Soil air

A part of the soil volume that is not occupied by soil particles, known as pore space, is filled partly with soil water and partly with soil air. As the pore space is occupied by both water and air, volume of air varies inversely with that of water. As the moisture content of the soil increases, the air content decreases and vice-versa.

The soil air contains a number of gases viz., nitrogen, oxygen, le and water vapor. Soil air differs from the atmosphere in several respects. First, soil air contains- much greater proportion of carbon dioxide and a lesser amount of oxygen than atmospheric air. Second, soil air has a higher moisture content than the atmosphere.

The content and composition of soil air is determined to a large degree by the soil-water relationships. Following a rain, large pores are the first vacated by the soil water, followed by medium-sized pores as water is removed by evaporation and plant utilization. Thus, the soil air ordinarily occupies the large pores. As soil further dries up, medium size pore spaces copy the soil air.