Terraces Iowa Job Sheet Natural Resources Conservation Service May 2001 Des Moines, Iowa Narrow base Grassed backslope Broadbase What is terracing? tillage, crop rotations, and field Where to get help Terraces are earthen structures that borders. For assistance in planning, design- intercept runoff on moderate to Terracing reduces sediment pollu- ing and laying out a terrace system steep slopes. They transform long tion of lakes and streams, and traps on your farm, contact your local slopes into a series of shorter phosphorus attached to sediment Natural Resources Conservation slopes. Terraces reduce the rate of particles. Grassed frontslopes and Service (NRCS) office. For more runoff and allow soil particles to backslopes of some terraces provide job sheets and conservation infor- settle out. The resulting cleaner cover for wildlife. mation visit the NRCS website at water is then carried off the field in www.ia.nrcs.usda.gov a non-erosive manner. Where the practice applies Terraces can be used on fields How it helps the land where sheet and rill erosion or Terraces are used to reduce sheet ephemeral gullies are a problem. and rill erosion and prevent gully They can also be used where runoff development. They are most effec- or sediment could impair water tive when used in combination with quality or cause damage other practices such as conservation downstream. Requirements of terracing — Narrow base terraces have 2:1 terraces. Also be careful not to Several important factors must be slopes on both the frontslope and crowd these grassed areas with considered when planning and design- backslope. Both front and back- farming operations. ing a terrace system: slope are seeded to perennial • There are two types of terraces. grasses. • Avoid farming too close to intakes. Storage terraces collect water and Farming operations can cause store it until it can infiltrate into — Broadbase terraces are flatter ridges that block drainage of the the ground or be released through looking terraces that are farmed on terrace channel. a stable outlet. Underground out- both slopes. They should not be lets with pipe intakes are the most built on land slopes greater than Maintaining the practice common type of outlet. Deep soils 8 percent. Farmable slopes should • Remove sediment build-up in the with high infiltration rates can not be steeper than 5:1. terrace channel to maintain the sometimes be used as outlets. required water holding capacity. Gradient terraces are designed as Applying the practice channels to slow runoff water and This practice is considered to be • Repair sections of the terrace carry it to a stable outlet like a installed when construction is com- which have eroded or have grassed waterway. pleted and seeding is established. excessive settlement. After terraces are built, chisel the • Terraces must generally fit the portion of the terrace that will be contour of the land. Deviations • Fill any settled or eroded areas in farmed to loosen compacted soil. The the tile trench. from the contour must be limited backslopes of grassed backslope ter- and are allowed only when neces- races and the front and backslopes of • Repair or replace damaged tile sary to obtain good alignment. narrow base terraces should be fertil- Always check with the NRCS ized and seeded according to the intakes. office before allowing any recommendations below. Oats may be deviation from the design. seeded as a nurse crop at the rate of • Remove sediment build-up and one bushel/acre during the spring. trash from around the intake. • Terraces are designed to control runoff from a 10-year frequency, Recommended fertilizer (lbs/ac) • Control rodents or burrowing 24-hour storm. For storage ter- N P K Lime animals. races, that capacity is increased to ______ _____ _____ _____ also hold the estimated volume of • Control weeds, brush, and trees by Recommended seeding rates for your 10 years’sediment accumulation. terrace species spraying or mowing. species lbs/ac • Terraces are spaced to control • Don’t operate farm equipment on sheet and rill erosion and stop _________________ _______ steep frontslopes and/or back- ephemeral gullying. Terrace spac- _________________ _______ slopes. ing is determined by several fac- tors including soil type, slope, and _________________ _______ • Reseed and fertilize as needed to the use of other conservation prac- maintain good vegetation. tices such as conservation tillage. Other considerations • Where terraces are parallel, there • Where grassed waterways are used • There are three typical terrace are very few problems with plant- as terrace outlets, they must be cross section shapes. The pictures ing. If terraces are not parallel, maintained to prevent gully on the front illustrate each shape. short rows should be kept between erosion. terraces rather than turning on ter- Following is a brief overview of The U.S. Department of Agriculture (USDA) each. races. A short row correction area prohibits discrimination in all its programs and could be left in grass rather than activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual turning on crops. orientation, or marital or family status. (Not all pro- — Grassed backslope terraces have hibited bases apply to all programs.) Persons with a farmable frontslope with a 2:1 disabilities who require alternative means for com- • If terraces are not the same length, munication of program information (Braille, large backslope (2 feet horizontal to print, audiotape, etc.) should contact USDA’s every 1 foot of vertical drop). plant from the longer terrace to the TARGETCenter at 202-720-2600 (voice and TDD). shorter one. To file a complaint of discrimination, write USDA, Downhill slope is seeded to Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, perrennial grass. SW, Washington, DC 20250-9410 or call (202) 720- • Do not farm the backslope of 5964 (voice and TDD). USDAis an equal grassed backslope terraces or the opportunity provider and employer. front or backslopes of narrow base.