First of all collect relevant data about each product like quantities in each month. Then apply reinforcement learning on your data set with each updation. you will come to know either quantity of product is increasing or decreasing in which month. figure out the unusual situation occur in that month (weather, soil etc.) meanwhile you can help farmers by telling them which product is more beneficial to be planted in which month. 

Please see:

https://www.quora.com/How-can-computer-engineers-or-computer-scientists-can-contribute-in-agricultural-field-in-India

https://www.ukessays.com/essays/computer-science/use-of-computer-in-agriculture-field-through-software-computer-science-essay.php

https://www.slideshare.net/BikashKumar19/agriculture-development-with-computer-science-and-enggppt

there are lot of image processing techniques that can help you find particular diseases in a particular product through image segmentation. on the other hand you may apply different mining algorithms to extracts patterns in annual profit and loss of a product as well. you may do mining to know which areas of world has more demand of a particular product.

In data analysis , both deterministic and stochastic.

Following steps may facilitate you

1)Gather data from the multiple farmers in targeted area where you want to facilitate farmers.

2)Develop multiple data sets to identify problems encountered by farmers.

3) Prioritize problems according to severity.

4) Find the most effective technique or remedy for solving problem e.g treatement or precautions to avoid diesease.

You can incorporate data analysis, image processing, solutions of disease available in Biotechnology etc.

Better the quality of the vegetables and fruits, the better quantity can be achieved.