C a s e St u d y: Nitrogen Cycling on

The Professional Animal Scientist 25 (2009):99 03 2009 American Registry of Professional Animal Scientists C a s e St u d y: Nitrogen Cycling on Pasture-Based Dairy Farms T. W. Downing* and S. Angima *Department of Animal Sciences, Oregon State University, Tillamook 974; and Department of Crop and Soil Science, Oregon State University, Newport 97365 ABSTRACT Most animal waste management plans for pasture-based dairy farms use estimates for the amount of manure produced and the yields of forage removed to design the waste plan. A trial was conducted to demonstrate how dairy producers could document agronomic nutrient application and removal on pasture-based dairy farms. This challenge was fairly complex because grazing animals are constantly harvesting forage and depositing manure. This work was conducted on a 60-head Holstein grazing dairy over 2 yr. The operator received a customized animal waste management plan, calibration of manure-handling equipment, and a detailed farm map. Standing forage was estimated daily, before and after grazing, by using a rising-plate meter, and measurements were recorded. Soil samples were taken at a depth of 30 cm at the end of each growing season (October ) and tested for nitrates to determine N application residues. Estimated annual standing grass yields ranged from 8,736 to 2,056 kg DM/ha, with a mean of 6,92 kg. This DM was the equivalent of 225 to 659 kg N/ha removed. The dairy producer found this increased level of management rewarding because he had actual data to make decisions. Additionally, this increased management was more profitable. The second-year estimated grass yields increased 9.6% Corresponding author: troy.downing@ oregonstate.edu (3,82 kg/ha) in total DM produced over yr. This project successfully demonstrated a new model of tracking N applications and removal in pasture-based dairy farms. Key words: nitrogen cycling, pasture-based dairy farm, pasture growth INTRODUCTION Inorganic N is taken up from the soil and incorporated into organic compounds during plant growth (Groot et al., 2003). Dairy producers typically use manure as a fertilizer source and add inorganic fertilizer only when extra nutrients are needed. However, it can be challenging to predict N availability after fertilizing with organically bound N and to predict N availability. Nitrogen losses in manure storage, handling, application, and mineralization can be highly variable, up to 80% of the total N excreted (Van Horn et al., 2003). Traditionally, the nutrient excretion standards most often used in the design of manure management systems are those of the American Society of Agricultural Engineers (200). However, these standards are average excretion values for cows standardized by BW and traditionally were not adjusted for diet, stage of lactation, or production level (Nennich et al., 2005). Dairy farmers in the coastal areas of Oregon rely heavily on pastures for both grazing and silage production. Managers should ideally be matching the nutrients supplied in the form of manure to their forage crops for maximum productivity, without excess application of specific nutrients. Several studies have shown that the timing of manure application is important in the uptake of nutrients from the soil (Moore and Gamroth, 995; Downing and Leonnig, 2002). The more frequent applications increase nutrient removal and total crop yield. Perennial plants are more effective in removing nutrients when compared with annual crops with similar requirements (Hensler et al., 970; Knezak and Miller, 976). Moore and Gamroth (995) studied 8 different cool-season grasses in Willamette Valley, Oregon. In plots treated with 336 kg N/ha, more than 448 kg N/ha was removed in plant growth annually. When plots were treated with manure (at 504 kg N/ha), plant removal rates approximated 560 kg N/ha. Variety trials conducted on the Oregon coast demonstrated N uptake by grasses of up to 750 kg/ha annually (Downing and Leonnig, 2002). Most animal waste management plans written for pasture-based dairy farms use estimates for manure produced and yields removed to design the waste plan. Landowners theoretically have been required to apply manure N in quantities equal to what they remove annually in a crop. As concerns for water quality have increased, so has the need to demon-

00 Downing and Angima strate that the nutrients applied are equal to what is removed. The state of Oregon requires dairy operators to apply manure (total manure N) to pastures at a rate equal to the N removed annually in the crop (Oregon Department of Agriculture, 2008). This is challenging enough to manage for dairy producers that harvest crops, and those that graze milk cows have not had a good system to help them comply. Over the past 2 yr, a trial was conducted to develop a system to document agronomic nutrient application and removal on a pasture-based dairy. This project was designed to be a model for documenting manure applications and forage removal in pasture-based dairies. MATERIALS AND METHODS The research was conducted on a commercial grazing dairy that was located on 48 ha divided into 9 paddocks. The dairy averaged 60 Holstein milk cows and 32 kg of milk/ cow daily in production. Lactating animals were grazed approximately 7 mo throughout the growing season Figure. Example recordkeeping page illustrating the types of entries by month and running N balance per hectare for the field. Traveler input is liquid manure applications. 2 Solids manure entries for N applied as manure solids. 3 Commercial fertilizers applied as urea. 4 Estimated manure N applied based on cow hours in field. 5 Estimated forage N removed based on standing forage heights before and after grazing. and additionally were fed alfalfa hay (Medicago sativa), corn silage (Zea mays), and a complete lactatingcow grain. Some paddocks were divided with portable electric fencing throughout the growing season to facilitate uniform stocking intensities and grazing times. A traditional animal waste management plan was developed that estimated manure volumes generated and pasture nutrient needs. Additionally, a recordkeeping system was developed that allowed the landowner to make daily recordings and have running totals of the N balance for each field throughout the 2-yr project. The N tracking spreadsheet, designed in Microsoft Excel (Microsoft Inc., Redmond, WA), allowed the producer to enter manure volumes applied by field and record forage removed into the spreadsheet and to automatically calculate a running balance of N applied and removed for the year. During the grazing season, the quantity of forage removed was measured daily to track DM removed and consequently estimate N removal rates. Standing forage height was recorded by using a Farm Tracker electronic rising-plate meter (Farm Works, Feilding, New Zealand) before and after grazing each pasture. Each pasture was measured before and after grazing with a minimum of 40 individual rising-plate meter measurements. The rising-plate meter was calibrated twice each year by clipping, drying, and weighing known areas ( m 2 ) in the field to determine standing DM. Although estimations of standing forage can be extremely variable (Sanderson et al., 200), it was reported that in uniform pastures in the Northeast, the level of error in measuring forage mass with a risingplate meter was within 0% in one study (Rayburn and Rayburn, 998) and within 3% in another (Earle and McGowan, 979). Standing forage averaged 30 kg DM/ha per centimeter of forage height. Forage samples were cut monthly down to 0 cm, frozen, and sent to Dairy One Forage Laboratory (Ithaca, NY) for analysis of N content, and estimates of total

Nitrogen cycling on pasture-based dairy farms 0 Table. Nitrogen applied, estimated N balance, DM yield, and nitrates recorded after the growing season (October ) by field for yr Field N applied N balance, 2 kg/ha DM yield, 3 kg/ha Fall soil nitrates, 4 kg/ha 225 47 5,904 92 2 353 09 5,904 57 3 395 78 6,576 8 4 428 65 6,576 09 5 420 04 7,472 63 6 436 9 9,72 22 7 398 85 6,576 24 8 424 9 4,784 98 9 452 6 7,248 62 0 399 94 6,576 2 385 28 7,248 09 2 455 78 7,920 7 3 400 53 8,592 90 4 397 76 5,904 74 5 404 50 8,592 84 6 388 26 20,60 89 7 264 3 8,736 60 8 230 78 0,304 43 9 30 82 3,26 62 Average 377 95 6,20 97 Nitrogen applied is presented as kilograms of N per hectare by field. 2 Balance is the difference between N applied and estimated removal per field. 3 Dry matter yield was estimated by measuring grass height before and after grazing. 4 Soil nitrates taken at a 30-cm depth at the end of the growing season. N removed per hectare were recorded. All cuttings and grazing cycles were totaled for DM yields and N removed through grazing. Ryegrass (Lolium perenne) and white clover (Trifolium repens) pastures were grazed intensively for 0-h periods twice daily. Solid manure that accumulated in the barn facility was Figure 2. Percentage of annual N application by month and origin in yr (comm = commercial N applied as urea). applied with a New Holland manure spreader (New Holland, New Holland, PA) and the liquid manure that was generated in the barns and milking facility was applied with an Evergreen hard hose traveling irrigator (Evergreen Irrigation, Brooks, OR). Soil samples (30 cm deep) were taken from all 9 fields individually at the end of the growing season (October ). These data were used to evaluate the effectiveness of N removal. Manure application equipment was calibrated and nutrient application rates were recorded by field. Manure applied by grazing animals was estimated by using standard excretion values (American Society of Agricultural Engineers, 200) and adjusted for the number of hours daily that cows were in a particular paddock. RESULTS AND DISCUSSION The operator kept daily records and recorded them on the spreadsheet record system. Running totals of N applied and removed were estimated by field and were used to add some additional commercial fertilizer. Figure is an example of the individual data entry page that was used for recordkeeping for each field. Table illustrates the total N applied, estimated N balance, yield, and nitrate soil results for each field on the farm. Estimated forage DM mass ranged from 8,736 to 20,60 kg/ha per year in yr and averaged 6,20 ± 2,87 kg DM/ha. Soil nitrate values ranged from 43 to 63 kg/ha and averaged 97 ± 49.4 kg/ha. Soil nitrates in yr are considered high (Sullivan and Cogger, 2003). After lengthy discussions with the landowner, it was determined that commercial fertilizer applications could have been applied too late in the growing season for proper utilization. Figure 2 illustrates the percentage of N applied by month throughout the year from liquid, solid, or grazing cow manure, in addition to commercial N fertilization. Table 2 illustrates the total N applied, estimated N balance, yield, and fall nitrate soil results for each field on the farm in yr 2. Year 2 yields

02 Downing and Angima Table 2. Nitrogen applied, estimated N balance, DM yield, and nitrates recorded in the fall (October ) by field for yr 2 Field N applied N balance, 2 kg/ha DM yield, 3 kg/ha ranged from 6,576 to 2,056 kg DM/ ha and averaged 9,392 ±,296 kg/ ha. During the second year, the operator decided to apply commercial N 2 mo earlier, beginning in March, to maximize the growing potential, Fall soil nitrates, 4 kg/ ha 47 3 8,44 30 2 479 64 2,056 58 3 664 43 2,056 73 4 637 0 8,592 85 5 636 8 9,040 72 6 32 69 6,576 76 7 593 8 9,936 72 8 589 9 20,608 56 9 63 6 20,800 44 0 469 2 20,60 50 428 45 20,60 49 2 575 75 9,264 68 3 603 29 9,72 66 4 498 227 20,60 73 5 57 28 9,72 29 6 533 69 9,040 36 7 375 79 8,592 30 8 502 7 9,264 38 9 399 97 6,576 20 Averages 548 05 9,392 54 Nitrogen applied is presented as kilograms of N per hectare by field. 2 Balance is the difference between N applied and estimated removal per field. 3 Dry matter yield was estimated by measuring grass height before and after grazing. 4 Soil nitrates taken at 30-cm depth at the end of the growing season. which meant that he stopped applying commercial fertilizer 2 mo earlier as well. Soil nitrate levels were appreciably lower in yr 2, ranging from 20 to 85 kg of N/ha and averaging 54 ± 9.5 kg of N/ha. Figure 3 Figure 3. Percentage of annual N application by month and origin in yr 2 (comm = commercial N applied as urea). illustrates the percentage of N applied throughout the year from liquid, solid, or grazing cow manure, in addition to commercial N fertilization. The original animal waste management plan for this farm was designed to spread all manure evenly (approximately 309 kg of N/ha) across the farm. The yields were estimated to be 2,320 kg DM/ha, with no commercial fertilizer added. By using this agronomic system to apply manure and commercial fertilizer, this dairy farm produced an average of 9.6% more feed (3,82 kg/ha) than was estimated in yr. After 2 yr of experience, the farm was milking 25 more cows than it had historically and reduced purchased hay (by 75 tons or $6,875) costs during the second summer. Although research has indicated that measuring standing forage DM can be accomplished with a level of error within 0 to 3% with a risingplate meter (Earle and McGowan, 979; Rayburn and Rayburn, 998), other researchers have warned that measuring forage mass on pasture can be inaccurate and imprecise, with error levels from 26 to 33% (Sanderson et al., 200). However, this system of documenting manure N applications and N removal in grazing dairy farms, coupled with the use of fall nitrate soil sampling as a monitoring tool, is essential to provide a feedback mechanism on the N balance. IMPLICATIONS Documenting agronomic utilization of N application in grazing dairy farms is a challenge. However, it is impossible for producers to make good decisions without attempting to gather and record good information. Over the past 2 yr, this trial has shown that forage measurements can be used to improve agronomic nutrient applications on pasturebased dairy farms. This model for documenting manure applications and forage removal in pasture-based dairy farms has shown promise in improving manure application and distribution and in increasing pasture productivity, and has shown a trend toward

Nitrogen cycling on pasture-based dairy farms 03 reducing soil nitrates at the end of the growing season. This system provides grazing dairy producers in Oregon with the tools they need to meet the agronomic expectations of the regulatory system. We would also contend that a biological system with as many variables as this will only improve over time as the operator becomes more proficient at managing the process. LITERATURE CITED American Society of Agricultural Engineers. 200. Manure production and characteristics. ASAE Standard D384.. Am. Soc. Agric. Eng., St. Joseph, MI. Downing, T. W., and T. T. Leonnig. 2002. Nutrient cycling in cool season grasses. J. Dairy Sci. 85(Suppl. ):333. Earle, D. F., and A. A. McGowan. 979. Evaluating and calibrating of an automated rising plate meter for estimating dry matter yield of pasture. Aust. J. Exp. Agric. Anim. Husb. 9:337. Groot, J. C. J., W. A. H. Rossing, E. A. Lantinga, and H. Van Keulen. 2003. Exploring the potential for improved internal nutrient cycling in dairy farming systems, using an eco-mathematical model. J. Life Sci. 5:65. Hensler, R. F., R. J. Olsen, and O. J. Attoe. 970. Effect of soil ph and application rate of dairy cattle manure on yield and recovery of twelve plant nutrients by corn. Agron. J. 62:828. Knezak, B. D., and R. Miller. 976. Application of sludges and wastewaters on agriculture land. A planning and educational guide. Ohio Agric. Res. Dev. Center Res. Bull. No. 090., Ohio Agric. Res. Dev. Center, Columbus, OH. Moore, J. A., and M. J. Gamroth. 995. Nitrogen Uptake by Cool Season Grass Species. Center for Applied Agric. Res., Oregon Dept. of Agric., Eugene. Nennich, T. D., J. H. Harrison, L. M. Van Wieringen, D. Meyer, A. J. Heinrichs, W. P. Weiss, N. R. St-Pierre, R. L. Kincaid, D. L. Davidson, and E. Block. 2005. Prediction of manure and nutrient excretion from dairy cattle. J. Dairy Sci. 88:372. Oregon Department of Agriculture. 2008. Confined animal feeding operations. http:// www.oregon.gov/oda/nrd/cafo_front.shtml Accessed August 20, 2008. Rayburn, E. B., and S. B. Rayburn. 998. A standardized plate meter for estimating pasture mass in on-farm research trials. Agron. J. 90:238. Sanderson, C., A. Rotz, S. W. Fultz, and E. Rayburn. 200. Estimating forage mass with a commercial capacitance meter, rising plate meter and pasture ruler. Agron. J. 93:28. Sullivan, D. M., and C. G. Cogger. 2003. Post-harvest soil nitrate testing for manured cropping systems west of the Cascades. Oregon State Univ. Ext. Rep. No. EM 8832-E. Oregon State Univ., Corvallis, OR. Van Horn, H. H., G. L. Newton, G. Kidder, E. C. French, and R. A. Nordstedt. 2003. Managing dairy manure accountably: Worksheets for nutrient budgeting. IFAS Ext. Circ. 96. Univ. Florida, Gainesville.