Question: query regarding how and when to use the fertilizer in potato which is cultivated by using rice straw. 
Answer: you can spray npk 19:19:19 10 gram/per liter of water after 30 days of sowing 2 times at 15 days interval in the evening time. to protect the plants from blight please spray indofil m-45 or ridomil gold 3 gram/liter of water once in a week in the evening time.