Análisis productivo, ambiental, energético y económico de sistemas de cultivo

Abstract

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. El objetivo principal de la tesis defendida ha sido el análisis productivo, ambiental y energético de los cultivos pomelo y lechuga, realizándose además un análisis económico en lechuga, comprando el sistema de cultivo en suelo con un sistema de cultivo hidropónico. El análisis ha evaluado la implementación en el agua de riego de recursos de agua no convencionales como el agua regenerada (AR) y agua desalinizada (AD) en diferentes proporciones. El análisis en pomelo ha considerado diferentes etapas del ciclo de vida del cultivo y el empleo de estrategias de riego deficitario controlado (RDC). Para la evaluación de los sistemas de cultivo se ha realizado un inventario de datos y aplicado los correspondientes factores de conversión a unidades energéticas y de emisiones de gases de efecto invernadero (GEI). La energía ha sido dividida en energía directa (labor humana, electricidad y combustible) e indirecta (maquinaria, fertilizantes, pesticidas, embalse, sistema de riego y sistema hidropónico). Las emisiones de GEI se han clasificado en debidas al uso de: a) combustibles fósiles y electricidad; b) maquinaria y sistema de riego; c) producción, transporte, almacenamiento y aplicación de químicos agrícolas; y d) fertilizantes nitrogenados. Los resultados, en el cultivo de pomelo, han mostrado que el mayor consumo de energía es atribuido a la fase de establecimiento del cultivo, donde las mayores entradas de energía directa e indirecta se atribuyen al combustible diésel y los materiales del sistema de riego respectivamente. En el resto de etapas el mayor consumo de energía es debido a la electricidad para riego. Respeto a las emisiones de GEI, las mayores emisiones en la etapa de establecimiento se deben al sistema de riego, mientras que en el resto de etapas se deben a la aplicación de fertilizantes nitrogenados. Las estrategias de RDC repercuten en ahorros de energía y reducciones de emisiones de GEI, independientemente de la fuente de agua empleada. El uso de AR apenas tiene efecto sobre los consumos de energía y emisiones de GEI. En el cultivo de lechuga los resultados han mostrado que el mayor consumo de energía en los sistemas corresponde a energía indirecta y que el consumo de energía total en el sistema hidropónico es 5,6 veces mayor que el calculado para el sistema en suelo, que es un 21% más eficiente en el uso de la energía. Los principales consumos de energía son el material vegetal y electricidad para riego en los sistemas en suelo e hidropónico respectivamente. La productividad de la tierra anual y la productividad del agua en el sistema hidropónico son 4,8 y 2,6 veces superiores respecto al sistema en suelo. Respecto a los GEI, el sistema hidropónico registra unas emisiones de GEI de área (debidas principalmente al sistema de riego hidropónico) que duplican a las del sistema en suelo (debidas principalmente al sistema de riego por goteo). El uso de AD para riego en ambos sistemas incrementa el consumo de energía y emisiones de GEI, debido a su elevado costo de producción. A partir de un porcentaje de mezcla de 29,6% de AD, el sistema TPN comienza a ser energéticamente más eficiente. Respecto al análisis económico, el sistema hidropónico presenta mayores costos, ingresos, beneficios y VAN respecto al sistema en suelo. El TIR, en cambio, es mayor en el sistema en suelo, lo que muestra la mayor rentabilidad del sistema de cultivo en suelo.

[ENG] This doctoral dissertation has been presented in the form of thesis by publication. The agriculture developed in the Segura River Basin (SRB), in the southeast of Spain, has been the engine of economic development in the region. However, this development is associated with a high consumption of water and energy, as well as emissions of greenhouse gases (GHG), whose consequences are environmental pollution and reduction of available water resources. This problem will be aggravated if we take into account that global food production has to increase by 70% for the year 2050, due to population growth (FAO 2009). The use of non-conventional resources for irrigation such as desalinated sea water (DS), regenerated water (RW), regulated deficit irrigation strategies and / or the use of closed hydroponic systems are presented as alternatives for traditional agriculture that could fight the environmental problems and the lack of water resources available in the SRV. The first line of action of the thesis consists of the characterization of two cultivation systems of lettuce production (Lactuca sativa L. cv. "Little Gem"), the soil cultivation system (SC) and the nutrient film technique system (NFT), and its later analysis of energy and greenhouse gas (GHG) emissions. In addition, different water supply scenarios (WSS) are considered: i) WSS-1, where 100% of water resources come from surface and underground water resources; it is, 100% ST; ii) WSS-2, with a mixing percentage of 50% of DS and 50% of ST; and iii) WSS-3, where 100% of the water resources for irrigation correspond to DS. The trial was developed during the 2016-2017 agricultural campaign in commercial farms of the SRV. Six study plots were chosen, three for the SC system and three for the NFT system, in that way both systems presented the three WSS. To analyze the systems, an inventory was performed based on the following inputs: human labor (h/ha), diesel (l/ha), water for irrigation (m3/ha), electricity (kWh/ha), machinery (h/ha), fertilizers (kg/ha), pesticides (kg/ha) and plant material (units/ha). In addition, data regarding the number of cycles (cycles/year), cycle duration (days) and planting density (plants/m2) were taken. The quantity, type and useful life of the water deposit, drip irrigation system and hydroponic irrigation system materials were also studied. As output of the system the production of lettuce (kg/ha and cycle) was taken into account. Once the data were recorded in a database, it was converted into energy units (MJ/ha) and GHG emissions (kg CO2eq/ha) by applying the corresponding conversion factors. Energy consumption was divided into direct energy consumption (human labor, diesel and electricity for irrigation) and indirect energy consumption (machinery, fertilizers, pesticides, water reservoir, drip irrigation system and hydroponic irrigation system). The GHG emissions were classified into: i) GHG emissions due to the use of fossil fuels and electricity; (ii) GHG emissions of machinery and irrigation systems; (iii) GHG emissions due to the production, transportation, storage and transfer of agricultural chemicals; and (iv) GHG emissions of NO2 to the soils due to the application of N-fertilizer. In addition, the efficiency in the use of energy, specific energy (MJ/ha), areal GHG emissions (kg CO2eq /ha) and specific GHG emissions (kg CO2eq/ kg) indices were calculated. The results showed that the highest energy consumption in the systems corresponds to indirect energy and that the total energy consumption in the NFT system is 5,6 times higher than that calculated for the SC system, which is 21% more efficient in the use of energy. The main representative inputs on total energy input were plant material and electricity for irrigation in the SC and NFT systems respectively. The annual land productivity and water productivity in the NFT system were 4,8 and 2,6 times higher than the SC system. Regarding the GHG, the NFT system registered areal GHG emissions (mainly due to the hydroponic irrigation system) that duplicates those of the SC system (mainly due to the drip irrigation system). The use of DS for irrigation in both systems increased energy consumption and GHG emissions, due to its high production cost. From a mix percentage of 29,6% of DS, the NFT system begins to be more energy efficient. Independently of the WSS, the GHG emissions were lower in the NFT system. The second line of action of the thesis evaluates a grapefruit orchard (Citrus Paradisi Macf) in its different stages of the life cycle of the crop (establishment of the plantation, unproductive juvenile state, productive juvenile state and productive adult state), from the energetic and GHG emissions point of view using different irrigation strategies (total irrigation and RDI combined or not with RW). The trial began in 2004 in a commercial orchard of 0,5 ha located in Campotéjar-Murcia and ended in 2014. A total of 192 trees were selected. Four treatments were performed depending on the water source used for irrigation and the application or not of RDI: i) TS without RDI, II) TS with RDI, III) RW without RDI and iv) RW with RDI. From 2005 to 2007 the totally orchard was irrigated with TS water and it was from 2008 onwards when RDI and RW were applied. Data of human labor (h), diesel (l), electricity (kWh), fertilizers (kg), pesticides (kg), plant material (units), machinery (h), water for irrigation (m3), irrigation system and production (kg) were collected. Once the data were recorded in a database, it was converted into energy units (MJ) and GHG emissions (kg CO2eq) by applying the corresponding conversion factors. Energy consumption was divided into direct energy consumption (human labor, diesel and electricity for irrigation) and indirect energy consumption (machinery, fertilizers, pesticides, plant material, water for irrigation and irrigation system). The GHG emissions were classified into: i) GHG emissions due to the use of fossil fuels and electricity; (ii) GHG emissions of machinery and irrigation systems; (iii) GHG emissions due to the production, transportation, storage and transfer of agricultural chemicals; and (iv) GHG emissions of NO2 to the soils due to the application of N-fertilizer. Additionally, the water productivity (kg/m3), energy use efficiency, specific energy (MJ), areal GHG emissions (kg CO2eq/ha) and specific GHG emissions (kg CO2eq/kg) indices were calculated. The energy balance carried out for each of the cases studied showed that the greatest energy input took place in the stage of establishment of the crop, where the highest direct and indirect energy inputs were attributed to the diesel and the materials of the irrigation system respectively. For the rest of the stages, the highest energy consumption was due to electricity for irrigation. Respect to the GHG emissions, the highest emissions in the establishment stage were due to the irrigation system, while in the rest of the stages it were due to the application of nitrogen fertilizers. RDI strategies had an impact on energy savings and reductions in GHG emissions, regardless of the source of water used. The use of RW had short effect on energy consumption and GHG emissions. The third line of action of the thesis is a continuation of the first one, in which the collected data is converted into economic data for the later comparative analysis of SC and NFT production systems in the different water supply scenarios. To perform this analysis, the costs, revenues and benefits of both systems were determined. Costs were divided into operational costs and investment costs. In addition, a discounted cash flow analysis (DCFA) was performed and the following economic parameters were calculated: internal rate of return (IRR) and net present value (NPV). The results showed that in the NFT system, the costs, revenues, benefits and NPV are higher than in the SC system, regardless of the water source applied. However, the IRR was higher in the SC system, which indicates the greater profitability compared to the NFT system.