Satellite based yield: water use relationships of perennial horticultural crops

Drought and several seasons of historically low water allocations in the period, 1996 – 2010, created demands for reliable data relating yield and water requirement of perennial high value horticultural crops grown in the Murray Darling Basin of Australia. To cope with drought, irrigators were required to decide whether to buy or sell water on the water market, and to answer basic agronomic questions concerning the viability of crops and the amount of water to be applied to crops. The drought established the demand for detailed data describing the dependence of yield on water supply. This study focused on apple, peach, nectarine, pear, apricot, plum and wine grape crops grown in the Goulburn Valley Irrigation Region of northern Victoria. Doorenbos and Kassam (1979) produced a simple yield-water use relationship where relative yield is related to relative crop water use. Relative yield is measured as actual yield/YMAX, where YMAX is maximum attainable yield. Relative water use is measured as ET/ETMAX, where ET is actual evapotranspiration and ETMAX is evapotranspiration for standard conditions with no water stress (Crop Water Requirement; CWR). This thesis applied the Doorenbos and Kassam model, subject to the condition that increases in yield are constrained to the region, ET _ CWR. The approach required estimates of YMAX and CWR for each crop. Implementations of the Doorenbos and Kassam model are commonly based on the assumption that regional crop-specific estimates of YMAX and CWR apply. However, the major variables in the Doorenbos - Kassam model (actual yield, ET, YMAX and CWR) depend on crop vegetation cover. The yield-water use relationship of each crop/field therefore depends on the site-specific vegetation cover. Vegetation cover can be estimated using on-ground measures of fractional radiation interception (f) and/or derived from Normalised Difference Vegetation Index (NDVI) measured by satellites. NDVI data facilitate the extension of field scale findings