We are working on a formula to calculate irrigation needs for agricultural soil, to help farmers (and the planet) with saving water. We work with water sensors in the agri fields and want to assist the farmers with a time sheet for telling them when they would need to start irrigation. Let's say you need to irrigate field A in 4 days and field B in 9, so they would have a timetable. We have many different factors at the moment, and we do not think it is realistic to account for them all because it would make the formula too complicated and maybe inaccurate. We have the following factors in mind:

Absolute and relative humidity of ambient air. (plus minus 2 meter)

Near surface soil humidity.

Soil humidity at the lower basis A(h) horizon (plus minus 30 cm), both absolute and relative.

Air temperature.

Soil temperature at the depths given above (1-5 cm and plus minus 30 cm).

Amount of precipitation over the last 24-48 hours.

Evaporation + transpiration= evapotranspiration rate.

Duration of sunshine exposure over last 12-24 hours.

Amount of water required by the crop for healthy growing circumstances (statistical data).

Stage of plant growth

Wind

Irrigation practice.

Climate

Type of soil (to account for soil drainage)

Plant density

They all affect the irrigation needs but some are not as important, please assist me with your expertise in telling me which are not as impactful/ important. And which are absolutely crucial to account for. Maybe we even have missed some?

With kind regards, Morris la Crois