Diagnostic analysis of spatial and temporal variations in crop water productivity: A field scale analysis of the rice-wheat cropping system of Punjab, Pakistan

Abstract

The rice-wheat cropping system is the most important source of food production for the world. To meet future demands, water productivity in this cropping system needs considerable improvement as water is becoming scarcer and competition among agriculture and other sectors is increasing. This paper studies the water productivity of rice and wheat in a system perspective by taking rice-wheat cropping system of Pakistan’s Punjab as a case study. Field scale water balance and water productivity is evaluated using measured data from the farmers’ field, simulation modeling and comprehensive set of water productivity indicators. The factors causing temporal and spatial variations in crop water productivity are identified and scope to enhance food production via improving water productivity is discussed. The study indicates that water productivity per unit of gross inflow ranged from 0.17 to 0.38 Kg/m3 for rice and 0.78 to 2.03 Kg/m3 for wheat. The economic water productivity measured in terms of gross margins per unit of gross inflow for rice, wheat and rice-wheat rotation ranged from 5 to 51 $/”000 m3, 50 to 150 $/ “000” m3 and 26 to 76 $/ “000” m3, respectively. Irrigation water productivity was higher than that of gross inflow and the difference was due to the proportion of rainfall in gross water input. The water productivity of rice was lower than wheat when measured in terms gross inflow, irrigation inflow and evapotranspiration. However, in terms of transpiration rice showed almost same physical water productivity as that of wheat. The water productivity varied both spatially and temporally. For sample areas, the spatial variability was mainly due to difference in water use, sowing dates, fertilizer use, soil quality and socio-economic conditions. Rainfall, amount and timing, emerged as the most important factor inducing temporal changes. Water productivity of both rice and wheat showed a decline during the period of investigation. The analysis reveals that the farmers tend to increase their food production, and gross margins per unit of land at the cost of decreased water productivity. To sustain and/or enhance water productivity, the management of uncontrollable factors such as climatic variability along with the improvements in controllable factors such as agronomic and water management practices need careful planning and actions. The application of a comprehensive set of water balance and water productivity indicators for spatial and temporal analysis could help in performance evaluation of irrigated crops and devising strategies for improving food production and water productivity.