Managing Irrigation Water to Enhance Crop Productivity Under Water-limiting Conditions: A Role for Isotopic Techniques

摘要

This paper summarizes results obtained from an FAO/IAEA Coordinated Research Project (CRP) on "Managing Irrigation Water to Enhance Crop Productivity under Water-Limiting Conditions: A Role for Isotopic Techniques", implemented from 2007 to 2012. Its objective was to identify approaches to improve crop water productivity (production per unit of water input) under water-limiting conditions using isotopic and related techniques. The CRP employed both isotopic and conventional techniques to separate soil evaporation (E) and crop transpiration (T) and to help identify factors that minimize soil evaporation losses and improve irrigation management. Field measurement of E and T were carried out on a range of crops (maize, paprika, winter wheat and coffee) under different frequencies andmethods of irrigation management practices and soil fertility levels. Using both nuclear, isotopic (Keeling plot and isotopic mass balance using delta oxygen-18 (6180)), the results showed that the proportion of evapotraspiration (ET) as E was much higher in the African studies (Malawi and Zambia) due to poor vegetation cover resulting from low soil fertility and inefficient irrigation management. However, by improving soil fertility, T increased by 50 percent in the Malawi maize study. In the North China Plain, through mulching, deficit irrigation and improved irrigation scheduling, soil E losses could be reduced by 10-30 percent of the total water loss compared with full irrigation. Soil E losses were also determined for 10-year old coffee trees in Central Vietnam over various growth stages. The E component was approximately 14 percent of ET during the bean development stage. When old branches and leaves were left as mulches on the ground, the T component could be as high as 92-95 percent compared with non-covered ground where total water loss through E could be three times more. The E and T results generated were also used to validate FAO's AquaCrop model for improving irrigation scheduling and agronomic practices. In the North China Plain, long-term simulation from AquaCrop showed that in wet years, only two irrigations at the planting and jointing stages were needed for wheat while no irrigation was needed for maize. In normal years, two irrigations were needed at the planting and jointing stages of wheat and one irrigation at the planting of maize, while in dry years, three irrigations were needed at the planting, jointing and booting stages for wheat and one irrigation at planting of maize.