Calculating dairy manure nutrient application rates

EM 8768 • No vember 2000 $1.50 Calculating Dairy Manure Nutrient Application Rates T. Do wning Whether yo ur go al is to manage manure applic atio n to balanc e fo r nitro gen o r fo r pho spho rus, kno wing ho w muc h nutrient yo u are applying is a c ruc ial step to ward ideal manure management. Determining the relatio nship between vo lume o f waste and the amo unt o f nutrients applied is essential. This public atio n desc ribes ho w to c alibrate waste-handling equipment and to c alc ulate nutrient applic atio n rates. It c o vers typic al equipment fo und o n Figu re 1. Plac e several straight-sided, flat-bo tto m buc kets in the area dairies and uses nitro gen in where the gun is to apply liquid. the examples. The same tec hniques c an be used with pho spho rus. Generally, it is desirable to apply no mo re than 100 po unds N per ac re at a time. See the public atio ns listed under “Fo r mo re To c alc ulate nutrient applic atio n rates, info rmatio n” o n page 6 to learn ho w to yo u need to kno w three things: determine appro priate nutrient applic atio n • The c o nc entratio n o f nitro gen in the rates fo r yo ur situatio n. manure—Fo r example, if yo u apply 100 po unds o r 100 gallo ns o f manure, yo u must kno w ho w muc h nitro gen is in eac h po und o r gallo n. Having a sample analyzed by a lab is the best way to determine nutrient c o nc entratio n, but using bo o k values usually puts yo u in the ballpark. Doing the calculations • Ho w muc h manure (po unds o r gallo ns) yo u have applied • The area (square feet o r ac res) that rec eived the applic atio n Tro y Do wning, Exte nsio n age nt ( dairy) , Tillamo o k Co unty, Ore go n State Unive rsity. Calculating rates with a stationary gun yo u applied 1⁄2 inc h o ver the 25,434 square feet. 1. Mea s u re the a m ou nt of m a nu re a p p lied . Plac e several straight-sided, flat-bo tto m buc kets in the area where the gun is to apply liquid (Figure 1). Run the gun fo r a predetermined amo unt o f time (fo r example, 30 minutes) and then turn o ff the pump. Po ur the c o ntents o f all the buc kets into o ne buc ket and measure the depth o f the liquid. Divide the depth by the number o f buc kets. The result is the inc hes o f liquid manure applied in 30 minutes. Let’s say yo u applied 1⁄2 inc h in 30 minutes. 2. Mea s u re the a rea covered . To c alc ulate the area o f a c irc le, multiply the radius squared by 3.14. (The radius is half the diameter.) Fo r example, if yo ur big gun c o vers a c irc le 180 feet ac ro ss, the radius is 90 feet. Multiply 90 ft x 90 ft x 3.14 to get the to tal area in square feet (25,434 square feet). There are 43,560 square feet in an ac re, so 25,434 square feet is appro ximately 0.58 ac res: 25,434 ft2 = 0.58 acre 43,560 ft2 per acre 3. Conver t the inches a p p lied to ga llons . If yo u had an average o f 1⁄2 inc h o f liquid manure in yo ur buc kets, yo u c an assume a. First, c o nvert the square feet to c ubic feet by dividing 25,434 by 24 ( 1⁄2 inc h in the buc ket is 1⁄24 o f a fo o t). This is equivalent to 1,059 c ubic feet o f liquid manure. 25,434 ft2 = 1,059 ft3 24 b. Now, c o nvert the c ubic feet to gallo ns. There are 7.5 gallo ns per c ubic fo o t, so multiply 1,059 c ubic feet by 7.5. The result is 7,948 gallo ns pumped in 30 minutes. 4. Deter m ine the p u m p ing ra te. Divide 7,948 gallo ns by 30 minutes. Yo ur pumping rate is 265 gallo ns per minute. 5. Ca lcu la te the tota l a m ou nt of nitrogen a p p lied . If the nitro gen c o nc entratio n o f the manure is 10 po unds per 1,000 gallo ns, and yo u applied 7,948 gallo ns, then yo u applied 79 po unds o f nitro gen. 7,948 gal x 10 lb N = 79 lb N 1,000 gal 6. Ca lcu la te the a m ou nt of nitrogen a p p lied p er a cre. Sinc e yo u c o vered 0.58 ac res, yo u applied the equivalent o f 137 po unds o f nitro gen per ac re. 79 lb N = 137 lb per acre 0.58 acres Calculating rates with a traveling gun Calibrating a traveler invo lves the same princ iples desc ribed fo r the statio nary gun, but yo u adjust fo r the speed o f the traveler (Figure 2). Yo u need to kno w the width o f applic atio n, the number o f feet o f ho se pulled o ut (the distanc e c o vered by a single pass), and the speed at whic h the gun is mo ving. Let’s say, fo r example, that yo ur applic atio n is 240 feet wide, eac h pass is 1,000 feet, and the traveler mo ves at 6 feet per minute. Figu re 2. Calibrating a traveler invo lves the same princ iples desc ribed fo r the statio nary gun, but yo u adjust fo r the speed o f the traveler. 2 1. Ca lcu la te the a rea covered . Multiply 4. Ca lcu la te the tota l a m ou nt of nitrogen a p p lied . If the manure c o ntains 8 po unds the 240-fo o t width by the 1,000-fo o t pass to determine that yo u c o vered 240,000 square feet. This represents 5.5 ac res. o f nitro gen (N) per 1,000 gallo ns, and yo u applied 50,002 gallo ns, then yo u applied 400 po unds N. 50,002 gal x 8 lb N 240,000 ft2 = 5.5 acres 43,560 ft2 per acre = 400 lb N 1,000 gal 2. Mea s u re the a m ou nt of liq u id a p p lied . 5. Ca lcu la te the a m ou nt of N a p p lied p er a cre. Fo ur hundred po unds o f N applied During the applic atio n, plac e several buc kets thro ugho ut the pass area. Co mbine the liquid waste c o llec ted in all the buc kets into o ne buc ket and measure the depth o f the liquid. Divide this amo unt by the number o f buc kets to determine ho w many inc hes yo u applied. Fo r example, let’s say yo ur applic atio n averaged 1⁄3 inc h. o ver 5.5 ac res equals aro und 73 po unds per ac re. 400 lb N = 73 lb N per acre 5.5 acres 6. Ca lcu la te a p p lica tion ra tes a t va riou s s p eed s . Fro m these c alc ulatio ns, yo u c an generate a table that easily demo nstrates the amo unt o f nitro gen applied at vario us speeds (see Table 1 fo r an example). In the example abo ve, the speed was 6 feet per minute. At 3 feet per minute, the applic atio n rate wo uld be twic e that at 6 feet, o r 146 po unds N per ac re. 3. Conver t the inches a p p lied to ga llons . a. First, c o nvert the square inc hes to c ubic feet by dividing 240,000 by 36 ( 1⁄3 inc h in the buc ket is 1⁄36 o f a fo o t). This is equivalent to 6,667 c ubic feet o f manure. 7. Es tim a te the p u m p ra te p er m inu te. At 240,000 ft2 = 6,667 ft3 36 6 feet per minute, it takes 166 minutes to c o mplete a 1,000-fo o t pass. b. Now, c o nvert the c ubic feet to gallo ns. 1,000 ft = 166 minutes 6 ft per minute There are 7.5 gallo ns in a c ubic fo o t, so multiply 6,667 c ubic feet by 7.5. The result is 50,002 gallo ns. Divide the to tal gallo ns pumped by the to tal minutes pumped. Fo r this example, 50,002 gallo ns divided by 166 minutes equals 301 gallo ns per minute. Table 1. — Example calibration chart. Traveler speed (feet/ minute) Inches applied N applied per acre (lb) (if 8 lb N/ 1,000 gal) Total N applied (lb) 500 ft hose pulled 1,000 ft hose pulled 1,500 ft hose pulled 2.0 1 219 600 1,200 1,800 4.0 0.5 inc hes 109 300 600 900 6.0 0.33 inches 73 200 400 600 8.0 0.25 inc hes 55 150 300 450 10.0 0.20 inc hes 44 120 240 360 3 Fill in your own farm’s numbers here. Traveler speed (feet/ minute) Inches applied N applied per acre (lb) (if 8 lb N/ 1,000 gal) Total N applied (lb) 500 ft hose pulled 1,000 ft hose pulled 1,500 ft hose pulled 2.0 4.0 6.0 8.0 10.0 Calculating rates with a liquid wagon The fo llo wing are two ways to c alibrate liquid wago ns to determine nutrient applic atio n rates. The most common method Determine the to tal vo lume o f liquid applied to a field, and then c alc ulate the nutrients applied. Fo r example: 1. Mea s u re the a m ou nt of liq u id a p p lied . If yo u hauled 30 lo ads o f liquid with a wago n that ho lds 3,000 gallo ns, yo u hauled 90,000 gallo ns o f liquid. 30 loads x 3,000 gal = 90,000 gal It is impo rtant to realize that altho ugh mo st liquid wago ns are rated fo r a spec ific vo lume, the ac tual wo rking vo lume is less. Fo r example, a 3,000-gallo n wago n might deliver o nly 2,700 gallo ns to the field. 2. Ca lcu la te the p er -a cre m a nu re a p p lica tion ra te. If the manure is applied to a 10-ac re field, this is equivalent to 9,000 gallo ns per ac re. 90,000 gal = 9,000 gal per acre 10 acres 3. Ca lcu la te the p er -a cre N a p p lica tion ra te. If the manure has a nitro gen c o nc entratio n o f 10 po unds N per 1,000 gallo ns, yo u applied 90 po unds o f N per ac re. 9,000 gal x 10 lb N = 90 lb N 1,000 gal A second method This metho d measures the vo lume o f liquid applied to a small area and uses that quantity to c alc ulate the vo lume applied o ver the entire field. It assumes that the applic atio n rate is c o nstant. Fo r example: 1. Mea s u re the a m ou nt of liq u id a p p lied . Figu re 3. Plac e several trays, pans, o r sho rt buc kets in the field to c atc h liquid applied with o ne pass. 4 Plac e several trays, pans, o r sho rt buc kets in the field to c atc h liquid applied with o ne pass (Figure 3). Po ur the c o ntents o f all the pans into o ne pan and measure the depth o f the liquid. Divide this number by the number o f pans. The result is the inc hes o f liquid manure applied. Let’s assume yo u applied 1⁄2 inc h. 2. Conver t the inches a p p lied to ga llons a p p lied p er a cre. a. First, c o nvert the inc hes to c ubic feet per ac re by dividing 43,560 (the number o f square feet in an ac re) by 24 ( 1⁄2 inc h in the buc ket is 1⁄24 o f a fo o t). This is equivalent to 1,815 c ubic feet o f liquid manure per ac re. 43,560 ft2 = 1,815 ft3 per acre 24 b. Now, c o nvert the c ubic feet per ac re to gallo ns per ac re. There are 7.5 gallo ns per c ubic fo o t, so multiply 1,815 c ubic feet by 7.5. The result is 13,612 gallo ns per ac re. 3. Ca lcu la te the nitrogen a p p lica tion ra te. If the c o nc entratio n o f nitro gen is 10 po unds per 1,000 gallo ns, the rate o f N applied is 136 po unds per ac re. 13,612 gal/ a x 10 lb N = 136 lb N/ a 1,000 gal Figu re 4. Plac e a tarp o r piec e o f plastic in the field and apply so lids o ver the area. 3. Ca lcu la te the a m ou nt of N a p p lied to the field . Rec o rd the number o f lo ads hauled o n eac h field. Multiply the number o f lo ads by the amo unt o f N per lo ad. Fo r example, if yo u hauled 25 lo ads o f so lids, multiply 25 lo ads by 40 po unds N per lo ad, fo r a to tal applic atio n o f 1,000 po unds N. 4. Ca lcu la te the nu m b er of p ou nd s of N a p p lied p er a cre. Divide the to tal amo unt o f N applied by the number o f ac res, in this example 10 ac res. Calculating rates with a solids spreader The fo llo wing are two ways to c alibrate so lids spreaders. 1,000 lb total N = 100 lb N per acre 10 acres The most common method A second method Calc ulate the nutrient (e.g., nitro gen) c o ntent o f eac h spreader lo ad and multiply that number by lo ads per ac re o r per field. This metho d measures the po unds o f so lids applied to a small area and uses that quantity to c alc ulate the vo lume applied o ver the entire field. It assumes that the applic atio n rate is c o nstant. Fo r example: 1. Ca lcu la te the ca p a city (in cu b ic feet) of you r s p rea d er. If yo ur spreader is 16 feet lo ng, 5 feet wide, and 5 feet deep, it ho lds 400 c ubic feet per lo ad. 3 16 ft x 5 ft x 5 ft = 400 ft 2. Ca lcu la te the nitrogen a p p lica tion ra te. If yo ur so lid manure has a c o nc entratio n o f 10 po unds N per 100 c ubic feet, yo u are applying 40 po unds o f N per lo ad o f so lids. 1. Mea s u re the a m ou nt of s olid s a p p lied . Plac e a tarp o r piec e o f plastic in the field and apply so lids o ver the area (Figure 4). A 10' x 10' tarp measures 100 square feet, whic h represents 1⁄435 o f an ac re. 100 ft2 = 1/ 435 acre 43,560 ft2 per acre 400 ft3 x 10 lb N = 40 lb N 100 ft3 5 After spreading ac ro ss the sample area, fo ld the tarp and weigh the so lids c o llec ted o n it. Let’s assume the so lids o n the tarp weigh 110 po unds. 2. Conver t the p ou nd s to w et tons p er a cre. a. First, c o nvert the po unds c o llec ted to po unds per ac re by multiplying 110 by 435. This is equivalent to 47,850 lb per ac re. 110 lb x 435 = 47,850 lb per acre b. Now, c o nvert the po unds per ac re to wet to ns per ac re by dividing 47,850 by 2,000 (the number o f po unds per to n). The result is 23.9 wet to ns per ac re. 47,850 lb/ acre 2,000 = 23.9 wet tons/ acre 3. Ca lcu la te the nitrogen a p p lica tion ra te. If the c o nc entratio n o f nitro gen is 5 po unds per wet to n, the rate o f N applied is 119 po unds N per ac re. 23.9 wet tons/ acre x 5 lb N/ wet ton = 119 lb N/ acre Manure sampling and testing Testing manure fo r nutrient c o ntent is relatively easy. Ho wever, it c an be a majo r pro blem to get o ne sample that represents the nutrient c o nc entratio n o f the manure. Nutrient c o ntent c an vary c o nsiderably within a lo ad, and agitatio n usually is inadequate to ac hieve tho ro ugh mixing. Analyzing the samples taken during the c alibratio n pro c ess is the mo st desirable metho d, espec ially when testing fo r nitro gen, bec ause these values sho uld represent what ac tually reac hes the so il. This metho d ac c o unts fo r nutrient lo sses that o c c ur during sto rage and applic atio n. Take samples fro m a liquid tank o r lago o n o nly after agitatio n. Bo o k values are a reaso nable appro ac h if testing is no t feasible, but ac tual values 6 vary fro m o peratio n to o peratio n depending o n water added, feed c o mpo sitio n (bo th quality and quantity), age and stage o f lac tatio n o f the c attle, and the manure sto rage system. For more information Hart, J., A List o f Analytical Labo rato rie s Se rving Ore go n, EM 8677 (Orego n State University, Co rvallis, revised 2000). No c harge. Hart, J., M. Gangwer, M. Graham, and E. Marx, Dairy Manure as a Fe rtiliz e r So urce , EM 8586 (Orego n State University, Co rvallis, published 1995, reprinted 1997). 75¢ Hart, J., E.S. Marx, and M. Gangwer, Manure Applicatio n Rate s fo r Fo rage Pro ductio n, EM 8585 (Orego n State University, Co rvallis, published 1996, reprinted 1997). $1.50 To o rder c o pies o f the abo ve public atio ns, send the c o mplete title and series number, alo ng with a c hec k o r mo ney o rder fo r the amo unt listed, to : Public atio n Orders Extensio n & Statio n Co mmunic atio ns Orego n State University 422 Kerr Administratio n Co rvallis, OR 97331-2119 Fax: 541-737-0817 If yo u wo uld like additio nal c o pies o f this public atio n, Calculating Dairy Manure Nutrie nt Applicatio n Rate s, (EM 8768), send $1.50 per c o py to the abo ve address. Yo u may o rder up to six no -c harge public atio ns witho ut c harge. If yo u request seven o r mo re no -c harge public atio ns, inc lude 25 c ents fo r eac h public atio n beyo nd six. We o ffer disc o unts o n o rders o f 100 o r mo re c o pies o f a single title. Please c all 541-737-2513 fo r pric e quo tes. Wo rld Wid e Web Yo u c an ac c ess o ur Public atio ns and Video s c atalo g and many o f o ur public atio ns thro ugh o ur Web page at eesc.orst.edu © 2000 Orego n State University This public atio n was pro duc ed and distributed in furtheranc e o f the Ac ts o f Co ngress o f May 8 and June 30, 1914. Extensio n wo rk is a c o o perative pro gram o f Orego n State University, the U.S. Department o f Agric ulture, and Orego n c o unties. Orego n State University Extensio n Servic e o ffers educ atio nal pro grams, ac tivities, and materials— witho ut discriminatio n base d o n race , co lo r, re ligio n, se x, se xual o rie ntatio n, natio nal o rigin, age , marital status, disability, o r disable d ve te ran o r Vie tnam-e ra ve te ran status. Orego n State University Extensio n Servic e is an Equal Oppo rtunity Emplo yer. Published No vember 2000.