Example #1: A 100-acre walnut orchard irrigated with Nelson R10 mini-sprinklers. The orchard has been divided into three 33 +/- acre irrigation sets. The orchard is close to the Sacramento River so static groundwater level was 20 feet and pumping draw down was 30 feet. A 75-horsepower turbine pump delivered 1010 gpm. A PGE Time-of-Use rate plan was selected to provide electricity at $0.17 per kw-hr.
Irrigation scheduling without the pressure chamber: the first irrigation was usually applied the third week of April and subsequent irrigations were applied about every ten days through mid-May. From June– first half of September, irrigation was applied weekly. From the last half of September through October, irrigations were applied every two weeks. All told, there were 26 irrigation events from April through October. Each irrigation consisted of three irrigation sets for 24 hours, tototal 72 hours of pumping per irrigation. The total hours of annual pumping under these irrigation scheduling practices totaled 1872 hours. The 75-horsepower pump had an equivalent power demand of 56 kilowatts (1 hp equals 0.746 kilowatt), so the annual kilowatt-hours of electricity demand was 104,738 kilowatt-hours (kw-hr) and the annual cost of the electricity (not accounting for standby charges and other fees) was about $17,805 or $178 per acre.
Irrigation scheduling with the pressure chamber: after the pressure chamber was adopted as an irrigation scheduling tool, the first irrigation was not applied until the first week of June, subsequent irrigations were applied every ten days from June through the first half of September. From the last half of September to October, irrigations were applied about every 15 days. All told, there were 13 irrigations, each consisting of 72 hours of pumping for a total of 936 hours of annual pumping. The annual kilowatt-hours of electricity demand totaled 52,416 kw-hr and cost $8,910 or $89 per acre. This represented nearly a 50 percent reduction in electricity demand and a total savings of $8,895 or $89 per acre.
Example #2: 200 acres of walnuts are irrigated with Nelson R10 mini sprinklers. The orchard is divided into four 50-acre irrigation sets. The orchard is located on westside Sacramento Valley terrace soils further from river or tributary influences. Static water table was 170 feet and pumping drawdown was about 230 feet. The 200-horsepower turbine pump delivers 1516 gpm. A PGE Time-of-Use rate has been selected to provide electricity at $0.155 per kw-hr.
Irrigation scheduling without the pressure chamber: the first irrigation was applied by mid-April, and subsequent irrigations were applied about weekly through mid-May. From June through the first half of September irrigations were applied about every five or six days. From mid-September through October, irrigations were applied about every ten days. A total of 29 irrigations were applied from April through October. Each irrigation event consisted of four by 24-hour sets for a total of 96 hours of pumping. The annual hours of pumping totaled 2784 hours. The 200-horsepower pump had an equivalent power demand of 149.2 kilowatts (kw). The annual electricity demand for this orchard totaled 415,372 kilowatt-hours (kw-hr) and cost $64,382 or about $322 per acre.
Irrigation scheduling with the pressure chamber: after adopting the pressure chamber for irrigation scheduling, the start of irrigation was delayed until the first week of May and irrigations were scheduled about every ten days through the end of May. Irrigations were applied about weekly from June through mid-September. Then the irrigation interval was increased to about every 12 to 14 days from mid-September through October. A total of 23 irrigations were applied with each irrigation consisting of 96 hours of total pumping. Annual pumping hours totaled 2208 hours. Annual electricity demand totaled 329,433 kw-hrs and a total cost of $51,062 or $255 per acre. This translated to a total cost savings for electricity of $13,320 or about $67 per acre.