Question

An air-dry soil with a moisture content of 25% by weight is to be used in a pot experiment. If each pot is to have 30kg oven-dried soil, how much of the air-dry soil should be weighed into the pot and how much of that moisture in kg?

Answer 1

$m_w$ =water mass

$m_t$ = total mass

$(30+m_w) = m_t \\ m_w = 0.25m_t \\ 30 + 0.25m_t = m_t \\ 30 = 0.75m_t \\ m_t = 40 \;kg$

40 kg of the air-dry soil should be weighed into the pot.

$m_w = 0.25 \times 40 = 10 \;kg$

10 kg of that is moist