Shakeel -

I am not familiar with this subject, but I am familiar with Official Statistics, and if this result is a surprise, you might inquire as to the relative standard errors of the yield estimates, and the data collection, data processing, and estimation methodologies.  Any metadata on the statistics may be important.  A statistical error may explain at least part of this.  If the true change was actually large, then you might consider weather, or policy changes, or some other actual cause.

Best wishes - Jim

PS - You might consider including your question under other topics in addition to "Reasoning," such as "Official Statistics," and an agricultural and/or political topic. Another topic might be the geopolitical region.

I think because you dint work on it in your M.tech .