As an essential factor of the earth’s critical zone, soil water has a remarkable influence on nutrient cycle and energy flow in terrestrial ecosystems and has attracted the attention of considerable scholars. Based on the online database of Web of Science, the bibliometric analysis was performed to evaluate the evolution feature of soil water research from 1934 to 2019. The results showed a rapid growth of scientific outputs with a gradually increasing proportion of internationally collaborative articles. Environmental Sciences, Water Resources, and Soil Science were the most frequently used subject categories, and the Journal of Hydrology had the highest number of publications in this field. The institutions from the USA and China were the most active, and the USA occupied a leading position in soil water research, producing the most articles and having the most considerable number of citations. Clusters of authors were mostly located in North America, Western Europe, West Asia, and East Asia. Keywords analysis demonstrated that climate change, drought, evapotranspiration, remote sensing, and irrigation were the current research hotspots. Scientific issues focusing on the interaction between soil water and environmental factors, drought forecast, relationships between soil structure and water/solute transport, improving the accuracy and depth of soil moisture monitoring with satellite, and spatio-temporal scaling transform require further research.

Nitrogen loss from paddy fields contributes to most of the nitrogen pollution load in the Ningxia Yellow River irrigation area, threatening the water quality of the Yellow River. Consequently, optimizing the nitrogen management practices in this area is essential, which can maintain paddy grain productivity and reduce nitrogen loss simultaneously. Five treatments with different nitrogen application rates and nitrogen fertilizer types were set in this study, including conventional urea application with zero nitrogen application rate (CK, 0 kg hm^-2), nitrogen expert-based fertilization application strategy (NE, 210 kg hm^-2), optimized nitrogen fertilizer application strategy recommended by local government (OPT, 240 kg hm^-2), and farmer’s experience-based nitrogen fertilizer application strategy (FP, 300 kg hm^-2), and controlled-release urea application (CRU, 180 kg hm^-2). The data from one growth season field experiment in 2021 revealed the dynamics of nitrogen concentration, paddy yield and its nitrogen uptake characteristic, and nitrogen balance in the paddy field under different nitrogen application practices. Most nitrogen leaching was observed during the seedling and tillering stages in the form of nitrate nitrogen (NO₃^–N). Compared with the FP, the CRU and OPT significantly reduced the nitrogen concentrations of total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), and NO₃^–N in the surface and soil water and reduced the nitrogen leaching at 100 cm soil depth. Meanwhile, the paddy grain yield in CRU (7737 kg hm^-2) and OPT (7379 kg hm^-2) was not significantly decreased compared with FP (7918 kg hm^-2), even though the nitrogen uptake by grain and straw was higher in FP (135 kg hm^-2) than in other treatments (52.10~126.40 kg hm^-2). However, the grain yield in NE (6972 kg hm^-2) was decreased compared with the FP. The differences in grain yield among these treatments were mainly attributed to the ear number and grain number changes. Also, the highest nitrogen use efficiency (40.14%), apparent nitrogen efficiency (19.53 kg kg^-1), and nitrogen partial productivity (43.98 kg kg^-1) were identified in CRU than in other treatments. Considering increased grain yield and reducing nitrogen loss in the paddy field simultaneously, the treatments of CRU (i.e., 180 kg hm^-2 nitrogen application rate with controlled-release urea) and OPT (i.e., 240 kg hm^-2 nitrogen application rate with conventional urea) were recommended for nitrogen fertilizer application in the study area.