Soils 205- General soils

Lecture 7- Management of soil physical properties

I.  Aggregate- many soils particles held in a single mass or cluster, such as a clod, block, or prism.

            aggregation = lower bulk density (higher porosity), greater numbers of macropores,               increased infiltration rates (decreased runoff and erosion).

    a.  processes leading to aggregation

        i.  physical-chemical

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        ii.  Biological processes

            - burrowing and casting of earthworms

            - enmeshment of particles by sticky networks of roots and fungal hyphae

            - production of organic glues (polysaccharides) by bacteria and fungi

    b. Influence of tillage

        Short-term

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        Long-term

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II.  Soil tilth- a general term that refers to the physical condition of a soil in relation to plant growth.

It depends on:  aggregate formation and stability, bulk density, soil moisture content, degree of aeration, rate of water infiltration, drainage, etc.

        a.  Soil crusting

            To prevent soil crusting:

            1) leave residue on the surface to protect from rain drop impaction

            2) light tillage (once the crust has formed)

            3) use of soil conditioners

               i.  Soil conditioners

                    1.  gypsum

                    2.  synthetic organics

                    3.  polyacrylamide (PAM)

        Guidelines for managing soil tilth

                    1.  Minimize tillage-

                    2.  Timing of tillage-

                    3.  Mulch with crop residues-

                    4.  Add soil conditioners if needed-