If you cannot locate the specific PDF by Subba Rao, you should not be discouraged. There are excellent free resources that cover the exact same syllabus:
In the Indian subcontinent and other tropical regions, this book is considered a standard textbook. Unlike Western textbooks that often focus on temperate climate soils, Subba Rao’s work focuses heavily on tropical soil conditions, making it indispensable for students in India, Southeast Asia, and Africa. soil microbiology subba rao pdf free download