Development of crop coefficient for forage safflower based on vegetation indices

The crop coefficient (KC) is essential to irrigation scheduling in agriculture. The objectives of this study were to monitor height and vegetation index NDVI in safflower during two growing seasons, develop a new crop coefficient (KC) based on NDVI and calculate crop evapotranspiration (ETC) taking KC values. The study was carried out in autumn-winter 2016-2017 and 2017-2018 growing seasons in Matamoros, Coahuila, Mexico. The cultivars evaluated were Guayalejo, Selkino and CD-868. Sowing was done in dry soil on December 10 and 12, of 2016 and 2017, respectively. In growing season 2016-2017 three irrigations were applied and 2017-2018 two. NDVIfield values were derived from GreenSeeker and NDVIsatellite were derived from Landsat 7 and 8 images. A relationship between NDVIfield and KC taken from FAO-56 Manual was established. The results indicated similar NDVI curves in both growing seasons. High determination coefficients (r(2) = 0.93 and 0.89) were recorded between NDVIfield and KC FAO-56. A linear equation (KC = 1.064 * NDVI + 0.212) for both growing seasons was generated. The new KC values were multiplied by the reference evapotranspiration (ETo) to calculate ETC. Whit this equation a calculation model is proposed to derive recommendation irrigation according to safflower phenological stage.