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Cadmium (Cd)-contamination of agricultural soils has been receiving attention worldwide due to its entry into food crops such as wheat ( Triticum aestivum L.). Little is known regarding the use of organic carbon (OC) sources in alleviating Cd toxicity in cereals. The current experiment was aimed to study the effects of different OC sources on the Cd accumulation by wheat. A pot study was conducted to determine the effects of rice husk biochar (RHB), farmyard manure (FYM), and lignite (LT) either alone or in combination on crop growth, Cd bioavailability and health risk assessment. The results proved that the application of OC sources like RHB, FYM, and LT either alone or in combination were highly effective in enhancing the wheat growth and yield as well as in minimizing the phyto-available fraction of Cd and its transfer to edible tissue of wheat. The RHB was the most efficient source in enhancing the plant growth and reducing the Cd concentration in wheat tissues. RHB increased grain yield by 91% and decreased Cd concentration in shoot, roots, grains, and bioavailable fraction of Cd by 67, 69, 62.5, and 74% than control, respectively. The RHB reduced the daily Cd uptake and health risk index in adults in comparison to control. Overall, where un-amended soil resulted in diminished plant productivity, the application of other OC sources also significantly proved their potential to enhance the dry weight and grain yield, suggesting that these OC sources may be used aiming to minimize the Cd concentration in crops. However, there is still a need to explore the potential of different OC sources in combination with other frequently available amendments for their large scale implementation in metal-contaminated soils. [ABSTRACT FROM AUTHOR]

Highlights: [•] Conventional tillage left negative carbon footprint. [•] CH4 was largest contribution to carbon footprint. [•] Continuous no tillage was highest yielding practice. [•] Discontinuous tillage practice was worst environmental performer. [ABSTRACT FROM AUTHOR]

We describe a summary model for the dynamics of carbon and nitrogen under varying weather, crop and soil conditions to investigate the role of soil organic carbon and nitrogen in yield formation in rice-based cropping systems of the Indo-Gangetic Plains (IGP). The model consists of three modules: soil organic matter (SOM), soil (SOIL), and crop growth (CROP). The SOM module consists of three pools: fresh, labile and stable. Carbon and nitrogen dynamics in the model are described in terms of carbon turnover, assimilation and dissimilation, with nitrogen linked through distinct C/N ratios. The SOIL module has two soil layers of variable depth (often 15cm each), and the labile and stable pools are replicated for these two layers. Water, crop and soil management practices and aeration characteristics of these layers affect the C and N dynamics of their respective pools. The CROP module calculates potential and actual biomass, leaf area index (LAI), evapotranspiration, total N demand, actual N uptake and N stress. Actual biomass is first partitioned between above (leaves, stem and storage organs) and below ground (roots and rhizodeposition), and a harvest index (HI) is applied to the aboveground biomass to calculate the yield. Independent data sets of 9 long-term experiments (LTEs) from the IGP of India were used for calibration and validation of the model. After calibration and validation, the model was used to explore the impact of various crop and soil management practices in rice-based cropping systems on different sites of the IGP. Overall, the model satisfactorily reproduced observed crop yields, SOC dynamics and total soil N dynamics for various cropping systems at different sites. Nitrogen mineralized from soil organic nitrogen contributed 5–75% to total N uptake in fertilized and non-fertilized treatments. With a recommended NPK application, a trend of significant decrease in simulated rice yield was found only at Ludhiana-3, and Pantnagar. Similarly, the simulated wheat yield also showed a significant trend of decline at Ludhina-3, Pantnagar and Barrackpore. Simulated SOC had a significant decline at Pantnagar, whereas at Ludhiana-3, it showed a significant increase. An increase in SOM is not always associated with an increase in yield, as the factor(s) improved by an increase in SOM may not be the limiting factor for crop growth. Depletion of many major macro (NPK) and micro (Zn, Fe, Mn, etc.) nutrients, essential for plant growth even with a balanced NPK fertilizer application and a maintained SOC, can lead to a decline in productivity. [Copyright &y& Elsevier]

Abstract: Soil organic matter (SOM) is the main energy resource of the great diversity of soil invertebrates but knowledge on the contribution of SOM pools of different ages to soil animal nutrition is sparse. In the present study natural stable isotope ratios were used to investigate the incorporation of decade old wheat-borne carbon into soil invertebrates of different trophic levels of a maize field 27 years after the replacement of wheat. For comparison a nearby continuous wheat field was investigated. Although the soil food web of the wheat and the maize field consisted of similar invertebrate taxa, most taxa were significantly more abundant in the wheat than in the maize field confirming that C4 plants are generally of poor food quality to soil animals due to low nutrient and high fibre contents. However, different cultivation strategies may also have contributed to differences in the abundance of invertebrates between both study sites. The mean incorporation of C3 carbon in soil animals in the maize field was 60.6±27.8%, but significantly differed between invertebrate species. Unfortunately, the field size did not entirely exclude incorporation of C3 carbon into the tissue of large and mobile invertebrates by feeding on C3 resources outside of the maize field. However, less mobile species such as endogeic earthworms incorporated high amounts of C3 carbon presumably due to the mobilisation of old carbon pools enclosed in soil aggregates and inaccessible to other soil invertebrates during gut passage. Furthermore, small and less mobile invertebrate species, such as most hemi- and epiedaphic Collembolans, also incorporated high amounts of C3 carbon likely by feeding on saprophytic fungi and microorganisms. In contrast, euedaphic Collembola incorporated only small amounts of C3 carbon suggesting preferentially feeding on maize resources. Overall, our data suggest that decade old carbon resources form an important component of the soil animal food web, but that the exploitation of old carbon resources by animal species varies with their distribution within the soil matrix, trophic position and exploitation of algae, and as an artefact to the small size of the study site, animal mobility. [Copyright &y& Elsevier]

Abstract: A spatially referenced biophysical model, the water and nitrogen management model (WNMM), was developed and shown to simulate dynamic soil water movement and soil–crop carbon (C) and nitrogen (N) cycling under a given agricultural management, for the purpose of identifying optimal strategies for managing water and fertiliser N under intensive cropping systems (mainly wheat–maize) in the North China Plain and other regions in the world. A uniform data structure, ARC GRID ASCII format, was used both in GIS and WNMM for achieving a close Model-GIS coupling. A significant part of WNMM adopts and modifies concepts and components from widely used models, with a focus on soil N transformations. WNMM simulates the key processes of water dynamics in the surface and subsurface of soils: including evapotranspiration, canopy interception, water movement and groundwater fluctuations; heat transfer and solute transport; crop growth; C and N cycling in the soil–crop system; and agricultural management practices (crop rotation, irrigation, fertiliser application, harvest and tillage). The model runs on a daily time step at any desired scale and is driven by lumped variables (meteorological and crop biological data) in text data format, and spatial variables (soil and agricultural management) in ARC GRID ASCII format. In particular, WNMM simulates all key N transformations in agricultural fields, including mineralisation of fresh crop residue N and soil organic N, formation of soil organic N, immobilisation in biomass, nitrification, ammonia (NH3) volatilisation, denitrification and nitrous oxide (N2O) emissions. WNMM has been successfully applied in Fengqiu County, Henan Province and Luancheng County, Hebei Province, China at site and regional scales. The key WNMM components were intensively calibrated and verified against comprehensive field measurements of soil water content, evapotranspiration, crop leaf area index and yield, NH3 volatilisation, denitrification and N2O emissions as well as nitrate (NO3 −)–N concentrations in the soil solution. A sensitivity analysis showed that WNMM was sensitive to changes in meteorological variables, soil hydraulic properties, land use and agricultural management. At the site scale, WNMM simulated well soil water content, crop growth and yield, NH3 volatilisation and soil NO3 −–N concentration. There was uncertainty in simulating soil denitrification and N2O emissions, when the predicted peaks of denitrification and N2O emissions at very wet conditions could not be confirmed because of limitations in the acetylene-inhibition method for measuring denitrification. At county scale, WNMM simulation of crop yield in Fengqiu County explained 22% of the variation in observed crop yields, and 31% of crop yield variation in Luancheng County where soil variation was less. These results are considered acceptable because factors such as soil salinity and other nutrient deficiencies, which have not been considered in this version of WNMM, may play a role. The source code for the WNMM is available on request. [Copyright &y& Elsevier]