Yield Prediction of Sunflower Based on Crop Coefficient and Water Production Function

Crop coefficient and water production function are important parameters for water saving irrigation. Through making use of data from the stage sowing test at Bayannaoer (40°45′N, 107°25′E, elevation 1039.3 m) of Inner Mongolia in 2012 and historical agro-meteorological data from two monitoring stations, most of the research is carried out in accordance with yield prediction methods based on crop coefficient and water production function. As far as results are concerned, variations in the standard sunflower crop are small in the early stage, large in the medium stage and small again in the late stage. The peak value (1.21) presents itself in the blossom period. There are strong quadratic and cubic polynomial relationships amongst standard crop coefficients days after germination and positive accumulated temperature values (determination coefficient is 0.93). Through comparison with FAO recommended stage values, standard crop coefficient from the test computing is reasonable. In addition, when calibration methods of standard crop coefficient and relative leaf area index are put forward, the actual evapo-transpiration of water production function can be calculated, and dynamic calculation equations of sunflower crop coefficient in the irrigated districts are obtained. There is a quadratic parabola relationship between sunflower water consumption and yield with a suitable water consumption limit. The suitable water consumption threshold is about 400-460 mm, and the yield is 496.7-500.6 g·m^-2. Moreover, when water supply is adequate, the water requirement of sunflowers during the entire growth period is 450 mm with an average frequency of 4.09 mm/d. The regular water requirement pattern indicates that minimum water is required during seeding stage, medium water is required during two pairs of true leaves-inflorescence formation stage and blossom-maturity stage, and maximum water is required during inflorescence formation-blossom stage. Additionally, when Jensen model is put forward and established through comparison with 4 sensitive indexes, the order of water deficit from high to low is blossom period, inflorescence formation period, maturity period and seeding period, which is consistent with the regular water requirement pattern. Through integrated utilization of sunflower crop coefficient equation and water production function model, the stage sowing production and production are obtained (504.36g·m^-2 and 493.83 g·m^-2, respectively), which show 4.4% and 4.1% deviations with actual production, respectively. There is preliminary evidence that the prediction method of production proposed is relatively reasonable with a great applicability in this region, and can be further applied to pre-assessment of production affected by water deficit in different stages.