Soil organic carbon (SOC) stabilisation in agricultural soils is governed by interactions between physical protection within aggregates and biochemical inputs derived from microbial activity, yet their relative importance remains poorly quantified in fruit tree-based horticultural systems. This study evaluated SOC stabilisation mechanisms under four fruit tree species (Pyrus communis, Prunus persica, Citrus reticulata and Psidium guajava) and a barren control by integrating aggregate-associated SOC, biochemical indicators and temperature sensitivity of carbon mineralisation. Across all systems, macroaggregates contained on average 12% higher SOC than microaggregates, with P. guajava macroaggregates exhibiting the highest SOC content (23.33 g kg-1). Cumulative SOC mineralisation at 35 degrees C and 60 days was lowest under P. guajava in both macro-and microaggregates (18.67 and 11.15 mg CO2 g-1, respectively), while barren soil showed the highest carbon loss. Polysaccharides and glomalin-related soil proteins were significantly higher under P. guajava and P. persica and were positively associated with aggregate stability (mean weight diameter). Temperature sensitivity analysis indicated that P. guajava exhibited the highest Q10 value (1.37) and the lowest activation energy (72.75 kJ mol-1), suggesting greater resistance of SOC pools to short-term warming. A categorical integration of physical, biochemical and thermal indicators highlighted clear species-specific differences in SOC stabilisation pathways. These findings indicate that fruit tree species selection strongly influences SOC stabilisation mechanisms in horticultural soils. Systems dominated by P. guajava and P. persica appear particularly effective in enhancing aggregate stability and SOC retention, underscoring their potential role in climate-smart perennial agriculture.

Context The Eastern Himalayan region exhibits strongly acid soils due to pedogenesis and topographical matrices under a sustained high precipitation regime. Prevalence of diverse and spatially varied land-use systems is a fundamental characteristic across these montane ecosystems and plays a key role in its impact on different soil nutrient pools. Aim The study was conducted to elucidate the impact of varied land use systems on nutrient mineralisation dynamics, including carbon (C) and its associated pools. Methods Throughout 14 selected land use systems, a random stratified sampling method was utilised with 56 quadrats that were exposed layer-wise down to a soil depth of 1.0 m. ResultThe analytical results indicated that the land use systems had a significant impact on soil pH. Likewise, total organic C (TOC) content showed significant variation (P < 0.01) across land uses (0.40-4.61%) and down the soil profile. Irrespective of land use type, the soil profile to a depth of 0.60 m had high TOC concentration (2.35-6.01%) and C-mediated microbial biomass nutrients (26.7-688.1 mu g g(-1)). The bacterial and fungal populations were concentrated at the top 0.6 m, but suddenly decreased beyond that depth. Conclusion The association and clustering pattern of soil properties and different land use types, identified through principal component analysis, suggested that forest areas and oak, alder, and apple plantations favoured increases in microbial biomass, enzyme activities, and viable bacterial populations.

Agroforestry systems play a critical role in enhancing soil organic carbon (SOC) stability and mitigating climate change by integrating trees and crops to improve soil fertility and carbon sequestration. This study investigates the SOC stability, aggregate dynamics, and temperature sensitivity of SOC mineralization across four agroforestry systems (Michelia oblonga, Parkia roxburghii, Alnus nepalensis, and Pinus kesiya). Tree traits, soil properties, and aggregate characteristics were analyzed alongside a 60-day incubation experiment under three temperature regimes (25°C, 30°C, and 35°C). The results revealed the SOC mineralization significantly varied amongst the agroforestry systems with highest value in M. oblonga (25.59 mg CO2 g− 1) and lowest in A. nepalensis (20.39 mg CO2 g− 1). Macroaggregates consistently showed higher SOC concentrations and biochemical indicators, such as polysaccharides and total glomalin-related soil proteins (TG-RSP), compared to microaggregates and bulk soil. The temperature and aggregate sizes statistically influenced the SOC mineralization rates, with noticeable interaction effect. SOC mineralization rates increased with temperature, but Alnus nepalensis exhibited the highest temperature sensitivity (Q10 = 0.955 and activation energy = 24.25 kJ mol− 1), highlighting its resilience to thermal stress. Strong positive correlations were observed between soil aggregate stability and soil biochemical indicators such as SOC, polysaccharides and TG-RSP of bulk soil and aggregates. Temporal trends indicated that carbon mineralization peaked at 30 days before stabilizing, reflecting the decomposition of labile carbon pools. These findings highlight the critical role of tree traits, soil aggregates, and thermal stability in driving SOC retention in agroforestry systems.

Understanding the physico-chemical properties of biochar is crucial for optimizing its use as a soil amendment to enhance crop growth. This study focuses on biochar produced from three types of biomass prevalent in the eastern Himalayan region: pine wood residue, maize stalk, and mixed weeds. The biochar was applied to soil at different rates (0, 5, 10, and 20 t ha−¹) to evaluate its effects on soil properties and French bean yield. The results revealed that mixed weed biochar (MWB) and maize stalk biochar (MSB) had alkaline pH values (9.83 and 9.31, respectively), whereas pine residue biochar (PRB) was acidic with a pH of 5.84. Notably, PRB contained 23–49

Mandarin fruits are the most widely grown citrus fruits in the world, particularly in the eastern Himalayas of India, which is the primary center of citrus diversity. Diagnosing potential nutritional imbalances using leaf tissue analysis is a mandatory practice for a higher yield. Regarding the nutritional diagnosis of Khasi mandarin plants, particularly in the acidic soil of the hilly ecology of the Eastern Himalayas, India, there is currently no information available. Therefore, the present study was conducted to identify nutrient constraints, establish leaf-based diagnostic recommended and integrated system (DRIS) norms, and determine nutrients' relationship with fruit yields in 144 orchards. The result showed that the DRIS indices predicted a nutritional optimum value for Khasi mandarin: 2.26-2.83% N, 0.11-0.16% P, 1.86-2.07% K, 1.85-2.12% Ca, 0.33-0.48% Mg, 170.10-225.10 mg kg(-1) Fe, 74.03-83.43 mg kg(-1) Mn, 1.24-2.45 mg kg(-1) Cu, and 19.84-21.28 mg kg(-1) Zn. The DRIS norms identified the nutrients Zn, P, Ca, K, N, and Mg as deficient to low levels (14.15 -> 2.14), while Fe, Mn, and Cu were at high to excessive levels (5.50 -> 18.25). The nutritional balance index had a significantly negative relationship with the fruit yield. Leaf nutrient concentrations of N (0.909**), P (0.827**), K (0.867**), Zn (0.833**), Ca (0.827**), and Mg (0.592**) had a significant positive correlation with fruit yield. The finding will facilitate the correct interpretation of leaf nutrient analysis, and the norms developed will enable a precise intervention through nutrient management for higher yields in mandarin citrus.

Crop production under stressful and fragile agro-ecologies is really formidable challenge. Under changing climate, the development of crop stress resilience is further challenging owing to its intricacies and linkage among abiotic and biotic stress responses and unprecedented prevalence of climatic vulnerabilities. Root mediated stress modulation and rhizosphere engineering is one of the novel approaches for improved crop growth and productivity under resource poor stressful environments. Holistic understanding and harnessing/tapping of inherent root associated traits including versatile root architecture and complex plant–microbe interactions in consonance with enhanced root exudation potential is one of the frontier areas of crop science research. Crop plants with wider root adaptability and root growth plasticity is quite essential for scavenging more quantities of essential nutrients under marginal and degraded lands. But the extent of employing root adaptability with differential exudation of organic compounds to drive selective plant–microbe interactions is merely exploited as source for crop resilience particularly under imminent multiple stresses. “Root microbiome” being integral reservoir of microbes is controlled by stress and cultivar specific root exudation and reported to evoke various cellular, biochemical, and molecular processes to improve the metabolic capability of crop under stressful environment. A systematic study of structure and function of root microbiome in accordance with expression of related candidate genes as directed by crop adaptability and environmental factors is critical for devising reliable crop production strategies to improve productivity. Conventional efforts to manage unabated crop stresses and to attain potential crop yields are not withstanding and long lasting. Comprehensive understanding of root adaptive mechanisms coupled with genetic and modern biotechnological approaches besides integrated and innovative fertilization practices are the need of the hour to yield economically feasible and environmentally sustainable results. In this backdrop this chapter deals with various root associated traits such as root architecture, root exudation potential, and root microbiome which are majorly important for developing crop stress resilience.

Biosolids produced at wastewater treatment facilities are extensively used in agricultural land and degraded mine sites to improve soil health and soil organic carbon (SOC) stocks. Many studies have reported increases in SOC due to application of biosolids to such sites. However, lack of a comprehensive quantification on overall trends and changes of magnitude in SOC remains. Here, we performed a meta-analysis to identify drivers with a relationship with SOC stocks. A meta-regression of 297 treatments found four variables with a relationship with SOC stocks: cumulative biosolids carbon (C) input rate, time after application, soil depth and type of biosolids. The cumulative biosolids C input rate was the most influencing driver. The highest mean difference for SOC% of 3.3 was observed at 0-15 cm soil depth for a cumulative C input of 100 Mg ha(-1) at one year after biosolids application. Although years after biosolids application demonstrated a negative relationship with SOC stocks, mineralization of C in biosolids-applied soils is slow, as indicated with the SOC% decrease from 4.6 to 2.8 at 0-15 cm soil depth over five years of 100 Mg ha(-1) biosolids C input. Soil depth illustrated a strong negative effect with SOC stocks decreasing by 2.7% at 0-15 cm soil depth at a cumulative biosolids C input of 100 Mg ha(-1) over a year. Overall, our model estimated an effect of 2.8 SOC% change, indicating the application of biosolids as a viable strategy for soil C sequestration on a global scale.

In order to establish a simple, rapid and cost effective method of estimating cation exchange capacity (CEC) of acidic soils, we tested the utility of methylene blue spot test (MBST) vis-à-vis commonly used neutral 1N ammonium acetate method (NAAM) in twenty acidic soils. The soils collected from ten different states of India varied widely in pH, organic carbon content and texture. Averaged across the soils, MBST-CEC was 37% lower than the NAAM-CEC, due possibly to the differences in pH at which the two methods operate. The CEC values estimated by MBST correlated strongly (R=0.89) with those obtained by NAAM, implying that MBST can be used satisfactorily to measure CEC of acidic soils. An equation for inter-conversion of CEC values obtained by the two methods was also worked out. Since NAAM is a time taking and tedious procedure, we recommend MBST method for routine estimation of CEC in acidic soils of India. The method is easily applicable with simple test equipments including filter papers, a glass rod or dropper and methylene blue dye. More than 60 samples a day can easily be analyzed for CEC using MBST method. Being a simple, rapid and cost effective method, the MBST can be included in rapid soil testing kits. Given the importance of CEC in soil fertility and plant nutrition, MBST-CEC may also be included in the soil health cards distributed to the farmers.

One hundred and two MAGIC indica plus lines, one hundred and four rice accessions, along with four standard checks of rice (Oryza sativa L.) were evaluated during Kharif 2017 to study the nature and extent of correlation among yield and yield attributing characters viz., days to 50 per cent flowering, plant height, number of productive tillers per plant, panicle length, number of filled grains per panicle, number of grains per panicle, spikelet fertility, thousand-grain weight, grain yield per plant. The results revealed that grain yield plant per plant to be positively and significantly associated with with number of filled grains per panicle (rp= 0.657**; rg= 0.665), spikelet fertility (rp= 0.301**; rg= 0.321), number of productive tillers per hill (rp= 0.153**; rg= 0.068), panicle length (rp= 0.133**, rg= 0.114) indicating importance of these traits as selection criteria in yield improvement programmes.

Global climate change has resulted in changes to the earth's geological, ecological, and biological ecosystems, which pose a severe threat to the existence of human civilization and sustenance of agricultural productivity vis-a-vis food security. In the last several decades, climate change has been linked to erratic rainfall distribution patterns and large variations in diurnal temperatures, because of a rise in atmospheric CO2 concentration. This, in turn, is thought to make world agricultural production systems more prone to failure. Soil organic carbon (SOC) is an important component for the functioning of agro-ecosystems, and its presence is central to the concept of sustainable maintenance of soil health. Soil is the largest terrestrial carbon sink and contains 2- and 3-times more carbon than the carbon in the atmosphere and vegetation, respectively. Therefore, a meager change in soil carbon sequestration will have a drastic impact on the global carbon cycle and climate change. The SOC has different pools and fractions including total organic carbon (TOC), particulate organic carbon (POC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), permanganate oxidizable carbon (KMnO4-C), and mineral associated organic carbon (MOC). Each has a varying degree of decomposition rate and stability. Researchers have identified many ways to offset the effect of climate change through modification of carbon sequestration in the soil. Identification of location-specific, suitable land use and management practices is one of the options to mitigate the impact of the climate change. It can be done by re-balancing different carbon pools and emission fluxes. Labile organic carbon pools including MBC, POC, and KMnO4-C are the most sensitive indicators for assessing soil quality after the adoption of alternate land use and management practices. Information on soil aggregation and SOC stabilization helps for long-term sequestration of carbon in the soil. Here we review the progress of work on SOC dynamics in the major ecosystems of the world. The information should enrich understanding of carbon sequestration and climate change mitigation strategies.

The use of phosphate potential (PP) and equilibrium phosphate potential (EPP), a measure of readily available phosphorus in soil, to predict the phosphorus supplying power of submerged soil is reliable but the information so for available is insufficient to draw a valid conclusion. An experiment was conducted with single super phosphate (SSP), diammonium phosphate (DAP) and Missouri rock phosphate (MRP) (applied @ 200 ppm P) and two period of submergence (up to 30 and 60 days) to study the effect of submergence and different sources of phosphatic fertilizers on PP and EPP. Due to submergence up to 30 days, decrease in PP and EPP was noticed in all four soils irrespective of different phosphatic fertilizer sources. This decrease in PP and EPP indicates the increased availability of inorganic phosphate (H2PO4-) ions due to the submergence. On prolonged submergence up to 60 days, decrease in PP and EPP was noticed in soils having low pH. Among the four soils, Shimoga soil recorded increased PP and EPP with all phosphatic fertilizer sources including control. Among the phosphatic fertilizers, the highly soluble fertilizers like DAP and SSP application significantly increased H2PO4- ion concentration in soil solution when compared to MRP, which is acid soluble one. The correlation studies revealed that changes in PP and EPP due to submergence and different phosphatic fertilizers application were found to be significant. However, available phosphorus was more negatively and significantly correlated with EPP.

The present study investigates the changes in land use pattern from fallow land (control) to fruit orchards on soil organic carbon (SOC) dynamics especially, organic carbon stocks, fractions, and CO2 efflux. The SOC fractions such as total organic carbon (TOC), particulate organic carbon (POC), readily oxidizable carbon (ROC), non labile carbon (C-NL), microbial biomass carbon (MBC), carbon management index (CMI) and their sensitivity to land use change were the focus of this study. The organic carbon fractions showed increasing trend (19.4-46%) under fruit orchards compared to control. Furthermore, the orchard with P. persica recorded the highest mean SOC stocks (59.4 Mg ha(-1)) and TOC (3.03 g 100 g(-1)) while orchard with C. reticulate showed the highest ROC (6.11 g kg(-1)) and MBC (401 mg kg(-1)). Fruit orchards were characterized by high Cmic:C-TOC (microbial quotient; qMIC) and POC: TOC ratios, indicating an increase in substrate availability. Furthermore, the CMI was highest under C. reticulata (226.4) followed by P. guajava (173.3), whereas P. communis showed relatively lower value (160.5). While, upper soil layer (0-15 cm) exhibited higher organic carbon stock and fractions viz., 35.1 % and 58.3%, respectively compared to the subsurface soil (15-75 cm) in all orchards. The labile SOC fractions (POC, ROC, and MBC) showed a positively significant correlation with TOC and CO2 efflux indicating that these labile fractions are the sensitive indicators of soil quality changes and improvements. Soil CO2 efflux exhibited a pronounced variation corresponding to land use change with values ranging from 22.80 mu g C g(-1) h(-1) (fallow land) to 27.39 mu g C g(-1) h(-1) (P. guajava). With temperature increment from 25 to 35 degrees C, the soil CO2 efflux increased from 55% (P. persica) to 88% (fallow) with an average increase of 72%. However, the microbial metabolic quotient (qCO(2)), also called as specific respiratory activity (SRA), was relatively lower (40.9 mu g CO2 mg MBC-1) in orchards compared to fallow land (50.4 mu g CO2 mg MBC-1). A multi-layered Artificial Neural Network model (ANN) was also developed, and the experimental CO2 efflux values obtained from different land uses are in good agreement with the predicted CO2 efflux. We conclude that, labile SOC fractions are highly sensitive to land use change and could be effectively used as the sensitive indicators along with CMI for land use change under mid-altitude subtropical ecosystems. In addition, fruit orchards could store more carbon thus could be a potential option to mitigate global warming.

A field study was conducted on two texturally different soils to determine the influences of biosolids application on selected soil chemical properties and carbon dioxide fluxes. Two sites, located in Manildra (clay loam) and Grenfell (sandy loam), in Australia, were treated at a single level of 70 Mg ha-1 biosolids. Soil samples were analyzed for SOC fractions, including total organic carbon (TOC), labile, and non-labile carbon contents. The natural abundances of soil δ13C and δ15N were measured as isotopic tracers to fingerprint carbon derived from biosolids. An automated soil respirometer was used to measure in-situ diurnal CO2 fluxes, soil moisture, and temperature. Application of biosolids increased the surface (0-15 cm) soil TOC by > 45% at both sites, which was attributed to the direct contribution from residual carbon in the biosolids and also from the increased biomass production. At both sites application of biosolids increased the non-labile carbon fraction that is stable against microbial decomposition, which indicated the soil carbon sequestration potential of biosolids. Soils amended with biosolids showed depleted δ13C, and enriched δ15N indicating the accumulation of biosolids residual carbon in soils. The in-situ respirometer data demonstrated enhanced CO2 fluxes at the sites treated with biosolids, indicating limited carbon sequestration potential. However, addition of biosolids on both the clay loam and sandy loam soils found to be effective in building SOC than reducing it. Soil temperature and CO2 fluxes, indicating that temperature was more important for microbial degradation of carbon in biosolids than soil moisture.

Tin (Sn) is a silver metal that occurs in the earth's crust, mainly as cassiterite or tinstone, and is the main source of commercial tin production. Since the collapse of the global tin market, tin mining has left unproductive and sometimes hazardous ex-tin mines. Natural attenuation has largely reduced the health risk associated with potential pollutants from tin tailings. This chapter presents a few case studies that illustrates human intervention can accelerate this process for specific land use. The tin mining industry has contributed enormously to the development of Malaysia as a nation. The rehabilitation program for ex-tin mines depends on the intended land use as well as the physicochemical characteristics of the tin tailings. Although most of the rehabilitation practices for ex-tin mines in Malaysia have focused on agricultural uses, there is an increasing trend in redeveloping ex-tin mines for commercial and housing purposes.