Chapter 10: Appendix 183
tion may result in a high surface runoff of pollutants (nutrient and pesticides).
Macropores develop under a no-till system. They permit deep percolation and the
transmittal of pollutants, both soluble and insoluble to be carried into the deeper
soil horizons and into the ground water.
systems disrupt or break down the macropores, incidentally in-
Reduced
the
corporate some of the materials applied to the soil surface, and
of wheeltrack compaction. The results are less runoff
less pollutants in the
Constructed Wetland (ASCS-999): A constructed aquatic ecosystem with
rooted emergent hydrophytes designed and managed to treat
water.
This is a conservation practice for which NRCS has developed technical require-
ments under a trial program leading to the development of a conservation prac-
tice standard.
Contour Farming (330): Farming sloping land in such a way that preparing
land, planting, and cultivating are done on the contour. This includes following
established grades of terraces or diversions.
This practice reduces erosion and sediment production. Less sediment and re-
lated pollutants may be transported to the receiving waters.
Increased infiltration may increase the transportation potential for soluble sub-
stances to the ground
Contour Orchard and Other Fruit Area (331): Planting orchards, vineyards,
or small fruits so that all cultural operations are done on the contour.
Contour orchards and fruit areas may reduce erosion, sediment yield, and pesti-
cide concentration in the water lost. Where inward sloping benches are used, the
sediment and chemicals will be trapped against the slope. With annual events, the
bench may provide 100 percent trap efficiency. Outward sloping benches may
allow greater sediment and chemical loss.
The amount of retention depends on the slope of the bench and the amount of
cover. In addition, outward sloping benches are subject to erosion form runoff
from benches immediately above them. Contouring allows better access to rills,
permitting maintenance that reduces additional erosion. Immediately after estab-
lishment, contour orchards may be subject to erosion and sedimentation in excess
of the now contoured orchard. Contour orchards require more fertilization and
pesticide application than did the native grasses that frequently covered the
slopes before orchards were started. Sediment leaving the site may carry more
adsorbed nutrients and pesticides than did the sediment before the benches were
established from uncultivated slopes. If contoured orchards replace other crop or
intensive land use, the increase or decrease in chemical transport from the site
may be determined by examining the types and amounts of chemicals used on the
prior land use as compared to the contour orchard condition.
Soluble pesticides and nutrients may be delivered to and possibly through the
root zone
amount proportional to the amount of soluble pesticides applied,
the increase in infiltration, the chemist: of the pesticides, organic and clay
Chapter 1 O-l 83:
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