Black carbon (BC) is an important pool of the global C cycle, because it cycles much more slowly than others and may even be managed for C sequestration. Using stable isotope techniques, we investigated the fate of BC applied to a savanna Oxisol in Colombia at rates of 0, 11.6, 23.2 and 116.1 t BC ha -1 , as well as its effect on non-BC soil organic C. During the rainy seasons of 2005 and 2006, soil respiration was measured using soda lime traps, particulate and dissolved organic C (POC and DOC) moving by saturated flow was sampled continuously at 0.15 and 0.3 m, and soil was sampled to 2.0 m. Black C was found below the application depth of 0-0.1 m in the 0.15-0.3 m depth interval, with migration rates of 52.4 ± 14.5, 51.8 ± 18.5 and 378.7 ± 196.9 kg C ha -1 yr -1 (± SE) where 11.6, 23.2 and 116.1 t BC ha -1 , respectively, had been applied. Over 2 years after application, 2.2% of BC applied at 23.2 t BCha -1 was lost by respiration, and an even smaller fraction of 1% was mobilized by percolating water. Carbon from BC moved to a greater extent as DOC than POC. The largest flux of BC from the field (20-53% of applied BC) was not accounted for by our measurements and is assumed to have occurred by surface runoff during intense rain events. Black C caused a 189% increase in aboveground biomass production measured 5 months after application (2.4-4.5 additional dry biomass ha -1 where BC was applied), and this resulted in greater amounts of non-BC being respired, leached and found in soil for the duration of the experiment. These increases can be quantitatively explained by estimates of greater belowground net primary productivity with BC addition.

Fate of soil applied black carbon: downward migration, leaching and soil respiration [Approved article]

Keeping in view the challenges concerning agro-ecosystem and environment, the recent developments in biotechnology offers a more reliable approach to address the food security for future generations and also resolve the complex environmental problems. Several unique features of cyanobacteria such as oxygenic photosynthesis, high biomass yield, growth on non-arable lands and a wide variety of water sources (contaminated and polluted waters), generation of useful by-products and bio-fuels, enhancing the soil fertility and reducing green house gas emissions, have collectively offered these bio-agents as the precious bio-resource for sustainable development. Cyanobacterial biomass is the effective bio-fertilizer source to improve soil physico-chemical characteristics such as water-holding capacity and mineral nutrient status of the degraded lands. The unique characteristics of cyanobacteria include their ubiquity presence, short generation time and capability to fix the atmospheric N2. Similar to other prokaryotic bacteria, the cyanobacteria are increasingly applied as bio-inoculants for improving soil fertility and environmental quality. Genetically engineered cyanobacteria have been devised with the novel genes for the production of a number of bio-fuels such as bio-diesel, bio-hydrogen, bio-methane, syngas and therefore, open new avenues for the generation of bio-fuels in the economically sustainable manner. This review is an effort to enlist the valuable information about the qualities of cyanobacteria and their potential role in solving the agricultural and environmental problems for the future welfare of the planet.

Cyanobacteria: A Precious Bio-resource in Agriculture, Ecosystem, and Environmental Sustainability

Biochar production and subsequent soil incorporation could provide carbon farming solutions to global climate change and escalating food demand. There is evidence that biochar amendment causes fundamental changes in soil nutrient cycles, often resulting in marked increases in crop production, particularly in acidic and in infertile soils with low soil organic matter contents, although comparable outcomes in temperate soils are variable. We offer insight into the mechanisms underlying these findings by focusing attention on the soil nitrogen (N) cycle, specifically on hitherto unmeasured processes of organic N cycling in arable soils. We here investigated the impacts of biochar addition on soil organic and inorganic N pools and on gross transformation rates of both pools in a biochar field trial on arable land (Chernozem) in Traismauer, Lower Austria. We found that biochar increased total soil organic carbon but decreased the extractable organic C pool and soil nitrate. While gross rates of organic N transformation processes were reduced by 50–80%, gross N mineralization of organic N was not affected. In contrast, biochar promoted soil ammonia-oxidizer populations (bacterial and archaeal nitrifiers) and accelerated gross nitrification rates more than two-fold. Our findings indicate a de-coupling of the soil organic and inorganic N cycles, with a build-up of organic N, and deceleration of inorganic N release from this pool. The results therefore suggest that addition of inorganic fertilizer-N in combination with biochar could compensate for the reduction in organic N mineralization, with plants and microbes drawing on fertilizer-N for growth, in turn fuelling the belowground build-up of organic N. We conclude that combined addition of biochar with fertilizer-N may increase soil organic N in turn enhancing soil carbon sequestration and thereby could play a fundamental role in future soil management strategies.

Biochar Decelerates Soil Organic Nitrogen Cycling but Stimulates Soil Nitrification in a Temperate Arable Field Trial

Does biochar improve soil water retention? A systematic review and meta-analysis

Renewable methanol and formate as microbial feedstocks

The study related to the effects of rice husk biochar (RHB) application on soil microbial aspects and paddy productivity in field condition is scare. Therefore, present study provides fresh insight into the effects of RHB on rice production in field conditions, with some updated information on soil microbial aspects. To study the impact of RHB and CSR-BIO (commercialized bio-formulation), on soil physico-chemical properties, soil microbial biomass (SMB) quantity and paddy productivity, four treatments were set up: control, RHB, CSR-BIO and RHB + CSR-BIO. The RHB with CSR-BIO both the amendments were applied at a rate of 10 t ha−1. Across treatments, the water holding capacity, total -C, -N, -P concentrations and soil moisture content were statistically higher in RHB and CSR-BIO treated soils over the control. The highest SMB-C, -N and -P (408.66 ± 0.57, 83.33 ± 2.08 and 25.66 ± 1.52 μg g−1 dry soil, respectively) was recorded in RHB + CSR-BIO treated soil. Across the sampling dates, SMB-C, -N, -P and inorganic-N (ammonium- and nitrate-N) concentrations were minimum on 35 day after transplantation (DAT) (tillering stage-active growth period), and maximum on 105 DAT (maturity stage). The paddy plant growth variables (panicle length, tiller number, rice grain and paddy straw yields) were found higher in treated plots compared to untreated (control) plots, and varied significantly (P ≤ 0.001) due to treatments. Among the various selected paddy agronomic variables, the application of RHB and CSR-BIO treatment was more pronounced to the yield of rice grains. Results indicate that an increase in the quantity of SMB due to RHB + CSR-BIO addition, improves the soil nutrient status and hence, paddy productivity in nutrient poor agriculture soils. It is suggested that RHB generation from rice husk biochar could be a sustainable crop residues waste management option to enhance the nutrient status, microbial biomass and paddy productivity of disturbed agriculture soils.

The effect of rice husk biochar on soil nutrient status, microbial biomass and paddy productivity of nutrient poor agriculture soils

Land use change: A key ecological disturbance declines soil microbial biomass in dry tropical uplands.

Microbes in Agriculture and Environmental Development

Paddy agriculture is one of the major anthropogenic sources of methane (CH4) emission at global level. A decrease in CH4 release in the atmosphere from paddy fields can add significantly to the management of global warming and climate change. Biochar production and application in agriculture prepared from crop straw has been proposed as one of the effective countermeasure to mitigate the greenhouse gas emissions (GHGs) during farming. Biochar, a co-product of a controlled pyrolysis process, can be used as a tool to offset GHGs emissions and as a soil conditioner. Biochar application increased rice productivity, soil pH, soil organic carbon, total N but decreased soil bulk density in the long term. Recent studies have confirmed that the use of biochar in paddy agriculture has the capability to minimise the CH4 production, but its essential mechanism has yet to be clarified. The additions of biochar to the agriculture soil showed higher CH4 consumption because it improves soil aeration and porosity and enhances methanotrophs performance. However, further investigations are needed to evaluate the effect of biochar addition on net CH4 emissions and consumptions, respectively, by methanogens and methanotrophs. Long-term experiments should be conducted to monitor any changes over the years on the influence of biochar amendments on soil–methanotrophs–paddy systems.

Biochar Application in Management of Paddy Crop Production and Methane Mitigation

Land use changes have been recognized as one of the key ecological drivers in regulation of methane (CH4) consumption from dry upland soils. This study investigated the impact of land use changes and different soil depths (0–10, 10–20 and 20–30 cm) on soil physicochemical properties and methanotrophs abundance in dry tropical region of Vindhyan uplands. Four different land use types (agriculture land, mixed forest, savanna and natural forest) were selected for a comparative study. Among the different land uses and soil depths, results indicated significantly higher soil moisture (SM), organic-C, inorganic nutrients, water holding capacity (WHC) and methanotrophs abundance at 0–10 cm depth of natural forest compared to other sites. Across different land uses, number (8.11 × 107 pmoA copies g−1 of dry soil) of methanotrophs isolated from the natural forest soil was statistically higher than the soils of other land use types. The variations in pmoA gene numbers across different land uses and soil depths were significant (P   mixed forest > savanna > agriculture land. The result suggest that land use changes (conversion of natural forest to agricultural land) alter the major soil properties (SM, WHC, organic matter, C/N ratio, etc.) and significantly reduce the methanotrophs and pmoA gene numbers. The land use management practices (application of bio-fertilizers in place of chemical fertilizers), especially for the degraded agricultural soils, could be beneficial option to mitigate the negative impacts on soil methanotrophs and their CH4 sink activity in the upland soil of Vindhyan region.

Shashank Tiwari

Papers

The effect of rice husk biochar on soil nutrient status, microbial biomass and paddy productivity of nutrient poor agriculture soils

Land use change: A key ecological disturbance declines soil microbial biomass in dry tropical uplands.

Microbes in Agriculture and Environmental Development

Biochar Application in Management of Paddy Crop Production and Methane Mitigation

Land use changes: a key ecological driver regulating methanotrophs abundance in upland soils