Estimating Applied Water in Alfalfa using the IWFM Demand Calculator Model
Department of LAWR
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Irrigation is vital to produce acceptable quality and yield of crops on arid climate croplands. Irrigation and crop evapotranspiration are also key drivers of hydrologic fluxes in semi-arid agricultural basins. In California, alfalfa (Medicago sativa) was the single largest user of water in 2010, with an estimated 5.2 million acre-feet of applied water. Irrigating alfalfa is different from most common commodities such as corn or soybeans: alfalfa is a perennial crop with a deep rooting system that can access water from deep within the soil profile. For hydrologic assessments, accurate estimation of applied water, root zone storage, crop water uptake, and groundwater recharge are critical outcomes. Agricultural crop water requirement is a function of climate, soil and land surface physical properties as well as land use management practices which are spatially distributed and evolve in time. These variables can be modelled using either integrated hydrologic models and/or irrigation scheduling models. The California Department of Water Resources (CADWR) has integrated the benefits from these two approaches and has developed a new model that estimates the irrigation water requirements and routes soil moisture through root zone in the context of an integrated hydrologic modelling tool, Integrated Water Flow Model (IWFM) - Demand Calculator (IDC). This root-zone simulation engine is a stand-alone program that simulates land surface and root zone flow processes as well as agricultural and urban water demands under user specified land-use, soil, climate and farm management conditions. In this study, we compare applied water estimates for alfalfa crops at eight alfalfa sites in semi-arid Scott Valley of California with measured water application, soil moisture data, and evapotranspiration.