Climate effects of recycled fertilizers and biochar: emissions of nitrous oxide, methane and ammonia in a field experiment

Background Nitrogen (N) fertilizers are essential for crop production. Farmyard manure and slurry traditionally constitute about half of the total N inputs into crop production in Switzerland. Recycled fertilizers such as biogas slurry, liquid digestates and compost enable simultaneous energy production and closing of nutrient cycles. There is evidence that recycled fertilizers can help to increase N use efficiencies and to improve N supply in organic farming. Biochar amendment has shown a potential to mitigate soil greenhouse gas (GHG) emissions, in particular nitrous oxide (N2O) emissions. Here, we combine one of the liquid recycled fertilizer treatments with biochar. In a 2.5-years on-farm experiment, we quantify GHG emissions and further gaseous N-losses via ammonia (NH3) emissions

Ammonia emissions from cattle slurry and digestates

The recycling of organic waste in biogas plants is proposed as a measure to close nutrient cycles and possibly reduce nitrogen losses such as nitrous oxide emissions and nitrate leaching. Ammonia volatilization after fertilizer spreading is yet another nitrogen loss pathway which is often understudied and not yet fully understood but the knowledge is needed in order to optimize fertilizer management. We therefore aimed to quantify the volatilization of ammonia after the trail-hose application of digestates compared to cattle slurry. We hypothesize that digestates have larger and longer lasting nitrogen losses via ammonia volatilization due to higher NH4+ contents and pH values compared to fresh manure. In this project, digested and un-digested organic fertilizers were applied twice per year in a 2.5-years field experiment with three consecutive arable crops (maize, winter wheat and winter barley) under organic farming. We used Automated Low Cost Impinger Systems to measure ammonia emissions after fertilizer application. The emissions were then modeled using the backwards Langrangian stochastic dispersal model with respect to wind conditions. A preliminary presentation of the data indicates that ammonia emissions from the cattle slurry, slurry-based digestate, and industrial digestate are alternately higher or lower. In 2018, emissions from cattle slurry tended to be lower than those from slurry-based digestate and industrial digestate, while in 2019 and 2020 all three liquid organic fertilizers had similar emissions. In the measurement period after the second fertilizer application in 2018, which took place at the end of May, conspicuously high emissions were measured. This can be explained by the high temperatures during this period. Adaptive strategies in fertilizer management should thus consider reduced inputs of organic fertilizers during warm periods

Nitrogen dynamics after slurry application as affected by anaerobic digestion, biochar and a nitrification inhibitor

Animal manures are valuable multi-nutrient fertilizers, but their short-term nitrogen (N) use efficiency (NUE) by plants is low, bearing the potential of harmful N losses to the environment, such as nitrate ( ) leaching. To develop strategies to increase the NUE of cattle slurry, a comprehensive understanding of slurry N dynamics in the soil–plant system is needed. In a 57-day microcosm experiment in the greenhouse, we assessed the effect of different slurry treatments on slurry N turnover in the soil and its uptake by ryegrass (Lolium multiflorum var. Westerwoldicum). Employing a two-factorial design, 15N cattle slurry (SLU), 15N anaerobically digested cattle slurry (SLA), and 15N anaerobically digested cattle slurry plus biochar (SLA+) were combined with and without the nitrification inhibitor 3,4-dimethyl-1H-pyrazole monophosphate (DMPP). As references, a mineral fertilizer (MIN) and an unfertilised treatment (N0) were included. The 15N recovery, hence NUE, in plant biomass was higher for SLA than for SLU, while recovery in soil at 55 days after set-up showed an opposite trend, with over 45% of N from SLU still being recovered in soil. DMPP and biochar only marginally affected NUE and fertilizer N recovery in soil. Although 15N recovery in soil was highest for SLU, residual N leaching from SLU was low (<1% of added N). We attribute this to the limited presence of slurry N in mineral forms at this point of time, with the majority being stored in the non-microbial organic soil N pool. Leaching of residual N from MIN was significantly higher for MIN than for SLU, while SLA and SLA+ ranged in between. Overall, anaerobic digestion appeared suitable for increasing NUE of cattle slurry, but further investigations under field conditions are necessary in order to assess its potential to reduce nitrate leaching in the long-term

Eficiência do uso de azoto de azevém e análise de genes funcionais proteolíticos microbianos em solos aráveis ​​geridos de forma diferente e sob regimes de chuva expectáveis no futuro.

Dissertação de Mestrado em Ecologia apresentada à Faculdade de Ciências e TecnologiaAs futuras mudanças climáticas projetadas e a escassez de recursos irão desafiar a produção de alimentos e forragem em escala global. Os sistemas agrícolas orgânicos renunciam aos fertilizantes e pesticidas sintéticos, a fim de promover a produção sustentável e apoiar a saúde do ecossistema. Já foi demonstrado que os solos cultivados organicamente implicam comunidades microbianas mais abundantes, mais ativas e mais diversas em comparação com os solos convencionalmente cultivados e, portanto, podem ser mais resistentes quando enfrentam as próximas mudanças climáticas. Apesar da importância fundamental do ciclismo de nutrientes mediada por microbios nos solos, nossa compreensão do desempenho microbiano em sistemas de agricultura gerenciados de forma diferente sob a futura variação da precipitação projetada ainda é fragmentária. Este estudo informa sobre proteólise e mineralização de nitrogênio orgânico e a subsequente absorção de nitrogênio pelo azevém, em uma experiência de crescimento de plantas usando solos do experimento de campo de DOK a longo prazo. O lote de lupina enriquecido em isótopos 15N foi utilizado como um marcador para fluxos de nitrogênio, enquanto as técnicas genéticas moleculares foram aplicadas como proxy para o potencial proteolítico microbiano do solo combinado com parâmetros geoquímicos tradicionais para monitorar os pools de nitrogênio do solo. Nossa principal descoberta é que, sob o estresse por seca, o azevém cultivado em solo de manejo orgânico absorve significativamente mais 15N em sua biomassa total derivada do lixo vegetal de lupina marcada em comparação com o azevém cultivado em solo convencionalmente gerenciado. Isso fornece novas evidências para um potencial de mineralização de nitrogênio mediado por microbios melhorado, seguido de aprovisionamento de nitrogênio melhorado para plantas em solo de manejo orgânico sob futuros cenários de seca projetados. Não foram identificadas diferenças na acumulação de 15N entre plantas cultivadas nos diferentes solos em condições úmidas ótimas. A quantificação de genes funcionais envolvidos na proteólise, o passo inicial e, portanto, limitante de velocidade de mineralização de nitrogênio, não poderia explicar completamente nossos achados. A abundância de genes funcionais pode servir como proxy para certas funções do solo, mas o tempo de amostragem é crucial e pode não ter sido ótimo no presente estudo. Além disso, não só a abundância de micróbios proteolíticos, mas também a atividade e a diversidade são essenciais e, portanto, mais profundas, as investigações microbianas são necessárias para entender completamente os fenômenos observados.Future projected climate change and resource scarcity will challenge food and fodder production on a global scale. Organic farming systems resign from synthetic fertilizers and pesticides in order to promote sustainable production and to support ecosystem health. It has previously been shown, that organically farmed soils entail more abundant, more active and more diverse microbial communities compared to conventionally farmed soils and thus might potentially be more resilient when facing upcoming climate change. Despite the fundamental importance of microbial mediated nutrient cycling in soils, our understanding of the microbial performance in differently managed farming systems under future projected rainfall variability is still fragmentary. This study reports on proteolysis and mineralization of organically bound nitrogen and the subsequent nitrogen uptake by ryegrass, in a plant growth experiment using soils from the DOK long-term field experiment. 15N isotope enriched lupine litter was used as a tracer for nitrogen fluxes whereas molecular genetic techniques were applied as a proxy for the soil microbial proteolytic potential combined with traditional geochemical parameters to monitor soil nitrogen pools. Our key finding is that under drought stress, ryegrass grown on organically managed soil assimilates significantly more 15N in their total biomass derived from the labeled lupine litter compared to ryegrass grown in conventionally managed soil. This provides novel evidence for an enhanced microbial mediated nitrogen mineralization potential followed by enhanced nitrogen provisioning for plants in organically managed soil under future projected drought scenarios. No differences in 15N accumulation between plants grown on the different soils were identified in optimal wet conditions. The quantification of functional genes involved in proteolysis, the initial and thus rate limiting step in nitrogen mineralization, could not fully explain our findings. The abundances of functional genes might serve as a proxy for certain soil functions but sampling timing is crucial and might not have been optimal in the current study. Furthermore, not only abundance of proteolytic microbes but also activity and diversity is essential and thus more in depths microbial investigations are required to fully understand the observed phenomena

Distinct Nitrogen Provisioning From Organic Amendments in Soil as Influenced by Farming System and Water Regime

The majority of soil organic nitrogen (N) is bound in protein-like compounds and therefore its proteolysis in peptides and amino acids is considered the initial and rate limiting step of N mineralization. Proteolysis of N bound in organic fertilizer and subsequent provisioning for crops is a central element in agro-ecological intensification. Long-term farming system effects on N provisioning from organic fertilizer to crops and its underlying functional microbial communities were analyzed in experiments conducted in soils from the “DOK” system comparison trial (bio-Dynamic, bio-Organic, and “Konventionell”) subjected to optimal and future projected drought scenarios. A plant nutrition experiment using 15N labeled lupine as a fertilizer (green manure) identified 30% higher amounts of N derived from fertilizer in ryegrass grown on organically compared to conventionally managed soil, but only when subjected to dry conditions. A second experiment, also amended with lupine green manure, assessed the effect of farming system and drought stress on N cycling microbes with a focus on alkaline (apr) and neutral (npr) metallopeptidase encoding microbial communities. apr encoding microbial communities were more strongly affected by farming system and water treatment than npr encoding communities. Differences in structure and diversity of apr encoding microbial communities showed concomitant patterns with distinct N provisioning from organic fertilizer in the plant nutrition experiment. It is suggested that conventionally managed systems are less capable in maintaining diversity and initial structure of apr encoding microbial communities when subjected to drought scenarios. Overall, we demonstrated organically managed soils to provide a more stable N provisioning potential from organic fertilizer under future drought scenarios, likely facilitated by a distinct and more adaptive proteolytic microbial community. This work contributes to an in-depth comprehension of yet poorly studied fundamental soil processes and helps developing strategies to maintain a versatile and functioning microbial community in a rapidly changing environment

Emissions of nitrous oxide and methane after field application of liquid organic fertilizers and biochar

The use of anaerobic digestates as fertilizer is proposed as a means to close agricultural nutrient cycles. However, digestates have higher inorganic nitrogen contents than raw manures, which could translate into increased emissions of potent greenhouse gases such as nitrous oxide (N2O) and methane (CH4). To mitigate these emissions, the addition of biochar with high nutrient absorption capacity is suggested. To quantify the effects of anaerobic digestion and biochar amendment on N2O and CH4 emissions, we conducted a study over 33 months with four different crops (silage maize, winter wheat, winter barley, and forage grass). We measured soil parameters such as mineral nitrogen, moisture, and temperature. The N2O emissions after application of digestates were generally similar to those observed after cattle slurry or mineral fertilizer application. The highest N2O emissions were observed in the first year of the experiment during maize cultivation and were strongly influenced by high soil nitrate concentrations, which were likely linked to enhanced soil organic N mineralization after ley termination. The CH4 emissions were mostly negative. The addition of biochar to co-digested manure before application at an annual rate of 2 t ha− 1 had no effect on N2O emissions but led to short-lived CH4 peaks from organic fertilizers directly after spreading. We conclude that digestates do not promote larger N2O emissions than mineral fertilizers or cattle slurry, and that biochar addition to digestates in small application quantities does not reduce N2O emissions but bears the risk of CH4 release.ISSN:0167-8809ISSN:1873-230

Distinct Nitrogen Provisioning From Organic Amendments in Soil as Influenced by Farming System and Water Regime

The majority of soil organic nitrogen (N) is bound in protein-like compounds and therefore its proteolysis in peptides and amino acids is considered the initial and rate limiting step of N mineralization. Proteolysis of N bound in organic fertilizer and subsequent provisioning for crops is a central element in agro-ecological intensification. Long-term farming system effects on N provisioning from organic fertilizer to crops and its underlying functional microbial communities were analyzed in experiments conducted in soils from the “DOK” system comparison trial (bio-Dynamic, bio-Organic, and “Konventionell”) subjected to optimal and future projected drought scenarios. A plant nutrition experiment using 15N labeled lupine as a fertilizer (green manure) identified 30% higher amounts of N derived from fertilizer in ryegrass grown on organically compared to conventionally managed soil, but only when subjected to dry conditions. A second experiment, also amended with lupine green manure, assessed the effect of farming system and drought stress on N cycling microbes with a focus on alkaline (apr) and neutral (npr) metallopeptidase encoding microbial communities. apr encoding microbial communities were more strongly affected by farming system and water treatment than npr encoding communities. Differences in structure and diversity of apr encoding microbial communities showed concomitant patterns with distinct N provisioning from organic fertilizer in the plant nutrition experiment. It is suggested that conventionally managed systems are less capable in maintaining diversity and initial structure of apr encoding microbial communities when subjected to drought scenarios. Overall, we demonstrated organically managed soils to provide a more stable N provisioning potential from organic fertilizer under future drought scenarios, likely facilitated by a distinct and more adaptive proteolytic microbial community. This work contributes to an in-depth comprehension of yet poorly studied fundamental soil processes and helps developing strategies to maintain a versatile and functioning microbial community in a rapidly changing environment

Table_3_Distinct Nitrogen Provisioning From Organic Amendments in Soil as Influenced by Farming System and Water Regime.XLSX

<p>The majority of soil organic nitrogen (N) is bound in protein-like compounds and therefore its proteolysis in peptides and amino acids is considered the initial and rate limiting step of N mineralization. Proteolysis of N bound in organic fertilizer and subsequent provisioning for crops is a central element in agro-ecological intensification. Long-term farming system effects on N provisioning from organic fertilizer to crops and its underlying functional microbial communities were analyzed in experiments conducted in soils from the “DOK” system comparison trial (bio-Dynamic, bio-Organic, and “Konventionell”) subjected to optimal and future projected drought scenarios. A plant nutrition experiment using ¹⁵N labeled lupine as a fertilizer (green manure) identified 30% higher amounts of N derived from fertilizer in ryegrass grown on organically compared to conventionally managed soil, but only when subjected to dry conditions. A second experiment, also amended with lupine green manure, assessed the effect of farming system and drought stress on N cycling microbes with a focus on alkaline (apr) and neutral (npr) metallopeptidase encoding microbial communities. apr encoding microbial communities were more strongly affected by farming system and water treatment than npr encoding communities. Differences in structure and diversity of apr encoding microbial communities showed concomitant patterns with distinct N provisioning from organic fertilizer in the plant nutrition experiment. It is suggested that conventionally managed systems are less capable in maintaining diversity and initial structure of apr encoding microbial communities when subjected to drought scenarios. Overall, we demonstrated organically managed soils to provide a more stable N provisioning potential from organic fertilizer under future drought scenarios, likely facilitated by a distinct and more adaptive proteolytic microbial community. This work contributes to an in-depth comprehension of yet poorly studied fundamental soil processes and helps developing strategies to maintain a versatile and functioning microbial community in a rapidly changing environment.</p

Table_4_Distinct Nitrogen Provisioning From Organic Amendments in Soil as Influenced by Farming System and Water Regime.DOCX

<p>The majority of soil organic nitrogen (N) is bound in protein-like compounds and therefore its proteolysis in peptides and amino acids is considered the initial and rate limiting step of N mineralization. Proteolysis of N bound in organic fertilizer and subsequent provisioning for crops is a central element in agro-ecological intensification. Long-term farming system effects on N provisioning from organic fertilizer to crops and its underlying functional microbial communities were analyzed in experiments conducted in soils from the “DOK” system comparison trial (bio-Dynamic, bio-Organic, and “Konventionell”) subjected to optimal and future projected drought scenarios. A plant nutrition experiment using ¹⁵N labeled lupine as a fertilizer (green manure) identified 30% higher amounts of N derived from fertilizer in ryegrass grown on organically compared to conventionally managed soil, but only when subjected to dry conditions. A second experiment, also amended with lupine green manure, assessed the effect of farming system and drought stress on N cycling microbes with a focus on alkaline (apr) and neutral (npr) metallopeptidase encoding microbial communities. apr encoding microbial communities were more strongly affected by farming system and water treatment than npr encoding communities. Differences in structure and diversity of apr encoding microbial communities showed concomitant patterns with distinct N provisioning from organic fertilizer in the plant nutrition experiment. It is suggested that conventionally managed systems are less capable in maintaining diversity and initial structure of apr encoding microbial communities when subjected to drought scenarios. Overall, we demonstrated organically managed soils to provide a more stable N provisioning potential from organic fertilizer under future drought scenarios, likely facilitated by a distinct and more adaptive proteolytic microbial community. This work contributes to an in-depth comprehension of yet poorly studied fundamental soil processes and helps developing strategies to maintain a versatile and functioning microbial community in a rapidly changing environment.</p