Materials and Reagents

1. Crop
   Note: The crop must be free of green weeds. The presence of spikes, flowers, etc. on the external part of the canopy may require using a specific calibration curve for that development stage.
   

Equipment

1. Conventional digital camera.
   Note: This is the only equipment required once the method has been calibrated for a range of crops similar to those where it has to be applied. Any commercial camera, compact or reflex, is suitable.
   
2. A digital area meter is required for calibrating leaf area index (LAI, e.g. DIAS II, Delta-T Devices)
   
3. A drying oven is required for calibrating biomass (e.g. Memmert, model: 800 , minimum precision required: 2 °C)
   
4. A precision balance is required for calibrating biomass (e.g. Mettler Toledo, model: PB3002-L , minimum precision required: 0.1 g)
   

Software

1. Image processing software that allows quantifying the average colour of the whole picture
   Note: The program BreedPix 2.0 described in Casadesús and Villegas (2014) is a suitable tool for processing a large number of pictures with the minimal required steps by the user. It can be obtained for free from the authors. General-purpose free software for quantitative image analysis (such as ImageJ or Fiji) can also be used but in this case a macro should be written specifically for this protocol.
   

Procedure