drainage engineers, and Soil Conservation 

 Service engineers — and the cost estimates re- 

 ported tended to center around a median value 

 of 23 cents per cubic yard for quantities in 

 the most common range of 350 to 499 cubic 

 yards per acre. Most agreed that the cost per 

 cubic yard would probably vary inversely with 

 the total quantity moved per acre. From frag- 

 mentary data, the following sliding scale of 

 cost was developed to illustrate the relationship 

 between the quantity of earth moved and unit 

 costs: 



Cubic yards of earth 



Cost 



per 



cubic 



; yard 



Under 150 





$0 



.27 





150 - 249 







.25 





250 - 349 







.24 





350 - 449 







.23 





450 and over 







.22 





These estimates are based on the assump- 

 tion that the contractor would use a carryall. 

 For building 14-foot benches, however, a road 

 grader could be used, probably at less cost. 

 On benches of 28 feet and wider, the use of 

 a road grader probably would not be prac- 

 tical. The data for 14-foot benches in table 3 



are probably overestimated for steep slopes, 

 and underestimated for gentle slopes. To 

 partially compensate for this possibility, a 

 lower limit of $25 per acre was arbitrarily 

 assumed. 



At the rates assumed, the cost per acre 

 for building 14-foot benches on a 1 -percent 

 slope would be $25 per acre, and would increase 

 to $40 per acre for 70-foot benches (table 5). 

 On a 10-percent slope, the cost per acre would 

 be $76.80 for 14-foot benches and would in- 

 crease to $352.66 per acre for 70-foot benches. 



The cost data shown in table 5 do not in- 

 clude any allowance for the work necessary to 

 survey and stake the field. There is no con- 

 venient way to estimate such costs accurately 

 except on a case-by-case basis, using topo- 

 graphic maps of the fields on which the benches 

 are to be constructed. 9 No allowance was made 

 for stockpiling and returning topsoil to exposed 

 subsoil areas where deep cuts are made. The 

 cost of this operation will vary, depending on 

 the depth of the A horizon, the depth of cut, 

 and the kind of equipment available. 



ECONOMIC ASPECTS 



For this analysis, a field of 100 acres 

 was assumed to be the basic land resource. 

 Thus, the land use figures can be used as 

 acres or percentages, whichever is more 

 convenient. 



slope. For 14-foot benches with contributing 

 areas, the net area in benches would be 38 

 acres on a 10-percent slope and 42 acres on 

 a 1 -percent slope. 



Yields 



Alfalfa Production 



Harvested Area 



The harvested area of the 100-acre field 

 was computed by deducting the acreage in 

 roads, lanes, fences, dikes, and backslopes as 

 explained earlier. The harvested area was then 

 divided into two parts: (1) The area actually 

 in benches, and (2) the area in natural slopes, 

 including contributing areas, turning areas, 

 and odd-shaped areas. For example, for 14-foot 

 benches without contributing areas, the net 

 area in benches would be 63 acres on a 10- 

 percent slope and 76 acres on a 1 -percent 



In computing alfalfa production, the acre- 

 age in each part of the harvested area was 

 multiplied by its respective average yield; 

 that is, 1.2 tons per acre for natural slopes, 

 3.0 tons for benches with contributing areas, 

 and 2.8 tons for benches without contributing 

 areas. For an entire field with a given bench 

 width the total alfalfa production would de- 

 crease with each increase in slope. For ex- 

 ample, a 100-acre field with 14-foot benches 



9 The layout and staking of the benches might possi- 

 bly be performed by engineers and technicians from the 

 local Soil Conservation District at no expense to the 

 farmer. 



