Net present value analysis for 120 cm drain depth. Net present value analysis for 200 cm drain depth. Net present value analysis for 240 cm drain depth. The net present value vs. drain spacing for the three drain depths is shown in figure 1. There seem to be a range of drain spacings for each depth of drain that result in a reasonably high yield.
Yield is lower at close drain spacings because dry stress is greater.
This shows the need to include both wet and dry years in drainage analysis for rain-fed agriculture. Thus, this is the alternative that should be selected. Because the total present value is positive, the alternative should be selected. The information in tables 6-8 is shown graphically in fig. Net present value vs. drain spacing for the three drain depths .