Research and Productivity in Wlieal and Maize: An International Analysis 61 



where 



p{t) Flow of indigenously created knowledge 

 b{t) Flow of borrowed knowledge. 



Knowledge can be subject to depreciation and obsolescence, 

 which will require the inclusion of depreciation terms in 4.3 and 

 4.4. Also, if Tis the "best" knowledge available — the "frontier of 

 knowledge" — a lag operator may have to be included in 4.3 and 

 4.4. 



Borrowing of knowledge is dependent on the existence, outside 

 of a country, of knowledge relevant to the country. The larger 

 such a stock, the higher the marginal productivity of borrowing 

 activity. The rate of borrowing will be affected by domestic 

 research, since at least some understanding of research effort in 

 other countries is inherent in its conduct. In agriculture, particu- 

 larly in field crops and orchards, less so in livestock production, a 

 characteristic of knowledge is its regional climate specificity. In 

 this case, the borrowable stock of knowledge of a country is the 

 pool of knowledge in similar climatic regions outside the country. 



To introduce the possibility of regional specificity of 

 knowledge, crop areas in the countries were assigned to agro-cli- 

 mate regions. The regions were adopted from the work of 

 Papadakis (1952). His classification is five-dimensional (see appen- 

 dix 3) and permits alternative regional definitions by combining 

 classificational dimensions. Two such alternatives, the two- 

 dimensional 3-4 and the five-dimensional 1-5, are used in this 

 analysis in wheat and maize, respectively. 



Available maps enable the assignment of crops in countries to 

 agro-climatic regions. With the possible exception of the United 

 States, data on research by region are not available, however. 

 Research work in a country was therefore assigned to regions 

 under the assumption that research in every crop in the country 

 is distributed, by regional affinity, in proportion to the regional 

 distribution of the country's crop areas. 



A regional stock of knowledge is defined as 



R^{t) = X r.K{t) (4.5) 



where r.. is the share of country /s wheat and maize area that 



