noun
dolomite lime
Agricultural lime made from dolomite, used to neutralize soil acidity and supply magnesium.
苦土石灰を畑にまいて土壌を改良する。
Spread dolomite lime on the field to improve the soil.
石灰 is general lime (calcium oxide/hydroxide), while 苦土石灰 specifically contains magnesium from dolomite.
Compound of 苦土 (くど, 'magnesia', from the bitter taste of magnesium compounds) and 石灰 (せっかい, 'lime').