Table 1. — Crop yields per acre on level benches: Summary of 

 3 sets of experiments, 1962-68 



Table 2. — Maximum depth of cut for benches, by slope 

 and bench width 



Item 



1962 



1963 



1964 



1965 



Mean, 

 1962-65 



Cropland study 

 Corn grain 



Bushels 



42.0 29.6 24.0 62.9 39.6 

 43.2 43.9 20.4 54.1 40.4 

 40.9 39.4 23.8 51.7 39.0 



Tons 

 7.62 6.84 5.74 11.86 8.02 

 7.81 7.61 6.06 9.84 7.83 

 7.21 7.40 6.20 9.27 7.52 



Bushels 



44.1 7.3 23.7 40.8 29.0 



48.2 10.3 36.5 42.2 34.3 

 48.2 11.1 38.2 42.3 35.0 



Corn silage 



Slope 



Bench without C.A. 



Bench with C.A. 



Wheat 





Grassland study 



1963 



1964 



1965 



1966 



Mean, 

 1963-66 



Alfalfa 



Tons 

 0.60 0.77 1.18 1.05 0.90 

 1.70 1.84 2.17 2.07 1.94 

 1.88 1.80 2.44 2.22 2.08 



1.02 0.84 0.98 0.93 0.94 

 1.49 1.56 1.93 1.31 1.57 

 1.76 1.62 1.78 1.40 1.64 



Bench without C.A. 



Bromegrass 



Slope 



Bench without C.A. 



Contributing area study 



1964 



1965 



1966 



1968 



Mean, 

 1964-68 



Alfalfa 



Tons 



Bench with C.A. 



2.59 

 2.75 



4.19 

 4.16 



3.84 

 4.08 



4.36 

 4.46 



3.74 

 3.86 



Percent- 

 age of 



Depth of cut when width of 

 bench in feet is — 



slope 



14 



28 



42 



56 



70 





Inches 



Inches 



Inches 



Inches 



Inches 



1 



0.9. 



1.8 



2.7 



3.6 



4.4 



2 



1.8 



3.6 



5.3 



7.1 



8.9 



3 



2.7 



5.3 



8.0 



10.7 



13.4 



4 



3.6 



7.1 



10.7 



14.2 



17.8 



5 



4.5 



8.9 



13.4 



17.8 



22.3 



6 



5.3 



10.7 



16.0 



21.4 



26.7 



7 



6.2 



12.5 



18.7 



24.9 



31.2 



8 



7.1 



14.2 



21.4 



28.5 



35.6 



9 



8.0 



16.0 



24.0 



32.1 



40.1 



10 



8.9 



17.8 



26.7 



35.6 



44.5 



1 For this calculation the slope is assumed to be 

 uniform throughout. 



C.A. = contributing area. 



Table 4. — Land area occupied by dikes and backslopes 

 (Percentage of total area in a field) 



TaDle 3. — Quantities of earth to be moved in con- 

 struction of benches of varying widths, by slope 



Percent- 



Amount of earth moved 

 bench in feet 



when width of 

 is — 



slope 1 



14 



28 



42 



56 



70 









yards per 



acre 2 











1 



1 



32 



64 



96 



128 



160 



2 



64 



128 



192 



256 



321 



3 



96 



192 



289 



385 



481 



4 



128 



256 



385 



513 



641 



5 



160 



320 



481 



641 



802 



6 



192 



385 



577 



769 



962 



7 



224 



449 



673 



898 



1,122 



8 



256 



513 



769 



1,026 



1,282 



9 



288 



577 



866 



1,154 



1,443 



10 



320 



641 



962 



1,282 



1,603 



1 For this calculation the slope is assumed to be 

 uniform throughout. 



2 Cut volume. The ratio of cut to fill is assumed to 

 be 1.3:1. 



Percent- 

 age of 



Proportion of < 



likes and 



aacks lopes 



when 





width of 



bench in 



feet is — 





slope 1 



14 



28 



42 



56 



70 





Percent 



Percent 



Percent 



Percent 



Percent 





Bei 



lches with 



3ut contributing area: 



1 



16.2 



9.5 



7.0 



5.7 



4.9 



2 



17.4 



10.8 



8.4 



7.1 



6.3 



3 



18.4 



12.1 



9.7 



8.5 



7.7 



4 



19.5 



13.2 



11.0 



9.8 



9.0 



5 



20.5 



14.4 



12.2 



11.0 



10.3 



6 



21.6 



15.6 



13.4 



12.3 



11.6 



7 



22.5 



16.7 



14.6 



13.5 



12.8 



8 



23.4 



17.8 



15.7 



14.6 



14.0 



9 



24.4 



18.9 



16.8 



15.8 



15.2 



10 



25.2 



19.9 



18.0 



16.9 



16.3 





Bei 



iches with 



1:1 contributing area: 



1 



8.8 



5.0 



3.6 



2.9 



2.5 



2 



9.5 



5.7 



4.4 



3.7 



3.3 



3 



10.1 



6.4 



5.1 



4.4 



4.0 



4 



10.8 



7.1 



5.8 



5.1 



4.7 



5 



11.4 



7.8 



6.5 



5.8 



5.5 



6 



12.1 



8.5 



7.2 



6.5 



6.2 



7 



12.7 



9.1 



7.9 



7.2 



6.9 



8 



13.2 



9.8 



8.5 



7.9 



7.5 



9 



13.9 



10.4 



9.2 



8.6 



8.2 



10 



14.4 



11.0 



9.9 



9.2 



8.9 



1 The slope is assumed to be uniform throughout the field. 



19 



