The effect of cover crops on N and weed dynamics was assessed within a pea (Pisum sativum L.) – cover crop – sweet corn (Zea mays L.) rotation. Cover crops of oat (Avena sativa L.), perennial rye (rye) (Secale cereale L.), oilseed radish (OSR) (Raphanus sativus L. var. oleoferus Metzg Stokes), and OSR plus perennial rye (OSR+rye) increased plant available N (PAN) over the cover crop growing season compared to the no cover control at the Bothwell site only. However, at neither site did cover crops result in increased PAN for the sweet corn, indicating that these cover crops will not reduce required N fertilizer applications. Also, cover crops posed neither an increased or decreased need for weed management during sweet corn production. However, OSR may be useful in pesticide reduced programs due to its potential ability to reduce fall herbicide applications, provided it does not set viable seed.

The study of biogeochemical cycles and their role in ecosystem function has helped to highlight the impacts of human activities on natural processes. However, our understanding of the effects of nitrogen (N) deposition on forested ecosystems remains limited due to the variable controls on N cycling. Soils, microclimate, and vegetation can influence rates and processes of N cycling, singly or in concert at multiple scales. Understanding how these factors influence N cycling across the landscape will help to elucidate the impacts of N deposition. The objectives of this study were to characterize variation in soils, microclimate and vegetation characteristics, and N cycling and decomposition dynamics across the landscape in a region impacted by N deposition. Relationships among these factors were explored to determine the main factors influencing N cycling and decomposition. Strong differences in net N mineralization and nitrification were found between forest stands with contrasting species composition and moisture availability. Nitrate production and leaching were related to sugar maple abundance, and base cation leaching was correlated with nitrate concentrations in soil solutions. Decomposition experiments were installed to examine the effects of substrate quality, microclimate and N availability on decay rates. Nitrogen amendments for the most part did not affect decomposition rates of wood and cellulose, and mass loss rates were correlated with microclimate and forest floor characteristics. In contrast, microclimate did not seem to affect leaf litter decay rates, and the results suggest that the presence of invertebrates may influence mass loss to a greater degree than moisture or litter quality. This work highlights the large degree of variability in N processing across the landscape and suggests that differences in microclimate and species composition may help to predict the impacts of chronic N deposition on N cycling and retention.

The transfer of N from legume green manures (GMr) can satisfy the needs of a successive cash crop, but rotations that have over-wintering legumes also carry an increased risk of off-season (Sep.–June) N losses, especially during spring thaw. Spring-wheat yield among four GMr systems were evaluated with respect to off-season (GMr; Sep.–June) and in-season (wheat; June–Sep.) N2O emissions, as well as full-year NO3– leaching and dissolved N2O losses during spring-thaw from a tile-drained sandy loam soil in Atlantic Canada over 2 rotations (2011–2013). Four GMr systems (treatments) differed in the timing and season of GMr incorporation and the use of additional N as fertilizer or manure. The majority (66%) of cumulative N2O emissions were measured during the off-season because of high N2O emissions events during spring thaw. There was no clear effect of GMr system on these emissions, which may have been a result of the pattern and duration of soil freezing and thawing. Spring thaw also coincided with the highest dissolved N2O concentrations (100–300 µg N2O-N L–1) in tile-drained water, which represented potential N2O emissions of 21 to 116 g N2O-N ha–1. Belowground N2O concentrations and soil water content measurements during winter provided further evidence of the relationship of N2O dissolved in drainage water and N2O emissions at the soil surface. Wheat yield among treatments in either year of study were not different, but was 1.5 times greater in Year 2 (2.62 ± 0.27 Mg ha–1), than Year 1 (1.05 ± 0.12 Mg ha–1). The highest NO3– concentrations in drainage water (Oct.; 13.8 mg NO3–-N L–1) were measured from the GMr system with the earliest fall incorporation (i.e., Sep.) and the addition of spring fertilizer when compared to the mean of all other treatments (9.8 mg NO3–-N L–1). The use of supplemental N did not translate into additional gains in yield, yet increased in-season N2O emissions and greater NO3– leaching. Off-season N losses proved to be a substantial part of the annual N loss budget and dissolved N2O in drainage water was identified as an additional pathway for N loss at spring thaw.

A framework for evaluating the risk of water pollution from the application of liquid dairy manure to agricultural fields was developed and applied. The GLEAMS (Groundwater Loading Effects of Agricultural Management Practices) (Ver 2.1) model was used to simulate NO₃-N leaching below the root zone for different land application rates of liquid dairy waste for fields in Georgia and Texas. Probability distributions of yearly-maximum nitrate concentrations were developed for each application rate at each site using the simulated nitrate concentrations. The probability of failure (exceeding 10 mg/L NO₃-N) for each application rate was determined from its corresponding distribution. An appropriate fine for farmers based on probability of failure for different land application rates was determined through economic analysis. The expected risk to farmers in monetary terms was determined for each application rate based on possible fines and the probability of failure. The monetary risk of nitrate leaching to ground water was compared to the social value of ground water. The probability of failure for liquid dairy waste application rates between 200 to 800 kg·N/ha/yr ranged from 0.0022 to 0.74 for Tifton, GA. The probability of failure for liquid dairy waste application rates between 0 and 1000 kg·N/ha/yr ranged from 0.00 to 0.85 for Overton, TX. The maximum application rate that was environmentally acceptable for both Texas and Georgia was 250 kg·N/ha/yr based on the probability of failure. Fines of $1100/ha and $700/ha for the Georgia and Texas sites, respectively, would provide farmers with economic incentives not to exceed an application rate of 250 kg·N/ha/yr. These fines resulted in risks to farmers of $814/ha in Georgia for 800 kg·N/ha/yr application rate and $595/ha in Texas for 1000 kg·N/ha/yr rate. This compares with a social value ranging from $860/ha to $1432/ha of clean ground water. / Master of Science

The economic impact of reducing the amount of nitrate leached out of the root zone under irrigation in the arid West was examined. A general introduction into the nature of the problem and a review of the literature was provided in chapter I. In chapter ll the economic incentives of irrigation management were evaluated under the assumptions of both profit-maximizing and utility-maximizing (in reducing cost and effort expended in irrigation) decision-making criteria. The results indicate that there is a coincidence of interests of the farmer and the environment. Both behaviors result in less nitrate leaching than less profitable or less utilityproducing irrigating practices. In chapter lli the economic impact of reducing the amount of nitrate leached out of the root zone under irrigation with various nitrogen sources and application methods was examined. The economic incentives of nitrogen management were evaluated under the assumption of profit-maximizing behavior. The results indicate that there is a coincidence of interests for irrigators who respond to economic incentives and environmentalists who wish to reduce nitrate residuals in irrigation drainage and the groundwater. Profit-maximizing behavior results in less nitrate leaching than less profitable irrigating practices when salt balance is not a major concern.

Corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) production in Illinois has a significant impact on the economy and environmental footprint in the state and the Midwest region. Nutrient leaching from Midwestern agricultural fields is one of the major reasons for the hypoxic zone developed in the Gulf of Mexico. Winter-fallow and early spring (after fertilizer application) are the two most critical periods for nutrient leaching due to increased precipitation and availability of nutrients. Cover crops (CCs) in these seasons are a promising best management practice (BMP) to reduce nutrient leaching in the winter-fallow season. No-till (NT) and reduced tillage (RT) are some other BMPs that farmers in Illinois adopt to reduce erosion. The adoption of CCs is limited due to the lack of knowledge and data on the yield and environmental benefits of CCs in different climatic and soil regimes. Thereby, this doctoral dissertation addresses several critical questions about CC and tillage impacts in claypan soils of southern Illinois with four principal projects with multiple objectives. Research study 1 was a field experiment conducted from 2013-to 2021 to understand the effect of CCs (CCs vs. noCC) and two tillage (NT and RT) practices on soil nitrate-N leaching. The experimental design was a complete randomized design with CC treatments that had two levels (two crop rotations) corn-cereal rye (Secale cereale L.)-soybean-hairy vetch (Vicia villosa R.) [CcrShv] and corn-noCC-soybean-noCC [CncSnc] and tillage treatments with two levels (NT and RT) replicated three times in the field. Each plot had a pan lysimeter installed below the A horizon (22-30 cm depth) to collect water samples weekly or biweekly depending on the rainfall. The corn yield was significantly greater in RT rotations compared to NT rotations with a 36% increase in the yield in 2019 and 2021 corn rotations. The yield was significantly greater in CcrShv rotations compared to the CncSnc rotations. The greatest yield was observed in the interaction of CcrShv-RT in all years. This increase in yield is inversely correlated to the remaining soil N values when the N credit from CCs was not accounted for. Soil nitrate-N leaching was significantly greater in CcrShv rotations compared to the CncSnc rotation in 2021 indicating vetch CC biomass decomposition can lead to increased leaching losses if the window between CC termination and corn planting is not minimized. Precipitation during the early spring can play a vital role in flushing the newly applied fertilizer as well as the N released from decomposing CC residue. The excessively wet year of 2019 showed that N losses are dominated by both nitrate-N leaching and nitrous oxide emissions, but in a typical growing season N losses are dominated by leaching compared to emissions. Research study 2 was designed to better understand the N cycling and fate of applied N in a complete corn-soybean rotation in southern Illinois with CCs and tillage practices. The research was overlayed in the same field with the same crop rotation and tillage practices. In this study, 15N labeled urea fertilizer (9.2% atom) was applied before the corn and soybean seasons. Soil, water, and biomass samples were collected to understand N distribution in each pool. In the corn season in 2017 a significantly greater 15N recovery was observed in CC (CcrShv) plots compared to the noCC plots in the sample collected seven days after planting (DAP). In the CC and depth interaction, a significantly greater 15N recovery was observed in 15-30 cm depth showing that the increased macropores due to CCs can lead to subsurface movement of N through the topsoil. The 15N recovery in water samples was high in CncSnc rotations in the cereal rye season but was significantly greater in CcrShv rotations (8.95 kg ha-1) in hairy vetch seasons. In the two years of complete rotation, the cumulative 15N recovery (quantity derived from fertilizer in water) was significantly greater in CC rotation. In the corn plants, the 15N recovered from the soil was greater than the 15N recovered from fertilizer. This shows the importance of the residual N from prior fertilizer and organic matter input. In the cereal rye season, CCs recovered significantly greater 15N from fertilizer compared to noCC rotations, assuring that cereal rye is an effective nutrient scavenger. A similar pattern was observed in the hairy vetch season as well. However, the soybean 15N recovery was greater in noCC rotations compared to CC rotations. The third study was a field trial on CCs and tillage to understand their individual and combined impact on soil physical parameters. Soil physical parameters were first measured in 2014 and were repeated in 2021. Bulk density at the 0-5 cm depth was 5% lower in 2021 compared to 2014 with the lowest BD in CC rotations with RT practices. For the depth of 0-15 cm, the lowest BD was observed in CC rotation with RT but, the largest reduction was observed in the CC rotation with NT. The wet aggregate stability was improved from 15-28 % over the years in all rotations. The lowest percentage improvement was observed in noCC rotation with RT practice. Penetration resistance was significantly lower in CC plots for the depth of 0-2.5 cm. CCs further improved the time to runoff in plots even though the infiltration rates were not affected. Chemical soil health indices were not significant overtime for CCs or tillage practices. However, a large number of earthworm counts were observed in NT systems compared to RT systems. The final project was a field trial to identify the soil P response to the CC and tillage practices. For this study, three different CC rotations, [corn-cereal rye-soybean-hairy vetch / corn-cereal rye-soybean-oats+radish / corn-noCC-soybean-noCC] and two tillage practices (NT and RT) were used. Soil samples were collected after the corn harvest in 2015 and 2021 and were analyzed for soil Phosphorus (P), inorganic P fractions by Chan and Jackson method, and dissolved reactive phosphorus (DRP) in leachate. The soil Mehlich-3 and Bray-1 P values indicate a great concentration of P in 0-15 cm depth for both years. More refined sampling in 2021 showed that the majority of P in 0-15 cm depth concentrates at the near-surface soil, in 0-5 cm depth irrespective of the CC and tillage treatment. Inorganic soil P fractions were not significantly different between CCs or tillage practices over time. Yet, irrespective of the treatment the non- labile P forms increased in 2021in the soil compared to 2015. The average and cumulative DRP values were highly dependent on the precipitation amounts and timing. However, in general, NT systems had greater average and cumulative DRP leaching compared to RT in both years. In general, CCs in the winter-fallow season is a good recommendation for farms that seek to maximize their production with a minimal environmental footprint. In the long run, CCs can improve soil physical and chemical properties which ultimately can increase the yield potential for corn and soybean. The added benefit of N credit due to leguminous CCs can reduce the fertilizer inputs. The CC benefits including the reduction in nutrient leaching depend on the type of CCs used in the field. More importantly, the CC termination time will be critical to obtain the maximum benefit of CCs. Even though the NT practices improve soil physical properties, long-term NT can increase the risk of soil P stratification in near-surface soils and can ultimately lead to more P loss via erosion, runoff, and soil water leaching. However, the combined use of CC and NT practices can help minimize the potential for erosion and runoff.

O manejo eficiente de fertilizações nitrogenadas em sistemas de exploração a pasto é peça chave para que melhores índices produtivos sejam alcançados. O conhecimento das perdas intrínsecas a esta prática e de fontes nitrogenadas alterntivas às normalmente usadas proporciona a determinação de melhores eficiências e flexibilidade na escolha da forma do nitrogênio aplicado. Assim o presente estudo teve o objetivo de avaliar as perdas por lixiviação de nitrato e volatilização de amônia, juntamente com a recuperação aparente do nitrogênio, em pastagens de capim elefante manejadas sob elevada fertilidade do solo. O experimento foi conduzido em área do depzrtamento de Zootecnia da ESALQ/USP, em Piracicaba. Adotou-se o delineamento experimental blocos ao acaso, com quatro blocos e seis tratamentos, que constaram da aplicação de 100 kg de N.ha-1 por ciclo, sob a forma de uréia, nitrato de amônio, etserco de curral, cama de frango e ajifer. Ao todo foram realizados três ciclos de amostragem, de novembro de 2006 a fevereiro de 2007, totalizando a aplicação de 300 kg de N.ha-1. Todos os resultados foram submetidos ao teste t à 5% de significância para a realização da análise estatística. As médias de produção de foram maiores para os tratamentos adubados com cama de frango e esterco, sendo de 3878,89 kg MSV.ha-1 e 3873,67 kg MSV.ha-1, respectivamente. Não foram observadas diferenças entre as recuperações aparentes do nitrogênio aplicado. As perdas por lixiviação de nitrato foram diferentes somente entre os ciclos, como consequência dos maiores índices de precipitação observados no terceiro ciclo amostrado, que apresentou média de -0,2.10-4 kg de NO3-.ha-1dia-1. Os valores de amônia volatilizada foram diferentes entre os ciclos e entre os tratamentos, sendo que no primeiro ciclo as maiores perdas foram atribuídas ao esterco, com 20,58% do nitrogênio aplicado. A cama de frango apresentou as maiores perdas de volatilização durante o segundo ciclo, com perda de 10,71% do nitrogênio aplicado, enquanto no terceiro ciclo a uréia apresentou a maior perda de nitrogênio, com 22,23% do nitrogênio volatilizado. As perdas por volatilização mais expressivas foram registradas até 60 horas após a aplicação das fontes. / The efficiency of nitrogen fertilization is one of the key elements to grass production. The knowledge of nitrogen losses within this practice associated with the application of alternative nitrogen sources provide efficient use and flexibility in choosing between nitrogen fertilizers. The objective of this study was to evaluate nitrate leaching, ammonium volatilization losses and apparent recovery of the applied nitrogen in elephant-grass pasture managed under high soil fertility. It was conducted at the Animal Science Department of ESALQ/USP, in Piraicaba - S.P. The statistical design was in complete randomized blocks, with four replicates and six treatments, which were the use of 100 kg N.ha-1 as urea, ammonium nitrate, dairy manure, chicken litter and ajifer. There were three cycles of evaluations, from November 2006 to February 2007, resulting in 300 kg N.ha-1 applied during the whole period. The results were statistically analysed by the t test with 5% significance. Chicken litter and dairy manure treatments provided the higher dry matter yields of 3878,89 DM.ha-1 and 3873,67 kg DM.ha-1, for each source respectively. Nitrate leaching losses were significant in the third cycle when -0,2.10-4 kg NO3-.ha-1.day-1 was lost. Ammonia volatilization was different between cycles and sources. In the first cycle the dairy manure resulted in higher losses of 26,42 kg N.ha-1. Chicken litter and urea lost 23,97 and 22,27 kg N.ha-1, respectively. In the second cycle urea presented the higher losses of 22,50, while dairy manure and chicken litter lost 6,01 and 15,88 kg N.ha-1. During the third cycle urea presented higher losses than , with 40,12 kg N.ha-1, dairy manure and chicken , which were 2,71 and 11,93 kg N.ha-1. Higher volatilization losses were observed until 60 hours after fertilization.

Efficient use of irrigation and nutrients are becoming increasingly important in commercial orchards in the Hawkesbury area. Proper irrigation scheduling practices can help in the better use of irrigation water and reduce environmental impacts. Field experiments were conducted during February 1999 to June 2000 to understand soil-water use, and to evaluate farmer’s irrigation practice under an alley cropping system consisting of turf and stone fruits. The study was carried out at Atlas Farm, 3.5 km from the University of Western Sydney, Hawkesbury campus. The experimental site is a floodplain of the Hawkesbury River. The river flows within 1 km of the farm boundaries. The study was conducted under the farmer’s existing irrigation water and nutrient management practices. The main aims of the thesis were to study the movement and redistribution of soil-water and soil-moisture dynamics in the turf and stone fruit alley cropping system and to understand deep percolation losses and nitrogen leaching using the water balance approach. The study indicated that drainage occurred mainly after heavy rainfall and when there was rainfall for a few consecutive days. Thus irrigation application should be delayed if there is a likelihood of rain in a few consecutive days to prevent loss of water due to deep drainage. Furthermore, the study showed irrigation scheduling was essential to reduce nitrate leaching in the field; that irrigation depths should be varied according to the stage of crop growth, and the proper timing of irrigation application could help reduce deep percolation and runoff losses. / Master of Science (Hons) (Agriculture)

No description available.

Grünland spielt eine große Rolle in der Landnutzung und nimmt ein Drittel der landwirtschaftlich genutzten Fläche von Europa ein. Als Konsequenz der Intensivierung landwirtschaftlicher Bewirtschaftungsmaßnahmen der letzten 60 Jahre nahm die Produktivität des Grünlands zu während die Diversität dieser Systeme abnahm. In Grünland-Ökosystemen spielt Stickstoff (N) eine Schlüsselrolle – N bedingt die Primärproduktion und beeinflusst die Biodiversität. Zudem kann eine steigende N-Verfügbarkeit gasförmige Emissionen, wie z.B. Distickstoffoxid (N2O) und Stickstoffmonoxid (NO) fördern, die eine große Rolle in der Atmosphäre spielen und zur globalen Erwärmung beitragen. Eine höhere Nitratauswaschung (NO3-) aus Böden kann eine Gefahr für die Grundwasserqualität sein. N-Verluste durch Ausgasung von N2O und NO sowie NO3--Auswaschung sind dabei die Folgen der mikrobiellen Prozesse Denitrifikation und Nitrifikation. In dieser Studie haben wir den Effekt von unterschiedlichen Bewirtschaftungsintensitäten und funktioneller Pflanzendiversität auf die N-Verluste und Ökosystemfunktionen untersucht. Die Studie ist Teil des Excellenzclusters „Funktionelle Biodiversitätsforschung“ der Georg-August-Universität Göttingen und wurde durch das Niedersächsische Ministerium für Wissenschaft und Kultur finanziert. Die Studie wurde im Rahmen von zwei interdisziplinären Projekten (BIOMIX & GRASSMAN) von 2008 bis 2010 im Solling, Niedersachsen, Deutschland durchgeführt. Wir untersuchten von Rindern und Schafen beweidetes Grünland (BIOMIX) und gemähtes Grünland mit unterschiedlichen Bewirtschaftungsintensitäten (GRASSMAN). In beiden Projekten wurde die funktionelle Pflanzendiversität durch Herbizide eingestellt. Der Fokus unserer Arbeit lag auf den N-Verlusten (N2O and NO Emissionen, NO3--Auswaschung) und der N Dynamik (Netto und Brutto Mineralisation). In GRASSMAN berechneten wir zusätzlich die N-Nutzungseffizienz und die N-Rückhalteeffizienz auf Ökosystemebene. Dabei ist die N-Nutzungseffizienz das Produkt der Aufnahmeeffizienz (definiert als N-Aufnahme der Pflanze pro verfügbares N) und der N-Nutzungseffizienz auf Pflanzenebene (definiert als Produktivität pro N-Aufnahme der Pflanze). Darüber hinaus berechnen wir N-Rückhalteeffizienz in Böden als einen Index, der das Verhältnis von N-Verlusten zu dem im Grünland verbleibenden N beschreibt. In BIOMIX haben wir die Auswirkung von Beweidung und Pflanzenarten-zusammensetzung auf N2O and NO Emissionen untersucht. Die mit einem Herbizid gegen Dikotyle vorbehandelten Weiden wurden mit Rindern oder Schafen Rotationsweise beweidet. Mittlere N2O Emissionen lagen bei 38.7 µg N2O-N m-2 h-1, mittlere NO Emissionen betrugen 2.4 µg NO-N m-2 h-1. Kumulative NO-N Emissionen waren höher auf den von Schafen beweideten Flächen als auf den von Rindern beweideten Flächen. In einem kontrollierten Applikations-Experiment führte die Behandlung mit Rinderurin zu höheren N2O Emissionen als die Behandlung mit Schafurin. Die Emissionshöchstwerte von 1921 µg N2O-N m-2 h-1 bei Behandlung mit Rinderurin im Vergleich zu 556 µg N2O-N m-2 h-1 bei Schafurin standen im Zusammenhang mit unterschiedlichen N-Einträgen pro Ausscheidung der Tiere. Die Emissionshöchstwerte der mit Dung behandelten Flächen waren im Vergleich mit den jeweiligen Urinbehandlungen viel geringer. Die N2O Emissionsfaktoren betrugen 0.4% für Rinderurin, 0.5% für Schafurin, 0.05% für Rinderdung und 0.09% für Schafdung. Sowohl das Beweidungs-Experiment, als auch das kontrollierte Applikations-Experiment zeigten, dass die Pflanzenartenzusammensetzung auf N-Emissionen im Vergleich zum Einfluss der Weidetierart auf N-Emissionen unbedeutend war. Trotz höherer N-Einträge auf Rinderweiden waren die N-Emissionen aus der Schafbeweidung höher. Wir führten dies auf die gleichmäßigere Verteilung von Schafs-Exkrementen im Vergleich zu Rindern-Exkrementen zurück. In GRASSMAN untersuchten wir die Auswirkungen von unterschiedlichen Bewirtschaftungsregimen (Düngung und Schnittintensität) und Pflanzenarten-zusammensetzung auf die N-Verluste (N2O Emissionen, NO3- Auswaschung) und die N-Dynamik (Netto und Brutto Mineralisation) und kalkulierten die N-Nutzungseffizienz und die N-Rückhalteeffizienz. Ein dreifaktorielles Design mit folgenden Faktoren wurde über einen Zeitraum von zwei Jahren etabliert: Düngung (180 – 30 – 100 kg NPK ha-1 yr-1 und keine Düngung), Schnittintensität (ein- und dreimal pro Jahr) und Pflanzenartenzusammensetzung (eine unbehandelte Kontrolle, eine Dikotyl-erhöhte und eine Monokotyl-erhöhte Grasnarbe). In 2009 wurden die N2O Emissionen erheblich von beiden Bewirtschaftungsfaktoren (Düngung und Schnittintensität) beeinflusst, während in 2010 nur die Düngung die N2O Emissionen beeinflusste. In 2009 wurden NO3- Auswaschungsverluste durch Düngung und in 2010 von beiden Bewirtschaftungsfaktoren (Düngung und Schnittintensität) beeinflusst. Die Netto N-Mineralisation Raten wurden in 2009 nur von der Düngung beeinflusst. In 2010, zeigte nicht nur die Düngung, sondern auch die Schnittintensität einen Einfluss auf die Netto N-Mineralisation Raten. Weder die Bewirtschaftung (Düngung) noch die Pflanzenartenzusammensetzung hatte einen Einfluss auf die Brutto N-Mineralisation. Die N-Nutzungseffizienz wurde vor allem durch die Düngung und als weiterer Faktor durch die Schnittintensität in 2009 beeinflusst, welche 41% bzw. 3% der Varianz erklärten. In 2010 hatte die Düngung mit 24% der erklärten Varianz einen geringeren Effekt auf die N-Nutzungseffizienz, während die Auswirkungen der Schnittintensität (12%) und die Pflanzenartenzusammensetzung (6%) stärker ausgeprägt waren. Die N-Nutzungseffizienz war auf ungedüngten Flächen größer als auf gedüngten, in den dreimal geschnittenen Flächen höher als in den einmal geschnittenen, und in der unbehandelten Kontrolle höher als in der Monokotyl-erhöhte oder Dikotyl-erhöhte Grasnarbe. Düngung verringert die N-Nutzungseffizienz durch die Abnahme in der N-Aufnahmeeffizienz und der N-Nutzungseffizienz auf Pflanzenebene, während die Schnittintensität und die Pflanzenartenzusammensetzung nur durch die N-Aufnahmeeffizienz beeinflusst werden. Die N-Rückhalteeffizienz wurde nur für 2010 berechnet und wurde durch die Düngung und die Pflanzenartenzusammensetzung mit 22% und 17% der erklärten Varianz beeinflusst. N-Rückhalteeffizienz nahm in der Reihenfolge unbehandelte Kontrolle > Dikotyl-erhöhte > Monokotyl-erhöhte Grasnarbe mit einem signifikanten Unterschied zwischen der unbehandelten Kontrolle und der Monokotyl-erhöhten Grasnarbe ab. Die N-Rückhalteeffizienz ist mit dem mikrobiellen Ammonium (NH4+) und der mikrobiellen Biomasse hoch und mit der N-Aufnahme der Pflanzen nur gering korreliert, was die Bedeutung der mikrobiellen N Retention im System Boden-Pflanze unterstreicht. Unsere Ergebnisse zeigen, dass die Bewirtschaftung der wichtigste und bestimmende Faktor der Ökosystemfunktionen eines Grünlands ist. Düngung, Schnittintensität und Beweidung beeinflussen die N-Nutzungseffizienz, die N-Rückhalteeffizienz und die N-Verluste. Die Zusammensetzung der botanischen Grasnarbe hat einen geringen Einfluss auf den N Kreislauf oder die N-Nutzungs- und die N-Rückhalteeffizienz. Wobei die Pflanzenartenzusammensetzung der unbehandelten Kontrolle (~70% Monokotyle und ~30% Dikotyle), die sich unter der extensiven Langzeit-Bewirtschaftung eingestellt hatte, die höchsten Effizienzen zeigte - sowohl eine Erhöhung der Monokotyledonen als auch eine Erhöhung der Dikotyledonen führte zu einer Verringerung der Effizienzen. Darüber hinaus sind N-Nutzungs- und N-Rückhalteeffizienz geeignete Werkzeuge, die sich zur Evaluierung ökologischer Nachhaltigkeit von Pflanzenartenzusammensetzungen und Management-Praktiken im Grünland eignen.