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The present study acknowledged climate variability induced periodic variation in localized extreme weather event occurrences under diverse agro eco-regions of Eastern Himalayas of India during past five decades. The widespread rise in warm nights (TN90p; 0.31-1.67 days year-1), reduced daily rainfall intensity (SDII) and changes in other weather extremes viz. temperature and precipitation extremes signified clear signals on regional atmospheric warming across eastern India. The agro-ecological regions under extended Bramhaputra valley and coastal belts of south Bengal experienced the most persistent shifts in temperature extremes, while the upper Himalayan range extended from North Bengal to Arunachal Pradesh experienced the steepest decline in average daily rainfall intensity and other absolute quantitative estimates of precipitation extremes over past five decades. Together with El Niño and La Niña events, large scale global atmospheric circulations particularly expansion of warmer Pacific Warm Pool (PWP) and changes in Atlantic Meridional Mode (AMM) contributed the periodic dynamics in weather extreme occurrences from monthly to annual time scale over eastern India. Our findings will be useful for better understanding of regional climatology, designing and successful implantation of location-specific suitable agricultural policies towards climate change adaptation in near future.

The net arable land area is declining worldwide rapidly due to soil erosion, drought, loss of soil organic carbon, and other forms of degradation. Intense rainfall, cultivation along steep slopes, unscientific land-use changes, shifting cultivation, soil acidity, and nutrient mining in hills and mountains make agriculture unsustainable and less profitable. Hills and mountain ecosystems of the Eastern Himalayan Region (EHR) are further prone to the impact of climate change posing a serious threat to agricultural production and the environment. Increasing soil carbon reserves contributes to multiple ecosystem services, improves soil nutrient and water-holding capacities, and advances climate-resilient agriculture. Thus, carbon sequestration is increasingly becoming an important aspect of farming among researchers in the region. The EHR predominantly practices shifting cultivation that degrades the ecosystem and promotes land degradation and biodiversity loss. Leaching of exchangeable bases is highly favored due to excess rainfall which in turn creates an acidic soil accounting for >84% of the region. Application of lime to raise the soil acidity for the cultivation of crops did not get adequate acceptance among the farming community due to multiple issues such as cost involvement, non-availability in time and place, and transportation issues. The application of biochar as soil amendments is widely known to improve soil’s physical, chemical, and biological properties. Biochar has also emerged as a potential candidate for long-term carbon sequestration due to its inbuilt structure and higher stability. Shift from traditional “slash and burn” culture to “slash and char” might lead to the sequestration of carbon from the atmosphere. Around 0.21 Pg of carbon (12% of the total anthropogenic carbon emissions by land-use change) can be sequestered in the soil if the traditional “slash and burnt” practice is converted to “slash and char”. The objective of this review is to provide detailed information about the role of biochar in altering the soil properties for sustaining agriculture and carbon sequestration, especially for hills and mountain ecosystems.

Success and acceptability of the bio energy conversion technology to a large extent depend upon management of the inevitable by-products generated during the conversion process. By-products can be considered favourable as organic fertilizer as they retain nutrients with varying composition depending upon input biomass. However, characteristics of these heterogeneous resources with respect to feedstock and processing conditions have to be assessed to state on their agricultural and environmental benefits. Therefore, 3 types of anaerobic digestion by-products (digestate) from surplus biomass viz. cow dung, Ipomoea carnea:cow dung (60:40 dry weight basis) and rice straw:green gram stover:cow dung (30:30:40 dry weight basis) and one gasification by-product (biochar) from rice husk are considered to understand the fertilizer prospects. Considering 3 potential application options, digestate from each feedstock option was further processed as separated solid, separated liquid and ash from solid digestates. Thus, a total of 10 by-products were investigated for understanding their prospects as fertilizer using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X ray Spectroscopy (EDX) and phyto-toxicity test to have a broad insight in terms of their organic, mineral, elemental composition, morphological feature and potential phyto-toxicity. In general, irrespective of origin of feedstock, solid digestate, ash digestate and char showed similarity in terms of composition of functional groups with some degree of variation in relative content as reflected by FTIR analysis. Dominance of organic functional groups in separated solid digestates compared to liquid fraction indicated the former as favourable organic amendments. Quartz was the prevalent mineral phase in all separated solid, ash digestate and rice husk char. Digestates in ash phase represent more concentrated plant nutrient source with higher content of K, Ca, P, Na and Mg than their respective solid phase. Application of ash digestates and char is likely to improve adsorptive capacity of soil for water and nutrient due to presence of relatively uniformly distributed porous particles. Liquid fraction of Ipomoea digestates exhibited inhibitory effect on seed germination of greengram (Vigna radiate) with significant reduction of germination index. Inhibitory effects of by-products were found to correlate negatively with their electrical conductivity and ammonia-nitrogen content. Understanding on spectroscopic, morphological and phytotoxic properties of different application options of bioenergy by-products would be useful for assessment of their appropriate use in agriculture.

Overburden and acid drainage from coal mining is transforming productive agricultural lands to unproductive wasteland in some parts of Northeast India. We have investigated the adverse effects of acid mine drainage on the soil of rice paddy and productivity by comparing them with non-mined land and abandoned paddy fields of Jaintia Hills in Northeast India. Pot experiments with a local rice cultivar (Myngoi) as test crop evaluated biological productivity of the contaminated soil. Contamination from overburden and acid mine drainage acidified the soil by 0.5 pH units, increased the exchangeable Al3 + content 2-fold and its saturation on clay complexes by 53%. Available sulfur and extractable heavy metals, namely Fe, Mn and Cu increased several-fold in excess of critical limits, while the availability of phosphorus, potassium and zinc contents diminished by 32–62%. The grain yield of rice was 62% less from fields contaminated with acid mine drainage than from fields that have not suffered. Similarly, the amounts of vegetation, i.e. shoots and roots, in pots filled with soil from fields that received acid mine drainage were 59–68% less than from uncontaminated land (average shoot weight: 7.9 ± 2.12 g pot− 1; average root weight: 3.40 ± 1.15 g pot− 1). Paddy fields recovered some of their productivity 4 years after mining ceased. Step-wise multiple regression analysis affirmed that shoot weight in the pots and grain yield in field were significantly (p < 0.01) and positively influenced by the soil's pH and its contents of K, N and Zn, while concentration of S in excess of threshold limits in contaminated soil significantly (p < 0.01) reduced the weight of shoots in the pots and grain yield in the field.

Insect infestation can adversely affect tomato ( Solanum lycopersicum L.; Solanaceae) development and yield. Fruit flies (Diptera: Tephritidae) are a serious pest of tomato, and are spreading to areas where they were not previously found. This study was undertaken to determine if tephritid fruit flies were present, which species were most abundant, how tomato cultivars responded, and what amount of damage occurred in the Eastern Himalayas of India during May 2014 and 2015. Mature and ripe fruit (n = 20) per cultivar were picked at random from 12 cultivars at weekly intervals to assess percentage of infestation, fly species composition, larval infestation, pupal mortality, adult emergence, and sex ratio during 2 seasons. Seasonal fluctuation of male adults of Zeugodacus tau (Walker) (Diptera: Tephritidae) in tomato was studied by installing 3 modified clear traps, made from plastic bottles, that were baited with 0.5 mL Cue-lure and the insecticide dichlorovos 76% EC (Nuvan®). Survey and subsequent identification confirmed the presence of Z. tau in tomato in the Himalayas of India. This is the first report of the insect in the province, and of population outbreaks resulting in serious damage to tomato in India. Among fruit fly species present on tomato, Z. tau was more abundant (71.4–96.4%) in all geographical regions of Mizoram, India, than were Bactrocera correcta (Bezzi), B. dorsalis (Hendel), and B. latifrons (Hendel), which ranged from 3.6 to 28.6%. The highest percentage of infestation was in Champhai (72.7 ± 6.7%) and Kolasib (80.7 ± 3.5%) and the lowest in Mamit (14.7 ± 4.8%) and Serchhip (19.3 ± 4.7%). Cultivar influenced pupal mortality and adult emergence of Z. tau . Seasonal fluctuation of Z. tau males on tomato varied; the greatest numbers were trapped during May and Dec. Occurrence of Z. tau at high population densities was associated with high levels of damage and could lead to high economic losses in tomato fruit production. Resumen La infestacion de insectos puede afectar negativamente al desarrollo y rendimiento del tomate ( Solanum lycopersicum L.; Solanaceae). Las moscas de la fruta (Diptera: Tephritidae) son una plaga seria del tomate, y se estan extendiendo a las areas donde no fueron encontradas anteriormente. Se realizo este estudio para determinar si las moscas de la fruta frutales estan presentes, cuales son las especies mas abundantes, como responden los cultivares de tomate y el nivel del dano que ocurrio en los Himalayas orientales de la India durante mayo del 2014 y 2015. Se seleccionaron frutos maduros y pasados (n = 20 por cultivar) al azar de 12 cultivares a intervalos semanales para evaluar el porcentaje de infestacion, la composicion de las especies de mosca, la infestacion de larvas, la mortalidad de pupas, la emergencia de adultos y la proporcion de sexos durante 2 estaciones. Se estudio la fluctuacion estacional de machos adultos de Zeugodacus tau (Walker) (Diptera: Tephritidae) en tomate por medio de la instalacion de 3 trampas claras modificadas, hechas de botellas de plastico, que fueron cebadas con 0,5 mL de Cue-lure y el insecticida Dichlorovos 76% CE (Nuvan®). El estudio y identificacion subsiguiente confirmaron la presencia de Z. tau en tomate en los Himalayas de la India. Este es el primer informe de este insecto en la provincia, y de los brotes poblacionales que resultaron en dano serio al tomate en la India. Entre las especies de moscas de la fruta presentes en el tomate, Z. tau fue la mas abundante (71,4 a 96,4%) en todas las regiones geograficas de Mizoram, India, que Bactrocera correcta (Bezzi), B. dorsalis (Hendel) o B. latifrons (Hendel), que fueron entre 3,6 y 28,6%. El mayor porcentaje de infestacion fue en Champhai (72,7 ± 6,7%) y Kolasib (80,7 ± 3,5%) y el mas bajo en Mamit (14,7 ± 4,8%) y Serchhip (19,3 ± 4,7%). El cultivar influyo en la mortalidad de pupas y en la emergencia de adultos de Z. tau . La fluctuacion estacional de los machos Z. tau en el tomate vario; el mayor numero de individuos fueron atrapados durante los meses de mayo y diciembre. La ocurrencia de poblaciones de Z. tau de alta densidad fue asocida con altos niveles de dano y estos podrian ocasionar grandes perdidas economicas en la produccion de tomate. View this article in BioOne

Plant’s nitrogen (N) requirement that is not fulfilled by available N in soil has to be supplied externally through chemical fertilizers. A reliable estimate of soil N-supplying capacity (NSC) is therefore essential for efficient fertilizer use. In this study involving a pot experiment with twenty acidic soils varying widely in properties, we evaluated six chemical indices of soil N-availability viz. organic carbon (C org ), total N (N tot ), acid and alkaline-KMnO 4 extractable-N, hot KCl extractable-N (KCl-N) and phosphate-borate buffer extractable-N (PBB-N), based on their strength of correlation with available-N values obtained through aerobic incubation (AI-N) and anaerobic incubation (ANI-N), and also with the dry matter yield (DMY), N percentage and plant (maize) N uptake (PNU). In general, the soils showed large variability in NSC as indicated by variability in PNU which ranged from 598 to 1026 mg/pot. Correlations of the N-availability indices with AI-N and ANI-N decreased in the order: PBB-N (r = 0.784** and 0.901**) > KCl-N (r = 0.773** and 0.743**) > acid KMnO 4 -N (r = 0.575** and 0.651**) ≥ C org (r = 0.591** and 0.531**) ≥ alkaline KMnO 4 -N (r = 0.394** and 0.548**) > N tot (r = 0.297** and 0.273*). Of all the indices evaluated, PBB-N showed the best correlations with plant parameters as well (r = 0.790** and 0.793** for DMY and PNU, respectively). Based on the highest correlations of PBB-N with biological indices as well as plant responses, we propose PBB-N as an appropriate index of N-availability in the acidic soils of India and other regions with similar soils.

Alternative fertilizer resources have drawn attention in recent times in order to cope up with ever increasing demand for fertilizer. By-products of bioenergy system are considered favourable as organic fertilizer due to their ability to recycle plant nutrients. Present study evaluates fertilizer suitability of by-products of two bioenergy systems viz. 3 types of anaerobic digestion by-products (digestate) from local surplus biomass such as cowdung, Ipomoea carnea:cowdung (60:40) and ricestraw:green gram stover:cowdung (30:30:40) and one gasification by-product (biochar) from rice husk. Digestates were assessed considering 4 different application options of each viz. whole, solid, liquid and ash from solid digestates. Digestate characteristics (organic matter, macronutrients, micronutrients and heavy metal content) were found to be a function of feedstock and processing (solid liquid separation and ashing). Ipomoea carnea based digestates in all application options showed comparatively higher N, P, K, NH4+-N, Ca, Mg, S and micro nutrient content than other digestates. Separation concentrated plant nutrients and organic matter in solid digestates, making these suitable both as organic amendments and fertilizer. Separated liquid digestate shared larger fraction of ammonium nitrogen (61–91% of total content), indicating their suitability as readily available N source. However, fertilizer application of liquid digestate may not match crop requirements due to lower total nutrient concentration. Higher electrical conductivity of the liquid digestates (3.4–9.3 mS cm−1) than solid digestates (1.5–2 mS cm−1) may impart phyto–toxic effect upon fertilization due to salinity. In case of by-products with unstable organic fraction i.e. whole and solid digestates of rice straw:green gram stover:cowdung digestates (Humification index 0.7), further processing (stabilization, composting) may be required to maximize their fertilizer benefit. Heavy metal contents of the by-products were found to be within the permitted range specified for organic fertilizer (vermicompost) in India. However, higher Al content of the digestates in whole, solid and ash phase (0.06–16.97g kg−1 fresh matter) can be a concern in acid soil which may cause Al toxicity. Understanding on agrochemical characteristics of bioenergy by–products with varying feedstock and application option is expected to promote their valorization opportunities considering user specific requirements. In the context of agriculturally dominant but energy deficient rural Indian scenario, integrated production of bioenergy and by-product based fertilizer could be very significant to meet the critical additional requirement of both energy and fertilizer.

International audience; The choice of cultivation system in arable agriculture exerts a strong influence not only on soil health and crop productivity but also on the wider environment. Conservation tillage using non-inversion methods conserves soil carbon, reduces erosion risk and enhances soil quality. In addition, conservation tillage has been shown to sequester more carbon within the soil than inversion tillage, reducing carbon dioxide losses to the atmosphere. Stable, well structured topsoils that develop following long-term conservation tillage lead to more energy efficient systems due to the reduced power requirements for cultivation. Long-term experiments, e.g. more than 20 years, that confirm the impact of conservation tillage over an extended period are not common. Here we evaluate the impact of different tillage methods and winter wheat straw management, either incorporated or removed, on organic matter turnover and soil quality indicators. No-till, chisel and mouldboard ploughing was carried out for 23 years on a silty clay loam soil in South West England that was not considered suitable for non-inversion tillage due to weak soil structure. In order to assess the effect of contrasting cultivation and straw disposal method on soil carbon dynamics, a range of assays were conducted, including water extractable organic carbon, hot water extractable carbohydrate, microbial biomass carbon, activity of β-glucosidase and acid phosphatase enzymes, C sequestration and the natural abundance of 13 C. Our results show that the soil organic carbon concentration in the topsoil was greater under no-till than mouldboard ploughing, while a reverse trend was observed in the lower depths. A 14-17% increase in soil organic carbon was observed in the topsoil for chisel plough and no-till treatments compared to mouldboard ploughing. Water extractable organic carbon was found to constitute only 1-7% of the microbial biomass carbon. Hot water extractable carbohydrate was one of the most sensitive indicators of soil quality and had a significant a negative correlation with bulk density and positive correlation with soil organic carbon microbial biomass carbon β-glucosidase and acid phosphatase. The choice of cultivation method exerted a major control on microbial and carbon dynamics. No-till and chisel ploughing maintained carbon in the soil surface horizons, which will benefit the stability of this weakly structured soil, but mouldboard ploughing distributed carbon more uniformly throughout the soil profile, particularly when straw was incorporated, hence leading to the retention of more carbon in the soil profile.

To achieve higher yields and better soil quality under rice–legume–rice (RLR) rotation in a rainfed production system, we formulated integrated nutrient management (INM) comprised of Azospirillum (Azo), Rhizobium (Rh), and phosphate-solubilizing bacteria (PSB) with phosphate rock (PR), compost, and muriate of potash (MOP). Performance of bacterial bioinoculants was evaluated by determining grain yield, nitrogenase activity, uptake and balance of N, P, and Zn, changes in water stability and distribution of soil aggregates, soil organic C and pH, fungal/bacterial biomass C ratio, casting activities of earthworms, and bacterial community composition using denaturing gradient gel electrophoresis (DGGE) fingerprinting. The performance comparison was made against the prevailing farmers’ nutrient management practices [N/P2O5/K2O at 40:20:20 kg ha−1 for rice and 20:30:20 kg ha−1 for legume as urea/single super-phosphate/MOP (urea/SSP/MOP)]. Cumulative grain yields of crops increased by 7–16% per RLR rotation and removal of N and P by six crops of 2 years rotation increased significantly (P

We used a long-term arable cultivation experiment to investigate spatial relationships between earthworm populations and soil physico-chemical properties using Spatial Analysis by Distance Indices methods (SADIE). Red-blue analyses showed that soil C and N were both spatially heterogeneous (patchy) as were total and juvenile earthworm counts. In contrast, theta probe and shear vane measurements, adult earthworm counts and earthworm biomass did not exhibit patchiness. All potential relationships between data classes were analysed using SADIE spatial association tests. Soil chemical properties were generally dissociated from earthworms whereas physical properties were positively associated. These results were largely attributable to juvenile counts, suggesting that this age group may be a more sensitive indicator of spatial relationships between earthworms and soil properties than are adults. We also found that earthworm counts had stronger spatial associations with soil chemical properties than did biomass; the obverse was seen with the measures of soil physical properties. This may provide evidence that earthworm dynamic responses vary between different aspects of the soil environment.

Quantitative assessment of soil quality is required to determine the sustainability of land uses in terms of environmental quality and plant productivity. Our objective was to identify the most appropriate soil quality indicators and to evaluate the impact of six most prevalent land use types (natural forestland, cultivated lowland, cultivated upland terrace, shifting cultivation, plantation land, and grassland) on soil quality in eastern Himalayan region of India. We collected 120 soil samples (20 cm depth) and analyzed them for 29 physical, chemical, and biological soil attributes. For selection of soil quality indicators, principal component analysis (PCA) was performed on the measured attributes, which provided four principal components (PC) with eigenvalues >1 and explaining at least 5 % of the variance in dataset. The four PCs together explained 92.6 % of the total variance. Based on rotated factor loadings of soil attributes, selected indicators were: soil organic carbon (SOC) from PC-1, exchangeable Al from PC-2, silt content from PC-3, and available P and Mn from PC-4. Indicators were transformed into scores (linear scoring method) and soil quality index (SQI) was determined, on a scale of 0–1, using the weighting factors obtained from PCA. SQI rating was the highest for the least-disturbed sites, i.e., natural forestland (0.93) and grassland (0.87), and the lowest for the most intensively cultivated site, i.e., cultivated upland terrace (0.44). Ratings for the other land uses were shifting cultivation (0.60) > cultivated low land (0.57) > plantation land (0.54). Overall contribution (in percent) of the indicators in determination of SQI was in the order: SOC (58 %) > exch. Al (17.1 %) > available P (8.9 %) > available Mn (8.2 %) > silt content (7.8 %). Results of this study suggest SOC and exch. Al as the two most powerful indicators of soil quality in study area. Thus, organic C and soil acidity management holds the key to improve soil quality under many exploitatively cultivated land use systems in eastern Himalayan region of India.