Vapour-pressure deficit temperature, the relative humidity and, if possible, the canopy air temperature. We must then compute the saturation pressure. Saturation pressure can be looked up in a psychrometric chart or derived from the Arrhenius equation, a way to compute it directly from temperature is where: To convert between Rankine and degrees Fahrenheit: formula_10 We compute this pressure for both the ambient and canopy temperatures. We then can compute the actual partial pressure of the water vapour in the air by multiplying by the relative humidity [%]: and finally VPD using formula_12 or formula_13 when the canopy temperature is known. Vapour-pressure deficit
Water in California million tons. About one-third of that, around 700,000 tons, went to China, Japan took about the same amount and Saudi Arabia bought 5,000 tons. Alfalfa farmers pay about $70 an acre-foot, in Los Angeles that same amount of water is worth $1000 per acre-foot. In 2012, California exported 575,000 tons of alfalfa to China, for $586 million. Other common crop water use, if using all irrigated water: fruits and nuts with 34% of water use and 45% of revenue, field crops with 14% of water and 4% of revenue, pasture forage with 11% of water use and 1% of revenue,