The US NSF (National Science Foundation) carefully analyzes government and private spending on research and development (R&D) around the world and periodically publishes its findings in dense, detailed reports. This answer focuses on NSF’s data on US federal government subject-wise research spending. Figures are from the NSF’s 2014 Science and Engineering indicators report:http://www.nsf.gov/statistics/se…

In subject-wise research budget allocations, life sciences leads the pack by leaps and bounds followed by engineering, physical sciences, math/computer sciences, environmental sciences, psychology and social sciences in that order (see figures below).