If the P concentration in the soil solution average 0.7 mg/L throughout the life cycle of a crop of tomatoes, which has a transpiration ratio of 700 g water per g plant dry matter. What is the proportion of P absorbed by the plant due to mass flow if the total yield of the crop is 20 tonnes dry matter / ha, the P concentration in the plant is 0.4 % and the average available P in the soil is 35 kg/ha.