Question: query regarding less production of fruits in lemon. 
Answer: please spray any one of the following vitamins- mohaphol/ biovita/ bahar 2ml/liter of water once at flowering stage and once at fruit setting stage. or you can also spray npk 19:19:19, 10 gram/liter of water 3 times at 15 days inteval in the evening time in the absence of rain.