In this book, attempts have been made to give simple, concise and updated information about the aspect relevant to agricultural sciences. The main objective of this book is to help the reader to quickly grasp the facts comprehensively and systematically from various branches of agriculture. In the 20th revised and enlarged edition of this book the latest information with model test papers have been incorporated to increase the utility and effectiveness of this book. We believe that this book will be also useful for fellow teachers, researchers and development officers for references and easy answering of many complicated questions. The book has been designed particularly for the aspirants of various competitive examinations like AIEEA-ICAR-JRF/NTS(PGs), Senior Research Fellowship (SRF), ICAR- National Eligibility Test (ICAR- NET) & Agricultural Research Services (ARS). It may be also useful to seek admission in Ph.D. through entrance examinations of SAU’s, various institutions and get through screening tests conducted by various states for jobs in Agricultural Sciences, Civil Services, Agricultural Officers, Bank P.O. (Agriculture), ADO and allied agricultural examinations conducted by different agencies.