184 Chapter 10: Appendix
tent of the soil, and amounts of surface residues. Percolating water below the
root zone may carry excess solutes or may dissolve potential pollutants as they
move. In either case, these solutes could reach ground water supplies
downslope from the contour orchard area. The amount depends on soil
type, surface water quality, and the availability of soluble material (natural or
Contour Stripcropping (585): Growing crops in a systematic arrangement of
strips or bands on the contour to reduce water erosion.
The crops are arranged so that a strip of grass or
crop is alter-
nated with a strip of clean-tilled crop or fallow or a strip of grass is alternated
with a close-growing crop [FIGURE
This practice may reduce erosion and the amount of sediment and related sub-
waters. The practice may increase the amount of
stances delivered to the
water which infiltrates into the root zone, and, at the time there is an overabun-
dance of soil
this water may percolate and leach soluble substances into
the ground water:
Controlled Drainage (335): Control
of surface and subsurface
water through use
of drainage facilities and water control structures.
The purpose is to conserve water and maintain optimum soil moisture to (1) store
and manage infiltrated rainfall for more efficient crop production;
surface water quality by
infiltration, thereby reducing runoff, which
may carry sediment and undesirable chemicals; (3) reduce nitrates in the drain-
age water by enhancing conditions for denitrification; (4) reduce subsidence and
wind erosion of organic soils; (5) hold water in channels in forest areas to act as
ground fire breaks; and (6) provide water for wildlife and a resting and feeding
place for waterfowl.
Cover and Green Manure Crop (340): A crop of close-growing grasses, le-
gumes, or small grain grown primarily for seasonal protection and soil improve-
ment. It usually is grown for year or less, except where there is permanent
cover as in orchards.
Erosion, sediment and adsorbed chemical yields could be decreased in conven-
systems because of the increased period of vegetal cover: Plants
available nitrogen and prevent its undesired movement. Organic
nutrients may be added to the nutrient budget reducing the need to supply more
soluble forms. Overall volume of chemical application may decrease because the
vegetation will supply nutrients and there may be allelopathic effects of some of
the types of cover vegetation on weeds. Temperatures of ground and surface
waters could slightly decrease.
Critical Area Planting (342): Planting vegetation, such as trees, shrubs, vines,
grasses, or legumes, on highly erodible or critically eroding areas. (Does not
mainly for wood products.)
This practice may reduce soil erosion and sediment delivery to surface waters.
Plants may take up more of the nutrients in the soil, reducing the amount that can
be washed into surface waters or leached into ground water.
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