Water Use Efficiency and Water Productivity PDF

Exercise 15. Water use efficiency and water productivity Water use Efficiency indicates how efficiently the water is utilized by the crop. There are two types of water use efficiencies described in the literature. Crop Water Use Efficiency: It is the ratio of economic yield of crop to amount of wat...

Exercise 15. Water use efficiency and water productivity Water use Efficiency indicates how efficiently the water is utilized by the crop. There are two types of water use efficiencies described in the literature. Crop Water Use Efficiency: It is the ratio of economic yield of crop to amount of water used in evapotranspiration and metabolic activities. It is also called as consumptive WUE. WUEcu= Y/ (ET + Q) WUEcu is Crop Water Use Efficiency (kg/ha-mm) Y is crop economic yield (kg/ha) ET is evaporation (mm) Q is the water used for metabolic purpose. Field Water Use Efficiency: It is the ratio of economic yield of crop to amount of water used in the field. It is calculated as WUEfu = Y/ WR WUEfu = Field water use efficiency (kg/ha-mm) Y = Crop economic yield (kg/ha) WR = Water requirement which includes evapotranspiration needs (ET), water used for metabolic purpose (Q), and deep percolation losses (D) Irrigation Efficiency: indicates how efficiently the irrigation water is used in crop production. Some important irrigation water efficiencies are: (a) Water Conveyance Efficiency Water delivered at the the field Ec (%) = ∗ 100 Water delivered by the source (b) Water Application Efficiency 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑜𝑓 𝑐𝑟𝑜𝑝 𝑖𝑛 𝑠𝑜𝑖𝑙 Ea (%) = ∗ 100 𝑊𝑎𝑡𝑒𝑟 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑖𝑒𝑙𝑑 𝐷𝑒𝑝𝑡ℎ 𝑜𝑓 𝑠𝑡𝑜𝑟𝑒𝑑 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 Ea (%)= ∗ 100 𝐷𝑒𝑝𝑡ℎ 𝑜𝑓 𝑖𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 𝑎𝑝𝑝𝑙𝑖𝑒𝑑 (c) Water storage Efficiency 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑎𝑓𝑡𝑒𝑟 𝑖𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 Es (%) = ∗ 100 𝑊𝑎𝑡𝑒𝑟 𝑛𝑒𝑒𝑑𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑝𝑟𝑖𝑜𝑟 𝑡𝑜 𝑖𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 (d) Water distribution efficiency 𝑦 Ed (%) = 1 − ∗ 100 𝑑 d = average depth of water stored in the field during irrigation y= average numerical deviation from d Farm Irrigation Efficiency  𝑖𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 Farm IE (%) = ∗ 100 𝑤𝑎𝑡𝑒𝑟 𝑑𝑒𝑙𝑖𝑣𝑒𝑑 𝑎𝑡 𝑓𝑎𝑟𝑚 ℎ𝑒𝑎𝑑𝑔𝑎𝑡𝑒 Field Irrigation Efficiency 𝐼𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 Field IE (%)= ∗ 100 𝑤𝑎𝑡𝑒𝑟 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑎𝑡 𝑓𝑖𝑒𝑙𝑑 𝑖𝑛 𝑖𝑛𝑙𝑒𝑡 Economic Irrigation Efficiency 𝑇𝑜𝑡𝑎𝑙 𝑓𝑎𝑟𝑚 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑜𝑟 𝑝𝑟𝑜𝑓𝑖𝑡 = 𝑇𝑜𝑡𝑎𝑙 𝑓𝑎𝑟𝑚 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑓𝑖𝑡 𝑒𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑢𝑛𝑑𝑒𝑟 ∗ 100 𝑖𝑑𝑒𝑎𝑙𝑙𝑦 𝑜𝑝𝑒𝑟𝑎𝑡𝑒𝑑 𝑠𝑦𝑠𝑡𝑒𝑚 𝑢𝑛𝑑𝑒𝑟 𝑖𝑑𝑒𝑎𝑙 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛 Operation Efficiency 𝐴𝑐𝑡𝑢𝑎𝑙 𝑝𝑟𝑜𝑗𝑒𝑐𝑡 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 𝑜𝑓 𝑎𝑛 𝑖𝑑𝑒𝑎𝑙𝑖𝑛𝑔 𝑑𝑒𝑠𝑖𝑔𝑛𝑒𝑑 𝑎𝑛𝑑 𝑚𝑎𝑛𝑔𝑒𝑑 ∗ 100 𝑠𝑦𝑠𝑡𝑒𝑚 𝑢𝑛𝑑𝑒𝑟 𝑠𝑎𝑚𝑒 𝑟𝑒𝑠𝑜𝑢𝑟𝑐𝑒𝑠 𝑎𝑛𝑑 𝑚𝑒𝑡ℎ𝑜𝑑𝑠 Calculations: Example 1: Calculate crop water use efficiency from following data Wheat yield= 45 q/ha Water required for ET= 660 mm Water required for metabolic needs = 5 mm Solution: WUEcu = Y/ (ET + Q) 4500 = = 7.44 kg/ha-mm 600+5 Example 2: Water required for ET was 120 cm and for metabolic purposes was 10 mm to grow rice on one ha area. Deep percolation loss was 400 cm. Calculate field water use efficiency, if rice production was 50 q. Solution: WUEfu = Y/ WR 5000 = (120∗10) + 10 +(40∗10) = 3.106 kg/ha-mm Example 3: Calculate water conveyance, water application and water storage efficiencies from the following data: Area = 1.8 ha Time required for irrigating the area = 10 h Discharge rate of canal = 150 litres per second (lps) Water delivered at root zone = 100 lps Depth of root zone = 1.5 m Available WHC of soil = 20 cm/m Runoff from the field = 400 m3 Irrigation was started at 80% depletion of available soil moisture (DASM) Solution:  𝑤𝑎𝑡𝑒𝑟 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑎𝑡 𝑓𝑖𝑒𝑙𝑑 (a) Water Conveyance Efficiency = ∗ 100 𝑤𝑎𝑡𝑒𝑟 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒𝑑 𝑏𝑦 𝑐𝑎𝑛𝑎𝑙 100 = ∗ 100 = 66.67 % 150 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑜𝑓 𝑐𝑟𝑜𝑝 (b) Water application efficiency= ∗ 100 𝑤𝑎𝑡𝑒𝑟 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑓𝑖𝑒𝑙𝑑 Amount of water delivered to field = Rate of water delivered at field (lps) x time for irrigation = 100 * 36000 = 3600000 litres = 3600 m3 Since 400 m3 water is lost as runoff, amount of water stored in root zone = 3600 – 400 = 3200 m3 3200 Water application efficiency = ∗ 100 = 88.89% 3600 𝑤𝑎𝑡𝑒𝑟 𝑠𝑡𝑜𝑟𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑎𝑓𝑡𝑒𝑟 𝐼𝑟𝑟𝑖𝑔𝑎𝑡𝑖𝑜𝑛 (c) Water storage Efficiency = ∗ 100 𝑤𝑎𝑡𝑒𝑟 𝑛𝑒𝑒𝑑𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑟𝑜𝑜𝑡 𝑧𝑜𝑛𝑒 𝑝𝑟𝑖𝑜𝑟 Available WHC of soil= 20 cm/m Depth of root zone = 1.5 m So, WHC of root zone = 0.2 * 1.5 = 0.3 m = 30 cm Irrigation was started at 80% DASM 80 Net depth of irrigation = 30 ∗ = 24 𝑐𝑚 100 This 24 cm depth of water in 1.8 ha area is required to supply by irrigation. = Depth x area = 24 x 18 x 100 = 4320 m3 So, amount of water required prior to irrigation = 4320 m3 3200 Water storage efficiency = ∗ 100 = 74.07%. 4320 Example 4: After irrigation the depth of water penetration at the head of field was 1.8 m and at the tail end of field was 1.2 m. Calculate the water distribution efficiency. Solution: Depth of water penetration at the head = 1.8 m Depth of water penetration at tail end = 1.2 m 1.8+1.2 𝑑 = = 1.5𝑚 2 Numerical deviation from average depth of penetration At head = 1.8 - 1.5 = 0.3 m At tail end = 1.5 - 1.2 = 0.3 m Therefore, y = (0.3 + 0.3)/2 = 0.3  𝑦 Ed (%) = 1 − ∗ 100 𝑑 0.3 =1− ∗ 100 = 80 % 1.5 Example 5: Calculate the irrigation efficiency of irrigation system which has 80% conveyance efficiency and 70% water application efficiency. Solution: Water conveyance efficiency = 80% Water application efficiency = 70% 80 70 So Overall Irrigation efficiency = ∗ ∗ 100 100 100 = 56 % Difference between Water use efficiency (WUE) and water productivity (WP) These two terms are two different terms. However, they seem to cause some confusion only among agronomists. The fact is, both terms do exist and both have different definitions and applications. Unlike engineers, agronomists are likely to confuse the two and some consider the productivity is efficiency. Efficiency: Any efficiency in our daily life is referred to as a ratio or percent. For example, when considering energy, work performance and heat storage efficiencies, we say 90% or 70% efficiency which represents the percentage or ratio of output divided by input, both with the same units. In irrigation, for example, if one adds 10 mm of water to the plant and the plant used 8 mm through the root water uptake followed by transpiration and 2 mm is lost by drainage below the root zone, then the water use efficiency here is 80%. WUE is a dimensionless ratio of total amount of water used to the total amount of water applied Productivity: Productivity is a different term and refers to what we can produce from a unit of input, it is also a ratio of output to input but both do not need to have the same units, e.g., WP is 50 kg grains per 1 m3 of water. In its broadest sense, water productivity, WP is the net return for a unit of water used” These two terms are however, not clearly explained in books and journals which are still following literature perhaps dating back to the 1960’s. Wherever, WUE is used with the meaning of WP, i.e., “so many kg per cubic meter of water”, this is water productivity (WP), not water use efficiency (WUE). There is a strong linkage between WUE and WP. Increase of WP follows the increase of WUE and other efficiencies such as weed control, fertilization, and pest and disease control. Any measures that improve WUE, raise crop yields on irrigated land also raise the productivity of irrigation water. (i) Water use efficiency (WUE) also called as Crop WUE is calculated based on the actual crop evapo-transpiration ( ETa), and the amount of water supplied by irrigation (I) and precipitation (P) WUE (%) = {ETa (m3 ha-1) / I + P (m3 ha-1)} x 100 (ii) Bio-physical water productivity (BPWP) also called as Real Water Productivity and Crop Water Productivity, is estimated by dividing the grain yield with ETa  BPWP (kg m-3) = Grain yield (kg ha-1) / ETa (m3 ha-1) (iii) Irrigation water productivity (IWP), also called as Apparent Water Productivity is the ratio between grain yield produced by a crop and the irrigation water applied (I) during the entire growing season IWP = Grain yield (kg ha-1) / I (m3 ha-1) (iv) Total water productivity (TWP) is the ratio between grain yield produced by a crop and the amount of water supplied by irrigation (I) and precipitation (P) during the entire growing season. TWP = Grain yield (kg ha-1) / I + P (m3 ha-1) (iv) Economic water productivity (EWP) is the ratio between the profits (net returns) in whatever currency produced by a crop along the growing season and the amount of water involved in production i.e., irrigation (I) plus precipitation (P). EWP = Net returns ($ ha-1) / I + P (m3 ha-1) Example 6: Calculate WUE (%), RWP, AWP, TWP in kg/m3 and EWP in Rs./ m3, from the given data. (Rainfall: 197.5 mm). Treatment Irrigation water ET (mm) Grain yield Net returns applied (mm) (q/ha) (Rs/ha) N-mulch 195 382.2 50.09 1,10,980 Mulch @ 6 t/ha 195 394.4 53.05 1,15,290 Mulch @ 9 t/ha 130 396.8 54.00 1,20,120 Solution: Treatment WUE RWP AWP AWP EWP (%) (kg/m3) (kg/m3) (kg/m3) (Rs./m3) N-mulch Mulch @ 6 t/ha Mulch @ 9 t/ha