Which of the following does not occur as a result of poor drained soil?

Increase in oxygen level of the soil does not occur as a result of poorly drained soil. Poorly drained soil has too much water and not enough air, which can lead to a decrease in rooting depth, mottling near the top, change in color of the subsoil, and a decrease in organic matter content. When there is excess water, soil pores are filled with water, which limits the amount of oxygen that can reach plant roots. This can lead to a decrease in rooting depth, and also make it harder for plants to absorb nutrients from the soil. The decrease in oxygen level and excess water also create anaerobic conditions that can lead to mottling near the top and a change in color of the subsoil. In these conditions, organic matter in the soil can break down and produce compounds like iron and manganese that cause the soil to change color. An increase in oxygen level of the soil is actually a benefit of well-drained soil, where excess water is able to drain away, allowing air to fill soil pores and reach plant roots.