I searched from my university website and found some papers which I think fit with your request. 

Here are some more.

Dear Fekadu,

Thank you so much for sharing with me these important documents. They are very useful for the work that I am currently doing.

Best regards,

Belay

Dear Prof.,

Here are some materials I found in my PC. I hope they are useful to you.

Best regards,

Bekele

Dear Dr. Bekele,

Thank you so much for your usual and continued support. Surely, the documents will be of use for my work.

Have a great day

Belay

Dear Dr Belay

You already have many documents. Here is another from Asia. Best regards

Mohammad

Dear Dr. Jabbar,

I hope all is well with you and your family. it is great to hear from you after long time. I would like to express my heart-felt thanks for sharing with me this useful document.

Have a great day

Belay

Dear there seems no alternate except investing in agriculture not only in the developing countries but also equally important (rather more demanding) on the part of developed nations. Since survival o and existence of countries is and will be dependent upon her food (plants and animals) production.

Dear Sir,

Thank you so much for your contribution. While I agree with your line of reasoning and explanation, my interest was to get copies of empirical studies (book chapters, articles, research reports etc.) on return to agricultural research investment. I would be very grateful to get your support in this line.

Thank you so much  again

Dear Dr Belay

Thanks for your message. I am glad to see that you are publishing regularly. Please keep it up. I am also glad to see Menale Kassi establishing himself as a highly productive researcher.  I saw  his potential when he worked for his MSc with you and me. Best wishes form him as well. 

Regards

Mohammad

Dear Dr, Kassa.

I risk duplicating the answer give by Dr. Bekele. However, where to look depends on whether you want theory and quantitative analysis and whether your focus is global, national in developed countries, regional aggregations or national statistics.  For the theoretical base I recommend Science Under Scarcity (J.Alston, P. Pardey and G. Norton).  IFPRI's "Agricultural Science and Technology Indicators (ASTI) grew out of this work. ASTI now is the source of global information collected from the Institute level, processed into Country databases, and comparable across countries and across time. (Search N. Beintema or IFPRI for the complete set of countries, including Ethiopia).

Since there are so many documents associated wth the four authors, I suggest you search and look for particular articles that describe in their title what you want.  There are three summary reports from ASTI on Africa covering three different decades.

For eastern Africa, there were various reports by ASARECA that attempted to calculate returns to research in thematic areas.  Check with Michael Waithaka at ASARECA. 

Dear Sir,

Thank you so much for your insightful response and advice.

Wishing you a great day

Belay

Dear Prof,

Here are some article I studied before. I hope they are useful to you.

Best regards,

Farzaneh

www.instepp.umn.edu/sites/default/.../oc51_4.pd

https://www.aaea.org/UserFiles/file/DoraHeng_final.pdf

Dear Farzaneh,

Many thanks for sharing with me these useful document.s.

Best regards,

Belay

Dear Farzaneh,

Many thanks for sharing with me these useful document.s.

Best regards,

Belay

Dear sir,

You can share your research findings on return to Investment  to Agriculture under the platform of CTA. Technical Centre for Agricultural and Rural and Development. CTA is a joint international institution of the African, Caribbean and Pacific (ACP) Group of States and the European Union (EU). The document could have a wide spread in their publication.

Dear Dr. Ndubueze-Ogaraku,

Thank you so much for your input.

Best regards,

Belay

Attached my research paper herewith.

Article The Economic Impact of Public Rice Research in Thailand*

Dear Sir,

Thank you so much for sharing with me your article. 

Best regards,

Belay