conditions the southeast, followed by the central area (Table 1). of fertility to the soil. Nonetheless, given that the It is important to emphasize that, while the data sodium is actually found in the water, each new presented in Table 1 present averages for each region, application of irrigation water will tend to increase the the maximum range is well above those levels concentration of sodium in the soil once again. (Castellanos et al., 2000b), which means that there is

166 CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

(a) (b) 0.4 6.5 y = -0.0067x + 0.2532 r = - 0.3504 0.3 5.5

0.2 4.5

0.1 3.5 y = 0.0651x + 4.3038 Carbonates (me/L) r = 0.4426 Bicarbonates (me/L) 0 2.5 0369121518 0 3 6 9 12 15 18 Time (years) Time (years)

(d) (c) 3.0 1.7 y = 0.0322x + 1.0694 y = 0.0157x + 0.9118 2.5 r = 0.3116 r = 0.2906 1.4

2.0 1.1 1.5

Sulfates (me/L) 0.8 1.0 Chlorides (me/L)

0.5 0.5 0369121518 0 3 6 9 12 15 18 Time (years) Time (years)

Figure 4. Carbonates, bicarbonates, sulfates, and chlorides in groundwater of the State of Guanajuato for the period 1982-1998. water in the State that shows excessively elevated soil. On the other hand, the mean transference of SAR levels, compared with the critical levels reported sulfur, magnesium and, in many cases, potassium is by Ayers and Wescot (1985). more than sufficient to satisfy the demands of the majority of the crops. Residual Sodium Carbonate (RSC) Possible Causes of the Increase in Salts and The tendency of this variable over time is Sodium in Groundwater presented in Figure 5b. The rise that is taking place each year is on the order of 0.06 me/L, a figure There are no systematic studies of the flow congruent with the SAR, and the tendency to increase systems of groundwater in the State of Guanajuato was statistically significant (P < 0.01). The water with that would allow us to understand the origin of the the highest RSC levels is found in the southeast region different salts and, in particular, of sodium. However, (Table 1). there is some evidence related to the management of In Table 2, what stands out is the extremely high the aquifers over several decades that do allow us to transference of sodium from the water to the soil. make certain inferences as to the causes of these There are waters that transfer more than a ton of this increases in salinity. One of the best-known processes cation, which damages the physical properties of the is the rise in the concentration of certain salts in

167 TERRA VOLUMEN 20 NUMERO 2, 2002

twenty. This has given rise to reductions in (a) piezometric levels of as much as 5 to 7 m yr-1 in some 6.0 regions. As a result, water levels that originally were quite close to the surface are now found at depths 5.0 greater than 100 m in many regions of the State and, in fact, up to 200 m in some places. Although the 4.0 relationship between the reduction of piezometric levels and the chemical evolution of groundwater has 3.0 not yet been analyzed, this may be a possibility, SAR (me/L) especially considering the experience of other aquifers y = 0.148x + 1.8714 in the world. 2.0 r = 0.6566** There are, however, other possibilities that should also be explored, such as the influence of local, 1.0 intermediate and regional flow systems of 0 3 6 9 12 15 18 groundwater upon chemical evolution (Tóth, 1999), Time (years) the distance from the recharging zones to the critical zones and the influence of the rocks and minerals (b) through which the water circulates (Ortega-Guerrero, 3.0 2000), the influence of the pressure and temperature of groundwater on the incorporation of salts (Drever, 2.5 1988), and the age of groundwater and modifications of the natural systems as the degree of exploitation of the aquifers is intensified (Domenico, 1972; Ellis and 2.0 Mahon, 1977), among others. In order to elucidate these causes, more detailed hydrogeological studies 1.5 must be undertaken. RSC (me/L)

1.0 y = 0.0623x + 1.3387 CONCLUSIONS r = 0.6466**

0.5 Over time, Guanajuato’s groundwater has been 0 3 6 9 12 15 18 experiencing an increase in the concentration of Time (years) soluble salts, sodium, bicarbonates, SAR and pH, possibly as a result of the reduction of piezometric levels, though the concentrations of Ca, Mg, and K, the beneficial cations have not been increased over the Figure 5. Sodium adsorption ratio (SAR) and residual sodium same period. The highest concentration of sodium is carbonate (RSC) in groundwater in the State of Guanajuato found in water extracted in the southeastern zone, for the period 1982-1998. where negative effects on soil and the nutritive properties of crops, such as sorghum, have already groundwater as piezometric levels are reduced, as in been observed. If measures are not taken to prevent the case of southeastern Spain, south Texas and the increasingly indiscriminate exploitation of the northern Chihuahua (Pulido, 1998; Samani, 1998). In aquifer and the resulting reduction in piezometric these cases, water is systematically extracted from levels, then problems may arise in terms of soil ever-greater depths, and such waters may be older or fertility in the near future that will be difficult to may have circulated through rocks containing more manage. By the same token, it is necessary to highly soluble minerals (Carrillo-Rivera, 2000). undertake systematic studies of groundwater that will In the case of the State of Guanajuato, the over- allow us to identify the processes that control this exploitation of groundwater has been evident for the increase in salinity and so be able to take them into past fifty years and, much more critically, in the last account in regional agricultural planning.

168 CASTELLANOS ET AL. CHANGES IN THE QUALITY OF GROUNDWATER FOR AGRICULTURAL USE IN GUANAJUATO

Table 2. Range and average amounts of nutrients and sodium contained in the groundwater of the State of Guanajuato, and the amount supplied to the soil by an irrigation depth of 50 cm.

Equivalent Contained in water Amount supplied to the soil by an irrigation Nutrient weight depth of 50 cm Average Range Average Range g ------me L-1 ------kg ha-1 ------

N-NO3 14.0 0.2 0.1-1.0 14 7-70 S-SO4 16.0 1.6 0.5-9.0 128 40-720 Calcium 20.0 2.3 0.5-7.0 230 50-700 Magnesium 12.2 1.3 0.2-6.0 80 12-360 Potassium 39.1 0.3 0.1-1.0 59 20-195 Sodium 23.0 4.1 1.0-12.0 471 115-1380

ACKNOWLEDGMENTS Drever, J.I. 1988. The geochemistry of natural waters. 2nd ed. Prentice Hall. Englewoods Clifts, NJ. Ellis, A.J. and W.A.J. Mahon. 1977. Geochemistry and We wish to thank the Fundación Guanajuato geothermal systems. Academic Press, New York. Produce A.C. and CONACYT Project No. 5286N for Levy, G.J. 2000. Sodicity. pp. G27-G55. In: M.E. Sumner (ed.). the economic support they provided for these research Handbook of Soil Science. CRC Press. Boca Raton, FL. projects, which made it possible to obtain the Ortega-Guerrero, M.A. 2000. Proyecto para el manejo sustentable del agua subterránea en la Cuenca de la Independencia, information contained in this report. municipios de San José Iturbide, Dr. Mora, San Luis de la Paz y , y San Diego LITERATURE CITED de la Unión, Gto. Instituto de Geología, Universidad Nacional Autónoma de México. Mexico, DF. Aceves, E. 1979. El ensalitramiento de los suelos bajo riego. Pulido, A. 1998. Problemática de la sobre-explotación de los Colegio de Postgraduados. Chapingo, Mexico. acuíferos en el sudeste español. pp. 48-60. In: Ayers, R.S. and D.W. Wescot. 1985. Water quality for agriculture. J.Z. Castellanos, J.J. Carrillo, and C. Hernández (eds.). Irrigation and Drainage Paper 29. FAO. Rome, Italy. Memoria del Simposio Internacional de Aguas Subterráneas. Burt, C., K. O'Connor, and T. Ruehr. 1995. Fertigation. Irrigation Sociedad Mexicana de la Ciencia del Suelo. León, Gto. Training and Research Center. San Luis Obispo, CA. Rhoades, J.D. 1996. Salinity: Electrical conductivity and total Carrillo-Rivera, J.J. 2000. Application of the groundwater-balance dissolved solids. pp. 417-437. In: D.L. Sparks, A.L. Page, equation to indicate interbasin and vertical flow in two P.A. Helmke, R.H. Loeppert, P.N. Soltanpour, semi-arid basins, Mexico. Hydrogeology J. 8: 503-520. M.A. Tabatabai, C.T. Johnston, and M.E. Sumner (eds.). Castellanos, J.Z., B. Hurtado, S. Villalobos, V. Badillo, P. Vargas, Methods of soil analysis. Part 3. Chemical methods. Book and S.A. Enríquez. 2000a. La calidad del agua subterránea Series 5. Soil Science Society of America. Madison, WI. para uso agrícola en Guanajuato. Reporte Técnico del Richards, L.A. 1954. Diagnostic and improvement of saline and Proyecto 47/99 de la Fundación Guanajuato Produce, A.C. alkali soils. Agriculture Handbook 60. ARS-US Department Instituto Nacional de Investigaciones Forestales y of Agriculture. Riverside, CA. Agropecuarias. Celaya, Guanajuato, México. Richards, L.A. 1990. Diagnóstico y rehabilitación de suelos Castellanos, J.Z., B. Hurtado, S. Villalobos, V. Badillo, P. Vargas, salinos y sódicos. 6th ed. Departamento de Agricultura de los and S.A. Enríquez. 2000b. Características físicas y químicas Estados Unidos de América. Limusa. Mexico, DF. del suelo en el estado de Guanajuato. Reporte Técnico del Samani, S. 1998. Recursos hídricos subterráneos y retos a vencer Proyecto 47/99 de la Fundación Guanajuato Produce, A.C. en la frontera México-Estados Unidos. pp. 43-47. In: Instituto Nacional de Investigaciones Forestales y J.Z. Castellanos, J.J. Carrillo, and C. Hernández (eds.). Agropecuarias. Celaya, Guanajuato, México. Memoria del Simposio Internacional de Aguas Subterráneas. Castellanos, J.Z., J.X. Uvalle-Bueno, and A. Aguilar-Santelises. Sociedad Mexicana de la Ciencia del Suelo. León, Gto. 2000c. Manual de interpretación de análisis de suelos y aguas. Instituto de Capacitación para la Productividad Suarez, D.L. 1981. Relation between pHc and sodium adsorption Agrícola. Celaya, Guanajuato, Mexico. ratio (SAR) and an alternative method of estimating SAR of Chávez G., R. 1998. Estado actual del conocimiento del agua soil or drainage waters. Soil Sci. Soc. Am. J. 45: 469. subterránea en el estado de Guanajuato. pp. 19-28. In: Sumner, M.E. and W.P. Miller. 1996. Cation exchange capacity J.Z. Castellanos, J.J. Carrillo, and C. Hernández (eds.). and exchange coefficients. In: D.L. Sparks, A.L. Page, Memoria del Simposio Internacional de Aguas Subterráneas. P.A. Helmke, R.H. Loeppert, P.N. Soltanpour, Sociedad Mexicana de la Ciencia del Suelo. León, Gto. M.A. Tabatabai, C.T. Johnston, and M.E. Sumner (eds.). Domenico, P.A. 1972. Concepts and models in groundwater Methods of Soil analysis. Part 3. Chemical methods. Book hydrology. McGraw-Hill. New York. Series 5. Soil Science Society of America. Madison, WI.

169 TERRA VOLUMEN 20 NUMERO 2, 2002

Tóth, J. 1999. Groundwater as a geologic agent: An overview of Uvalle-Bueno, J.X., J.F. Limon G., and R. Osorio A. 1996. the causes, processes and manifestations. Hydrogeology J. 7: Aplicación foliar de nitrato de potasio en algodonero en el 1-14. Valle del Yaqui, Sonora. XXVII Congreso Nacional de la Ciencia del Suelo. La Investigación Edafológica en México 1995-1996.

170