Search

Agriculture is a key to the Zambian economy, contributing 20% to the country’s GDP and 12% to the national export earnings. However, climate change has a negative impact on Zambian agriculture production. In line with its Vision 2030 to have an efficient, competitive, sustainable and export-led agriculture sector, Zambia is aiming to improve irrigated agriculture through large investment in irrigation. Considering climate change and variability, it is important to adopt best water and nutrient management practices for sustainable use of agricultural resources. Maize being the major staple crop of Zambia, a study was carried out to improve irrigation management by optimizing water and nitrogen use efficiency for maximum maize productivity at field level under varying water and fertilizer applications. To achieve this goal, our study used and adapted nuclear (neutron probe) and isotope (15N and 13C) techniques to the Zambian agro-ecological conditions. Drip irrigation was used as the targeted system. The experiment was implemented based on three water application levels, i.e., deficit (50% and 75% Evapotranspiration) versus optimal (100% Evapotranspiration)and three nitrogen (N) levels (140 kg.ha-1, 112 kg.ha-1 and 84 kg.ha-1, widely practiced being 112 kg.ha-1). Maize was grown as a sole crop, under drip irrigation, in rotation with a legume over the dry season of Zambia in 2021 and 2022. For both years, maize yield was ranging between 2 and 7 ton.ha-1. Results showed that deficit irrigation can be practiced without a significant negative impact on yield (with higher N levels showing significantly higher yields under deficit irrigation) and nitrogen use efficiency. The total N yield and agronomic water use efficiency were significantly higher, up to 1.5 and 3 times respectively, under deficit irrigation as compared to the optimal. Intrinsic water stress (d 13C results) was higher, though not statistically significant, under deficit irrigation. Thus, considering climate change and sustainable use of resources, deficit irrigation should be considered as the option to achieve higher yield and food security.

Ammonia volatilization (AV) is one of the main pathways of nitrogen fertilizer loss, resulting in reduced crop yields, and a negative impact on the environment. Therefore, reducing AV through proper fertilizer management is essential. We can, however, only provide appropriate management advice when based on accurate measurements, along with understanding the processes involved. For this purpose, the 15N technique has a unique advantage over other methods to precisely identify the sources of ammonia production.A field experiment was established at the SWMCN laboratory in Seibersdorf on maize with four replications and 120 kg N ha-1 was applied through two equal split applications at 20 DAP (Days After Planting) and 34 DAP. Two 15N microplots inside each main plot were installed. In these microplots, 15N-labeled urea replaced the unlabeled urea according to the time of fertilizer application. Each microplot for 15N-labelled urea was 2.5 m by 2.5 m,and the buffer zone between microplots was 1 m to minimize 15N contamination from adjacent microplot. For these microplots, 15N-labeled urea was used with an enrichment of 5.23 atom% 15N excess. The first microplot received 15N-urea at 20 DAP and unlabeled urea at 34 DAP, the second microplot received 15N-urea at 34 DAP and unlabeled urea at 20 DAP. Ammonia volatilization was measured with semi-static chambers and chambers were installed inside the 15N microplots.The total cumulative NH3 emissions from urea after the first and second split applications were 13.9 kg N ha-1 and 18.0 kg N ha-1, respectively. This calculation is based on the difference in AV between experimental treatments and control treatment, assuming that AV in control plots indicates the amount of AV from the soil source, whereas AV of the fertilized treatments presents AV from soil and fertilizer sources. It also assumes that all nitrogen transformations, i.e., mineralization, immobilization, and other process in the case of nitrogen, are the same for control and experimental plots. Therefore, the amount of AV in urea treatment was subtracted from the amount of AV in control treatment. The cumulative NH3 emissions from the control treatment (without nitrogen fertilizer) at the same time were 2.7 kg N ha-1 and 3.6 kg N ha-1, respectively. Accordingly, about 20% of the ammonia volatilized from the soil source and the rest could be attributed to the added urea fertilizer.However, using the 15N labelled fertilizer, it was found that the above assumption shows some flaws. The fraction of nitrogen in the ammonia samples derived from the soil is not constant but changes significantly due to nitrogen fertilizer application. The results show that the nitrogen in the ammonia derived from the fertilizer was 65% and 53% after the first and second split applications, respectively. Therefore, the fraction of nitrogen in the ammonia samples derived from the soil source was 35% and 47% after the first and second split applications. So, the use of the 15N technique shows that adding nitrogen fertilizer likely increased the rate of mineralization by changing the ratio of carbon to nitrogen.

The release of radiocaesium radionuclides (RCs) has affected food safety after the accidents at Chernobyl and Fukushima Daiichi nuclear power plants. 137Cs, in particular, is of major concern in terms of agriculture due to its relatively long half-life (30.2 years for 137Cs), its strong fixation by the soil, and easy absorption by plants. Therefore, several countermeasures have been undertaken. For instance, topsoil removal and potassium fertilizer successfully reduced the level of RCs contamination in agricultural products. However, the relation between the transfer factor and exchangeable potassium (Kex) differs depending on the soil, meaning that there are several parameters including Kex that influences caesium (Cs) uptake by plants. The reason remains unclear, but a previous studies suggested that exchangeable 137Cs could be a crucial factor in explaining the variation. Also, some factors such as solid/liquid distribution coefficient (Kd) of Cs, or the ratio of exchangeable 137Cs versus total 137Cs (137Csex / 137Cstotal) in the soil could be involved in the determination of the risk of 137Cs uptake by plants. Furthermore, a rapid risk assessment is needed while these parameters can take a huge amount of time to be determined. Hence, Mid-Infrared Spectroscopy (MIRS), being faster, more cost-effective, and non-destructive, may be utilized for the determination of these parameters. However, the prediction of these parameters using MIRS has yet to be assessed. In this study, we aimed to assess whether MIRS can predict Cs-related parameters in the soil such as Kd, 137Csex / 137Cstotal, Kex and other parameters that may be of influence on the behaviour of RCs in the soil, such as CEC, pH, and soil organic carbon.In total about 1700 soil samples were collected from agricultural fields in the Fukushima Prefecture in Japan. The soil samples were air-dried and ground. The MIRS data were obtained using a Thermo Scientific Nicolet iS20 spectrometer. Using Partial Least Squares Regression as a baseline, the spectra data and the wet chemistry data including Kd, 137Csex / 137Cstotal, and Kex, among other soil parameters, were used for modelling and prediction. Even though until present (at submission of this abstract) only 176 samples have been measured, we found that balancing the range of values between training and validation sets enabled Partial Least Regression Estimation methods to provide a relatively high R2 valid score for the prediction of each wet chemistry data, especially soil organic carbon, CEC, Mgex and Caex, ranging between 0.73 and 0.88. Using less than 200 samples, however, the validation scores of Cs -related parameters were less than 0.5. Further MIRS data are expected for up to about 1600 soil samples, for 137Csex / 137Cstotal in the soil. Additional processing and modelling techniques will be tested aiming at further improving the validation scores, and results will be shown at EGU.

Use of cover crops, mulches and other soil management practices have been widely promoted within the EU, as measures to draw down carbon dioxide and increase soil organic carbon in the fight against climate change. These approaches are being investigated in a number of programs and projects EU-wide, for example the EJP-SOIL program.We used a long-term fully replicated maize based field trial with different crop and soil management practices, namely residue incorporation and/or inclusion of a cover crop, to explore carbon sequestration potential. We used natural abundance stable isotope approaches to follow the fate and residence time of mulched residues and to determine the most stable organic matter pools in these systems. We measured isotope signatures in particulate organic matter (POM), mineral associated organic matter (MOAM), stable aggregate bound organic matter (IA-POM) and soil microbial biomass (Mi-BIO) to characterize the impact of the soil fraction, on the fate and stability of the carbon pool and to test a number of emerging paradigms in soil science. We hypothesized that the residence time of the POM fraction and MOAM fractions would be lower under higher nitrogen inputs and that it would be possibly to detect these shifts using a stable isotope approach. Moreover, we used handheld and unmanned aerial vehicle UAV-captured multispectral data to investigate impacts of management on a plot scale.Preliminary results show that even at low mulch rates (

Studies on worm-composting or vermicomposting, the addition and use of worms to recycle food and other organic wastes into a nutrient-rich product called vermicast, have shown that when used as soil amendment or activator, they have numerous positive effects on soil physico-chemical properties including: soil aeration, water-holding capacity, nutrient supply and they could be valuable peat substitutes in nursery production. Furthermore, vermicompost is an interesting proposition in the circular economy, particularly with food wastes in peri-urban areas. Despite these advantages, some studies have indicated that worm produce potent greenhouse gases (GHG), notably nitrous oxide (N2O). It has been suggested that the addition of biochar (BC) to the systems worm-compost-soils could substantially reduce the N2O emissions. The use of Biochar (BC), a biomass pyrolysis by-product, as soil amendment has been proposed essentially for its vast carbon sequestration potential as a “nature based solution” to combat anthropogenic induced climate change.In this study, in addition to quantifying the GHG emissions from the entire worm-composting process and assessing the impact of BC addition on the vermicomposting process, particularly the nitrous oxide emissions (N2O), we determined the potential influence of the timing of the BC addition, whether biochar added before (BC-Compost-worms) or after (Compost-BC-worms) in the initial hot composting process had an influence on overall GHG emission; targeting essentially how biochar (BC) reduces the GHG emissions from the wormication process. We followed right through to the crop production stage using spinach as a test crop, to both determine and compare the N2O emissions from conventionally grown and organically produced products in a greenhouse experiment. To fully assess and compare these emissions from compost, compost-worms and biochar (BC) additions, we also added a treatment with equivalent inorganic fertilizer using nitrogen stable isotope (15N) labelling with the aim to see the pathway of the fertilizer, matching the nitrogen uptake with observed emissions.In all seven treatments were established: compost only, compost worms, BC-Compost worms, Compost-BC worms, equivalent inorganic 15N fertilizer, soil only, and soil only no plants. Using a novel experimental set-up and cavity ring down laser based flow through system for analysis we explored the impacts of treatments on both GHG emissions and plant production. Our central hypothesis is that biochar will reduce N2O emissions from the worm treatments and that, this will lead to greater reductions in worm emissions when BC is added after (Compost-BC-worms) the initial hot composting process than compared to when added before (BC-compost-worms). The results and conclusions of this study will be presented.

Spent mushroom substrates, Tremella fuciformis (Tf), Flammulina velutipes (Fv), and Lentinula edodes (Le), were used to produce biochar at different temperatures (300 °C, 400 °C, 500 °C, 600 °C, and 700 °C). Elemental compositions and surface properties of derived biochar were determined. The yield and volatile matter (VM) of the biochars decreased as the pyrolysis temperature increased with Le300 having the highest yield (47.4%). The highest VM was obtained in Tf300 (79.6%). The biochars were alkaline, with Fv700 having the highest pH (11.6). Pyrolysis temperature and feedstock influenced nutrient composition of biochars and highest values were obtained in: Tf300 (N=2.07%), Fv700 (P=12.0 g/kg), Le700 (K=21.9 g/kg), Fv600 (CEC=32.3 cmol/kg), Fv700 (Ash=33.4%) and Le700 (C=58.6%). Heavy metals in the Fv biochar were highest but within their tolerable limits. Fourier transform infrared spectra showed various functional groups on the biochar surfaces with C-O being dominant (except on Le biochar). X-ray diffraction revealed that SiO2 and CaCO3 were present on biochar surfaces. The Fv biochars had the largest surface area with Fv400 having the highest value (210.6 m2g-1) while Le400 had the highest average pore diameter (159.7 Å). These properties render the biochars suitable as soil amendment and in environmental remediation.

Nitrogen (N) fertilizer management is challenging due to the many factors and have low N use efficiency (NUE). Heavy N losses from soil reduce plant yield and have negative impacts on the environment. Nitrogen processes inhibitors, such as urease and nitrification inhibitors (UI and NI), are chemical compounds which reduce urea hydrolysis and nitrification respectively. By coating ammonium based chemical fertilizers with N process inhibitors allows N to stay in a more stable form of ammonium (NH4+) thus minimising N losses as well as improving NUE and consequently enhancing crop yield.A field experiment was established at the Soil and Water Management and Crop Nutrition Laboratory (SWMCNL) in Seibersdorf, Austria to determine the effect of different N fertilizers coated with N process inhibitors on maize yield in summer 2020. The field site is characterised by a moderately shallow Chernozem soil with significant gravel content. Three combinations of N fertilizer (urea or NPK) with N process inhibitors (UI and/or NI)) were tested and compared with a control treatment (without N fertilizer) and a urea application without any inhibitor. All treatments received 60 kg ha-1 P2O5 and 146 kg ha-1 K2O. The amount of N added to each treatment receiving N fertilizer was 120 kg N ha-1. The inhibitors used were (i) UI (2-NPT: N-(2-nitrophenyl) phosphoric acid triamide), (ii) NI-1 (MPA: N-[3(5)-methyl-1H-pyrazol-1-yl) methyl] acetamide), and (iii) NI-2 (DMPP: 3,4-dimethylpyrazole phosphate). DMPP, a nitrification inhibitor, was used in combination with NPK fertilizer. A randomized complete block design with four replications was used in this study. Treatments were: T1 (control treatment - without N fertilizer), T2 (Urea only), T3 (Urea + UI), T4 (Urea + UI + NI-1), and T5 (NPK + NI-2). Urea was applied through two split applications in the T2 treatment. In T3, T4, and T5 treatments, N fertilizers were applied only once. Supplemental irrigation was only applied in the early stages of growth, to ensure that the crop could establish. Harvest was carried out at 98 days after planting.The yield data showed that different fertilizer treatments had a significant (p ≤ 0.01) effect on maize yield (dry matter production). There was no significant difference between treatments 4 and 5, which had the highest yield followed by treatments 2 and 3. The comparison between T2 and T3 showed that the application of a urease inhibitor avoids the need for a split application of urea, which decreases labour costs. Adding NI-1 (under T4) further increases the yield. Also, the package of NPK, a common choice by farmers in Austria, in combination with the nitrification inhibitor NI-2 showed equally good results as urea combined with two inhibitors. Based on the yield results, it can be concluded that N process inhibitors play a significant role in enhancing maize yields.

The Danube is Europe`s second longest river, stretching from Germany to the Black Sea. Water quality in the Danube River Basin is regularly monitored by the national authorities of all riparian countries and in addition for specific water quality data during the Joint Danube Surveys (JSD), which is organised by the International Commission for the Protection of the Danube River every 6 years.This study presents the results of water stable isotopes and stable isotopes (15N and 18O) of nitrate as well as major ion analysis from 3 JDS (2001, 2007, 2019). Results indicate that water stable isotopes allow to trace differences in the amount of snowmelt contribution to the Danube and hence the dilution effects of pollutants e.g. nitrate. The oxygen and nitrogen isotope compositions of nitrate are clearly indicating that nitrate in the Danube main stream mainly derives from waste water effluents, which input is increasing along the stream. This can furthermore be confirmed by results of micropollutant studies that demonstrate an increase of widely consumed pharmaceuticals (carbamazepine, diclofenac and caffeine) at different sections of the Danube River affected by tributary inflows and discharge from urban settlements.In summary, this study is an example of combining isotope techniques, hydrological methods but also emerging compounds in order to approach the fate of anthropogenically derived nitrate within the Danube Basin. The results of this study aim to support the 2021 update of the Danube River Basin Management Plan as well as water monitoring practices across the Danube countries.

Accurate measurements of nitrous oxide (N2O) fluxes from soils are necessary to understand dynamic changes in soil nitrogen cycles. Laboratory incubation experiments provide a controlled condition to measure these N2O fluxes. Before incubation experiments, soils are often stored at certain conditions to minimize the microbial activities. However, the effect of soil storage on N2O emission has been poorly studied. A laboratory incubation experiment was conducted using disturbed soils to study the storage effect. The soil was sieved to 2mm and the following four treatments were tested: fresh undisturbed (FU), fresh sieved (FS), fridge stored at 4ºC (ST), and stored at room temperature after drying (PI). After soil samples were brought to 60% water-filled pore space (WFPS), 15N labelled urea (1 At%) was applied at the rate of 50 mg N kg-1 soil and the soil was incubated at room temperature (23 ºC). The N2O fluxes were measured for 7 weeks using off-axis integrated cavity output spectroscopy (OA-ICOS, Los Gatos Research, California, USA). Cumulative N2O fluxes and Keeling plot intercepts (δ15N source) were calculated. The results showed that soil storage has a significant effect on N2O emission. Over the 7-week period, ST produced the highest cumulative N2O emissions (2.70 µg N g-1 soil) as well as the largest amount of N derived from fertiliser (Ndff) (1.4 µg N g-1 soil). FU produced the lowest cumulative N2O emissions (1.0 µg N g-1 soil) but the largest amount of N derived from soil (Ndfs) (0.6 µg N g-1 soil). The daily N2O fluxes of FS and FU declined rapidly after the peak emissions, but the fluxes of PI and ST fluctuated after the peaks. These results indicate that soil storage affects microbial processes and therefore N2O emissions. Our results suggest using fresh soil to avoid storage effects. If this is not possible the effect of soil storage should be considered before the experiment.

Changes in climate will bring along changes in precipitation patterns, and as such, it will determine the availability of water in agricultural systems. We aimed to investigate the impact of climate-induced altered precipitation regimes on crop performance and soil processes such as organic matter mineralisation and nutrient release. The experiment took place at the lysimeter station located in Hirschstetten, Vienna, Austria (48° 15' 22" N, 16° 289 3" E, 160 m a.s.l.) where a future precipitation scenario was compared with current precipitation patterns on two different soil types – a sandy calcaric Phaeozem and a calcic Chernozem, both being representative for the Marchfeld region in Lower Austria. The future precipitation regime was calculated from four regionalised scenarios from Euro-Cordex out of the ÖKS 15 ensemble following the GHG emission scenarios RCP 4.5 and RCP 8.5.Stable isotope analysis has become a useful tool for sensitively tracing biogeochemical processes in soils. In this study, plant residues of white mustard (Sinapis alba), isotopically labelled with carbon 13C and nitrogen 15N in a controlled laboratory environment were applied as organic fertiliser (green manure) on the lysimeter soils in April 2018. Soil, plant, gas and groundwater samples were collected from the lysimeters throughout the growing season of 2018 and 2019 and analysed using cavity ring-down spectrometry (CRDS) for 15N-N2O in the field and by isotope ratio mass spectrometry.Crop results showed an increase in the shoot 13C signatures, indicative of drought stress, which resulted in diminished plant production by -20 to -50% under the decreased precipitation. Isotope analysis showed lower decomposition and mineralisation rates of labelled green manure only during the first few days under the future precipitation treatment, followed by an increase in 15N enrichment of soil solution NO3- during summer, emphasising the importance of plant biomass production on root NO3- uptake from the soil. N2O emissions were higher after the application of synthetic fertiliser during the first year, highlighting the importance of available NO3- in agricultural systems for nitrification and denitrification processes. However, lower N2O emissions were observed during the second year, indicating possible N stress. Overall we found that N losses through NO3- leaching and N2O emissions were most sensitive to reduced precipitation when NO3- is available, which can cause aggravating environmental problems in the future.The stable isotope labelling technique proved to be successful for tracing and identifying drought stress effects on plant and soil processes in agricultural systems, allowing for a better understanding of soil-plant processes under changing climate conditions.

RATIONALE Carbon-13 (13 C)-labelled plant material forms the basis for experiments elucidating soil organic carbon dynamics and greenhouse gas emissions. Quantitative field-scale tracing is only possible if plants are labelled homogeneously in large quantities. By using a laser spectrometer to automatically steer the isotopic ratio in the chamber, it is possible to obtain large amounts of homogeneously labelled plant material. METHODS Ninety-six maize plants were labelled for 25 days until tassel formation in a 15 m3 walk-in growth chamber with a continuous air δ13 C-CO2 value of 400‰. A Los Gatos Research laser absorption spectrometer controlled the ambient δ13 C-CO2 value in the chamber through steering of the mass flow controllers with 13 C-enriched and natural abundance CO2 gas. RESULTS Laser absorption spectroscopy steering kept the δ13 C value of chamber air between 368 and 426‰. The resulting 1 kg dry matter of 13 C-labelled shoots showed an average δ13 C value of 384‰ and accuracy of 8‰ (half width of the 95% confidence interval). Only the oldest leaves showed larger heterogeneity. The growth chamber eliminated variability between plants. The δ13 C value of the stabile material did not differ significantly from that of bulk material. CONCLUSIONS Laser spectroscopy controlled 13 C labelling of plants in a walk-in growth chamber successfully kept the isotopic ratio of the CO2 in the chamber air constant. Therefore, large quantities of material were labelled homogeneously at the inter- and intra-plant level, thus establishing a method to provide high-quality input for quantitative isotopic tracer studies.

Soil management techniques, such as mulching, are used to enhance soil organic carbon sequestration. However, we demonstrate that the potential of crop residue mulching to increase soil organic carbon (SOC) sequestration varies by cropping system and soil type in Austrian agricultural soils. Effects of mulch (as harvested crop residues applied at 1.0 t C ha−1) on soil and microbial carbon (C) and nitrogen (N) and soil δ13C were measured in an Austrian Cambisol field experiment with sole maize or vetch or vetch-maize rotation cropping systems after five years with or without mulching to elucidate how SOC is affected. The direct role of mulch on SOC in different soil types was also investigated in a similar greenhouse mesocosm study with controlled moisture using the same Cambisols and an Austrian agricultural Chernozem. Only sole maize cropping in the field experiment resulted in higher SOC with mulching and when legumes were included in a legume-maize rotation SOC did not improve. Mulching in the field experiment only resulted in higher SOC in the top 0–5 cm of soils with sole maize cropping (by 22%) compared to soils without mulch. Although mulch did not increase SOC in vetch-maize rotation, the δ13C of SOC was less negative with mulch indicating larger C contribution from maize than vetch mulch. After four years of annual soybean-maize rotation in the mesocosm experiment, no significant differences in SOC were observed in Cambisols with or without mulch. Again, δ13C of both soil types was less negative with mulching indicating a larger C contribution from maize than soybean mulch. No relationships between microbial biomass C and N and SOC were observed in either experiment and only soil N concentration was positively correlated with SOC. Together these studies indicate that maize can increase SOC when crop residues are applied in Austrian Cambisols but that inclusion of legume production and legume mulch in rotation can mute these benefits.

Biochar amendment in soils has been proposed as an important strategy to improve soil C retention. However, while the exact roles of different biochar types on soil organic carbon (SOC) dynamics are not clear, the effect of their interactions with chemical fertilization on SOC, the dynamics of C-cycling enzyme activities and key C-cycling-related bacteria in rhizosphere soil remain unexplored. Therefore, biochars derived from rice straw, bamboo, cow, and pig manure were applied with/without chemical fertilizer to study soil C dynamics, the activities, diversity, and abundance of different C-cycling-related bacteria in the plant-soil system. Biochar + fertilizer (BF), irrespective of biochar source, induced an initial increase in dissolved organic and inorganic C (DOC and DIC) that were subsequently reduced compared to biochar over 15-weeks. Higher intensities of C-containing functional groups rather than the total C content of biochar induced the mineralization of SOC. Also, higher nutrient uptake, biomass, and CO2 concentration in plants under BF had an insignificant influence on SOC. Similarly, the reduction in mineral-associated organic C, DOC, DIC, and invertase activity in BF soils was associated with a decrease in the relative abundance of some key C-cycling related bacterial orders: Gemmmatimonadales, Myxococcales, Nitrosomonadales, and Acidimicrobiales, while the hydrocarbon-degrading taxa (Sphingmonadales and Xanthomonadales), and N-cycling bacteria were stimulated. Hence, BF amendment could exert varied influences on C-cycling-related bacteria and on global C-cycling. The use of BF limited C-cycling and its loss by providing more N-substrates for N-cycling organisms, which also competed with most C-cycling-related bacteria for organic C to regulate C mineralization and its associated loss.

Carbon-13 (Ninety-six maize plants were labelled for 25 days until tassel formation in a 15 mLaser absorption spectroscopy steering kept the δLaser spectroscopy controlled

Black carbon (BC) from incomplete combustion of organic materials is abundant in many soils. Its age is often higher than that of thermally unaltered soil organic carbon (SOC) owing to the presence of BC from fossil sources or to a high recalcitrance against microbial decomposition compared to that of plant residues. For a meaningful application of radiocarbon as an indicator for soil carbon age and turnover, the relative contribution of BC needs to be quantified, but BC is difficult to separate physically from soil. However, BC is thermally more stable than SOC, and hence thermal stability may provide a quantitative BC indicator. Here, we analyzed 30 light particulate organic carbon (POC) soil fractions for their thermal stability and for their 14C signature. POC is particularly sensitive to “contamination” with BC, because it is obtained by combined size and density fractionation. A steady-state “bomb” 14C model was used to derive mean POC ages. Soils from four sample sets, each consisting of six to eight individual POC samples and representing different field sites and POC types, were analyzed. Samples from one of the sets were virtually BC free, and their mean POC ages ranged from 60 to 100 yr. The 14C signature of samples from the other three sets indicated the presence of very old carbon, with mean POC ages of several hundred and up to 3500 yr. Two indicators for thermal stability—(1) the amount of heat released at temperatures >450°C and (2) the amount of heat released at 500°C (the latter representing the peak temperature of heat released from charcoal isolated from soil)—correlated both significantly and nonlinearly with POC age, indicating that samples with high BC content were older than those with low BC content. It can be concluded that at an individual site with increasing abundance of BC, both the age and the thermal stability of POC increase. However, thermal stability proved to be a reliable predictor for BC in only one sample set, whereas thermal signals of the other two BC-containing sample sets were not significantly different from those of BC-free samples. Thermal stability thus gives no unequivocal indication for the presence of BC in POC across different sites.

There is a deficit of mineral micronutrients in global food systems, known as ‘hidden hunger’, especially in the global south. This review focuses on zinc (Zn) and iron (Fe), whose entry into food systems depends primarily on soil and crop factors. Approaches to increase dietary supplies of Zn and Fe include: (1) supplementation, (2) food fortification, (3) dietary diversification, and (4) crop biofortification, including breeding and fertilizer-based approaches. Supply-based estimates indicate that Zn deficiency might be more widespread than Fe deficiency in sub-Saharan Africa, although there are major knowledge gaps at an individual biomarker level. Recent analytical advances, including the use of stable isotopes of Zn and Fe, can play an increasing role in improving our understanding of the movement of micronutrients in food systems, and thereby help to reduce the immense human cost of ‘hidden hunger’.

In order to evaluate the sustainability and efficiency of soil carbon sequestration measures and the impact of different management and environmental factors, information on soil organic matter (SOM) stability and mean residence time (MRT) is required. However, this information on SOM stability and MRT is expensive to determine via radiocarbon dating, precluding a wide spread use of stability measurements in soil science. In this paper, we test an alternative method, first developed by Conen et al. (2008) for undisturbed Alpine grassland systems, using C and N stable isotope ratios in more frequently disturbed agricultural soils. Since only information on carbon and nitrogen concentrations and their stable isotope ratios is required, it is possible to estimate the SOM stability at greatly reduced costs compared to radiocarbon dating. Using four different experimental sites located in various climates and soil types, this research proved the effectiveness of using the C/N ratio and δ15N signature to determine the stability of mOM (mineral associated organic matter) relative to POM (particulate organic matter) in an intensively managed agro-ecological setting. Combining this approach with δ13C measurements allowed discriminating between different management (grassland vs cropland) and land use (till vs no till) systems. With increasing depth the stability of mOM relative to POM increases, but less so under tillage compared to no-till practises. Applying this approach to investigate SOM stability in different soil aggregate fractions, it corroborates the aggregate hierarchy theory as proposed by Six et al. (2004) and Segoli et al. (2013). The organic matter in the occluded micro-aggregate and silt & clay fractions is less degraded than the SOM in the free micro-aggregate and silt & clay fractions. The stable isotope approach can be particularly useful for soils with a history of burning and thus containing old charcoal particles, preventing the use of 14C to determine the SOM stability. publisher: Elsevier articletitle: Predicting soil organic matter stability in agricultural fields through carbon and nitrogen stable isotopes journaltitle: Soil Biology and Biochemistry articlelink: http://dx.doi.org/10.1016/j.soilbio.2015.05.011 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: Soil Biology & Biochemistry vol:88 pages:29-38 status: published

A diffusion method for the preparation and measurement of 15N abundance of ammonium and nitrate in KCl extracts of soil using optical emission spectrometry (OES) was compared with conventional continuous flow isotope ratio mass spectrometry (IRMS). There were highly significant correlations between the values obtained by using OES and IRMS. The 99% confidence interval of the intercept included the value 0 and the 99% confidence interval of the slope included the value 1 for both nitrate and ammonium measurements, suggesting that the results from the two methods did not differ significantly. In another experiment, 15N values of nitrate and ammonium from soil extracts prepared by using the standard distillation procedures for OES were compared against the microdiffusion preparation method. Again, there was a highly significant correlation between the values: the 95% confidence interval of the intercept included the value 0, and the 95% confidence interval of the slope included the value 1, again su...

Until recently, the only reliable way of doing 12C-13C analysis was using a mass spectrometer. For many developing countries, the high initial cost and running costs of a mass spectrometer precluded the purchase of such an instrument. Recent developments in optical systems have provided a robust, low-cost option for undertaking 13C analysis. Although these machines were initially developed for breath testing for Helicobacter pylori, they have an enormous potential as a research tool for soil science. The relatively low cost of the equipment at US$15,000–25,000 is within the research budgets of most institutes or universities. The simplicity of the mechanisms and optical nature mean that the equipment requires relatively low maintenance and minimal training. 13C may be used to study numerous areas including: organic matter turnover, shifts in δ 13C from C4 to C3 vegetation, organic matter residence times, determination of sources of stable organic matter, δ 13C differences in drought and salt tolerant isol...

To utilise wisely the manure resource, a better understanding of the processes that control the breakdown of organic N to inorganic N (mineralization) is required. 15N isotope dilution techniques should allow estimates of plant N uptake and gross mineralization from organic manures under non-N limiting conditions to be made. In natural systems the study of organic nitrogen breakdown to inorganic nitrogen, mineralization, is confounded by the processes of nitrification, nitrate leaching, gaseous N losses and plant N uptake. The 15N isotope dilution approach allows measurement of gross mineralization independently of these processes. Greenhouse experiments were conducted to determine plant N uptake from organic manures under non-N limiting conditions using the soil pre-labelling isotope dilution approach. The soil was pre-labelled with 15N and maize plants were then grown on the control treatments (no organic amendment) or on the manure treatments. The principle is thus that the control crop has a 15N abundance which reflects the 15N status of the soil and the treatment crop has a 15N enrichment diluted by the contribution of mineralized unlabelled manure N. Using this technique, it was estimated that maize plants derived 17 and 34% of their N from sewage sludge and turkey manure, respectively. The soil pre-labelling isotope dilution approach allowed yield-independent estimation of nitrogen derived from manures under non-N limiting conditions. Estimates of gross N mineralization were made to determine the breakdown of manure under field conditions. Results suggested that there was a rapid mineralization of turkey manure N in the initial weeks after application, in the order of 50 kg N ha−1, which tailed off in the following weeks. The technique suggested that the soil used in the study had an extremely low basal mineralization rate, and a high nitrification rate.

Recent developments in optical systems (isotope-selective non-dispersive infrared spectrometry) for breath testing have provided a robust, low-cost option for undertaking (13)C analysis. Although these systems were initially developed for breath testing for Helicobacter pylori, they have an enormous potential as a soil science research tool. The relatively low cost of the equipment, US$15,000-25,000, is within the research budgets of most institutes or universities. The simplicity of the mechanisms and optical nature mean that the equipment requires relatively low maintenance and minimal training. Thus methods were developed to prepare soil and plant materials for analysis using the breath test analyser. Results that compare conventional mass spectrometric methods with the breath test analyser will be presented. In combination with simple (13)C-plant-labeling techniques it is possible to devise methods for estimating carbon sequestration under different agronomic management practices within a short time frame. This enables assessment of the carbon credit value of a particular agronomic practice, which can in turn be used by policy makers for decision-making purposes. For global understanding of the effect of agricultural practices on the carbon cycle, data are required from a range of cropping systems and agro-ecological zones. The method and the approach described will enable collection of hard data within a reasonable time.