With each passing day, the amount of energy in the sun's rays increases, and the sun rises higher and higher in the horizon. This results in warmer and longer days, which in turn means the soil becomes warmer. Below are a few factors to consider in answering these questions.
Clay soils have the ability to hold more water than sandy soils.
Water has a high specific heat - meaning it takes a large amount of energy to raise the temperature of water. Therefore, clay soils, with their high water-holding capacity, require a lot of heat to warm them. Clay soils thus do not warm early in spring. Sandy soils are very much the opposite of clays. They hold little water, and thus warm much faster in the spring.