After several decades, the incorporation of desalinated seawater into agricultural areas with scarce water resources has become one of the main water supply strategies. Compared to the several currently available desalination techniques, reverse osmosis (RO) is now the reference technology because it lowers energy uses and production costs. Nevertheless, its main limiting factor lies in the membranes used for this system not efficiently retaining boron, which is a problem because the concentration of this element in seawater is high. For 3 years, the present work analysed the impact of seawater temperature on the kinetic parameters of boron rejection in an RO system to establish their annual behaviour and the existing correlation between both parameters. A comparison was made using the values simulated in the projection software provided by the manufacturer of the membranes. The obtained results indicated a high correlation, and the R2 correlation coefficients came very close to the unity. Nonetheless, this correlation lowered with time due to typical membrane ageing and compaction because of the system’s continuous operation. Under the tested working conditions and by applying analysed temperature intervals, it was impossible to reach the 0.3 mg·L−1 boron concentration value that ensures lack of crop toxicity. Thus, incorporating other boron reduction techniques is necessary.

Infiltration estimation is made by tests such as concentric cylinders, which are prone to errors, such as the lateral movement under the ring. Several possibilities have been developed over the last decades to compensate these errors, which are based on physical, electronic, and mathematical principles. In this research, two approaches are proposed to measure the water infiltration rate in a silty loam soil by means of the mass values of a lysimeter weighing under rainfall conditions and different moisture contents. Based on the fact that with the lysimeter it is possible to determine acting soil flows very precisely, then with the help of mass conservation and assuming a downward vertical movement, 12 rain events were analyzed. In addition, it was possible to monitor the behavior of soil moisture and to establish the content at field capacity from the values of the weighing lysimeter, from which both approach are based. The infiltration rate of these events showed a variable rate at the beginning of the rainfall until reaching a maximum, to descend to a stable or basic rate. This basic infiltration rate was 1.49 ± 0.36 mm/h, and this is because soils with fine textures have reported low infiltration capacity. Four empirical or semi-empirical models of infiltration were calibrated with the values obtained with our approaches, showing a better fit with the Horton’s model.

Resumen: La velocidad de infiltración permite estimar la penetración del agua en el suelo, se puede medir como una lámina en función de la profundidad y el tiempo. Existen algunos métodos para medir el comportamiento de la lámina de agua en el suelo. En esta investigación se empleó un lisímetro compacto desarrollado por el grupo de investigación Ingeniería Agromótica y del Mar de la Universidad Politécnica de Cartagena. Se instaló en una finca con suelo de textura franco-limosa, y se registraron los valores minutales del peso del recipiente de cultivo y del depósito de drenaje. Los resultados obtenidos permitieron conocer la evolución de la velocidad de infiltración a lo largo del tiempo. La máxima velocidad de infiltración fue de 0,093 mm/minuto, en el suelo saturado. Con los datos obtenidos en campo se calibró el modelo empírico de Kostiakov, con un error cuadrático medio de 0,00024. Se concluyó que con el empleo de los nuevos lisímetros de pesada que permiten conocer, en tiempo real, la velocidad de infiltración del agua en suelos saturados, es posible calibrar modelos matemáticos empíricos para su empleo cuando no se dispone de esta nueva tecnología. En el suelo franco-limoso estudiado, el comportamiento fue similar al descrito por Kostiakow, para el cual se obtuvo una ecuación exponencial calibrada.Palabras clave: humedad del suelo, modelo de infiltración, hidrología, balance hídrico IntroducciónLa demanda de agua en la agricultura de regadío es especialmente relevante en países o regiones de clima árido o semiárido, donde se desarrolla bajo un escenario crítico de limitación de agua. Esta situación, hace necesario que se incrementen los esfuerzos para lograr una gestión óptima de los recursos hídricos disponibles para el riego. Se requiere, por tanto, conocer con la mayor exactitud posible el agua que necesita el cultivo para una producción óptima, ya sea en forma de precipitación o de su aplicación desde fuentes superficiales o subterráneas.La capacidad de retención del agua en el suelo y el movimiento del agua depende de sus características hidrodinámicas. La ecuación de Richards modela el movimiento del agua en el suelo. Se basa en la transferencia de agua en medios porosos considerando la ley de Darcy generalizada y el concepto de potencial de capilaridad [1]. Debido a la complejidad de la estimación de los parámetros de la ecuación de Richard, fueron desarrollados un gran número de modelos empíricos simples de infiltración por [2], [7], [4], entre otros. También, es posible

Water use efficiency is essential in semiarid regions of Spain, and it can be achieved through a precise knowledge of the real crop water requirements (CWR). The Food and Agriculture Organization of the United Nations (FAO) offers standardized crop coefficients to establish the CWR. However, these coefficients can change due to different conditions, such as climatic variations and cultivation practices. In this work, the evapotranspiration (ETClys) and crop coefficients (KClys) of bell pepper were obtained with a compact removable weighing lysimeter between February and August for two crop seasons (2019 and 2020). ETClys was determined from the water balance, and the KClys values were determined as the ratio of the crop evapotranspiration, measured on the removable weighing lysimeter, and the reference evapotranspiration. The KClys average values for the bell pepper in the initial, middle, and final stages were 0.57, 1.06, and 0.80, respectively. KC regression models were obtained as a function of the fraction thermal units, achieving a maximum correlation of 0.67 (R2). In general, the KC values obtained in this research work were lower in the initial and in the final stages and larger in the middle stage in comparison with the FAO-56 values and other research works values in semiarid conditions. The bell pepper yield increased by 7.72% in 2019 and by 3.49% in 2020 compared to the yield reported by the Ministry of the Environment and Rural and Marine Areas of the Spanish Government in 2019 and with a minimum water loss through drainage. The results in this work can help farmers to determine the crop water requirements and to improve the system efficiency in semiarid locations with similar conditions to those in the study.