For the wet bulk density (total bulk density) this sample is weighed, giving the mass M t {\displaystyle M_{t}} . For the dry bulk density, the sample is oven dried and weighed, giving the mass of soil solids, M s {\displaystyle M_{s}} . The relationship between these two masses is M t = M s + M l {\displaystyle M_{t}=M_{s}+M_{l}} , where M l {\displaystyle M_{l}} is the mass of substances lost on oven drying (often, mostly water).