Because its decayed organisms. So all the nutrients from that decayed organism goes into the soil and makes it rich with nutrients.
<em>The </em><em>energy </em><em>released</em><em> by</em><em> the</em><em> </em><em>hydrolysis</em><em> </em><em>of </em><em>ATP </em><em>is </em> <em><u>7.3 kcal/mol of </u></em><em><u>energy.</u></em>