12 BULLETIN 512, U. S. DEPAETMENT OF AGEICULTURE. 



and (3) the weeds which often are allowed to grow on the terrace 

 tend to seed the entire field, and harbor objectionable insects in the 

 winter. Owing to these objections, this type of terrace is losing 

 favor rapidly among the most adA'anced farmers. 



Some attempts have been made to cultivate this terrace and thus 

 do away with the objectionable features, but such attempts have 

 been attended with very little success, except where the soil is very 

 sandy and capable of absorbing most of the rain water as fast as it 

 falls. Where this water is not absorbed readily by the soil, it con- 

 centrates above the terrace, generally breaks it and rushes down the 

 slope, usually washing a deep gully and carrying away large quanti- 

 ties of fertile soil. 



The hroad-hase for^iv.— The many disastrous attempts to cultivate 

 the narrow-base level-ridge terrace on all types of soil have led to 

 the development of a terrace with a broader base, known as the 

 broad-base level-ridge terrace. (Fig. 2-C and D, and PI. Y, fig. 1.) 

 The broad-base embankment of earth provides the strength necessary 

 to withstand the weight of the impounded water above, and the ter- 



** w 



Fig. 5. — Cross section of two adjacent broad-base level-ridge terraces. 



race is built sufficiently high to hold all run-off water from the drain- 

 age area above the terrace. 



Surveys and examinations were made of several fields provided 

 with these broad-base terraces in Alabama, Georgia, North Carolina, 

 and South Carolina, and much information was obtained from farm- 

 ers with many years of experience in the successful use of this type of 

 terrace. A thorough study has been made of the data collected in 

 connection with existing field conditions for the purpose of standard- 

 izing the dimensions employed in the construction of this terrace for 

 different slopes of land and types of soil. 



Figure 5 represents a cross section of two adjoining broad-base 

 level-ridge terraces, with the various dimensions designated by letter. 

 The vertical height of the terrace above the point c is represented by 

 h; w is the width of the base of the terrace, d the horizontal distance, 

 and V the vertical distance between terraces. These dimensions were 

 obtained from surveys of eight fields representing the best practice 

 in the use of this form of terrace. The average dimensions of the 

 terraces in eacli field were determined. The minimum and maximum 

 of these field averages are shown in the following table, together 



