Response of tanier (Xanthosoma spp.) to evapotranspiration deficits estimated with the FAO water balance method

Abstract

Field experiments in Puerto Rico have shown that with adequate drainage and plant nutrition, good yields of tanier (Xanthosoma spp.) are consistently obtained under high frequency irrigation. Still lacking, however,is quantitative information on yield variations under different irrigation scheduling scenarios. A well-known tool for this purpose is the FAO (Food and Agriculture Organization) water balance model, which calculates relative decreases in crop yields (RYD) from relative evapotranspiration deficits (RETD) which are estimated from crop, soil, irrigation and weather data. A simple form of the FAO model calculates RYD as the product of RETD for the growing season multiplied times a proportionality constant or yield sensitivity coefficient (K_y), which must be experimentally determined for each specific crop. The objective of this study was to estimate K_y for tanier, by examining published data from three irrigation experiments conducted at various locations in Puerto Rico over a 20-year period. The FAO model was used to estimate seasonal RETD from crop and soil parameters and irrigation and weather records, and this value was used together with experimental yield data to calculate K_y. A first analysis yielded K_y values between 3.1 and 4.2, which considerably exceeded values on the order of 1.0 reported in the literature for most crops. Suspecting that the discrepancy could have been due to incorrect tanier crop parameters assumed in the FAO model, we adjusted crop parameters as far as seemed reasonable in ways which would minimize estimation of K_y. The minimum K_y values obtained in this manner ranged between 2.4 and 3.3, which are still quite high. They imply that a 10 percent water deficit relative to evapotranspiration demand is sufficient to reduce tanier yields between 24 and 33 percent. It is postulated that the high K_y values for tanier could reflect a synergistic effect of several plant stress factors associated with soil moisture, mainly water stress, soil mechanical impedance and pathogenic stress. Results in general confirm previous observations regarding sensitivity of tanier to drought stress, and indicate a significant response of tanier to irrigation under even moderate drought conditions.