AquaCitrus: Soil water balance model for irrigation management in citrus orchards

Abstract

Climate change scenarios have projected that more frequent and severe droughts are likely to occur, especially in arid and semi-arid regions such as a gran part of the Mediterranean basin, where the effects of climate change on irrigated agriculture are more accentuated. These regions are generally characterized by an agroecosystem based on perennial crops that are sensitive to water scarcity. Citrus is among perennial crops in the Mediterranean area currently facing climate change effects and water scarcity. In the Mediterranean region, the changes in rainfall patterns and the increase in temperature caused by climate change will lead to higher evapotranspiration and consequently, increased irrigation needs for this crop that already has high water requirements.Thus, it is mandatory to develop climate change adaptation measures to reduce their impacts on water resources in arid and semi-arid regions with intensive use of water for irrigation to increase capacity and efficiency for irrigation and ease the projected water stress.  One approach to ensure efficient water management is the development of decision-support tools to improve water management efficiency in irrigation. Crop simulation models are a key tool in extrapolating the impacts of climate change on irrigation water management.In this context, our study aims at developing an agronomic model for woody crops, especially for citrus, since agronomic models for woody crops are practically absent, in contrast to the wide range of alternatives for annual crops, to define water resource management strategies. The model, named AquaCitrus, is a new functional soil water balance for citrus that simulates on daily time step water fluxes in the soil-plant-atmosphere complex. In short, AquaCitrus is composed of a set of sub-models computing the fluxes of effective precipitation, infiltration, runoff, soil evaporation, drainage, and crop transpiration. The model includes the routine of rainfall interception by the canopy, and computes the soil evaporation and crop transpiration separately. Soil evaporation is calculated using the model of Ritchie and citrus transpiration is calculated by the transpiration coefficient method. AquaCitrus considers the heterogeneity of the soil, given that localized irrigation keeps a small fraction of the soil frequently wet while the remaining area remains dry, unless it rains. Therefore, the model is divided into two compartments that solve the water balance separately for each soil zone.To assess its predictive power, AquaCitrus was evaluated using a 2-year period of soil moisture data from an experimental field conducted in a citrus orchard in Valencia, Spain.  The results pointed out a good agreement between simulated and measured soil water contents at different soil depths; the model predicts the water balance of the system satisfactorily. We concluded that AquaCitrus is a useful tool to simulate strategies for improving irrigation water use efficiency in citrus crops, highlighting that there is additional room for improving its robustness. Acknowledgements: This research has been supported by the ADAPTAMED project (RTI2018-101483-B-I00), funded by the Ministerio de Economía y Competitividad (MINECO) of Spain including EU FEDER funds; and by the GoNEXUS project (GA. 101003722), funded by the European Union Horizon Programme call H2020-LC-CLA-2018-2019-2020.