Search

The combined application of organic and mineral fertilizers is an appropriate agronomic measure and is particularly important for smallholders who have limited access to mineral fertilizers. However, fertilizer recommendations in terms of crop nutritional value and nutrient efficiency strongly vary in dependence of site-specific conditions. In this study, seven different ratios of bio-waste compost (comp) and mineral fertilizers (MF), consisting of nitrogen (N), phosphorus (P), and sulfur (S), were tested in a two-year field experiment on a Nitisol soil in order to assess their effects on nutritionally important minerals in maize (Zea mays, L. Bako-hybrid) grains as well as the nutrient use efficiency. The application of fertilizers corresponded to an N supply of about 100 kg ha−1, whereby the application of only MF (100 MF) was gradually replaced by compost. Compared to 100 MF the treatments with 40 to 70% of N supply given with compost had a higher concentration of most grain minerals. The most pronounced elevations were found for Fe (570 vs. 304 mg kg‒1) and Mn (70.1 vs. 36.3 mg kg‒1) when 50% of the N was given with compost in comparison to the 100 MF treatment. The P use efficiency increased particularly when compost was part of the nutrient supply. The results suggest that replacing mineral fertilizer with compost accounting for 40 to 70% of the total N supply would be a suitable option for increasing the nutritional quality of maize grains and to efficiently use fertilizers on this Nitisol.

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N2O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N2O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0–10 cm to determine water-filled pore space, ammonium (NH4+), and nitrate (NO3−) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N2O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH4+ and NO3− were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N2O–N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N2O emissions and improve NUE and biomass production.

Nitrification inhibitors can effectively decrease nitrification rates and nitrous oxide (N2O) emission while increasing crop yield under certain conditions. However, there is no information available on the effects of nitrification inhibitors and tillage practices on N2O emissions from maize cropping in Iran. To study how tillage practices and nitrapyrin (a nitrification inhibitor) affect N2O emission, a split factorial experiment using a completely randomized block design with three replications was carried out in Northeast Iran, which has a cold semiarid climate. Two main plots were created with conventional tillage and minimum tillage levels, and two nitrogen (N) fertilizer (urea) management systems (with and without nitrapyrin application) were created as subplots. Tillage level did not have any significant effect on soil ammonium (NH4+) and nitrate (NO3–) concentrations, cumulative amount and yield-scaled N2O emission, and aboveground biomass of maize, whereas nitrapyrin application showed significant effect. Nitrapyrin application significantly reduced the cumulative amount of N2O emission by 41% and 32% in conventional tillage and minimum tillage practices, respectively. A reduction in soil NO3– concentration by nitrapyrin was also observed. The average yield-scaled N2O emission was 13.6 g N2O-N kg–1 N uptake in both tillage systems without nitrapyrin application and was significantly reduced to 7.9 and 8.2 g N2O-N kg–1 N uptake upon the application of nitrapyrin in minimum tillage and conventional tillage practices, respectively. Additionally, nitrapyrin application increased maize biomass yield by 4% and 13% in the minimum tillage and conventional tillage systems, respectively. Our results indicate that nitrapyrin has a potential role in reducing N2O emission from agricultural systems where urea fertilizers are broadcasted, which is common in Iran due to the practice of traditional farming. UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro en Investigación en Contaminación Ambiental (CICA)

Soil heterotrophic respiration and its temperature sensitivity are affected by various climatic and environmental factors. However, little is known about the combined effects of concurrent climatic and environmental changes, such as climatic warming, changing precipitation regimes, and increasing nitrogen (N) deposition. Therefore, in this study, we investigated the individual and combined effects of warming, wetting, and N addition on soil heterotrophic respiration and temperature sensitivity. We incubated soils collected from a temperate forest in South Korea for 60 d at two temperature levels (15 and 20 °C, representing the annual mean temperature of the study site and 5 °C warming, respectively), three moisture levels (10%, 28%, and 50% water-filled pore space (WFPS), representing dry, moist, and wet conditions, respectively), and two N levels (without N and with N addition equivalent to 50 kg N ha–1 year–1). On day 30, soils were distributed across five different temperatures (10, 15, 20, 25, and 30 °C) for 24 h to determine short-term changes in temperature sensitivity (Q10, change in respiration with 10 °C increase in temperature) of soil heterotrophic respiration. After completing the incubation on day 60, we measured substrate-induced respiration (SIR) by adding six labile substrates to the three types of treatments. Wetting treatment (increase from 28% to 50% WFPS) reduced SIR by 40.8% (3.77 to 2.23 µg CO2-C g–1 h–1), but warming (increase from 15 to 20 °C) and N addition increased SIR by 47.7% (3.77 to 5.57 µg CO2-C g–1 h–1) and 42.0% (3.77 to 5.35 µg CO2-C g–1 h–1), respectively. A combination of any two treatments did not affect SIR, but the combination of three treatments reduced SIR by 42.4% (3.70 to 2.20 µg CO2-C g–1 h–1). Wetting treatment increased Q10 by 25.0% (2.4 to 3.0). However, warming and N addition reduced Q10 by 37.5% (2.4 to 1.5) and 16.7% (2.4 to 2.0), respectively. Warming coupled with wetting did not significantly change Q10, while warming coupled with N addition reduced Q10 by 33.3% (2.4 to 1.6). The combination of three treatments increased Q10 by 12.5% (2.4 to 2.7). Our results demonstrated that among the three factors, soil moisture is the most important one controlling SIR and Q10. The results suggest that the effect of warming on SIR and Q10 can be modified significantly by rainfall variability and elevated N availability. Therefore, this study emphasizes that concurrent climatic and environmental changes, such as increasing rainfall variability and N deposition, should be considered when predicting changes induced by warming in soil respiration and its temperature sensitivity.

Lack of sanitation is the underlying cause of many diarrheal infections and associated deaths. Improving sanitation through the set-up of ecological sanitation dry toilets, followed by the thermophilic composting of human excreta, could offer a solution. In addition, treating the excreta via thermophilic composting allows us to recycle the nutrients to be used as fertilizer for agriculture. However, for this purpose, the compost should be free of pathogens. We conducted a thermophilic composting trial over 204 to 256 days with human excreta, along with vegetable scraps and teff straw, with and without biochar. A sawdust–cattle manure mixture with the same supplements served as a control treatment. To evaluate the hygienic quality of the mature compost, the bacterial indicators Escherichia coli and Salmonella were assessed using the cultivation-based most probable number method. In addition, Ascaris lumbricoides eggs were quantified through light microscopy. The amount of detected E. coli was below the thresholds of German and European regulations for organic fertilizer. Salmonella and Ascaris eggs were not detected. No significant differences between the treatments were observed. Thus, the composting process was efficient in decreasing the number of potential human pathogens. The mature compost fulfilled the legal regulations on organic fertilizer regarding potential human pathogens.

The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO2 , CH4 and N2 O emissions increased by an average of 3.7%, 0.3%, 24.3% and 91.3% under N enrichment, respectively, and that the soil CH4 uptake decreased by 6.0%. Furthermore, the percentage increase in N2 O emissions (91.3%) was two times lower than that (215%) reported by Liu and Greaver (Ecology Letters, 2009, 12:1103-1117). There was also greater stimulation of soil C pools (15.70 kg C ha-1 year-1 per kg N ha-1 year-1 ) than previously reported under N deposition globally. The global N deposition results showed that croplands were the largest GHG sources (calculated as CO2 equivalents), followed by wetlands. However, forests and grasslands were two important GHG sinks. Globally, N deposition increased the terrestrial soil C sink by 6.34 Pg CO2 /year. It also increased net soil GHG emissions by 10.20 Pg CO2 -Geq (CO2 equivalents)/year. Therefore, N deposition not only increased the size of the soil C pool but also increased global GHG emissions, as calculated by the global warming potential approach.

Global population projections foresee the biggest increase to occur in Africa with most of the available uncultivated land to ensure food security remaining on the continent. Simultaneously, greenhouse gas emissions are expected to rise due to ongoing land use change, industrialisation, and transport amongst other reasons with Africa becoming a major emitter of greenhouse gases globally. However, distinct knowledge on greenhouse gas emissions sources and sinks as well as their variability remains largely unknown caused by its vast size and diversity and an according lack of observations across the continent. Thus, an environmental research infrastructure—as being setup in other regions—is more needed than ever. Here, we present the results of a design study that developed a blueprint for establishing such an environmental research infrastructure in Africa. The blueprint comprises an inventory of already existing observations, the spatial disaggregation of locations that will enable to reduce the uncertainty in climate forcing’s in Africa and globally as well as an overall estimated cost for such an endeavour of about 550 M€ over the next 30 years. We further highlight the importance of the development of an e-infrastructure, the necessity for capacity development and the inclusion of all stakeholders to ensure African ownership.

Carbon (C) and greenhouse gas (GHG) research has traditionally required data collection and analysis using advanced and often expensive instruments, complex and proprietary software, and highly specialized research technicians. Partly as a result, relatively little C and GHG research has been conducted in resource-constrained developing countries. At the same time, these are often the same countries and regions in which climate change impacts will likely be strongest and in which major science uncertainties are centered, given the importance of dryland and tropical systems to the global C cycle. Increasingly, scientific communities have adopted appropriate technology and approach (AT&A) for C and GHG research, which focuses on low-cost and low-technology instruments, open-source software and data, and participatory and networking-based research approaches. Adopting AT&A can mean acquiring data with fewer technical constraints and lower economic burden and is thus a strategy for enhancing C and GHG research in developing countries. However, AT&A can have higher uncertainties; these can often be mitigated by carefully designing experiments, providing clear protocols for data collection, and monitoring and validating the quality of obtained data. For implementing this approach in developing countries, it is first necessary to recognize the scientific and moral importance of AT&A. At the same time, new AT&A techniques should be identified and further developed. All these processes should be promoted in collaboration with local researchers and through training local staff and encouraged for wide use and further innovation in developing countries.

Significant research has been conducted on the effects of soil salinity issue on agricultural productivity. However, limited consideration has been given to its critical effects on soil biogeochemistry (e.g., soil microorganisms, soil organic carbon and greenhouse gas (GHG) emissions), land desertification, and biodiversity loss. This article is based on synthesis of information in 238 articles published between 1989 and 2022 on these effects of soil salinity. Principal findings are as follows: (1) salinity affects microbial community composition and soil enzyme activities due to changes in osmotic pressure and ion effects; (2) soil salinity reduces soil organic carbon (SOC) content and alters GHG emissions, which is a serious issue under intensifying agriculture and global warming scenarios; (3) soil salinity can reduce crop yield up to 58 %; (4) soil salinity, even at low levels, can cause profound alteration in soil biodiversity; (5) due to severe soil salinity, some soils are reaching critical desertification status; (6) innovate mitigation strategies of soil salinity need to be approached in a way that should support the United Nations Sustainable Development Goals (UN-SDGs). Knowledge gaps still exist mainly in the effects of salinity especially, responses of GHG emissions and biodiversity. Previous experiences quantifying soil salinity effects remained small-scale, and inappropriate research methods were sometimes applied for investigating soil salinity effects. Therefore, further studies are urgently required to improve our understanding on the effects of salinity, address salinity effects in larger-scale, and develop innovative research methods.

Vegetation restoration on degraded lands has been encouraged worldwide due to its ecological services and function of controlling soil erosion and improving carbon (C) stocks in terrestrial ecosystems. Although the processes of runoff and sediment detachment and transport are well recognized, the effects of vegetation restoration on organic C loss through soil erosion are not fully understood within a given landscape. This study conducted a synthesis from 66 sites to evaluate the effects of vegetation restoration on annual C loss induced by soil erosion across the key areas of the ‘Grain for Green’ Program (GGP) in the Loess Plateau, China. The results showed that vegetation restoration has significantly reduced the annual C loss in sediment and from runoff. Since 2000, a total of 8.6 × 106 ha degraded land has been converted to forests, shrubs and grasslands under the GGP, which has reduced runoff by 1.5 × 109 m3 and is associated with 7.3 × 103 Mg C; furthermore, lost sediment has reduced by 348.7 Tg, which is associated with 1.8 Tg C per year, across the Loess Plateau. In the zone with a mean annual precipitation (MAP) 550 mm, the degraded lands that have been converted to forests have less soil erosion than do the lands that have been converted to grasslands and shrubs. Moreover, C loss induced by soil erosion was mainly affected by plant cover, soil porosity, slope, land-use change, and rainfall intensity on the Loess Plateau. This study suggests that optimal vegetation restoration measures should be adopted based on local conditions to reduce C loss induced by soil erosion.

Wetlands contain a large proportion of carbon (C) in the biosphere and partly affect climate by regulating C cycles of terrestrial ecosystems. China contains Asia's largest wetlands, accounting for about 10% of the global wetland area. Although previous studies attempted to estimate C budget in China's wetlands, uncertainties remain. We conducted a synthesis to estimate C uptake and emission of wetland ecosystems in China using a dataset compiled from published literature. The dataset comprised 193 studies, including 370 sites representing coastal, river, lake and marsh wetlands across China. In addition, C stocks of different wetlands in China were estimated using unbiased data from the China Second Wetlands Survey. The results showed that China's wetlands sequestered 16.87 Pg C (315.76 Mg C/ha), accounting for about 3.8% of C stocks in global wetlands. Net ecosystem productivity, jointly determined by gross primary productivity and ecosystem respiration, exhibited annual C sequestration of 120.23 Tg C. China's wetlands had a total gaseous C loss of 173.20 Tg C per year from soils, including 154.26 Tg CO2 -C and 18.94 Tg CH4 -C emissions. Moreover, C stocks, uptakes and gaseous losses varied with wetland types, and were affected by geographic location and climatic factors (precipitation and temperature). Our results provide better estimation of the C budget in China's wetlands and improve understanding of their contribution to the global C cycle in the context of global climate change.

Greenhouse gas (GHG) research has traditionally required data collection and analysis using advanced and often expensive instruments, complex and proprietary software, and skilled technicians. Partly as a result, relatively little GHG research has been conducted in resource-constrained developing countries and a critical data gap exists in these regions. At the same time, these are the same countries and regions in which climate-change impacts will likely be strongest, and in which major science uncertainties are centered, given the importance of dryland and tropical systems to the global carbon cycle and climate. Increasingly, scientific communities have adopted appropriate technology and approach (AT&A) for GHG research, including low-cost and low-technology instruments, open source software and data, and participatory and networking-based research approaches. Adopting AT&A can mean acquiring data with fewer technical constraints and lower economic burden, and is thus a strategy for enhancing GHG research in developing countries. However, AT&A can be characterized by higher uncertainties; these can often be mitigated by carefully designing experimental set-up, providing clear protocols for data collection, and monitoring and validating the quality of obtained data. For implementing this approach in GHG research of developing countries, first, it is necessary to recognize the scientific and moral importance of AT&A. At the same time, new AT&A techniques should be identified and further developed. Finally, these processes should be promoted through training local staff and encouraged for wide use and further innovation in developing countries.

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N

Urea is the most common nitrogen (N) fertilizer used in the tropics but it has the risk of high gaseous nitrogen (N) losses. Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields. In a field trial on a tropical Andosol pastureland in Costa Rica, gaseous emissions of ammonia (NH3) and nitrous oxide (N2O) and grass yield were quantified from plots treated with urea (U; 41.7 kg N ha-1 application-1) and urea plus the nitrification inhibitor nitrapyrin (U + NI; 41.7 kg N ha-1 application-1 and 350 g of nitrapyrin for each 100 kg of N applied) and control plots (without U and NI) over a six-month period (rainy season). Volatilization of NH3 (August to November) in U (7.4% ±1.3% of N applied) and U + NI (8.1% ±0.9% of N applied) were not significantly different (P > 0.05). Emissions of N2O in U and U + NI from June to November were significantly different (P < 0.05) only in October, when N2O emission in U + NI was higher than that in U. Yield and crude protein production of grass were significantly higher (P < 0.05) in U and U + NI than in the control plots, but they were not significantly different between U and U + NI. There was no significant difference in yield-scaled N2O emission between U (0.31 ±0.10 g N kg-1 dry matter) and U + NI (0.47 ±0.10 g N kg-1 dry matter). The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site. Organismo Internacional de Energía Atómica/[No.CRP D1.50.16]/IAEA/Austria Organización de las Naciones Unidas para la Alimentación y la Agricultura/[No.COS5031]/FAO/Italia Universidad de Costa Rica/[802-B7-505]/UCR/Costa Rica Universidad de Costa Rica/[802-B5-138]/UCR/Costa Rica UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro en Investigación en Contaminación Ambiental (CICA) UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Agroalimentarias::Estación Experimental de Ganado Lechero Alfredo Volio Mata (EEAVM)

Smallholder farmers struggle to achieve food security in many countries of sub-Saharan Africa (SSA). It is urgently required to find appropriate practices for enhancing crop production while avoiding large increases in greenhouse gas (GHG) emissions in SSA. This review aims to identify common smallholder farming practices for enhancing crop production, to assess how these affect GHG emissions and to identify strategies that not only enhance crop production but also mitigate GHG emissions in SSA. To increase crop production and ensure food security, smallholder farmers usually expand agricultural land, develop water harvesting and irrigation techniques and increase cropping intensity and fertilizer use. These practices may result in changing carbon stocks and GHG emissions, potentially creating trade-offs between food security and GHG mitigation. Agricultural land expansion at the expense of forests is the most dominant source of GHG emissions in SSA. While water harvesting and irrigation can increase soil organic carbon, they can trigger GHG emissions. Increasing cropping intensity can enhance the decomposition of soil organic matter, thus releasing carbon dioxide. Increasing nitrogen fertilizer use can enhance soil organic carbon, but also leads to increasing nitrous oxide emissions. An integrated land, water and nutrient management strategy is necessary to enhance crop production and mitigate GHG emissions. Among the most relevant strategies found, agroforesty practices in degraded and marginal lands could replace expanding agricultural croplands. In addition, water management, via adequate rainwater harvesting and irrigation techniques, together with appropriate nutrient management should be considered. Therefore, a land-water-nutrient nexus (LWNN) approach will enable an integrated and sustainable solution to increasing crop production and mitigating GHG emissions. Various technical, economic and policy barriers hinder implementing the LWNN approach on the ground, but these may be overcome through developing appropriate technologies, disseminating them through farmer to farmer approaches and developing specific policies to address smallholder land tenure issues and motivate long-term investment.

Composting organic waste and human excreta could significantly reduce the amount of waste dumped and increase soil fertility and agricultural yields. However, studies focusing on the replacement of mineral fertilizer with compost from these resources are rare. The presented study quantifies the potential of human excreta and other organic waste for compost production. During wet and dry seasons, the generation and composition of household solid waste (HSW) was measured from three wealth categories: poor, medium, and rich, as well as the organic waste generated from 20 commercial facilities. Furthermore, the amount of human excreta, when converting unimproved into ecological sanitation facilities, was assessed. The HSW generation was significantly higher in the wet (0.77 ± 0.07 kg fresh weight (FW) cap−1 day−1) compared to the dry season (0.54 ± 0.04 kg FW cap−1 day−1). Organic waste was the main component of HSW in the dry and wet seasons, accounting for 84% and 76% of the total HSW, respectively. Annually, about 6824 Mg of organic dry matter could be collected from households, 212 Mg from commercial units, and 12,472 Mg from ecological sanitation. With these resources, 11,732 Mg of compost could be produced annually and used for fertilizing 470 ha of farmland, completely replacing mineral fertilizer.

Climate change may affect soil fertility because it can alter various soil physicochemical characteristics through different mechanisms. Currently, a better understanding of its effect on soil physicochemical characteristics is required for sustainable soil management. Therefore, the main purposes of this study were to assess the effect of climate change on key soil physicochemical characteristics (i.e., soil moisture, organic carbon content, and macro-nutrients) and to develop a suitable soil management strategy to enhance climate resilience of smallholder farming in a Tunisian oasis, called Gabes Oasis. An investigation methodology was developed based on future climate projection and simulation of climate change effects on key soil physicochemical characteristics from 2019 to 2050 using the HP1 model. The HP1 model was calibrated and validated based on intensive field measurements over four years (from January 2015 to December 2018) in a pomegranate-field in Gabes Oasis. The results showed that the HP1 model could simulate soil physicochemical characteristics under the baseline scenario. Compared to the no climate change scenario, significant effects of climate change (i.e., RCP8.5, RCP6.0, and RCP4.5 scenarios) on the investigated key soil characteristics were predicted by 2050. Among the investigated soil characteristics, it was predicted that soil organic carbon content was most critically affected. By 2050, it is expected that this content will decrease by 14% for RCP4.5 scenario, 16% for RCP6.0 scenario, and 23% for RCP8.5 scenario. Finally, it is recommended to apply the following cow manure amount to enhance soil characteristics resistance to future climate change: 3748 kg ha−1 year−1. However, more experiments on fields are necessary to investigate the sustainability of the proposed level of cow manure.

Natural vegetation restoration can enhance soil organic carbon (SOC) sequestration, but the mechanisms and control factors underlying SOC sequestration are still unknown. The objectives of the study are to quantify the temporal variation of soil and aggregate‐associated organic carbon (OC) and identify factors controlling the variation following natural vegetation restoration after farmland abandonment. We collected soils from sites having 5, 30, 60, 100, and 160 years of a natural vegetation restoration chronosequence after farmland abandonment in the Loess Plateau, China. The results showed that natural vegetation restoration increased macroaggregates (0.25–2 mm; 46.6% to 73.9%), SOC (2.27 to 9.81 g kg⁻¹), and aggregate OC (7.33 to 36.98 g kg⁻¹) in the top 20‐cm soil compared with abandoned farmland, and the increases mainly occurred in the early stage (

It is increasingly recognized that the addition of biochar to soil has potential to mitigate climate change and increase soil fertility by enhancing carbon (C) storage. However, the effect of biochar on yield and nitrous oxide (N2O) emissions from upland fields remains unclear. In this study, a one-year field experiment was conducted in an area of calcareous fluvo-aquic soil to assess and quantify the effect of maize straw biochar in reducing N2O loss during 2014–2015 in the North China Plain. Eight treatments were designed as follows: no nitrogen (N) fertilizer (control, CK); biochar application at rates of 3 (B3), 6 (B6) and 12 (B12) t ha−1; chemical fertilizer (NPK) application at 200 kg N ha−1 (F); and fertilizer plus biochar application at rates of 3 (FB3), 6 (FB6) and 12 (FB12) t ha−1. Crop yield, N2O fluxes, soil mineral N concentrations, and soil auxiliary parameters were measured following the application of treatments during each season. During the maize growing season, N2O emission was 0.57 kg N2O-N ha−1 under CK treatment, and increased to 0.88, 0.93 and 1.10 kg N2O-N ha−1 under B3, B6 and B12, respectively. In contrast, N2O emissions were significantly reduced by 31.4–39.9% (P

Nitrous oxide (N2O) is a potent greenhouse gas and precursor of ozone layer depletion. Managed terrestrial ecosystems are major anthropogenic sources of N2O, primarily generated in the soil. The physical makeup of the soil interplays with the underlying biochemistry that produces N2O. Therefore, it has been conceptualized that either compacting or loosening the soil will alter N2O emissions; however, a unified framework of these relationships is yet to be established. Here, we compiled, reviewed and analyzed available field studies that have evaluated how applied compaction or alleviation of compacted soils impacts N2O emissions. Of the 108 available pairwise comparisons, 82 % of the cases showed detrimental increases in N2O emissions caused by increased compaction. Overall, N2O emissions nearly doubled because of soil compaction effects (P

Carbon sequestration through ecological restoration programs is an increasingly important option to reduce the rise of atmospheric carbon dioxide concentration. China’s Grain for Green Program (GGP) is likely the largest centrally organized land-use change program in human history and yet its carbon sequestration benefit has yet to be systematically assessed. Here we used seven empirical/statistical equations of forest biomass carbon sequestration and five soil carbon change models to estimate the total and decadal carbon sequestration potentials of the GGP during 1999–2050, including changes in four carbon pools: aboveground biomass, roots, forest floor and soil organic carbon. The results showed that the total carbon stock in the GGP-affected areas was 682 Tg C in 2010 and the accumulative carbon sink estimates induced by the GGP would be 1697, 2635, 3438 and 4115 Tg C for 2020, 2030, 2040 and 2050, respectively. Overall, the carbon sequestration capacity of the GGP can offset about 3%–5% of China’s annual carbon emissions (calculated using 2010 emissions) and about 1% of the global carbon emissions. Afforestation by the GGP contributed about 25% of biomass carbon sinks in global carbon sequestration in 2000–2010. The results suggest that large-scale ecological restoration programs such as afforestation and reforestation could help to enhance global carbon sinks, which may shed new light on the carbon sequestration benefits of such programs in China and also in other regions.

Nitrous oxide (N2O) is one of the major greenhouse gases causing global warming and climate change. Recently, studies showed that the nitrogen (N) input producing optimum amount of crop yields may minimise yield-scaled N2O emissions in agricultural production. Objectives of the study were to 1) investigate theoretical backgrounds of yield, N2O emission, and yield-scaled N2O emission responses to N input, 2) suggest concepts of optimum N input rate and optimum yield-scaled N2O emission and derive equations for them and 3) test with field observations, and 4) assess usage and limitations and suggest future studies. We have proposed a concept and equations for optimum N input rate and optimum yield-scaled N2O emission, and applied them to field-measured data from 10 independent experimental studies worldwide. Field-measured data showed that the suggested equations could be used to determine optimum N input rate and optimum yield-scaled N2O emissions. However, in some cases, any N input resulted in increased yield-scaled N2O emission and minimum yield-scaled N2O emissions occurred when N input was zero. The suggested optimum N input rate and optimum yield-scaled N2O emission can be useful indicators for best management practices to mitigate greenhouse gas emissions and secure food supply. However, in some cases, taking into account yields and N2O emissions separately is required to identify best management practices. Further studies are needed to better understand the characteristics of yield-scaled N2O emissions response to N input and its use for management purposes.

This study quantified changes in soil organic carbon (SOC) and total nitrogen (STN) stocks from the conversion of natural forest to crop field followed by afforestation of these fields. Soil (0–100 cm), leaf and fine roots were collected in the natural forest, the adjacent to 50-year-old crop fields converted from the natural forest, and 5, 8, and 17-year-old Cupressus lusitanica plantation sites (hereafter P5, P8 and P17, respectively) established on the converted crop fields in Southern Ethiopia. Soil and leaf pH, soil texture, bulk density, fine root mass, and SOC and STN contents and stocks were determined. The results showed that soil pH was lower and clay fraction was higher in P17 site than natural forest. Leaf pH of Cupressus lusitanica in plantation sites was lower than those of trees in natural forest. Fine root mass was greater in the plantation sites than the crop field. Soil bulk density (0–40 cm) was higher in the crop fields than the natural forest but there was no significant difference between crop field and plantation sites. SOC and STN stocks (0–100 cm) were higher in the natural forest than the crop field and all plantation sites and there was no significant difference between the crop field and all plantation sites. Overall, SOC and STN stocks decreased by 22.9% and 40.3%, respectively, in conversion of natural forest to crop field. However, after 17 years of afforestation, the crop field showed no change of stocks. The results suggest that afforestation in agricultural lands may not guarantee, or take a long period, to restore SOC and STN to the original natural forest level.

The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO

Extreme droughts have serious impacts on the pools, fluxes and processes of terrestrial carbon (C) and nitrogen (N) cycles. A deep understanding is necessary to explore the impacts of this extreme climate change events. To investigate how soil C and N pools and fluxes respond to drought and explore their mechanisms we conducted a meta-analysis synthesizing the responses of soil C and N cycles to droughts (precipitation reduction experiments) in three main natural ecosystems: forests, shrubs and grasslands. Data were collected from 148 recent publications (1815 sampling data at 134 sites) with the drought experiments from 1 to 13 years across the globe. Drought reduced soil organic C content (-3.3%) mainly because of decreased plant litter input (-8.7%) and reduced litter decomposition (-13.0%) across all the three ecosystem types in the world. Drought increased mineral N content (+31%) but reduced N mineralization rate (-5.7%) and nitrification rate (-13.8%), and thus left total N unchanged. Compared with the local precipitation, drought increased the accumulation of dissolved organic C and N contents by +59% and +33%, respectively, due to retarded mineralization and higher stability of dissolved organic matter. Among the three ecosystem types, forest soils strongly increased litter C (+64%, n=8) and N content (+33%, n=6) as well as microbial CO2 (+16%, n=55), whereas total CO2 emission remains unaffected. Drought decreased soil CO2 emission (-15%, n=53) in shrubs due to reduction of microbial respiration and decreased root biomass. The 98% (n=39) increase of NH4+ concentration in forest soils corresponds to 11% (n=37) decrease of NO3- and so, it reflected the increase of N mineralization rate, but the decrease of nitrification. For shrubs and grasslands, however, stabilized or decreased N mineralization and nitrification mean less N uptake by plants under drought. Overall, the effects of drought on soil C and N cycles were regulated by the ecosystem type, drought duration and intensity. The drought intensity and duration intensify all effects, especially on the decreasing total CO2 emission. However, the most studies mainly focused on the short-term droughts, and there is a lack of comprehensive understanding of how drought effects in a long-term consequences. So, future studies should strengthen drought frequency impacts on ecosystem C and N dynamics in the long-term sequence (> 10 years) in order to face the impacts of global change.

While there have been many valuable individual studies of the effects of agroforestry on changes in net greenhouse gas (GHG) emissions, this information has not yet been brought together to provide an overall assessment of the effects of agroforestry. We therefore compiled and analysed data from 109 earlier observations from 56 peer-reviewed publications of net rates of change of biomass and/or soil carbon (C) stocks in agroforestry systems, and from 26 data sets from 15 peer-reviewed publications of net changes in the emissions of methane (CH4) and nitrous oxide (N2O). We categorized agroforestry into two distinct types: tree-crop coexistence types where trees and agricultural crops are grown together (type 1) and tree-crop rotation type where trees and crops are grown alternately on the same piece of land (type 2). We primarily assessed the changes in C storage and net GHG emissions between agriculture and type 1 agroforestry. The data showed high variability in net C sequestration rates in both biomass and soils depending on the type of agroforestry, with reported C increments ranging from 0.3 to 7.7 t C ha−1 y−1 in biomass and 1.0 to 7.4 t C ha−1 y−1 in soils. On average, type 1 stands sequestered 3.8 ± 1.3 t C ha−1 y−1 in above-ground biomass, with no evidence of changed rates for stands aged 5–25 years. All available studies exclusively reported increases in soil C stocks, with highest reported soil C sequestration rates of more than 8 t C ha−1 y−1 for the first year after agroforestry establishment. Averaged across all observations, soil C sequestration rates were about 2 t C ha−1 y−1 in youngest stands that gradually diminished with time since stand establishment. Overall, type 1 agroforestry stands (at an average age of 14 years) sequestered 7.2 ± 2.8 t C ha−1 y−1, with biomass and soil C sequestration contributing about 70% and 30% of that increment, respectively. Soils under agroforestry also oxidised 1.6 ± 1.0 kg CH4 ha−1 y−1 and emitted 7.7 ± 3.3 kg N2O ha−1 y−1. Comparing agroforestry and adjacent agricultural lands, we found only minor differences in net CH4 and N2O emissions, with no clear overall direction of change. Overall, agroforestry was estimated to contribute to mitigating 27 ± 14 t CO2 equivalents ha−1 y−1 at least for the first 14 years after establishment. It is suggested that future studies should consider strategic approaches for data acquisition that develop comprehensive approaches to quantify all components of the GHG balance, relate net GHG emissions with quantification of the yield of produce, and develop models to summarise the findings.

Ammonia (NH3) released to the atmosphere leads to a cascade of impacts on the environment, yet estimation of NH3 volatilization from cropland soils (VNH3) in a broad spatial scale is still quite uncertain in China. This mainly stems from nonlinear relationships between VNH3 and relevant factors. On the basis of 495 site-years of measurements at 78 sites across Chinese croplands, we developed a nonlinear Bayesian tree regression model to determine how environmental factors modulate the local derivative of VNH3 to nitrogen application rates (Nrate) (VR, %). The VNH3-Nrate relationship was nonlinear. The VR of upland soils and paddy soils depended primarily on local water input and Nrate, respectively. Our model demonstrated good reproductions of VNH3 compared to previous models, i.e., more than 91% of the observed VR variance at sites in China and 79% of those at validation sites outside China. The observed spatial pattern of VNH3 in China agreed well with satellite-based estimates of NH3 column concentrations. The average VRs in China derived from our model were 14.8 ± 2.9% and 11.8 ± 2.0% for upland soils and paddy soils, respectively. The estimated annual NH3 emission in China (3.96 ± 0.76 TgNH3·yr(-1)) was 40% greater than that based on the IPCC Tier 1 guideline.

Evidence shows that there is a close link between the intensification of shifting cultivation (SC) and the Amazon forest resilience. However, SC, to this day, is a widely implemented agricultural practice around the Amazon region due to its cultural, social, and economic relevance. In pristine indigenous communities, which have not experienced Western influence, SC will continue to be the main livelihood as part of the conservation of a patrimony of the humanity. Nevertheless, the main adverse effects of SC on ecosystems (i.e. forest degradation), particularly on Amazon forests, are our grounds to justify the implementation of public policies aiming to the substitution by agroforestry systems (AFS) as a sustainable food system. In this context, we propose linking AFS to Reducing Emissions from Deforestation and forest Degradation (REDD+ strategies) in shifting cultivation landscapes where there is high local-scale expansion and intensification of SC. AFS has higher potential as sustainable food systems for degraded forest rehabilitation and reduction of the expansion and intensification of SC. Consequently, AFS reduce deforestation of new forest areas for SC, meanwhile, sustainable management of second-growth forests could also be implemented through improved fallows, increasing the planting density of long-cycle agroforestry tree species. AFS should be implemented in local communities, in particular, those undergoing human-modified Amazon landscapes, where there is a high intensification of SC.

This paper summarizes currently available data on greenhouse gas (GHG) emissions from African natural ecosystems and agricultural lands. The available data are used to synthesize current understanding of the drivers of change in GHG emissions, outline the knowledge gaps, and suggest future directions and strategies for GHG emission research. GHG emission data were collected from 75 studies conducted in 22 countries (n = 244) in sub-Saharan Africa (SSA). Carbon dioxide (CO2) emissions were by far the largest contributor to GHG emissions and global warming potential (GWP) in SSA natural terrestrial systems. CO2 emissions ranged from 3.3 to 57.0 Mg CO2 ha−1 yr−1, methane (CH4) emissions ranged from −4.8 to 3.5 kg ha−1 yr−1 (−0.16 to 0.12 Mg CO2 equivalent (eq.) ha−1 yr−1), and nitrous oxide (N2O) emissions ranged from −0.1 to 13.7 kg ha−1 yr−1 (−0.03 to 4.1 Mg CO2 eq. ha−1 yr−1). Soil physical and chemical properties, rewetting, vegetation type, forest management, and land-use changes were all found to be important factors affecting soil GHG emissions from natural terrestrial systems. In aquatic systems, CO2 was the largest contributor to total GHG emissions, ranging from 5.7 to 232.0 Mg CO2 ha−1 yr−1, followed by −26.3 to 2741.9 kg CH4 ha−1 yr−1 (−0.89 to 93.2 Mg CO2 eq. ha−1 yr−1) and 0.2 to 3.5 kg N2O ha−1 yr−1 (0.06 to 1.0 Mg CO2 eq. ha−1 yr−1). Rates of all GHG emissions from aquatic systems were affected by type, location, hydrological characteristics, and water quality. In croplands, soil GHG emissions were also dominated by CO2, ranging from 1.7 to 141.2 Mg CO2 ha−1 yr−1, with −1.3 to 66.7 kg CH4 ha−1 yr−1 (−0.04 to 2.3 Mg CO2 eq. ha−1 yr−1) and 0.05 to 112.0 kg N2O ha−1 yr−1 (0.015 to 33.4 Mg CO2 eq. ha−1 yr−1). N2O emission factors (EFs) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers invariably resulted in significant changes in GHG emissions, but results were inconsistent as the magnitude and direction of changes were differed by gas. Soil GHG emissions from vegetable gardens ranged from 73.3 to 132.0 Mg CO2 ha−1 yr−1 and 53.4 to 177.6 kg N2O ha−1 yr−1 (15.9 to 52.9 Mg CO2 eq. ha−1 yr−1) and N2O EFs ranged from 3 to 4 %. Soil CO2 and N2O emissions from agroforestry were 38.6 Mg CO2 ha−1 yr−1 and 0.2 to 26.7 kg N2O ha−1 yr−1 (0.06 to 8.0 Mg CO2 eq. ha−1 yr−1), respectively. Improving fallow with nitrogen (N)-fixing trees led to increased CO2 and N2O emissions compared to conventional croplands. The type and quality of plant residue in the fallow is an important control on how CO2 and N2O emissions are affected. Throughout agricultural lands, N2O emissions slowly increased with N inputs below 150 kg N ha−1 yr−1 and increased exponentially with N application rates up to 300 kg N ha−1 yr−1. The lowest yield-scaled N2O emissions were reported with N application rates ranging between 100 and 150 kg N ha−1. Overall, total CO2 eq. emissions from SSA natural ecosystems and agricultural lands were 56.9 ± 12.7 × 109 Mg CO2 eq. yr−1 with natural ecosystems and agricultural lands contributing 76.3 and 23.7 %, respectively. Additional GHG emission measurements are urgently required to reduce uncertainty on annual GHG emissions from the different land uses and identify major control factors and mitigation options for low-emission development. A common strategy for addressing this data gap may include identifying priorities for data acquisition, utilizing appropriate technologies, and involving international networks and collaboration.

One of the environmental impacts of land-use change (LUC) is a change in the net exchange of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Here we summarize findings based on a new global database containing data sets of changes in soil organic carbon stocks and soil CH4 and N2O fluxes. We combine that with estimates of biomass carbon stock changes and enteric CH4 emissions following LUC. Data were expressed in common units by converting net CH4 and N2O fluxes to CO2 equivalents (CO2 eq) using established global warming potentials, and carbon-stock changes were converted to annual net fluxes by averaging stock changes over 100 yr. Conversion from natural forest to cropland resulted in the greatest increase in net GHG fluxes, while conversion of cropland to secondary forest resulted in the greatest reduction in net GHG emissions. Specifically, LUC from natural forest to crop and grasslands led to net fluxes of 6.2 ± 1.6 (Mean ± 95% confidence intervals) and 4.8 ± 1.6 t CO2 eq ha−1 yr−1 to the atmosphere, respectively. Conversely, conversion from crop and grasslands to secondary forest reduced net emissions by 6.1 ± 4.1 and 3.9 ± 1.2 t CO2 eq ha−1 yr−1, respectively. Land-use change impacts were generally dominated by changes in biomass carbon. A retrospective analysis indicated that LUC from natural forests to agricultural lands contributed a cumulative 1326 ± 449 Gt CO2 eq between 1765 and 2005, which is equivalent to average emissions of 5.5 ± 1.6 Gt CO2 eq yr−1. This study demonstrates how specific LUCs can positively or negatively affect net GHG fluxes to the atmosphere.

Transport and fate of dissolved nitrous oxide (N2O) in groundwater and its significance to nitrogen dynamics within agro-ecosystems are poorly known in spite of significant potential of N2O to global warming and ozone depletion. Increasing denitrification in riparian buffers may trade a reduction in nitrate (NO3−) transport to surface waters for increased N2O emissions resulting from denitrification-produced N2O dissolved in groundwater being emitted into the air when groundwater flows into a stream or a river. This study quantifies the transport and fate of NO3− and dissolved N2O moving from crop fields through riparian buffers, assesses whether groundwater exported from crop fields and riparian buffers is a significant source of dissolved N2O emissions, and evaluates the Intergovernmental Panel on Climate Change (IPCC) methodology to estimate dissolved N2O emission. We measured concentrations of NO3−; chloride (Cl−); pH; dissolved N2O, dissolved oxygen (DO), and organic carbon (DOC) in groundwater under a multi-species riparian buffer, a cool-season grass filter, and adjacent crop fields located in the Bear Creek watershed in central Iowa, USA. In both the multi-species riparian buffer and the cool-season grass filter, concentrations of dissolved N2O in the groundwater did not change as it passed through the sites, even when the concentrations of groundwater NO3− were decreased by 50% and 59%, respectively, over the same periods. The fraction of N lost to leaching and runoff (0.05) and the modified N2O emission factor, [ratio of dissolved N2O flux to N input (0.00002)] determined for the cropped fields indicate that the current IPCC methodology overestimates dissolved N2O flux in the sites. A low ratio between dissolved N2O flux and soil N2O emission (0.0003) was estimated in the cropped fields. These results suggest that the riparian buffers established adjacent to crop fields for water quality functions (enhanced denitrification) decreased NO3− and were not a source of dissolved N2O. Also, the flux of dissolved N2O from the cropped field was negligible in comparison to soil N2O emission in the crop fields.

iv CHAPTER 1. GENERAL INTRODUCTION 1 References 4 CHAPTER 2. EMISSION OF THE GREENHOUSE GAS NITROUS OXIDE FROM RIPARIAN FOREST BUFFERS, WARM-SEASON AND COOL-SEASON GRASS FILTERS, AND AN ADJACENT CROP FIELD Abstract 7 Introduction 7 Materials and methods 9 Results 15 Discussion 19 Conclusions 23 References 24 CHAPTER 3. TRANSPORT AND FATE OF NITRATE AND DISSOLVED NITROUS OXIDE IN GROUNDWATER UNDER RIPARIAN BUFFERS ADJACENT TO CROP FIELDS Abstract 40 Introduction 40 Materials and methods 42 Results 46 Discussion 50 Conclusions 53 References 55

The main objective of this study was to determine how the conversions of home gardens to mono-crop fields affect soil organic carbon (SOC) and total nitrogen (TN) stocks. The study compared SOC and soil TN stocks in 7 paired sites of home gardens and converted mono-crop fields (khat and sugar cane; cultivated for 1–20 years after conversion) in Wondo Genet, Southern Ethiopia. Except two recently converted mono-crop fields (1 and 4 years after conversion), most of converted mono-crop fields had significantly lower contents of SOC (18.3–47.1 %) and soil TN (14.9–45 %) compared to home gardens. Converted mono-crop fields over 10–20 years old showed significantly lower SOC stocks (18.2–30.2 %) and soil TN stocks (16.7–28.7 %) compared to home gardens. There was no significant relationship between the periods after conversion and the rate of decrease of SOC and TN stocks in the mono-crop fields. Study results show that conversion of home gardens to mono-crop fields decreases SOC and TN stocks. Further studies are needed to identify the major mechanisms causing the decrease and quantify the change of SOC and TN in different environment and climate conditions.

One of the environmental impacts of land-use change (LUC) is a change in the net exchange of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Here we summarize data of changes in soil organic carbon (SOC) stocks and net soil CH4 and N2O emissions associated with LUC. We combine that with estimates of biomass carbon (C) stock changes and enteric CH4 emissions following LUC. Data were expressed in common units by converting net CH4 and N2O fluxes to CO2 equivalents (CO2 eq) using established 100-year global warming potentials, and carbon-stock changes were converted to annual net fluxes by averaging stock changes over 100 years. Conversion from natural forest to cropland or grassland resulted in a change in net emissions of 7.3 ± 0.6 (mean ± 95% confidence intervals) or 5.9 ± 0.3 t CO2 eq ha−1 y−1, respectively, while conversion of cropland or grassland to secondary forest reduced emissions by 5.3 ± 0.9 or 3.6 ± 0.7 t CO2 eq ha−1 y−1, respectively. In all LUCs involving forests, changes in biomass C dominated the overall change in net GHG emissions. A retrospective analysis indicated that LUC from natural forests to agricultural lands contributed a cumulative 1569 ± 43 Gt CO2 eq between 1765 and 2005, which is equivalent to average emissions of 6.5 ± 0.2 Gt CO2 eq per year.