Page 65 - Soil Degradation, Conservation and Remediation

2.2 Surface Sealing, Crusting, Hardsetting, and Compaction (Pc) 51

Organic Matter

Organic substances may stabilize soil structure in two different ways: (1) organic
substances can reduce interaction of water with inorganic colloids, and (2) it can
bind soil particles together physically or chemically. Humic materials act as cements
that bind particles together. The organic polymers expose along their long complex
surfaces negative and positive edges of amides, carboxyl, hydroxyl, and other polar-
izable groups.

Iron and pH

Iron oxides may bind soil particles together. Kaolinitic soils rich in iron oxides and
lower in pH may develop crusts.

2.2.2.2 Management of Soil Crust

Reduced infiltration is the most damaging problem of crusted soils. Low infi ltration
increases runoff and erosion and decreases available soil moisture for plants. There

are three methods of augmenting infiltration: the use of soil amendments, conserva-
tion farming, and tillage management. These methods may be used separately or
combined.

Soil Amendments

There are some soil amendments to prevent slaking and dispersion of soil aggregates.
One way to reduce the risk of crusting is to improve soil structure and aggregate
stability at the soil surface. Increasing electrolyte concentration by spreading
phosphogypsum on the soil surface may be employed (Agassi et al. 1981 ).
++
Phosphogypsum dissolves quite readily during rainstorms and releases Ca and
−−
SO 4 ions into the soil solution to support concentrations high enough to prevent
clay dispersion. Adding phosphogypsum improves the physical properties of the
++
+
soils by replacing Na by Ca on the soil colloids. Improving soil structure and
reducing crust formation by using organic polymers (e.g., PAM–polyacrylamide)
have been under intensive investigation for many years.

Conservation Farming

Conservation farming systems effectively reduce soil crusting. Conservation

farming includes some specific tillage systems, such as no tillage, mulch farming,
stale mulch, and minimum tillage. These systems are widely used in the USA and
Australia to counteract water and wind erosion. There are two main goals for