Application of ET-NDVI-relationship Approach and Soil-Water-balance Modelling for the Monitoring of Irrigation Performance of Treed Horticulture Crops in a Key Fruit-Growing District of Australia

Remotely sensed data from Landsat-8 and Sentinel-2 were used to demonstrate the estimation of irrigation water requirement (rho) for treed horticulture crops in an important irrigation district of Australia. Crop- and region-specific relationship between satellite-derived evapotranspiration (ET) and normalized difference vegetation index (NDVI) was combined with daily step soil water balance to investigate the performance of horticulture crops for their water use during the peak irrigation demand period (summer) over three years from 2014-15 to 2016-17. Relative irrigation water use (RIWU) as the key irrigation performance indicator was calculated by comparing the irrigation water supply (psi) records and the rho estimates. psi and rho of the treed horticulture crops showed a strong positive correlation (Coefficient of determination, R-2 > 0.70; p < 0.001) for each of the three summer seasons investigated, indicating an overall consistency in irrigation pattern. However, the values of both rho and psi varied considerably at farm level over the seasons, highlighting the changing demand and supply of crop water over the years. Most farms remained within the optimal irrigation range (0.5-1.5 RIWU) over the seasons - 75% in 2014-15, 68% in 2015-16, and 80% in 2016-17. However, some farms were over-irrigated (>1.5 RIWU) - 12% in 2014-15, 5% in 2015-16, and 8% in 2016-17.