Lab 6 question 2.b

Hello, I don't understand what exactly we need to compare in question 2.b. It says "differences in pH values obtained by the two methods". Do we need to subtract pH (water) from pH (CaCl2) and compare these differences to organic matter content?

Yes, that is exactly it. And in the discussion to accompany that comparison, you should explain why certain samples have quite a large difference between pH values determined in water and in a salt (CaCl2) and others don't. Also, what does that difference tell us about soil's capability to resist pH change when we add bases (eg lime) and acids (eg N-fertilizers) to the soil.