Plants and animals that live in the forest depend on the calcium that is taken up from the soil. An experiment is conducted to investigate the effect fire has on calcium levels. A forest is segmented into 12 homogeneous plots. Soil samples are taken from each plot prior to a controlled burn and again after a controlled burn. The average difference in calcium levels for each plot are tested to see if the calcium levels decreased after the burn. What type of procedure is appropriate for this scenario