The question
Name: ______________________ Date: ____________ Irrigation: water use per area, efficiency and cost (10 points)
Data
A farm considers switching from furrow to drip irrigation
| Item | Value |
|---|---|
| Area of the farm | 120 hectares |
| Water applied with furrow irrigation | 9,000 m³ per hectare |
| Efficiency of furrow irrigation (share of applied water the crop takes up) | 60% |
| Efficiency of drip irrigation | 90% |
| Price the farmer pays to pump water | 0.12 dollars per m³ |
| Cost to install drip irrigation | 2,500 dollars per hectare |
A 120-hectare farm in a dry valley grows vegetables with furrow irrigation. All of its water is pumped from an aquifer whose water table has dropped 20 meters in the last 30 years. The farmer is thinking about switching to drip irrigation. The crop would need the same amount of water under either method.
(a) Calculate the total volume of water, in cubic meters, the farm applies in one season with furrow irrigation. Show your setup with units. [2 points]
(b) Calculate the volume of water per hectare the farm would need to apply with drip irrigation to give the crop the same amount of water it takes up now. Show your setup. [2 points]
(c) Calculate how much money, in dollars, the farm would save on water in one season by switching the whole farm to drip irrigation. Show your setup with units. [2 points]
(d) Calculate the number of years of water savings it would take to pay for installing drip irrigation on the whole farm. Show your setup. [2 points]
(e) Explain how years of furrow irrigation can lower the yield of the farm's soil through salinization. [1 point]
(f) The aquifer under the valley is shared by many farms. Propose a policy that the state could adopt to slow the drop in the water table, and explain how it would work. [1 point]