Current status of global rice water use efficiency and water-saving irrigation technology recommendations

Rice has a high water requirement, but water use efficiency (WUE) in rice has always been low, and the status of rice WUE and the factors influencing it in various countries around the world is currently unclear. Therefore, this paper collected 56 articles from 2000 to 2022, through which WUE data from different countries and different provinces in China were collated, and the effects of various water-saving irrigation technologies on WUE of rice and irrigation water use were analysed using the method of Meta-analysis. The results of this paper show that rice WUE is low in most countries, with the lowest WUE of 0.28 kg/m(3) in Thailand and the highest WUE of 1.25 kg/m(3) in Bangladesh among the countries included in this study, and flood irrigation is used in most countries. Compared to flood irrigation, all water-saving irrigation involved can increase rice WUE and reduce irrigation water input, alternate wet and dry irrigation (W1), and controlled irrigation (W2) were able to increase the WUE of rice by 49.86%, 84.74%, and reduce the irrigation water input by 36.55%, 39.55% respectively. Among the six types of water-saving irrigation input, dry cultivation (W3) had the most significant effect on increasing WUE and reducing irrigation water, reaching 2.02 times and 67.53%, respectively. Based on the annual rainfall (R) and the application of water-saving irrigation in Asia, sub-regionally applicable water-saving irrigation technologies are recommended. W3 is recommended when R <200 mm, W2 is recommended when 200 mm < R < 800 mm, and W1/W2/shallow alternate wet and dry irrigation (W5) is recommended when R >800 mm. According to the data collected in this paper, W1, W2, W3, and W5 can save 3.40 x 10(11) m(3), 3.78 x 10(11) m(3), 2.52 x 10(8) m(3), 2.22 x 10(11) m(3) of irrigation water, respectively. Based on the calculations in this paper, different water-saving irrigation techniques can save 3.50 x 10(11) m(3) of water in Asia according to the recommendations. To promote water-saving irrigation technology, countries need to formulate policies to ensure the development of water-saving irrigation technology, raise farmers' awareness of water conservation, and provide training and financial support. Promoting the use of different water-saving irrigation technologies for different regions can significantly reduce irrigation water and increase the WUE of rice, which is important in addressing the challenges of global water scarcity.