Pre- and post-harvest evapotranspiration, carbon exchange and water use efficiency of a mature peach orchard in semi-arid climate

Better knowledge of the evapotranspiration and carbon exchange of fruit trees is needed to optimize the trade-off between water use and carbon assimilation and to better understand the role of agriculture in the biogeochemical cycles. In this work we measured water and carbon fluxes with eddy covariance and transpiration with sap flow in a drip irrigated peach orchard of 70% ground cover located in southern Spain for two years. The empirically measured crop coefficient (Kc) under good watering conditions in the summer ranged from 1 to 1.1. The daytime Net Ecosystem Exchange (NEE) flux of the orchard averaged 30 g CO2 m2 day-1 during the period of maximum activity in July. The daytime ecosystem water use efficiency (WUE) of the orchard reached a minimum in late June, flattened around 4 g CO2 L-1 throughout the summer, and increased in autumn, but was unaffected by fruit removal or post-harvest irrigation reduction imposed by the farm (30% reduction). The response of instantaneous peach ecosystem WUE to VPD was also investigated. Both Kc, NEE, leaf water potential and stomatal conductance decreased sharply after harvest. Transpiration data from some purposely over-irrigated experimental trees demonstrated that the post-harvest alterations we found were not caused by fruit removal, but are result of mild water stress originated by the irrigation reduction. Hence, the often-observed alterations in water relations after harvest in well-watered trees were not observed in this experiment. This work adds insight on peach irrigation efficiency and on the contribution of orchards to agricultural carbon budgets

Estimating marginal value of water for irrigated olive grove with the production function method

Economic valuation of irrigation water is done through the use of production functions for the case of the olive grove. In order to do so the integration of an agronomic model (based on the production function) and an economic model linked to the profitability of the crop (the ratio of revenue and operating costs) in the area under study is proposed. The study case encompasses the Guadalbullon River Sub-basin area, belonging to the Guadalquivir River Hydrologic Demarcation (Southern Spain). Within the overall deficit of the Guadalquivir River basin, the Guadalbullon River poses a special problem as it is unregulated and there are important irrigated fields on its banks, most of them olive groves. Net marginal value of water obtained (having deducted the variable costs of production including harvesting and irrigation) is� 0.60 m�3 for the allocation of 1,000 m3 ha�1 and � 0.53 m�3 for the water right allowance of 1,500 m3 ha�1 (average for period 2005/2008). The results obtained support the recommendation by other authors suggesting the use of deficit irrigation in olive, additionally the high value of water estimated contributes to explain the substantial increase in irrigated olive area in Andalucia

Respuestas del olivar tradicional a diferentes estrategias y dosis de agua de riego

En un olivar tradicional (80 olivos / ha) en Santisteban del Puerto (Jaén) se aplicaron durante seis años consecutivos tres programas de riego, comparándose con un testigo en secano. El tratamiento con mayor dotación de agua (3.200 metros cúbicos / ha) se programó reponiendo la evapotranspiración (ET) del árbol. Para su calculo se utilizo la metodología RAO, utilizando los datos medios de ETo y lluvia eficaz del año medio. Se aplicaron también otros dos programas de riego deficitario diseñados para utilizar una parte de la reserva hídrica del suelo. Estos programas aplicaron 150 metros cúbicos / ha (80 1 / olivo / día en el período marzo-octubre ) y 2.000 metros cúbicos / ha (120 l / olivo / día en el período abril-octubre). El suelo de la parcela experimental es profundo, y de alta capacidad de retención de agua. La precipitación media anual durante el experimento fue de 506 mm. El riego incrementó espectacularmente la producción media sobre el secano (de 60 kg / olivo en secano a 100 kg / olivo en los tratamientos regados), aumentando igualmente el número de frutos por árbol, el tamaño de fruto y el rendimiento graso de las aceitunas. El aumento de producción en regadío se atribuye a un aumento del volumen de copa de los árboles, así como del índice de área foliar. No se observaron diferencias significativas entre los tres tratamientos de riego para ninguno de los mencionados parámetros. Para la zona del ensayo y el sistema productivo tradicional, se recomienda programar los riegos con aportaciones diarias y constantes, entre 80 y 120 l / árbol y día, en función de la reserva hídrica del suelo a la salida de] invierno, reduciéndose la programación del riego a identificar las fechas de comienzo y final del período de riego