A comprehensive analysis of water productivity in natural vegetation and various crops coexistent agro-ecosystems

Abstract

Water productivity (WP) expressed as the yield produced per unit volume of water is an important indicator of water use in arid and semi-arid areas. Due to complex plant cover and hydrological processes, the quantification and assessment of WP are usually difficult to determine, especially at the regional scale. In this study, an arid irrigated agro-ecosystem in the upper Yellow River basin was selected as a case study area. Based on field observation and model simulation results, the WP of irrigation water (WPI), water applied (WP(I+P)) and evapotranspiration (WPET) were calculated. Equivalent water productivity (EWP) of irrigation water (EWPI), water applied (EWP(I+P)) and evapotranspiration (EWPET) were proposed and calculated to unify the disparate WP for various crops and natural vegetation. Results showed WPI and WP(I+P) decreased with the increase of water application for all plants except watermelon, indicating supplemental irrigation to watermelon is urgent to improve its production and WP(I+P). The spatially averaged WPET (kg m−3) was 2.47 for maize, 0.80 for sunflower, 12.3 for watermelon, 1.39 for wheat and 0.65 for natural vegetation. WPET for natural vegetation was usually lower in this salt stressed area compared with other water stressed areas. The EWP revealed the rank order of WP for different crops and natural vegetation: watermelon > wheat > maize > sunflower for EWPI; natural vegetation > wheat > watermelon > maize > sunflower for EWP(I+P); and wheat > sunflower > watermelon > maize > natural vegetation for EWPET. The relationship between EWP(I+P) and EWPET was scale dependent due to the water reuse phenomena among different land cover types and the canals through the shallow groundwater system. Ignoring natural vegetation will result in considerable bias in the estimation of the regional scale water productivity (16 % in this study). WP improvement strategies such as transferring irrigation water from less productive (sunflower) areas to productive (vegetable and natural vegetation) areas, reducing bare soil evaporation and constructing a timely and accurate irrigation-drainage system were provided.