Figure 6.6. Plants growing in silt loam soil with (a) good tilth and (b) with all three types of compaction. a) good soil structure b) compacted soil porous (loose- fitting) crumbs and blocks) surface crust tightly packed crumbs germinating seed large blocks with few cracks subsoil compaction

Figure 6.7. Soil consistency states for a sand and a clay soil (friable is best for tillage). saturation 0 plastic liquid clay sand loose hard plastic limit friable soil water content

soil hardness 300 psi critical level well-aggregated soil compacted soil Figure Compacted soils harden more quickly upon drying than well-aggregated soils.

Figure The optimum water range for crop growth for two different soils well structured soil very dry Compacted soil saturated poor aeration optimum water range optimum water range field capacity poor aeration drought stress root resistance soil water content