Estudio de viabilidad del uso de agua regenerada y riego deficitario controlado en cítricos

Abstract

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. La población mundial alcanzará unos 10.000 millones de personas en 2050, según recientes proyecciones (ONU, 2017). Para satisfacer la demanda de alimentos, la agricultura necesitará producir casi el 50% más en 2050 que en 2012. Así pues, el incremento de la productividad agrícola de una manera sostenible, conservando el agua y previniendo la contaminación del suelo debe de ser, actualmente, uno de los principales retos de la investigación agronómica a nivel de ecosistema. Es sabido que el agua es el factor de producción más limitante (CE, 2017), especialmente en áreas semiáridas, como la del Mediterráneo, donde el agua de riego no está siempre disponible debido a su escasez (Pedrero et al., 2015). Al mismo tiempo, las predicciones actuales sobre el cambio climático señalan que en el sur de Europa las olas de calor extremo y la reducción de las precipitaciones y del agua disponible limitarán más aún la productividad agraria dado que se está incrementando la frecuencia e intensidad de los periodos de sequía (García-Galiano et al., 2015; FAO, 2016). El uso de fuentes de agua no convencionales como el agua regenerada (AR) y de estrategias de riego deficitario controlado (RDC) podrían ser alternativas adecuadas para los agricultores. En este sentido, el AR puede ser beneficiosa para los cultivos dado que la presencia de macronutrientes (N, P, K) puede ayudar a reducir los requerimientos de fertilizantes, como el nitrato, dando lugar a importantes ahorros (Pedrero et al., 2013). No obstante, se requiere una gestión adecuada y cuidadosa del N para que sea absorbido por la planta y no se lixivie, contaminando así el suelo y los acuíferos (Laslo et al., 2012). En Murcia, una región agronómica semiárida, el 93% del AR tiene una conductividad eléctrica por encima de 2 dS·m-1 y un 37% por encima de 3 dS·m-1, según datos de ESAMUR. La salinidad está entre los factores ambientales más importantes responsables de pérdidas sustanciales de producción en la agricultura a nivel mundial y es uno de los problemas más serios que confronta la viabilidad a largo plazo de la agricultura en sistemas de producción regados con AR en regiones semiáridas. Esto es un inconveniente especialmente en cítricos, dado que son uno de los cultivos, más significativos a nivel mundial, considerados sensibles a la salinidad (Al-Yassin, 2005) y a la acumulación de boro (B) (Grattan, 2015). Entre los efectos más destacados de las altas concentraciones de estos fitotóxicos se encuentra el cierre estomático (Gimeno et al., 2012), que reduce la disponibilidad de CO2 para la fotosíntesis (García-Sánchez y Syvertsen, 2006) y aumenta la acumulación de iones (Brumos et al., 2009; Mouhaya et al., 2010) y el daño en las hojas, lo que generalmente conduce a una reducción en la producción total de fruta (Murkute et al., 2005). Por consiguiente, el B y la salinidad pueden limitar la viabilidad a largo plazo del uso de AR en cítricos a medida que aumenta el tiempo de exposición a los mismos. El conocimiento del papel que desempeñan la fenología, la capacidad fotosintética, así como el estado hídrico de la planta en la función fisiológica, y sus interacciones durante el ciclo de cultivo, es clave para evaluar la productividad de los árboles frutales (MirásÁvalos et al., 2011) y para la caracterización del impacto de las distintas prácticas agronómicas. En este sentido, la presente Tesis Doctoral trata de evaluar la respuesta agronómica y fisiológica de los cítricos al riego con AR combinado con RDC. Los ensayos se llevaron a cabo en una finca comercial de cítricos, localizada en el noreste de la región de Murcia, a 7 km de Molina de Segura (38◦07´18´´N, 1◦13´15´´W) Con un clima BSk, según la clasificación de Köppen-Geiger (Peel et al., 2007) durante el periodo 2012-2015. [ENG] This doctoral dissertation has been presented in the form of thesis by publication. World population will reach 10,000 million in 2050 by recent projections (ONU, 2017). To meet the demand for food, agriculture in 2050 will need to produce almost 50% more than in 2012. Thus, the increase of agricultural productivity in a sustainable way, conserving water and preventing soil contamination must be, currently, one of the main challenges of agronomic research at the ecosystem level. It is known that water is the most limiting factor of production (CE, 2017), especially in semi-arid areas, such as the Mediterranean, where irrigation water is not always available due to its scarcity (Pedrero et al., 2015). At the same time, current predictions on climate change indicate that extreme heatwaves and the reduction of rainfall and available water in southern Europe will limit agricultural productivity as the frequency and intensity of drought periods is increasing (García-Galiano et al., 2015, FAO, 2016). The use of unconventional water sources such as reclaimed water (RW) and strategies of regulated deficit irrigation (RDI) could be suitable alternatives for farmers. In this sense, RW can be beneficial for crops since the presence of macronutrients (N, P, K) can help reduce fertilizer requirements, such as nitrate, leading to significant savings (Pedrero et al., 2013). However, an adequate and careful management of the N is required so that it is absorbed by the plant and is not leached contaminating the soil and aquifers (Laslo et al., 2012). In Murcia, a semi-arid agronomic region, 93% of the RW has an electrical conductivity above 2 dS m-1 and 37% above 3 dS · m-1, according to recent data from ESAMUR. Salinity is among the most important environmental factors responsible for substantial losses of production in agriculture worldwide and is one of the serious problems confronting the long-term viability of agriculture in production systems irrigated with RW in semi-arid regions. This is a disadvantage, especially in citrus fruit, as they are one of the most significant crops worldwide considered sensitive to salinity (Maas, 1993; Al-Yassin, 2005) and to the accumulation of boron (B) (Grattan, 2013). The primary effect of the high concentrations of these phytotoxics is stomatal closure (Gimeno et al., 2012), which reduces the availability of CO2 for photosynthesis (García-Sánchez y Syvertsen, 2006) and increases the accumulation of ions (Brumos et al. al., 2009; Mouhaya et al., 2010) and leaf damage, which generally leads to a reduction in total fruit production (Murkute et al., 2005). Therefore, B and salinity can Tesis Doctoral Estudio de viabilidad del uso de AR y RDC en cítricos 54 limit the long-term viability of the use of RW in citrus fruits as the time of exposure to them increases. The knowledge of the role played at the leaf level by the phenology, the structure and the photosynthetic function, as well as the hydric state of the plant in the physiological function, and their interactions during the crop cycle is important to evaluate the productivity of fruit trees (Mirás-Ávalos et al., 2011) and for the characterization of the impact of the different agronomic practices. In this sense, the Doctoral Thesis tries to evaluate the agronomic and physiological response of citrus fruits to irrigation with RW combined with RDI. The experiments were carried out in a commercial citrus farm, located in the northeast of the region of Murcia, 7 km from Molina de Segura (38◦07'18''N, 1◦13'15' 'W) with a BSk climate, according to the Köppen-Geiger classification (Peel et al., 2007) during the period 2012-2015.

[ENG] This doctoral dissertation has been presented in the form of thesis by publication. World population will reach 10,000 million in 2050 by recent projections (ONU, 2017). To meet the demand for food, agriculture in 2050 will need to produce almost 50% more than in 2012. Thus, the increase of agricultural productivity in a sustainable way, conserving water and preventing soil contamination must be, currently, one of the main challenges of agronomic research at the ecosystem level. It is known that water is the most limiting factor of production (CE, 2017), especially in semi-arid areas, such as the Mediterranean, where irrigation water is not always available due to its scarcity (Pedrero et al., 2015). At the same time, current predictions on climate change indicate that extreme heatwaves and the reduction of rainfall and available water in southern Europe will limit agricultural productivity as the frequency and intensity of drought periods is increasing (García-Galiano et al., 2015, FAO, 2016). The use of unconventional water sources such as reclaimed water (RW) and strategies of regulated deficit irrigation (RDI) could be suitable alternatives for farmers. In this sense, RW can be beneficial for crops since the presence of macronutrients (N, P, K) can help reduce fertilizer requirements, such as nitrate, leading to significant savings (Pedrero et al., 2013). However, an adequate and careful management of the N is required so that it is absorbed by the plant and is not leached contaminating the soil and aquifers (Laslo et al., 2012). In Murcia, a semi-arid agronomic region, 93% of the RW has an electrical conductivity above 2 dS m-1 and 37% above 3 dS · m-1, according to recent data from ESAMUR. Salinity is among the most important environmental factors responsible for substantial losses of production in agriculture worldwide and is one of the serious problems confronting the long-term viability of agriculture in production systems irrigated with RW in semi-arid regions. This is a disadvantage, especially in citrus fruit, as they are one of the most significant crops worldwide considered sensitive to salinity (Maas, 1993; Al-Yassin, 2005) and to the accumulation of boron (B) (Grattan, 2013). The primary effect of the high concentrations of these phytotoxics is stomatal closure (Gimeno et al., 2012), which reduces the availability of CO2 for photosynthesis (García-Sánchez y Syvertsen, 2006) and increases the accumulation of ions (Brumos et al. al., 2009; Mouhaya et al., 2010) and leaf damage, which generally leads to a reduction in total fruit production (Murkute et al., 2005). Therefore, B and salinity can Tesis Doctoral Estudio de viabilidad del uso de AR y RDC en cítricos 54 limit the long-term viability of the use of RW in citrus fruits as the time of exposure to them increases. The knowledge of the role played at the leaf level by the phenology, the structure and the photosynthetic function, as well as the hydric state of the plant in the physiological function, and their interactions during the crop cycle is important to evaluate the productivity of fruit trees (Mirás-Ávalos et al., 2011) and for the characterization of the impact of the different agronomic practices. In this sense, the Doctoral Thesis tries to evaluate the agronomic and physiological response of citrus fruits to irrigation with RW combined with RDI. The experiments were carried out in a commercial citrus farm, located in the northeast of the region of Murcia, 7 km from Molina de Segura (38◦07'18''N, 1◦13'15' 'W) with a BSk climate, according to the Köppen-Geiger classification (Peel et al., 2007) during the period 2012-2015.