Question

why the cost of cultivation is rising fast?

Answer 1

As every student of economics knows, price is a function of supply and demand. 
  When demand for a commodity rises on constant supply, prices usually rise.  Conversely, when demand falls at constant supply, prices usually fall.  The same thing works with supply.  Rising supply on constant demand causes a fall in prices while falling supply on constant demand causes prices to increase.  
So one could conclude that rising food prices have been caused by falling supply or increased demand.  
This is true, but there is a lot going on behind the scenes causing this.

Answer 2

There are many reasons why the cost of cultivation is rising fast like
1) due to increase in population area of cultivation is decreasing
2) due to increase in population need of food is also increasing
3) Cost of raw materials are increasing so their outcome'outcome's cost also increases.