The most likely answer to your question is that the "modern agricultural revolution" began in England. This depends, though, on what you mean by "modern." In much more recent times there has been an agricultural revolution brought on by the creation of better chemicals and by the breeding of better types of plants. This, however, is commonly called the Green Revolution.
Therefore, I assume that you are asking about the agricultural revolution that happened in Britain during the 1700s. This was a revolution that involved such things as
- The abandonment of the open field system.
- The creation of a class of agricultural workers as opposed to small farmers working their own land.
- The introduction of new crops and new technologies.
So, if this is the agricultural revolution you are talking about, its origins were in Britain.
A book that will answer where the modern agricultural revolution originated is:
Mazoyer, Marcel, and Laurence Roudart. 2006. A History of World Agriculture from the Neolithic Age to the Current Crisis. New York: Monthly Review Press. Translated by James H. Membrez.
Chapters 7-11 of this book, pages 259-494, make good use of social history, how social movements and evolution affected agriculture and how agriculture affected them. Chapters 10 and 11 make good use also of economics and politics, interrelating them and agriculture with each other.
Chapter 7 is about the agricultural revolution of the Middle Ages in northwestern Europe. Chapter 8 is about the more recent revolution in agriculture brought about by crop rotation; chapter 9 concerns the mechanization of agriculture; 10 is about motorization, synthetic fertilizers, seed selection and specialization of farmers–the second agriculture revolution of modern times; 11 is about agriculture crises.
Earlier portions of the book are very good as history, but that early history of agriculture, I do not find as important for understanding the modern world as chapters 7-11, so I tended to slight it.
A little book by Colin Tudge, Neanderthals, Bandits and Farmers: How Agriculture Really Began, 1999, is better on the Neolithic agricultural revolution than the chapter on that topic in Mazoyer and Roudart.
I do not have this book before me at this moment, so I cannot give you a more precise answer.
If neither your school nor your local public library have this book (I would be surprised if either did.), you can call you state agricultural college's library, speek to the Reference Librarian, ask him or her this question and give this book as one possible place where the answer might be found. They will call you back.