Estimation of Crop Coefficient and Pistachio Plant's (Pistacia vera L.) KC-NDVI Relationship Using Remote Sensing (Case study: Pistachio orchards of Abarkuh desert margin, Yazd province)

One of the most important issues in water resources management in agriculture is determining the plant water requirement by estimating the actual evapotranspiration of the crop. One of the empirical methods for determining the plants and crops evapotranspiration is the method mentioned in FAO 56's report. One of the main problems of this method is the KC coefficient estimation, especially when the percentage of crop cover, irrigation methods, and other factors in the region varies. The aim of the present study was to estimate the KC and pistachio plant's (Pistacia vera L.) KC-NDVI relationship in different stages of pistachio phenology in Pistachio orchards of Abarkuh desert margin in Yazd province. The KC-NDVI relationship has the main role in plant water management requirements. First, the actual daily evapotranspiration rate over the 16 different periods corresponding to a full pistachio's growth period is calculated. Then, by dividing the actual plant evapotranspiration to evapotranspiration of reference plant on the same day, the Kc maps were created. Finally, the relationship between KC and the NDVI index was obtained. Based on the results, there was a significant correlation between the pistachio plant coefficient and the NDVI index at a 99% level (P-value <0.01). At the beginning and end of the pistachio growth period, the lowest correlation was found between the pistachio plant coefficient and the NDVI index. The highest correlation was observed in the mid-growing season, which is coincident with the peak of heat and evapotranspiration. In general, the pistachio vegetation coefficient is between 0.3 and 0.9 concerning NDVI index in the study area. Relationship between KC and NDVI at the 1)beginning of growth season, 2) development stage, 3) mid-growth stage, and finally 4) harvest season were KC-1 = 1.66 NDVI + 0.261, KC-2 = 1.29 NDVI + 0.338, KC-3 = 2.10 NDVI + 0.147, KC-4 = 1.21 NDVI + 0.231, respectively.