Incorporating field wind data to improve crop evapotranspiration parameterization in heterogeneous regions

Accurate parameterization of reference evapotranspiration ( ET0) is necessary for optimizing irrigation scheduling and avoiding costs associated with over-irrigation (water expense, loss of water productivity, energy costs, and pollution) or with under-irrigation (crop stress and suboptimal yields or quality). ET0 is often estimated using the FAO-56 method with meteorological data gathered over a reference surface, usually short grass. However, the density of suitable ET0 stations is often low relative to the microclimatic variability of many arid and semi-arid regions, leading to a potentially inaccurate ET0 for irrigation scheduling. In this study, we investigated multiple ET0 products from six meteorological stations, a satellite ET0 product, and integration (merger) of two stations’ data in Southern California, USA. We evaluated ET0 against lysimetric ET observations from two lysimeter systems (weighing and volumetric) and two crops (wine grapes and Jerusalem artichoke) by calculating crop ET ( ETc) using crop coefficients for the lysimetric crops with the different ET0. ETc calculated with ET0 products that incorporated field-specific wind speed had closer agreement with lysimetric ET, with RMSE reduced by 36 and 45% for grape and Jerusalem artichoke, respectively, with on-field anemometer data compared to wind data from the nearest station. The results indicate the potential importance of on-site meteorological sensors for ET0 parameterization; particularly where microclimates are highly variable and/or irrigation water is expensive or scarce

Irrigation scheduling for cotton cultivation

Crops need water for evaporation (E) and transpiration (T), known as evapotranspiration (ET). However, too much water is not good for various crops. Crop water need depends on growth stage, climate, and crop type. Approximately 40% cotton is produced under irrigated conditions. Water for irrigation is becoming limited in many cotton-growing regions and competition for water is increasing speedily in areas normally having plentiful water resources. So, many cotton producers and the associations representing cotton producers are interested in the scheduling of irrigation strategies that increase water use efficiency (WUE). Responses of cotton under water stress depend on stage of growth, duration, time, and extent of stress. Cotton is a drought-tolerant crop; however, it performs better under optimum water conditions. The water requirement of cotton is 27-51 acre inches depending upon growing duration and prevailing climatic conditions. However, it is essential to apply uniform and accurate amount of water at proper time for maximum cotton yield. Normally, cotton uses less water from sowing to emergence. However, pre-sowing irrigation is mandatory to ensure good cotton seed germination. After germination, crop water demand increases from 0.2 to 0.44 in. per day. Lack of water can reduce plant growth, the number of fruiting sites because of shedding of young bolls, and boll size, consequently resulting in loss of yield potential. There are various irrigation scheduling tools, the main purpose of which is to supply water according to the need of the plant. Water balance method, estimating crop water use, and sensor-based scheduling are a few important tools to maintain irrigation scheduling in cotton