he more than 300,000 dairy cows in the Texas Panhandle generate a considerable amount of manure. This manure is a valuable fertilizer, but growing concerns with greenhouse gas (GHG) emissions has prompted research into methods for reducing GHG from land-applied manure. The objectives of this research were to 1) quantify nitrous oxide (N2O) emissions from surface-applied and incorporated dairy cattle manure, 2) determine how irrigation affects N2O emissions, and 3) determine the mechanism for N2O emissions. A laboratory study was conducted to compare N2O emissions from four treatments (TRT) consisting of commercial fertilizer (U, urea), surface-applied manure (MS), incorporated manure (MI), and soil alone (S, control). Soil and manure were placed into glass containers (4 reps per treatment) and monitored for a 14-day period, during which two simulated irrigation events were applied. Emissions were measured from each container once per hour using a multiplexer and real-time N2O analyzer. Nitrous oxide emissions were ranked (high to low): U, MI, MS, and S. While MI is often used as a best management practice to reduce ammonia emissions following land application, it produced higher N2O emissions than MS. Emissions of N2O increased immediately after simulated irrigation in all TRT. Based on initial and final soil nutrient concentrations, the N2O was most likely generated from the nitrification of ammonium to nitrate. Further research is warranted to quantify GHG emissions from land-applied dairy manure under field conditions.

Crop rotations, organic nutrient amendments, reduced tillage practices, and integration of cover crops are practices that have the potential to increase the sustainability of crop production, yet they also impact nitrous oxide (N2O) emissions. Agricultural soil management has been estimated to contribute 79% of the total N2O emissions in the U.S., and inorganic nitrogen (N) fertilization is one of the main contributors. Nitrous oxide is a potent greenhouse gas that has a global warming potential which is approximately 298 times that of carbon dioxide (CO2) over a 100-year period and is currently the dominant ozone-depleting substance. Few studies have assessed the effects of organic N amendments on direct N2O within the context of a typical dairy forage cropping system. Most research has been limited to studying the effects of one or two sources of N inputs on N2O emissions; however, dairy forage cropping systems often apply manure and have more than two N sources that likely both contribute to N2O emissions. This study investigated how different dairy cropping practices that include differences in crop residues, N inputs (dairy manure and inorganic fertilizer), timing of N amendment applications and environmental conditions influenced N2O emissions from no-till soil planted to corn (Zea mays L.). A two-year field study was carried out as part of the Pennsylvania State Sustainable Dairy Cropping Systems Experiment, where corn was planted following annual grain crops, perennial forages, and a green manure legume crop; all were amended with dairy manure. In the corn-soybean (Glycine max (L.) Merr.) rotation, N sources (dairy manure and inorganic fertilizer) and two methods of manure application (broadcasted and injected) were also compared.Chapter 1 reviews the scientific literature; describing the biotic and abiotic processes of N2O production in soils, summarizing current research on N2O emissions in agricultural systems, and emphasizing the main management and environmental drivers contributing to the emissions. This chapter reviews methods for matching N supply with crop demand, coupling N flow cycles, using advanced fertilizer techniques, and optimizing tillage management. Also, the applicability and limitations of current research to effectively reduce N2O emissions in a variety of regions are discussed.Chapter 2 analyzes the effect of corn production management practices and environmental conditions contributing to N2O in the Pennsylvania State Sustainable Dairy Cropping Systems Experiment. Significantly higher N2O emissions were observed 15-42 days after manure injection and 1-4 days after mid-season UAN application. Manure injection had 2-3 times greater potential for N2O emissions compared to broadcast manure during this time period. Integration of legumes and grasses in the cropping system reduced inorganic fertilizer use compared to soybean with manure or UAN, however, direct N2O emissions were not reduced. The Random Forest method was used to identify and rank the predictor variables for N2O emissions. The most important variables driving N2O emissions were: time after manure application, time after previous crop termination, soil nitrate, and moisture. These field research results support earlier recommendations for reducing N losses including timing N inputs close to crop uptake, and avoiding N applications when there is a high chance of precipitation to reduce nitrate accumulation in the soil and potential N losses from denitrification.Chapter 3 reports the comparison of N2O fluxes predicted with the biogeochemical model DAYCENT compared to measured data from the two-year dairy cropping systems study. Daily N2O emissions simulated by DAYCENT had between 41% and 76% agreement with measured daily N2O emissions in 2015 and 2016. DAYCENT overestimated the residual inorganic N fertilizer impact on N2O emissions in the corn following soybean with inorganic fertilizer and broadcast manure. Comparisons between DAYCENT simulated and measured N2O fluxes indicate that DAYCENT did not represent well organic N amendments from crop residues of perennials and legume cover crops, or manure application in no-till dairy systems. DAYCENT was generally able to reproduce temporal patterns of soil temperature, but volumetric soil water contents (VSWC) predicted by DAYCENT were generally lower than measured values. After precipitation events, DAYCENT predicted that VSWC tended to rapidly decrease and drain to deeper layers. Both the simulated and measured soil inorganic N increased with N fertilizer addition; however, the model tended to underestimate soil inorganic N concentration in the 0-5 cm layer. Our results suggest that DAYCENT overestimated the residual N impact of inorganic fertilizer on N2O emissions and mineralization of organic residues and nitrification happened faster than DAYCENT predicted. Chapter 4 highlights the impact of manure injection and the importance of timing organic N amendments from manures and/or crop residue with crop N uptake to mitigate N2O emissions. More research is needed to better understand the tradeoffs of these strategies in no till dairy cropping systems to help farmers in their operational management decisions. Improving the parametrization of DAYCENT for dairy cropping systems in no-till systems with high surface legume crop residues from perennials and cover crops, will make the model a more useful tool for testing different mitigation scenarios for farmers and policy-designer decision making.

"Nitrogen inputs, crop N removal, and cumulative N2O emissions were measured from spring 2011 to fall 2012 in three dairy forage production systems receiving liquid and solid manure, as well as synthetic N fertilizer"--Page vii.

"Soil nitrous oxide (N2O) emission varies in magnitude and occurs sporadically during the spring freeze-thaw period in cold humid temperate regions. Fluctuations in soil N2O emissions are related to soil biophysical properties, which are influenced by agricultural practices like fall application of manure and fall-sown cover crops, as well as rainfall and other weather events. The objectives of this thesis were to (1) quantify N2O emissions in the spring period from agricultural soils that received manure and were planted with a cover crop in the previous fall, (2) estimate the influence of fall-applied manure and cover crops on the spring soil N2O emissions in changing climate, (3) determine the biophysical factors that control soil N¬2O emissions after a rain-induced thawing event, and (4) propose a monitoring method to estimate N2O emissions in agricultural soils. First, I quantified the soil N2O emissions with a two-year field experiment. Soil N2O emission in the spring freeze-thaw period (c.a. 30 d) was -2.35 to 13.57 g N ha-1 and not affected by dairy manure application (solid or liquid) or cover crops (ryegrass and ryegrass/hairy vetch), possibly due to the low manure N application rate and N loss over winter. Second, I evaluated soil N2O emissions in the spring freeze-thaw period under three climate scenarios (baseline, from 1981–2010; Representative Concentration Pathway 4.5 and 8.5 from 2071–2100) with the Decomposition-Denitrification model. The model predicted that more reactive N will be retained by cover crops under future climate scenarios, but the soil N2O emissions will not increase. However, applying solid manure without a cover crop led to more soil N2O emissions than other treatments tested under three climate scenarios (9.90 to 61.50 g N ha-1, P

Manure application to grassland and arable land is an important source of ammonia and nitrous oxide losses. For both gasses, national and international policies have been developed with the objective of reducing the emissions. Since the early 1990s, measurements have been carried out in The Netherlands to assess the gaseous losses from manure application, especially for ammonia. Measurements of nitrous oxide emissions are relatively scarce. This paper presents the results of these measurements with the objective of providing an updated quantification of the effect of techniques for application and incorporation of manure, and to assess influencing factors. The manure application techniques differ in their spreading or placement of the manure onto the grass or soil surface or into the soil. The following techniques are treated in this paper: surface spreading, narrow-band application, shallow injection with open slots on grassland, and surface spreading, surface incorporation, deep placement on arable land. Low emission techniques such as narrow band application, shallow injection, incorporation or injection on arable land show a significant reduction of ammonia emission compared to surface spreading. On grassland, average emission factors (% of total ammonium nitrogen) were 74% for surface spreading and 16% for shallow injection. On arable land, the emission factors were 69% for surface spreading and 2% for deep placement. However, the nitrous oxide emission factor from manure applied with low ammonia emissions techniques is higher than the emission factor for surface applied manures. In a whole farm context, the higher nitrous oxide emission with shallow injection is partly offset directly by reduced emissions from fertilizer savings and indirectly from lower ammonia losses.