automatic plant watering system using microcontroller
Have you measured this voltage with resistor detached? You should measure it relative to GND and then relative to +5V to make sure. Otherwise it is hard to determine wrongly configured pin.

Try to debug your code. Add 4-5 LEDs since you have many free pins and output highest bits of ADC to these LEDs.

Or output the ADC values to UART and read them via terminal.

BTW, why AVCC is connected to +5 via capacitor? Are you sure ADC is powered properly this way?


  In the above circuit design I have not made any connection at pin MOSI,MISO,RESET and SCK (of ATmega 16) with AVR programmer. Will I have to make this?


I do not understand. You need these connections when programming of course, but not when running :)