Impacts of Rice Field Winter Planting on Soil Organic Carbon and Carbon Management Index

To tackle with the problem of prevailing farmland abandonment in winter, 5 treatments includes Chinese milk vetch-double cropping rice (CRR), rape-double cropping rice (RRR), garlic-double cropping rice (GRR), winter crop multiple cropping rotation (ROT), winter fallow control (WRR) were set up. By measuring soil total organic carbon, active organic carbon and its components and calculating the soil carbon pool management index in 0~15 cm and 15~30 cm soil layers in the early and late rice ripening stage. The effects of different winter planting patterns on the changes of soil organic carbon and carbon pool management index were discussed. In order to provide theoretical basis for the optimization and adjustment of winter planting pattern of double cropping rice field in the middle reaches of Yangtze River. The results showed that soil total organic carbon, active organic carbon and its components in different winter cropping patterns were increased, and ROT and CRR treatments were more beneficial to the accumulation of soil total organic carbon, active organic carbon and its components as well as the improvement of soil carbon pool management index, which should be preferred in the adjustment of cropping patterns.

Effect of coal fly ash and vermicompost amendment on soil earthworm and nematode count, and change in soil carbon pool in rice nursery

Fly ash (FA) as a byproduct from the coal-fired power plants needs timely, effective, productive and safe disposal. Its application to soil at lower concentration is advocated by many researchers due to its soil ameliorative properties. Combined application of FA along with organic substrates such as farm yard manure, compost, and microbial culture has positive influence on soil biota and crop performance. But the xenobiotic effect of FA in presence of vermicompost (VC) has not yet been studied fully. The present investigation was carried out in western Odisha, India with native soil, FA and VC at 0%, 20%, 40%, 60%, 80% and 100% combinations (by weight) to study their effects on earthworm and nematode count, and change in soil carbon pool in rice nursery. The experiment was laid out in a factorial complete randomized design with three replications. The earthworm and nematode population at 40 DAS of rice was positively influenced by the concentration of VC in rhizosphere of rice nursery but FA addition affected earthworm survivability to an extent that no earthworm was found with more than 20% FA. Rhabditis terricola and Dorylaimids in the rhizosphere of rice nursery was also positively linked with VC concentration while FA had antagonistic effects. Absence of nematodes and earthworm at higher concentration of FA could be linked to xenobiotic effects of FA. Mild addition (20% each) of FA and VC to native soil could increase in carbon stock to the maximum extent due to combined effect of larger surface area of FA and minimized microbial activity limiting respirational carbon loss.

CARBON IN SOILS IN FOREST REGIONS OF EUROPEAN-URAL PART OF RUSSIA

Soil carbon pool in the block of the European-Ural part of Russia was assessed on a topological basis of lands categories adopted in State Forest Inventory (21 biotopes in total). The published data on 675 soil profiles were linked to biotopes and forest regions through coordinates and descriptions of profiles (13). The total carbon stock in the soils in forest regions of the European-Ural part were 19.3*109 t C for a depth of 0–30 cm, 26.6*109 t C for a depth of 0–50 cm, and 34.2*109 t C for a depth of 0–100 cm. Forest area in the European part of Russia for these forest regions is estimated at 181.13*106 ha. Aggregated data are presented both for biotopes of the entire region and for forest regions. We compared the results obtained on top basis of dominant tree species and non-forest lands with the estimates of other authors obtained for various soil types.

Soil carbon pool under organic and conventional crop production system of semi arid tropics

Regardless of land use, the results indicated significant differences in all the studied parameters. Total % SOC ranged from 0.52 to 0.72 for conventional farm samples (mean 0.62%) and 0.63 to 1.59 for the organic samples (mean 1.19). Bulk density (g/cc) ranged from 0.43 to 0.81 (mean 0. 62) for conventional and 0.17 to 0.28 (mean 0.20) organic farm soils. Organic manures increased microbial biomass carbon by 117% and dissolved organic carbon (DOC) concentration by 181% over conventional farming. The results suggested that organic matter is better protected in organic soils and are consequently less vulnerable to mineralization.

Re-visiting a long-term Free Air CO2 Enrichment (FACE) experiment in a Danish heathland/grassland ecosystem (CLIMAITE) reveals highly dynamic soil carbon

<p>The feedback of the terrestrial carbon cycle to global climate change is among the largest uncertainties in climate change research. To test the potential ecosystem effects of future climate scenarios, a field-scale FACE (Free Air CO<sub>2</sub> Enrichment) experiment combined with increased temperatures and extended summer drought was performed in the period 2005–2013 on a temperate heathland/grassland ecosystem in Denmark (the CLIMAITE project). A major finding from the original experiment was that the soil carbon pool increased by approximately 20% under elevated CO<sub>2</sub> over the 8 years of the study*.</p><p>The FACE treatment was in effect also an in situ labeling experiment because the added CO<sub>2</sub> was depleted for <sup>13</sup>C （<sup>13</sup>CO<sub>2FACE</sub>=-29‰）compared to ambient atmospheric CO<sub>2</sub>（<sup>13</sup>CO<sub>2AIR</sub>=-8‰）. Therefore, the isotopic signal of the remaining soil carbon can be used to investigate the turnover of soil carbon during the time since the end of the original study.</p><p>During the growing season in 2020, seven years after the CO<sub>2</sub> fumigation experiment was terminated, soil samples were extracted in all plots using the same sampling strategy as in previous samplings. Interestingly, the direct soil C pool measurements showed that the extra soil carbon, which was stored during the eight years with elevated CO<sub>2</sub> had been lost again over the course of the following seven years. The isotopic composition of the different soil layers had also changed back towards the values measured in control plots, although still being slightly more depleted for <sup>13</sup>C. Still, the convergence of the isotopic composition in the different treatments confirms the trend observed from the direct C pool measurements and also hints that a part of the more recalcitrant carbon taken up during the elevated CO2 experiment is still there while most of the labile/less recalcitrant carbon has been decomposed and reemitted to the atmosphere. The results show that the soil carbon pool in the ecosystem is extremely dynamic and may change fast in response to changes in major ecosystem drivers, and in particular is highly sensitive to the atmospheric CO<sub>2</sub> concentration.</p><p>*Dietzen CA, Larsen KS, Ambus P, Michelsen A, Arndal MF, Beier C, Reinsch S, Schmidt IK (2019) Accumulation of soil carbon under elevated CO<sub>2</sub> unaffected by warming and drought. Global Change Biology, 25: 2970–2977. doi: 10.1111/gcb.14699.</p>

Effects of Stand Density on Soil Respiration and Soil Labile Organic Carbon and Their Influence Mechanism in Larix Principis-Rupprechtii Plantations

BackgroundForest soil carbon pool plays a vital role in the global carbon sequestration and carbon emission. Forest management can regulate the sequestration and output of forest soil carbon pool to a certain extent, but mechanism of forest density effects on soil carbon pool still needs to be further researched. MethodsWe established sample plots with density gradients in three-age stands of Larix principis-rupprechtii plantation and measured soil respiration (RS), soil organic carbon (SOC), soil dissolved organic carbon (DOC), and microbial biomass carbon (MBC), light fraction organic carbon (LFOC), and easily oxidizeable organic carbon (ROC). Results and ConclusionsThe results showed that, among the forest stands of three ages, RS, heterotrophic respiration (RH), MBC, LFOC, ROC of different stand density levels were significantly different. Moderate density promotes RS rate and RH rate and the sequestration of MBC and LFOC and inhibits ROC sequestration. With the increase of forest stand density, RS, RH, LFOC, and MBC first increased and then decreased, and ROC first decreased and then increased, the quadratic function could fit these changing trends. The RS, RH, and autotrophic respiration (RA) rates of older forest stands were relatively fast, and contents of SOC, MBC, LFOC, DOC, and ROC were higher, and they were more sensitive to changes in stand density. SOC, LFOC, MBC, DOC, and ROC explained 56.05% variations of RS, Rh, and RA. MBC, LFOC, and ROC in soil labile organic carbon were closely related to RS and Rh, but not SOC. Among them, LFOC and MBC played the role of "warehouse" and "tool" and significantly correlated with RS and Rh. ROC, as "raw material," had a significant negative correlation with RS and RH. When the RS and RH rate were fast, ROC maintained a dynamic and stable state of low soil content. Stand density could regulate RH by affecting soil labile organic carbon, an essential path for stand density to regulate soil respiration. Given soil carbon pool significance in forest ecosystems, Continuous research on soil respiration and stand density is suggested to bridge the gaps in our comprehension of the Regulation of Forest Management on forest soil carbon pool.