Soil structure & plant growth.

Highest yields on heavy clay soils were obtained when Peerlkamp's visual index of structure (S. & F. XXII [2129]) was at least 5 1/2, corresponding to an air content of at least 15% (by volume) at pF2; a visual index of 5 1/3-6 for these soils corresponds to a structure characterized by dense clods of 0.5-1 cm mean diameter or by porous aggregates of 5-10 cm. A pore space of 48-50% (by volume), corresponding to an air content of 14-17% (by volume) at pF2, was required for high yields on loamy soils. Optimum air content at pF2 in sandy soils (used as an index of soil structure) was about 20-25% (by volume); higher air contents decreased yields through moisture deficiency & lower air contents caused the mechanical resistance of sand to limit root growth. (Abstract retrieved from CAB Abstracts by CABI’s permission)