In the mid-1980s, productivity in some agricultural sectors began to level off. why did this happen, even during the midst of the green revolution?

The Green revolution began in early 1960s and was instrumental in developing high-yeild farming practices and hybrid seeds.

In countries such as Pakistan and India, wheat production doubled in just 5 years and by the 1970's, both countries were self sufficient in the production of wheat and other cereals.

However, by 1980s a notable decrease the rate of increase of production was observed all over the world. This was both due to nature and market economics.

Per acreage yield has it's natural limits and could not cross a specific threshold. By the 1980s, this was leveling off, showing a lower rate of increase.

Also, high production of important crops also let to lower prices in the market. This lead many farmers to focus on crops that could provide higher returns, resulting in lower production of wheat and rice.