Light intensity and duration are the most important because it affects photosynthesis if not limited by other factors such as abiotic stress (drought, salinity, heat or cold stress). in terms of crop management, fertilization in general specially N.

soil organic matter or organic carbon

climate

topography

soil depth & fertility

crop rotating

fertilizing

usually drought and water logging (totally climate extreme) have significant influence.

in next step, topography and altitude can be effective

Temperature

Atmospheric Moisture

Light etc.

Soil quality and fertility

All the above factors must be in the optimal conditions for better photosynthetic activities in the plants.

If any of the above deviate from the required proportion then biochemistry, physiology and other processes in the plant gets altered and synthesis of amino acids and proteins also get affected including their quality.....

Need to work on HSPs for high temperature tolerance.

Light intensity and duration are the most important because it affects photosynthesis if not limited by other factors such as abiotic stress (drought, salinity, heat or cold stress). in terms of crop management, fertilization in general specially N.

Assuming that the plants are not exposed to abiotic stress, I believe that the most important factors determine protein contents are, nitrogen fertilization (or soil fertility), and light.