ENERGY, WATER & YIELD 11/18/2016
Most do not realize that running a farm operation is energy intensive.
Let’s define two terms to start:
1) Pumping, and 2) Irrigating
Pumping is transporting the water to the field by pumping from the ground water or by transporting the water across the fields. In California, many of our farmers are members of irrigation co-ops through which water is delivered for irrigation by open channels or irrigation pipes.
Irrigation, on the other hand, is the actual act of dispersing water across a field for crop growth. In California, we see flood irrigation, sprinklers, drip and micro sprayers.
The cost associated with both Pumping and Irrigating:
As stated above, pumping is the raising of water from the water table or transporting the water across land to the fields. Since many farmers are using groundwater due to the drought, we are going to focus on ground pumping. Here are the numbers for 100 acres of a crop with an annual of (evapotranspiration) ETo of 40. To lift water from a depth of 100 feet requires 34,000 kWH, if the pump is functioning at 100% efficiency. Most pumping systems run at 70% efficiency, although there are a number of studies being conducted in this arena that involve ways to increase the efficiency factor.
Then, there is the actual irrigation cost, which is where the sprinklers, drip or other irrigation system must be pressurized. This is hard for many urban dwellers to imagine because, when we turn on a faucet, the water is already pressurized by our municipality. This is done in several ways; but, the most common are the large water tanks seen high up in the nearby hills. Water is pumped to this high level, then gravity creates the required pressure as the water races down the hill into our city pipes.
To use water in an irrigation system like sprinklers, the farmer needs to create the required pressure. The typical pressure needed is usually 60 PSI (pressure per square inch). Each PSI is equal to 2.3 of lift. So, a 60 PSI demand is equal to 130 feet of lift; and, the energy requirement is 37,536 kWH for the same crop above. This means the farmer is paying twice the dollar amount to irrigate by sprinkler.
Extending these dollar amounts over 1000’s of acres of crops, one begins to realize the cost pressures farmers are under today.
Example Crop: Pistachios, ETo 44 , 100 acres
Total water needed: 367 acre feet
Water allotment from irrigation district: $4.00 an acre foot
Flood Irrigation Cost: $0.0 zero
Greenhouse Gas Production From Flood Irrigation: $0.0 zero
Total water operating cost: $1,468.00
Water pumped from 100 feet: 37,400kWH @ 0.14 kWh = $5,236.00
Irrigation sprinklers Cost: 41,290 kWh @ 0.14 = $5,780.60
Greenhouse gas emissions for producing electricity needed: 57,900 lbs.
As Californians, we are stuck in a difficult place. We are saving water by using irrigation techniques; but, we are increasing energy consumption and greenhouse gases.
Here are some new innovations being written about and how they help our farmers, thereby helping us as consumers of farm products:
Drip tape irrigation:
Saves water consumption by applying water near the plants roots while avoiding non-planted areas
Small surface wet spot equals a small area subject to surface evaporation
Low pressure needed to operate… 30 PSI on average
Disadvantage: Low useful life (Much of the drip tape ends up in landfills after 1 or 2 seasons of use.)
Saves water, since the droplets are smaller and finer mist can be absorbed into the soil
Lower pressure needed to operate… 30 PSI on average
Longer useful life… estimated at 7 to 10 years
Disadvantage: Irrigated water is distributed across the whole field; thus, a greater amount is subject to evaporation.
Saves water by applying below ground to avoid water lost to evaporation, while creating a suspended virtual water table at the desire root depth
No pressure needed; gravity fed (This is like fallow irrigation, but below ground away from evaporation effects.)
Long useful life… estimated at 85 years plus
Made 100% with recycle plastic bags or other material marked #4 recycle
Disadvantage: Permanent irrigation solution placed in the ground for long-term use (85+ years)
Special note: Both drip tape and micro spray have some additional energy lost due to pre-filtering. We did not take that into account.
This is part of a series on farming aimed at informing urban dwellers on the challenges farmers face with water, energy, yield and other variables when producing crops.