Calibrating Stationary Big Gun Sprinklers for Manure Applications

You can avoid the potential adverse effect on ground and surface water caused by overfertilization by applying only the amount of waste and wastewater necessary to maintain soil fertility for crop production.

The calibration of liquid manure spreading equipment is important because it lets you know the amount of waste and wastewater you are applying to an area.

The calibration rate and the nutrient concentration level of the liquid manure lets you know the amount of plant nutrients you are applying. Then, you can adjust your fertilization rate to avoid overfertilization.

The wastewater application rate from a stationary big gun sprinkler depends on the flow rate, coverage diameter, the amount of time it operates at a location and the sprinkler location pattern. To attain acceptable application uniformity with multiple sprinkler setups, the sprinkler spacing should be 70 to 85 percent of the sprinkler’s coverage diameter (see Figure 1).

The necessary steps to calibrate stationary big gun sprinklers are given in the example below.

1) Determine flow rate in gallons per minute (G P M) from available manufacturer’s literature or Table 1.

Example: From Table 1: 0.75" nozzle at 90 P S I has a flow rate of 155 G P M

Your Numbers: " nozzle at ____ P S I has a flow rate of ____ G P M

2) Determine the coverage diameter (D I A) in feet from available manufacturer’s literature or Table 1.

Example: From Table 1: 0.75" nozzle at 90 P S I has a 306 foot coverage diameter (D I A)

Your Numbers: " nozzle at ____ P S I has a foot coverage diameter (D I A)

3) Calculate the needed sprinkler spacing (S S) as 70 to 85 percent of the coverage diameter (D I A) from Step 2. Refer to Figure 1 for a diagram of a stationary gun setup.

Example: 306 feet x 77percent ÷ 100 = 236 feet sprinkler spacing (S S); use 230 to 240 feet

Your Numbers: feet x percent ÷ 100 = feett sprinkler spacing (S S); use _________ ft

4) To calculate the average application rate (inches per hour), multiply 96 by the G P M from Step 1 then divide by the Step 3 sprinkler spacing (S S) twice.

Example:96 x 155 G P M ÷ 236 feet S S ÷ 236 feet S S = 0.27 inches per hour

Your Numbers:96 x G P M ÷ S S ÷ S S = inches per hour

5) To determine the inches of wastewater to apply for a given N rate, divide the desired number of pounds of N per acre by the number of pounds of N in a 1000 gallons of wastewater¹. Then divide the result by 27 to get the inches of wastewater.

Example: 150 pounds N per acre ÷     5  pounds N per 1000 gallons ÷ 27 =    1.1 inches

Your Numbers:             pounds N per acre ÷ ____ pounds N per 1000 gallons ÷ 27 =        inches

6) To determine the number of hours to operate the sprinkler at each location divide the inches of wastewater from Step 5 by the application rate from Step 4.

Example:        1.1 inches ÷ 0.27 inches per hour =      4   hours

Your Numbers:    ______ inches ÷        inches per hour = _____ hours

5) To determine the inches of wastewater that were applied multiply the application rate from Step 4 by the number of hours the sprinkler operated at a location.

Example:     0.27 inches per hour x     4   hours = 1.1   inches

Your Numbers:    ______ inches per hour x _____ hours = _____ inches

6) The N applied per acre (pounds N per acre) is calculated by multiplying the inches of wastewater applied from Step 5 by the pounds of N in a 1000 gallons of wastewater and then multiply this result by 27.

Example:           1.1 inches x 5 pounds N per 1000 gallons x 27 = 150 pounds N per acre

Your Numbers:          inches x        pounds N per 1000 gallons x 27 =        pounds N per acre

Table 1. General Flow Rates and Coverage Diameters for Big Gun Sprinklers. Nozzle size is in inches. Flow rate is gallons per minute (G P M). Operating pressure is in pounds per square inches (P S I). Coverage diameter (D I A) is in feet (f t)
P S I	Nozzle 0.5"		Nozzle 0.75"		Nozzle 1"		Nozzle 1.25"		Nozzle 1.5"		Nozzle 1.75"		Nozzle 2"
P S I	G P M	D I A	G P M	D I A	G P M	D I A	G P M	D I A	G P M	D I A	G P M	D I A	G P M	D I A
50	50	205	115	256	204	300	325	353	--	--	--	--	--	--
60	55	215	126	270	224	316	358	373	515	430	695	470	912	512
70	60	225	136	283	243	338	385	388	555	450	755	495	980	528
80	64	235	146	295	258	354	413	403	590	470	805	515	1047	548
90	68	245	155	306	274	362	440	418	625	485	855	535	1105	568
100	72	255	163	316	289	372	463	430	660	500	900	550	1167	592
110	76	265	171	324	304	380	485	440	695	515	945	565	1220	607
120	--	--	--	--	--	--	--	--	725	530	985	580	1277	622
130	--	--	--	--	--	--	--	--	755	540	1025	590	1333	640
Note: If your exact numbers are not in the table, then estimate your value based on the numbers yours.

Karl VanDevender - Extension Agricultural Engineer
Phil Tacker - Extension Agricultural Engineer
John Langston, Extension Agricultural Engineer

DR. KARL VANDEVENDER, PHIL TACKER and JOHN LANGSTON are Extension agricultural engineers, Cooperative Extension Service, University of Arkansas, Little Rock.

ANGELA RIECK, former assistant specialist - waste management, is co-author of this publication

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Calibrating Stationary Big Gun Sprinklers for Manure Applications