Question

from where do small farmers obtain the inputs that they require

Answer 1

Mainly, farmers buy the inputs on local markets or, if they're looking for plants which are not native for the place they're living in it might be wise to travel once a year to another market farther away to get better prices and quality of some plants. 

Over they year, a farmer will use purchased inputs to grow their harvest. Their income is calculated by substracting the amount of money spent on input, fertilizers, workforce and other key-resources from the amount earned from selling crops. 

The idea is that each year the difference should be bigger