Régimen hídrico del suelo y evapotranspiración en áreas agrícolas y forestales

Abstract

[Abstract] Water and soil are the most important resources for food production, and are also the basis for rural development, distribution of population and environmental conservation. In this sense, this thesis aimed to study the water regime, the dynamics of soil water and evapotranspiration in areas under agriculture and forest vegetation, using capacitance probes FDR (Frequency Domain Reflectometry) in the province of La Coruña. The study was conducted from June 2008 to December 2010, in soils of a watershed forest (specifically, an Eucalyptus globulus stand) called the Abelar, the Agricultural Research Center of Mabegondo (CIAM) (soils under grassland and corn) and natural grass plots located in the manor of Longora. All these sites are located in the province of La Coruña, Galicia, Spain. To study the soil water regime, PVC access tubes were installed in the study plots and soil water content was estimated using FDR probes. Then, using a water balance the evapotranspiration of the plots (ETr) was calculated. Simultaneously, crop evapotranspiration (E c) was estimated through the equation proposed by FAO, based on climatic variables. There was a wide variation of water content in the upper soil layers, this behavior was caused by the presence of crops and pastures in the CIAM, natural grassland in Longora and Eucalyptus trees in Abelar; this favors a rapid evaporation and transpiration from soils. During the dry seasons, summer and autumn, there wass less frequent rainfall affecting surface soil layers, causing a large variation in moisture content within the soil profile. In Abelar, due to the presence of deeper roots, a decrease of soil moisture was observed in the lower horizons during the drier seasons, whereas in the case of grassland and corn plots, which are sites with less influence of roots, this tendency was reduced. In general, in all the studied plots, ETc overestimates the ETr, especially in periods of low rainfall (summer and autumn); this trend decreased in periods of higher precipitation. The results allows us to affirm that, to calculate the evapotranspiration of vegetation cover and water balance using FDR capacitance probes, it is very important that water input data should be as accurate as possible, since those currently available, generally, are approximative. FDR sensors are viable as a tool for estimating water consumption in and to study of the dynamics of soil water in the studied plots.

[Resumo] Os recursos auga e solo son os máis importantes para a produción de alimentos e conforman a base do desenvolvemento rural, a distribución da poboación no territorio e a conservación ambiental. Nese senso, esta tese ten por obxectivo estudar o réxime hídrico do solo, a dinámica da auga no solo e a evapotranspiración en áreas agrícolas e forestais, utilizando sondas de capacitancia FDR (Reflectometria no dominio da frecuencia) na provincia da Coruña. O estudo foi realizado a partir de Xuño de 2008 ata decembro de 2010, en solos dun bosque nunha conca hidrográfica (especificamente, un cultivo de Eucalyptus globulus), chamado Abelar, no Centro de Investigacións Agrarias de Mabegondo (CIAM) (solos baixo pasto e millo) e parcelas de herba natural situadas no Pazo de Longora, todos eles localizados na provincia da Coruña, Galicia, España. Para estudar o réxime de auga no solo, instaláronse tubos de PVC de acceso nas parcelas de estudo e estimouse contido de auga no solo con sondas FDR. A continuación, cun balance hídrico calculouse a evapotranspiración das parcelas (E r). Simultáneamente se estimou a evapotranspiración do cultivo (ETc) de acordo coa ecuación proposta pola FAO, baseada en variables climáticas. Houbo unha gran variación do contido de auga nas capas superiores do perfil do solo, este comportamento é debido á presenza de cultivos e pastos no CIAM, herba natural en Lóngora e ás árbores do Abelar, que favorecen a rápida evaporación e transpiración de auga dos solos. Durante a estación seca, verán e outono, hai choivas menos frecuentes que afectan os horizontes superficiais, creando unha gran variación no contido de humidade nos mesmos. Nas parcelas do Abelar, debido á presenza de raíces máis profundas, podemos ver que nos horizontes máis baixos e nas estacións máis secas, houbo unha caída de humidade do solo mentras que en sitios con menor influencia radicular, como é o caso dos pastos e o millo, esta tendencia é moi reducida. En xeral, en todas as parcelas estudadas a ETc sobreestima á ETr, especialmente en períodos de falta de chuvia (verán e outono), tendencia decrecente nos períodos de maior precipitación. Á luz dos resultados, podemos afirmar que, para calcular a evapotranspiración da cuberta vexetal e do balance hídrico, utilizando as sondas de capacidade FDR, é moi importante que os datos de entrada de auga sexan tan precisos como sexa posible, xa que os dispoñibles actualmente, xeralmente, son aproximados. O uso de sensores FDR é viable como ferramenta para calcular o consumo de auga nos cultivos e no estudo da dinámica da auga no solo nas parcelas de estudo.