40 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 



The graded terrace is adapted particularly for use on impervious 

 and worn-out soils, and on shallow open soils with an impervious 

 foundation — in short, soils that will not absorb much water and that 

 necessitate the removal of most of it over the surface. 



By the selection and proper construction of suitable types of ter- 

 races erosion can be controlled on slopes up to 20 per cent, or even 

 more. Instances were found where erosion was controlled by the use 

 of terraces on land which had a slope of 30 per cent. However, slopes 

 steej)er than 20 per cent usually can be devoted more profitably to 

 grasses or timber than to cultivated crops. Of all types of terraces, 

 the use of the broad-base level-ridge terrace is recommended wherever 

 conditions will permit. This type, supplemented with efficient tile 

 drains, offers the most ideal method of preventing soil erosion on 

 any type of soil. 



The success of a terrace system depends largely upon its proper 

 lajdng off. A good leveling instrument in the hands of a competent 

 and experienced levelman is the best insurance against failure. 



Construction always should begin with the highest terrace in the 

 field, and each terrace shoiild be completed before starting the next 

 lower one. The late fall and early winter is the best time to build 

 terraces. 



A terrace is susceptible to failure until it has become thoroughly 

 settled. To facilitate settling it is best not to cultivate a terrace the 

 first year, but to sow it to a cover crop. The best results are obtained 

 where crop rows are run parallel with the terraces. 



The instructions given herein for the selection and design of ter- 

 race systems are based upon the results of surveys, observation, and a 

 study of terraced fields in the best-terraced sections in this country 

 and it is believed that if they are followed carefully a great increase 

 in the efficiency of terrace systems will result and that much better 

 opportunity will be afforded to observe the results with a view to fur- 

 ther improving the practice of terracing. At the same time a close 

 study of local conditions — particularly of soil — should be made 

 which no doubt will afford more definite information for improving 

 further the design of a terrace system adapted to a particular 

 locality. 



Since the primary purpose of terracing is to hold the soil of the 

 farm in place and thereby both maintain its fertility and render pos- 

 sible an increase of fertility by proper farming methods, all of the 

 benefits, such as greater yields and land values, which result from the 

 preservation and increased fertility of the soil may be attributed di- 

 rectly to the practice of terracing. In short, the terracing of farm 

 lands saves the soils the most substantial and valuable asset of the 

 country. 



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