Search

Nitrate, ammonium, total dissolved nitrogen (TDN), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) concentrations and flux were measured for one year in bulk deposition and throughfall from three stand types (upland deciduous, upland conifer and wetland conifer) on the Boreal Plain, Canada. Annual (November 2006 to October 2007 water year) flux rates in bulk deposition were 80, 216, 114 and 410 mg N m−2 for nitrate, ammonium, DON and TDN, respectively, and 3.5 g C m−2 for DOC. The nitrate and ammonium flux in throughfall were approximately 50% of the flux in bulk deposition, while TDN flux in throughfall was 60–74% of the flux in bulk deposition. The DOC flux in throughfall was approximately 2 times greater than DOC flux in bulk deposition, while there was no detectable difference in DON flux. The forest canopy generally had the most impact on throughfall chemistry during the active growing season as compared with the dormant season, although DOC concentrations in throughfall of deciduous stands was highest during autumn. For the upland stands, TDN flow-weighted mean concentrations in the snowpack were not detectably different from the concentrations in throughfall and bulk deposition throughout the rest of the year. However, ammonium concentrations were lower and DON concentrations were higher in the snowpack than in either throughfall or bulk deposition for the other seasons, suggesting some transformation of ammonium to DON within the snowpack.

This investigation in the Swan Hills, Alberta, located on the Canadian Boreal Plain, examined May through October runoff before, during and six years after wildfire in a 4th order watershed, compared to a 3rd order reference watershed. It also examined runoff and inorganic nitrogen flow-weighted mean concentration and areal export for 1 year after winter harvest in four 1st order watersheds compared to five reference 1st and 2nd order watersheds. Runoff and areal exports were normalized to precipitation at each site. Runoff impact ratios (year 1 post-disturbance value divided by the pre-disturbance value) for burned and harvested watersheds were 60 and 70% higher, respectively, than reference watersheds (P = 0.06). Runoff from the burned watershed remained elevated 6 years after fire. A trend for higher nitrate and ammonium concentrations, combined with higher runoff yielded impact ratios for areal ammonium and nitrate exports that were 130 and 170% higher, respectively, in harvested than reference watersheds (P = 0.08 for both). The proportion of the watershed harvested was positively related to runoff (r2 = 0.94, P = 0.03) and ammonium impact ratios (r2 = 0.96, P = 0.02), but not nitrate impact ratios (P = 0.30). Areal nitrate export in snowmelt was low in harvested watersheds compared to their pre-harvest condition and to reference watersheds.

This paper summarizes currently available data on greenhouse gas (GHG) emissions from African natural and agricultural lands, outlines the knowledge gaps and suggests future directions and strategies for GHG emission studies. GHG emission data were collected from 73 studies conducted in 22 countries in sub-Saharan Africa (SSA). Soil GHG emissions from African natural terrestrial systems ranged from 3.3 to 57.0 Mg carbon dioxide (CO2) ha−1 yr−1, −4.8 to 3.5 kg methane (CH4) ha−1 yr−1 and −0.1 to 13.7 kg nitrous oxide (N2O) 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. Greenhouse gas emissions from African aquatic systems ranged from 5.7 to 232.0 Mg CO2 ha−1 yr−1, −26.3 to 2741.9 kg CH4 ha−1 yr−1 and 0.2 to 3.5 kg N2O ha−1 yr−1 and were strongly affected by discharge. Soil GHG emissions from African croplands ranged from 1.7 to 141.2 Mg CO2 ha−1 yr−1, −1.3 to 66.7 kg CH4 ha−1 yr−1and 0.05 to 112.0 kg N2O ha−1 yr−1 and the N2O emission factor (EF) ranged from 0.01 to 4.1 %. Incorporation of crop residues or manure with inorganic fertilizers resulted in significant changes in GHG emissions but these were different for CO2 and N2O. Soil GHG emissions in 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 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, respectively. Improving fallow with nitrogen (N)-fixing trees increased CO2 and N2O emissions compared to conventional croplands and type and quality of plant residue is likely to be an important control factor affecting N2O emissions. 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 equivalent (eq) emissions from African natural and agricultural lands were 56.9 ± 12.7 Pg CO2 eq yr−1 and natural and agricultural lands contributed 76.3 and 23.7 %, respectively. Additional GHG emission measurements throughout Africa agricultural and natural lands are urgently required to reduce uncertainty on annual GHG emissions from the different land uses and identify major control factors and mitigation options on emissions. There is also a need to develop a common strategy for addressing this data gap that may involve identifying priorities for data acquisition, utilizing appropriate technologies, and establishing networks and collaboration.

Few field studies examine greenhouse gas (GHG) emissions from African agricultural systems resulting in high uncertainty for national inventories. We provide here the most comprehensive study in Africa to date, examining annual CO2, CH4 and N2O emissions from 59 plots, across different vegetation types, field types and land classes in western Kenya. The study area consists of a lowland area (approximately 1200 m a.s.l.) rising approximately 600 m to a highland plateau. Cumulative annual fluxes ranged from 2.8 to 15.0 Mg CO2-C ha−1, −6.0 to 2.4 kg CH4-C ha−1 and −0.1 to 1.8 kg N2O-N ha−1. Management intensity of the plots did not result in differences in annual fluxes for the GHGs measured (P = 0.46, 0.67 and 0.14 for CO2, N2O and CH4 respectively). The similar emissions were likely related to low fertilizer input rates (≤ 20 kg ha−1). Grazing plots had the highest CO2 fluxes (P = 0.005); treed plots were a larger CH4 sink than grazing plots (P = 0.05); while N2O emissions were similar across vegetation types (P = 0.59). This case study is likely representative for low fertilizer input, smallholder systems across sub-Saharan Africa, providing critical data for estimating regional or continental GHG inventories. Low crop yields, likely due to low inputs, resulted in high (up to 67 g N2O-N kg−1 aboveground N uptake) yield-scaled emissions. Improving crop production through intensification of agricultural production (i.e. water and nutrient management) may be an important tool to mitigate the impact of African agriculture on climate change.

Rice production is increasingly challenged by irrigation water scarcity, however covering paddy rice soils with films (ground cover rice production system: GCRPS) can significantly reduce water demand as well as overcome temperature limitations at the beginning of the vegetation period resulting in increased grain yields in colder regions of rice production with seasonal water shortages. It has been speculated that the increased soil aeration and temperature under GCRPS may result in losses of soil organic carbon and nitrogen stocks. Here we report on a regional scale experiment, conducted by sampling paired adjacent Paddy and GCRPS fields at 49 representative sites in the Shiyan region, which is typical for many mountainous areas across China. Parameters evaluated included soil C and N stocks, soil physical and chemical properties, potential carbon mineralization rates, fractions of soil organic carbon and stable carbon isotopic composition of plant leaves. Furthermore, root biomass was quantified at maximum tillering stage at one of our paired sites. Against expectations the study showed that: (1) GCRPS significantly increased soil organic C and N stocks 5–20 years following conversion of production systems, (2) there were no differences between GCRPS and Paddy in soil physical and chemical properties for the various soil depths with the exception of soil bulk density, (3) GCRPS had lower mineralization potential for soil organic C compared with Paddy over the incubation period, (4) GCRPS showed lower δ15N in the soils and plant leafs indicating less NH3 volatilization in GCRPS than in Paddy; and (5) GCRPS increased yields and root biomass in all soil layers down to 40 cm depth. Our results suggest that GCRPS is an innovative rice production technique that not only increases yields using less irrigation water, but that it also is environmentally beneficial due to increased soil C and N stocks at regional scale.

Increasing concentrations of in surface water and groundwater can cause ecological and public health effects and has come under increased scrutiny by both environmental scientists and regulatory agencies. For many regions though, including the Sahel of Tunisia, little is known about the sorption capacity of soils. In this project we measured sorption by a profile of an iso-humic soil from Chott Meriem, Tunisia. Soil samples were collected from four soil depths (0–25, 25–60, 60–90, and 90–120 cm) on 1 June 2011, and their sorption capacity was determined using batch experiments under laboratory conditions. The effects of contact time, the initial concentration, and the soil-solution ratio on sorption were investigated. In general, the results suggested that was weakly retained by the Chott Meriem soil profile. The quantity of sorption increased with depth, contact time, initial concentration, and soil-solution ratios. To evaluate the sorption capacities of the soil samples at concentrations ranging between 25 and 150 mg L −1 experimental data were fitted to both Freundlich and Langmuir isotherm sorption models. The results indicated that Freundlich model was better for describing sorption in this soil profile.

Conversion of agricultural systems from conventional to no tillage practices usually increases soil carbon storage. However, adoption of no tillage may increase emissions of N2O, a very potent greenhouse gas. The objective of the study was to determine the effects of tillage (mouldboard plough [MP] and no-tillage [NT]) and three mineral N application rates (0, 80 and 160 kg N ha−1) on annual and biennial (2004–2005) N2O fluxes. The experiment was organized using a split-plot design using tillage as the main plots and fertilizer rates as the sub-plot. The site was an artificially drained and therefore well structured humic gleysol near Montreal QC, on a maize (Zea mays L.)–soybean (Glycine max L.) rotation. Emissions (April–November) ranged from 1.0 to 2.5 kg N2O–N ha−1. Throughout both years tillage had no effect (P > 0.05) on N2O emissions. During 2004, under maize cultivation, N2O emissions increased with the N fertilization rate (P