Improving the efficiency of nitrogen use and reducing ammonia emissions from Pennsylvania dairies

Improving the efficiency of nitrogen use and reducing ammonia emissions from Pennsylvania dairies

Summary

Twelve cooperator dairies have been identified. The project team met with the producers and their consulting nutritionists and explained the objectives of the project. First sampling event occurred in Fall’09 on 12 dairy farms. Next sampling is scheduled for Spring’10. All participating dairies feed diets with crude protein concentration around or above 17% (DM basis), which is within the goals of the project. Ammonia emission data collected at the first sampling event indicate significant nitrogen losses from all types of manure handling systems. Methane emissions were significantly greater for dairies with gravity flow manure system. Background IOFC and farm nitrogen balance-related data are being collected during monthly farm visits.

Objectives/Performance Targets

Reduce whole-farm nitrogen inputs on 50 Pennsylvania dairies, representing 5,000 cows and 10,000 acres by approximately 150 tons/yr and reduce ammonia emissions from these dairies by 50 tons/yr while maintaining or improving profitability as measured through Income Over Feed Cost (IOFC).

Accomplishments/Milestones

During this reporting period, the team has been working through Milestone 1: Nine Pennsylvania dairies representing all management styles serve as demonstration sites by reducing N inputs by approximately 6,000 lbs/yr/dairy, increasing the efficiency of conversion of feed nitrogen into milk protein by 13%, and decreasing ammonia emissions by approximately 2,000 lbs/yr/dairy (a 20-25% reduction). Milestone 1 scheduled to be completed by Year 2 of the project.

The number of farms involved in this stage of the project has been increased from 8 to 12. All 12 farms agreed to participate in the project. The goals of the project, requirements, and benefits were explained in detail to the producers and their consulting nutritionists by the project team. During Year 1 of the project, the dairies have to maintain the high-CP feeding until all sampling and data collection is completed. Preliminary sampling of the total mixed rations (TMR) of the cooperator dairies indicated that they all feed diets with CP >17% (see tables in Document 1).

It was decided that ammonia emission measurements and all related sample and data collections will occur 4 times per year – 2 times each in fall and spring (a total of 4 sampling events/year). Two weeks prior to ammonia emissions measurements, TMR samples will be collected from each dairy to verify the CP level before the ammonia emission measurements take place. The first round of sampling was executed in Oct –Nov’09.

The 1st emission measurement took place in Oct-Nov’09, simultaneously with the TMR sampling event. In the barn, manured-surface ammonia emissions were determined using a non-steady state, internal air recirculating, flux chamber. Flux chamber internal gas concentrations were measured using a photoacoustic field gas monitor (INNOVA, model 1412; photograph showing P. Topper and K. Heyler collecting gas emission data). Data for manure emissions of ammonia, nitrous oxide, methane, and carbon dioxide were collected. The INNOVA analyzer allows simultaneous analyses of all 4 gases. Ambient air temperature and relative humidity at the farm were monitored during gas emission measurements via electronic dataloggers. Manure surface temperature was measured with hand-held infrared temperature instrument. Manure depth distance from storage top was also measured.

Eight farms, representing the most common manure handling systems in Pennsylvania (2 farms per each of 4 manure handling systems) were selected for measuring ammonia emissions using the flux chamber method. Each of these farms was measured twice during the 1st sampling event. The 8 farms include the following manure systems: tie stall/gravity flow, tie stall/gutter scraped, freestall scraped, and freestall flush.

Data for the 1st ammonia measurement event are shown in Table 1. Farm names have been coded for confidentiality reasons. Generally, ammonia emissions were significant in all farms and tended to be higher in tie-stall farms with gravity flow or gutter scraped manure systems. Nitrous oxide emissions were negligible in all farms. There was a significant variation in methane emissions depending on the manure system. Farms with gravity flow systems (predominant in Amish farms) tended to have significantly greater methane emission than all other farms. The high methane emissions with the gravity flow farms were a reflection of the longer period manure was stored in the barn, which allows for more vigorous manure fermentation and methane production. These farms also had the thickest manure during the measurement event.

Ammonia, nitrous oxide, methane, and carbon dioxide emitting potential of manure was also measured in a steady-state gas emission system in laboratory conditions. Briefly, this system consists of 3.8-L capacity glass jars (incubation chambers) placed in a controlled temperature water bath, sweep air flow regulators, a multiplexer relay board, and a gas analyzer. Emission measurements were conducted at 20°C with 2 L/min sweep air flow. Manure from all participating farms was analyzed using this system. Feces and urine collected from randomly selected cows were mixed 1.7:1 (252 g feces and 148 g urine per jar) and incubated at 20 degrees C for 24 h. Manure slurry pH was measured just after the urine and feces were mixed, but before being added to the sample containers. At the completion of the 24 h emission monitoring, manure slurry pH was measured again. Ammonia, methane, and carbon dioxide concentrations in the gas leaving the chambers were measured with the INNOVA gas analyzer. Gas measurements were taken every 30 min.

Results from this analysis are shown in Table 2. The effect of manure system on gaseous emissions in laboratory conditions was less pronounced, which was expected. This technique is affected solely by composition of the manure as all other environmental factors are similar for all samples.

Other analyses: Total mixed ration samples were analyzed for chemical composition (Figure 2). Income-over-feed-cost is being monitored monthly (Figure 3). Milk composition is also monitored on a monthly basis. Data for milk urea N concentration (as an indicator of dietary protein level and utilization) are shown in Figure 4.

The chemical analyses of the TMR samples showed no significant variation between cooperator dairies. Dry matter averaged 47.4% (range from 46 to 52%), CP averaged 17.9% (16.8 to 18.9% of DM), neutral-detergent fiber (NDF) averaged 30.7% (28.2 to 34.9% of DM), and total digestible nutrients (TDN) averaged 71% of DM. These values are within the range common for commercial dairy operations in Pennsylvania. The high CP levels are in line with the objectives of the project.

Income-over-feed-cost was very variable during the reporting period, mostly reflecting variable milk price. Information shown in Figure 3 is incomplete for some farms as data were being processed during the preparation of this report. Income-over-feed-cost information will be collected on a monthly basis during the entire duration of the project.

Unlike the diet composition data, specifically dietary CP concentration, MUN was quite variable between farms (Figure 4). Except one farm (at one sampling event), MUN varied around 16 to 17 mg/dl, averaging 16 mg/dl. The reason for the exceptionally low MUN for this particular farm is unknown. Milk urea nitrogen will be monitored throughout the project and will be used as an indicator for efficiency of CP utilization following conversion of the farms to low-CP feeding in Year 2.

• Figures and Tables.pdf

Impacts and Contributions/Outcomes

The project began in Sept’09. It is in its 1st year. One out of the 3 sampling events planned for Year 1 has been completed. These samplings are to collect whole-farm nitrogen input and ammonia emission information that will be used as a background to reduce nitrogen losses and ammonia emissions from the 12 demonstration farms. This will be used to implement low-protein feeding strategies in 50 Pennsylvania dairies and accomplish the performance target of the project, i.e. reduce nitrogen inputs by approximately 150 tons/yr and reduce ammonia emissions from 50 PA dairies by 50 tons/yr while maintaining or improving farm IOFC.

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