Blue-green water migration and utilization efficiency under various irrigation-drainage measures applied to a paddy field

The study area was Nanjing, Jiangsu Province, eastern China. Blue-green water utility assessment in crop cultivation is profound to better sustainability of regional resources, agriculture and ecosystems. The aim of current study is to establish a blue-green water differentiation and efficiency evaluation methods for paddy fields, based on daily water migration observation under four irrigation-drainage protocols. The blue-green water use performance under different irrigation-drainage protocols and precipitation patterns in paddy fields and the advantage of the water resources analysis model proposed in the current study were analyzed and discussed. The green and blue water efficiency indices (GWE and BWE) were significantly affected by precipitation. GWE (0.495) was 35.1% higher in dry years than in wet years, and BWE was mainly affected by precipitation distribution during the crop growth season. The green and blue water productivity indices (GWP and BWP) showed pronounced differences among various irrigation-drainage measures, and the controlled irrigation (COI) performs the best. BWE and GWP obtained by previous method were 48.9% and 38.9% greater than those reported here, showing that the neglect of interactive blue-green water migration process would overestimate the field irrigation efficiency. The methods employed and results obtained in the present study suggest that it is important to assess the water footprint and blue-green performance for crop cultivation systems.