Distributive law (1) The oxygen(O) and silicon( Si) are main two elements in the earth crust. The second elements are iron and aluminum. Four elements occupy about 88.7% weight of the le earth crust (2) The essential elements for plant growing are very low and distribute unbalance in earth crustDistributive law （1）The oxygen( O) and silicon( Si) are main two elements in the earth crust. The second elements are iron and aluminum. Four elements occupy about 88.7% weight of the earth crust. （2）The essential elements for plant growing are very low and distribute unbalance in earth crust