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Nitrogen (N) budgets are a valuable tool for improving N efficiency because they assess the size and interactions of various N pools, as well as their gains from the atmosphere and losses to the environment. To understand the impact of changes in management practice upon a farming system, it is necessary to increase the complexity of the N budgets to include N flows. Therefore, a project was undertaken in lowland irrigated systems of Bangladesh to study the N budgets of Boro rice grown under ecological and conventional farming systems in four locations (Dhamrai, Daulatpur, Gabtali and Shibgonj) in Bangladesh in 2007 and 2008. The N budget focuses on the total-N inputs and losses of the entire system. The budgets were negative for both farming systems in both years. Overall, ecological farming system produced a less negative balance in both years (−6 to −36 kg N ha−1 in 2007 and −76 to −160 kg N ha−1 in 2008) than the conventional farming system (−28 to −80 kg N ha−1 in 2007 and −91 to −157 kg N ha−1 in 2008). Nitrogen balance studies highlighted losses of mineral N (26–53 kg N ha−1) which accumulated prior to irrigation and also losses due to N removal (13–28 kg N ha−1) by weeds. Beneficial impacts of ecological farming on N balances were observed due to the elimination of fertiliser N loss (30–133 kg N ha−1). The difference between conventional and ecological management reflects the high losses of fertiliser N under conventional management. These fertiliser N losses reflect the low agronomic efficiency of N fertiliser. An understanding of various N losses and their consequences is important to provide a basis for developing efficient N management strategies in boro rice. These N budgets can be used to improve or design new technologies that tackle soil fertility management problems and also can help improve the financial performance of the farmers. Soil N budgets will continue to challenge agricultural scientists by slowly revealing fundamental principles. By understanding these principles and the factors influencing them, basic and applied scientists will have a stronger foundation for improving N use efficiency and concurrently reducing N losses to the environment.

Long-term changes in soil organic carbon (SOC) resulting from management change are documented for many experimental situations, and corresponding trends in the field have been observed by national survey. Since these changes are relevant to atmospheric carbon balance a practical measure to confirm the impact of recent management decisions at any location, without resorting to repeated sampling, is highly attractive but none has previously been tested. This study assessed intra-aggregate C to fulfil the role, based on a temporary deviation from its predictable contribution to total SOC under stable management. A total of 166 surface soil samples (0-15 cm) were analyzed for intra-aggregate C using an established physical fractionation protocol or compatible scaled-up procedure. Soils were arable (or ley-arable) managed by conventional or minimum-tillage, or permanent grassland, and assigned 'stable' or 'changing' status on the basis of a verbal account of management history. Log-normal populations of intra-aggregate C were compared for soils of stable and changing status using F-tests. Intra-aggregate C shows promise as an indicator of changing SOC in arable soils up to 30% clay content, particularly soils < 20% clay. A larger dataset is required to establish its utility in grassland soils. It is not certain that intra-aggregate C is capable of confirming direction of change or trajectory (endpoint), and functions to indicate change, rather than confirm stable status. Supplementary information on the history of soil use and management is therefore essential in the interpretation of such measurements.

The implications for greenhouse gas emissions of optimizing a slow pyrolysis-based bioenergy system for biochar and energy production rather than solely for energy production were assessed. Scenarios for feedstock production were examined using a life-cycle approach. We considered both purpose grown bioenergy crops (BEC) and the use of crop wastes (CW) as feedstocks. The BEC scenarios involved a change from growing winter wheat to purpose grown miscanthus, switchgrass, and corn as bioenergy crops. The CW scenarios consider both corn stover and winter wheat straw as feedstocks. Our findings show that the avoided emissions are between 2 and 5 times greater when biochar is applied to agricultural land (2--19 Mg CO2 ha(-1) y(-1)) than used solely for fossil energy offsets. 41--64% of these emission reductions are related to the retention of C in biochar, the rest to offsetting fossil fuel use for energy, fertilizer savings, and avoided soil emissions other than CO2. Despite a reduction in energy output of approximately 30% where the slow pyrolysis technology is optimized to produce biochar for land application, the energy produced per unit energy input at 2--7 MJ/MJ is greater than that of comparable technologies such as ethanol from corn. The C emissions per MWh of electricity production range from 91-360 kg CO2 MWh(-1), before accounting for C offset due to the use of biochar are considerably below the lifecycle emissions associated with fossil fuel use for electricity generation (600-900 kg CO2 MWh(-1)). Low-temperature slow pyrolysis offers an energetically efficient strategy for bioenergy production, and the land application of biochar reduces greenhouse emissions to a greater extent than when the biochar is used to offset fossil fuel emissions.

This chapter explores some of the implications of adopting a research approach that focuses on people and their livelihoods in the rice-wheat system of the Indo-Gangetic Plains. We draw on information from a study undertaken by the authors in Bangladesh and then consider the transferability of our findings to other situations. We conclude that if our research is to bridge the researcher-farmer interface, ongoing technical research must be supported by research that explores how institutional, policy, and communication strategies determine livelihood outcomes. The challenge that now faces researchers is to move beyond their involvement in participatory research to understand how to facilitate a process in which they provide information and products for others to test. Building capacity at various levels for openness in sharing information and products–seeing research as a public good for all–seems to be a prerequisite for more effective dissemination of the available information and technologies.

The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is pro- posed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver im- mediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (

Knowledge of the stocks and the potential range of soil organic carbon (SOC) in various land–soil combinations is an important precursor to policies aimed at linking, for example, management of SOC to greenhouse gas emission controls. To investigate the factors controlling the percentage of SOC (%SOC) of soils in England and Wales, we made a multiple regression analysis of data for the 2448 arable and ley-arable sites in the 1980 England and Wales National Soil Inventory (NSI). Clay content, average annual precipitation and depth of topsoil explained 25.5% of the variation in %SOC, when calcareous and peaty soils and those susceptible to flooding were excluded. Using ‘robust’ statistics, ‘indicative SOC management ranges’ were estimated for different physiotopes, that is, landscape units for which the environmental factors governing %SOC are similar, namely soil clay content and precipitation. These ranges describe the expected %SOC range for an arable soil in a given physiotope. They have potential to support approximate targets for the %SOC of arable soils and for estimating upper and lower limits for sequestered soil carbon in arable systems.

A range of spectroscopic, wet chemical, gas chromatographic (GC) and mass spectrometric (MS) techniques was applied to the characterisation of three soil organic matter (SOM) fractions that have been proposed as the basis of a new SOM turnover model based on measurable, physically defined fractions. The fractions were: the free light fraction (obtained by density separation in NaI solution at a density of 1.80 g cm � 3 , without disruption of aggregates), the intra-aggregate light fraction (obtained using a second density separation after disrupting aggregates using ultrasonic dispersion) and the organomineral fraction corresponding to the residual heavy material. The techniques employed to investigate the composition of the organic constituents of each fraction were: 13 C nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) to study bulk composition. Lipid, lignin and carbohydrate fractions were assessed using GC and GC/MS with appropriate derivatisation, following oxidative and hydrolytic treatments, respectively, in the case of the latter two classes. Proteinaceous components were determined as amino acids using reversed-phase high performance liquid chromatography (HPLC) following 6 M HCl treatment and derivatisation. Each technique revealed marked differences in chemical composition between the organomineral and the two light fractions, with the results being consistent with the organomineral fraction having different biological sources or having undergone a greater degree of degradation or transformation. Several techniques detected differences between the composition of the free light fraction and the intra-aggregate light fraction. With the exception of carbohydrate composition, the results were consistent with the order of reactivity previously proposed from incubation studies with isotopically labelled substrates, namely: free > intra-aggregate > organomineral. The investigation illustrates the importance of using a range of different chemical characterisation techniques in studies of complex SOM fractions as each has limitations that could, if used alone, produce ambiguous findings or fail to detect differences between them. � 2005 Elsevier Ltd. All rights reserved.

Current models of soil organic matter (SOM) turnover tend to invoke pools that are defined by their contrasting first-order reactivity constants but which cannot be directly measured. New models may be based around fractions defined by procedures that can be used to isolate them experimentally. The drawback of such fractions is that they may display properties that are not sufficiently distinct or which vary in time or space. In this study the properties of two fractions from soils of contrasting geographical origin and under different nutrient management were examined using 13 C nuclear magnetic resonance (NMR) spectroscopy. The fractions were free SOM (FR-SOM, discrete organic particles located between stable aggregates), and intra-aggregate SOM (IA-SOM, discrete organic particles within stable aggregates). The composition of both fractions was highly consistent across soil types and environments, but the fractions differed significantly in the proportion of C present in five of the seven functional C groups identified by NMR (P

Bangladesh is currently self sufficient in rice ( Oryza sativa L.), which accounts for approximately 80% of the total cropped area, and 70% of the cost of crop production. However, farmers are increasingly concerned about the perceived decline in productivity, expressed as the return on fertiliser inputs. Agronomic efficiency is a measure of the increase in grain yield achieved per unit of fertiliser input that can provide a way to quantify the observation of farmers. This study indicates that the yields achieved where only P and K fertiliser were applied ranged from 3–5 t ha −1 , indicating good soil fertility, particular in terms of soil N supply (37–112 kg N ha −1 ). However, at recommended rates and at rates used by farmers, the yield response to application of fertiliser N was low. Data shows that grain yields were significantly correlated in both years ( R 2 = 0.77 and R 2 = 0.67) with plant uptake in nitrogen. The internal nitrogen use efficiency seems to confirm that sink formation was limited by factors other than nitrogen. Low agronomic efficiency (5–19 kg grain kg −1 N) was caused by poor internal efficiency (45–73 kg grain kg −1 N), rather than low supply of soil N or loss of fertiliser N. Thus, often the applications of large amounts of N fertiliser (39–175 kg N ha −1 ) by farmers to increase yields of high yielding variety Boro rice were not justified agronomically and ecologically. A rate of 39 kg N ha −1 is very low, hardly an environmental threat. No one single factor could be identified to explain the low internal efficiency. Therefore, it is concluded that the data presented tend to confirm the indication that yields are limited by a factor other than nitrogen, which could be crop establishment, plant density, water or pest management, micro-nutrients deficiency, poor seed and transplanted seedling quality, varieties and low radiation.

We used thermal analysis to compare the proportions of active and more stable components in soil organic matter (SOM) fractions and whole soil under contrasting agricultural land-uses. The fractions (free light, intra-aggregate, and organomineral fractions) were isolated using density fractionation. Exothermic weight loss between 300 and 350°C was attributed to a relatively labile portion comprising carboxyl and aliphatic C, and that between 400 and 450°C to the decomposition of material rich in aromatic components. Under arable cultivation, free light SOM showed much greater weight loss in the first exothermic range than intra-aggregate SOM. In soil receiving very small inputs of organic matter (a long-term bare fallow) the free light and intra-aggregate fractions displayed similar characteristics and resembled the intra-aggregate fraction from the arable soil. The difference between the free light and intra-aggregate fractions was also small for the grassland soil but the fractions resembled the free light fraction from the arable soil. Small total weight loss for whole soil and organomineral fractions demonstrated the value of physical fractionation techniques in establishing the effect of land-use on SOM with greater precision than is possible whole (unfractionated) soil.

The technology for site-specific applications of nitrogen (N) fertilizer has exposed a gap in our knowledge about the spatial variation of soil mineral N, and that which will become available during the growing season within arable fields. Spring mineral N and potentially available N were measured in an arable field together with gravimetric water content, loss on ignition, crop yield, percentages of sand, silt, and clay, and elevation to describe their spatial variation geostatistically. The areas with a larger clay content had larger values of mineral N, potentially available N, loss on ignition and gravimetric water content, and the converse was true for the areas with more sandy soil. The results suggest that the spatial relations between mineral N and loss on ignition, gravimetric water content, soil texture, elevation and crop yield, and between potentially available N and loss on ignition and silt content could be used to indicate their spatial patterns. Variable-rate nitrogen fertilizer application would be feasible in this field because of the spatial structure and the magnitude of variation of mineral N and potentially available N.

A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for measuring microbial biomass C (CBIO) and N (NBIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots or changing soil water content (0.44–0.55 kg kg–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both CBIO and NBIO (P

The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding.

About half of the world's wetlands area is found in the tropics. The importance of wetlands to the global carbon cycle, water balance, wildlife, biodiversity and human food production is much greater than their proportional surface area on Earth (7%) would suggest. High net primary production of organic matter produced by retarded decomposition make natural tropical wetlands an important sink for carbon. About 250 Gt carbon are conserved in tropical wetlands. Tropical wetlands are also a significant source for atmospheric methane. Wetland rice agriculture alone contributes 5 to 20% to the global methane budget. Rice, the stable food for about half of mankind, is grown on tropical wetlands. Small differences in climate, water and nutrient regimes, and land use can drastically change the delicate balance of tropical wetlands.

Methane production in soil is a microbiological process that occurs under strict anaerobic conditions. A laboratory incubation study was conducted using 10 wetland rice (Oryza sativa L.) soils from the Philippines to establish soil characteristics that govern the redox characteristics and CH 4 production of soils upon wetting. Labile soil organic matter in the Ap horizon was quantified as enrichment of C and N and non-clay-protected C and N fractions. The C/N ratio of the enriched fraction controlled the rate of reduction upon flooding, whereas the buffering capacity, measured as extractable Fe 3+ content, controlled the reduction capacity for the soils. Methane production was influenced both by the reduction characteristics of the soils and labile organic substrates.

Soil–plant N dynamics lie at the heart of some of the questions being asked of researchers by farmers, environmentalists and policy makers. Our aim in this paper is to highlight areas in which research is needed to address these questions. Although we have a general understanding of many processes, fundamental understanding of the processes of the soil–plant system is not complete. Improved understanding of crop and soil processes should lead to the continuous improvement of simulation models, which are able to integrate the complex effects of management and environmental factors. However, farmers cannot wait for the achievement of perfect models, but need researchers to put their current knowledge to use. We suggest that for both crops and soils, diagnostic measurements be used in conjunction with the best of, or a combination of, current models. Development work should be carried out with all possible speed to draw suitable models and diagnostics together. We stress the importance of conducting research to understand and improve N efficiency at a range of scales and indicate the need for the involvement of related disciplines, such as statistics, to allow the development of robust guidelines and methodologies for up- and down-scaling measurements and models. Above all, it is essential that our understanding of the processes of soil–plant dynamics continues to underpin the development of strategies for dynamic optimisation and improve simulation models that are used in fertiliser recommendation systems.

Black carbon (BC) is an important fraction of many soils worldwide and plays an important role in global C biogeochemistry. However, few studies have examined how it influences the mineralization of added organic matter (AOM) and its incorporation into soil physical fractions and whether BC decomposition is increased by AOM. BC-rich Anthrosols and BC-poor adjacent soils from the Central Amazon (Brazil) were incubated for 532 days either with or without addition of 13 C-isotopically different plant residue. Total C mineralization from the BC-rich Anthrosols with AOM was 25.5% ( P P P P 13 C-enriched microbial culture. The recovery was found to be 21–41% lower ( P

This study evaluated the effect of cultivation and reseeding on the distribution and fate of soil mineral N (SMN), soluble organic N (SON) and potentially mineralisable N (PMN) in the soil profile of two long-term grasslands in the UK. Cultivation and reseeding significantly increased the total soluble N concentration (SMN plus SON) of the soil profile (0–90 cm), with over 50 mg SON kg–1 observed. By contrast, the PMN pool was unaffected by cultivation and declined with increasing soil depth. The flush in SON and SMN observed in both soils disappeared within 1 year following cultivation. The fate of SON appeared to be dependent on soil type, with considerably more movement to deeper layers apparent in the profile of a silty clay loam (30% clay) than in a clay loam (49% clay). Mineralisation and/or immobilisation of SON in the topsoil probably accounted for the changes observed in the SON content of the clay loam. SON is an important N pool in grassland soils and cultivation has a significant impact on its release. Measurements of SON should therefore be included in studies of N cycling in agricultural cropping systems, so that full account may be taken of its potential as a source or sink of mobile N.

A laboratory study was conducted to compare methods of labelling the soil NH4+ pool with 15N as a prerequisite to the measurement of gross N mineralisation. Composite soil (0–12 cm) was collected from 12 sites differing in land use and soil texture. Three methods were used to apply 15N to the soil: (i) addition of a 15NH3–air gas mixture to the headspace above the soil (gas jar), (ii) injection of a 15NH3–air gas mixture into re-packed soil cores (gas injector) and (iii) addition of a (15NH4)2SO4 solution pipetted onto the soil surface (solution). 15N isotopic dilution was determined between 24 and 72 h after 15N application. Of the applied 15N 52 to 93% was recovered as inorganic N 24 h after application. Less 15N was recovered in the clay loam compared to the sandy loam and silty clay loam for all methods. Recovery from the gas injector was lower than from the gas jar or solution treatments in the sandy loam and silty clay loam. No difference in the recovery of applied 15N between methods was observed in the clay loam. 15N isotopic dilution was less in the gas jar compared to the gas injector and solution treatments. This resulted in significantly lower estimates of gross N mineralisation rates and NH4+ consumption for the gas jar treatment. The non-uniform distribution of 15N through the soil probably caused these differences as a consequence of 15NH3 dissolving quickly in the surface of the soil. In seven of the 12 soils, gross rates of N mineralisation were not significantly different when 15N was applied as solution or by gas injection. In the remaining five soils, estimates of gross N mineralisation rates were greater in the solution treatment. Ammonium consumption was significantly different between the solution and gas injector treatments in three soils. Where there were differences in values for gross N mineralisation and NH4+ consumption rates between methods, the effects were not associated with a particular soil texture or land use. Greater nitrification of 15NH4+ to 15NO3− and shorter pseudo-residence times of the NH4+ pool were observed in the solution treatment compared to gas injector. This suggests a difference in the distribution of 15N within soil microsites, with the 15N applied in the solution treatment being more accessible for microbial consumption. Nevertheless, application of 15N as an NH4+ solution, or injection of 15NH3 gas into soil, resulted in estimates of a similar magnitude for gross N mineralisation rates and identified the same differences between soil type and land use.

As the result of a recent BBSRC-funded workshop between soil scientists, modellers, statisticians and others to discuss issues relating to the derivation of complex environmental models, a set of modelling guidelines is presented and the required associated research areas are discussed.

Monitoring and modeling the dynamics of N in flooded rice fields require reliable methods for both sampling and analysis. Destructive soil sampling and centrifugation and in situ sampling of soil solution using microporous polymer tubes (rhizon soil solution samplers; RSSS) were used to study the dynamics and variability of NH⁺₄ in two field experiments. Both methods gave similar results in unfertilized treatments, whereas significant differences were measured in treatments with N application. The RSSS were suited for measuring point dynamics or microvariation of nutrients in the root zone, whereas soil-core sampling was a better method to obtain quantitative N data integrated across a particular depth range. We observed a highly significant linear relationship between the logs of soil exchangeable and solution NH⁺₄ only until panicle initiation (PI). Microvariability accounted for a large proportion of the within-field variation and was significantly reduced by bulking of soil cores. Coefficients of variation were higher in the fertilized field compared with an unfertilized field and were changing throughout the growth period of rice, with the highest variability between PI and flowering. Sampling to obtain representative mean values at the plot or field scale can be optimized with regard to temporal changes in the spatial distribution patterns of NH⁺₄. Before transplanting (TP) and at the end of the growth period, less samples are needed and can be taken as composite samples of the whole puddled soil layer. Between TP and flowering, more samples are needed and should be taken in several depth ranges.