The importance of aeration in providing the right conditions for plant growth

As plant roots and soil organisms absorb oxygen and evolve carbon dioxide, they alter the gaseous composition of their environment. Molecular diffusion of these two gases between soil and atmosphere opposes this change and for optimum plant growth it must provide for interchange at a sufficient rate to avoid deficits of oxygen and excesses of carbon dioxide limiting to plant growth. Diffusion of gases in soil depends on the amount and distribution of the air‐filled pore space. Its sensitivity to moisture content depends on the pore‐size distribution and hence the soil structure. Two phases may be recognized in soil aeration: (1) gases diffuse within the macro‐pore spaces (usually air‐filled at field capacity), and (2) they diffuse within the microstructure between crumb surface and root surface in both the gaseous and aqueous phases. This second phase is of importance in naturally cohesive soils where the size and internal geometry of natural peds and cultivated crumbs can determine the adequacy of aeration in the micro‐environment of the root. Four soils from the continuous wheat plots of Broadbalk illustrate the importance of microstructure for which a possible index of quality is proposed.