Assessment of water productivity and supply:demand ratio index in sugar beet (Beta vulgaris L.) in Khorasan Razavi province, Iran using growth simulation models

The rapid population growth and the need for more agricultural production necessitate more attention to water shortage and enhancing water productivity. To assess water productivity and supply:demand ratio index in sugar beet, this experiment was carried out using SUCROS growth simulation model. Long-term climatic data and collecting questionnaires from farmers were used to assessing water productivity in sugar beet agroecosystems in 10 counties of Khorasan Razavi province, Iran and investigating the role of water management in water productivity and drought stress conditions in sugar beet. Results of long-term simulations showed that the actual yield (33.5 t.ha-1) by farmers was only one-third of the attainable yield (97.3 t.ha-1) of sugar beet in the targted areas. Forty eight percent of this yield gap was due to water constraints. The results indicated the low productivity (1.5-1.8 kg root m-3) of sugar beet in the targeted areas. The results also showed that inappropriate irrigation management, despite the high water consumption in some counties, led to decrease in water productivity and occurance of drought stress during the growing season. Results also showed a positive and significant relationship between water productivity and supply:demand ratio index in different locations. The index, over growing season, in different counties was highly depended on water management, air temperature (particularly during warmer months of the year) and soil water holding capacity. These results indicated the need for a more scientific attention to appropriate irrigation schedules according to the plant water requirement and soil water retention capacity during the warm seasons to meet the moisture requirement of sugar beet.