Effects of grazing exclusion on soil organic carbon: Hillslope and soil profile results (an Australian example)

Soils are the largest terrestrial pool of organic carbon and it is now known that as much as 50% of soil organic carbon (SOC) can be stored below 30 cm. Therefore, knowledge of the mechanisms by which soil organic carbon is stabilised at depth and how land use affects this is important.This study aimed to characterise topsoil and subsoil SOC and other soil properties under different land uses to determine the SOC stabilisation mechanisms and the degree to which SOC is vulnerable to decomposition. Samples were collected under three different land uses: arable, grassland and deciduous woodland on a silty-clay loam soil and analysed for TOC, pH, C/N ratio and texture down the first one metre of the soil profile. Soil organic matter (SOM) physical fractionation and the extent of fresh mineral surfaces were also analysed to elucidate SOM stabilisation processes.Results showed that soil texture was similar among land uses and tended to become more fine down the soil profile, but pH did not significantly change with soil depth. Total C, total N and C/N ratio decreased down the soil profile and were affected by land use in the order woodland > grassland > arable. SOM fractionation revealed that the free particulate organic matter (fPOM) fraction was significantly greater in both the topsoil and subsoil under woodland than under grassland or arable. The mineral associated OC (MinOC) fraction was proportionally greater in the subsoil compared to topsoil under all land uses: arable > grassland > woodland. Clay, Fe and Mn availability play a significant role (R2=0.87) in organic carbon storage in the top 1 m of the soil profile.It is evidently clear from the findings that land use change has a significant effect on the dynamics of the SOC pool at depth, related to litter inputs to the system.

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Jena Soil Model: a microbial soil organic carbon model integrated with nitrogen and phosphorus processes

10.5194/gmd-2019-187 ◽

2019 ◽

Author(s):

Lin Yu ◽

Bernhard Ahrens ◽

Thomas Wutzler ◽

Marion Schrumpf ◽

Sönke Zaehle

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Profile ◽

Model Performance ◽

Nutrient Release ◽

Co2 Concentration ◽

Beech Forest ◽

Forest Site ◽

Nitrogen And Phosphorus ◽

Soil Model

Abstract. The plant-soil interactions in a changing environment, such as the response of soil organic matter (SOM) decomposition, nutrient release, and plant uptake to elevated CO2 concentration, is essential to understand the global carbon (C) cycling and predict potential future climate feedbacks. These processes are poorly represented in current terrestrial biosphere models (TBMs) due to the simple linear approach of SOM cycling and the ignorance of variation within the soil profile. While the emerging microbially-explicit soil organic carbon models can better describe C formation and turnover processes, they lack so far a coupling to nutrient cycles. Here we present a new SOM model, JSM (Jena Soil Model), which is microbially-explicit, vertically resolved, and integrated with nitrogen (N) and phosphorus (P) cycle processes. JSM includes a representation of enzyme allocation to different depolymerisation sources based on the microbial adaptation approach, and a representation of nutrient acquisition competition based on the equilibrium chemistry approximation (ECA) approach. We present the model structure and basic features of the model performance against a German beech forest site. The model is capable of reproducing the main SOM stocks, microbial biomass, and their vertical patterns of the soil profile. We further test the model sensitivity to its parameterisation and show that JSM is generally sensitive to the change of microbial stoichiometry and microbial processes.

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Stability and storage of soil organic carbon in a heavy-textured Karst soil from south-eastern Australia

Soil Research ◽

10.1071/sr13296 ◽

2014 ◽

Vol 52 (5) ◽

pp. 476 ◽

Cited By ~ 13

Author(s):

Eleanor Hobley ◽

Garry R. Willgoose ◽

Silvia Frisia ◽

Geraldine Jacobsen

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Profile ◽

C Sequestration ◽

Mineral Association ◽

Radiocarbon Dates ◽

Organic C ◽

Soil C ◽

Eastern Australia ◽

Particle Size Fractionation

Both aggregation and mineral association have been previously found to enhance soil organic carbon (SOC) storage (the amount of organic C retained in a soil), and stability (the length of time organic C is retained in a soil). These mechanisms are therefore attractive targets for soil C sequestration. In this study, we investigate and compare SOC storage and stability of SOC associated with fine minerals and stored within aggregates using a combination of particle-size fractionation, elemental analysis and radiocarbon dating. In this heavy-textured, highly aggregated soil, SOC was found to be preferentially associated with fine minerals throughout the soil profile. By contrast, the oldest SOC was located in the coarsest, most highly aggregated fraction. In the topsoil, radiocarbon ages of the aggregate-associated SOC indicate retention times in the order of centuries. Below the topsoil, retention times of aggregate-SOC are in the order of millennia. Throughout the soil profile, radiocarbon dates indicate an enhanced stability in the order of centuries compared with the fine mineral fraction. Despite this, the radiocarbon ages of the mineral-associated SOC were in the order of centuries to millennia in the subsoil (30–100 cm), indicating that mineral-association is also an effective stabilisation mechanism in this subsoil. Our results indicate that enhanced SOC storage does not equate to enhanced SOC stability, which is an important consideration for sequestration schemes targeting both the amount and longevity of soil carbon.

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Litter contribution to soil organic carbon in the processes of agriculture abandon

Solid Earth ◽

10.5194/se-6-425-2015 ◽

2015 ◽

Vol 6 (2) ◽

pp. 425-432 ◽

Cited By ~ 51

Author(s):

A. Novara ◽

J. Rühl ◽

T. La Mantia ◽

L. Gristina ◽

S. La Bella ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Soil Profile ◽

Secondary Succession ◽

Co2 Emission ◽

Soil Cores ◽

Soil Layers ◽

C Stock ◽

One Year

Abstract. The mechanisms of litter decomposition, translocation and stabilization into soil layers are fundamental processes in the functioning of the ecosystem, as they regulate the cycle of soil organic matter (SOM) and CO2 emission into the atmosphere. In this study the contribution of litters of different stages of Mediterranean secondary succession on carbon sequestration was investigated, analyzing the role of earthworms in the translocation of SOM into the soil profile. For this purpose the δ13C difference between meadow C4-C soil and C3-C litter was used in a field experiment. Four undisturbed litters of different stages of succession (45, 70, 100 and 120 since agriculture abandon) were collected and placed on the top of isolated C4 soil cores. The litter contribution to C stock was affected by plant species and it increased with the age of the stage of secondary succession. One year after the litter position, the soil organic carbon increased up to 40% in comparison to soils not treated with litter after 120 years of abandon. The new carbon derived from C3 litter was decomposed and transferred into soil profile thanks to earthworms and the leaching of dissolved organic carbon. After 1 year the carbon increase attributed to earthworm activity was 6 and 13% in the soils under litter of fields abandoned for 120 and 45 years, respectively.

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Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands

PLoS ONE ◽

10.1371/journal.pone.0146757 ◽

2016 ◽

Vol 11 (1) ◽

pp. e0146757 ◽

Cited By ~ 12

Author(s):

Ding Wen ◽

Nianpeng He ◽

Jinjing Zhang

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Aggregate Stability ◽

Grazing Exclusion

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Yield and nitrogen use efficiency in wheat, and soil fertility status as influenced by substitution of rice with pigeon pea in a rice - wheat cropping system

Australian Journal of Experimental Agriculture ◽

10.1071/ea04046 ◽

2006 ◽

Vol 46 (9) ◽

pp. 1185 ◽

Cited By ~ 13

Author(s):

V. K. Singh ◽

B. S. Dwivedi

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Bulk Density ◽

Nitrogen Use Efficiency ◽

Soil Profile ◽

Soil Depth ◽

Pigeon Pea ◽

Grain Legume ◽

Nitrogen Use ◽

Use Efficiency

Rice–wheat cropping systems managed on 10 million ha in the Indo-Gangetic Plain region (IGPR) of India are the most important production systems for national food security. Recent reports, however, indicate that the system is under production fatigue and the growth rates of rice and wheat have started declining. We, therefore, conducted field experiments at Modipuram, Meerut, India, for 3 consecutive years (1998–99 to 2000–01), to study the conservation of soil organic carbon, improvement in nitrogen use efficiency and increase in system yields through inclusion of a grain legume (pigeon pea) in place of rice. The wheat yields following pigeon pea crops were significantly (P<0.05) greater than those following rice crops during 1999–2000 and 2000–01, but not during 1998–99. The economic optimum doses of fertiliser N for wheat in the pigeon pea–wheat system were smaller (128–133 kg N/ha) than those in the rice–wheat system (139–173 kg N/ha), owing to increased N supply, greater N use efficiencies and a better crop growth environment in the pigeon pea–wheat system. The post-wheat harvest nitrate-N (NO3-N) at 90–105 cm soil depth in plots fertilised with 120 or 180 kg N/ha was greater for the rice–wheat system (6.5–8.1 mg/kg) than for the pigeon pea–wheat system (5.8–6.0 mg/kg), suggesting that inclusion of pigeon pea may help to minimise NO3-N leaching to deeper soil profile layers. In plots of pigeon pea, soil organic carbon at 0–15 cm and 15–30 cm soil depths was increased at the end of the experiment compared with the initial organic carbon content. With continuous rice–wheat cropping, the bulk density of soil increased over the initial bulk density, at different soil profile depths in general, and at 30–45 cm soil depth in particular. Inclusion of pigeon pea in the system maintained soil bulk density at its initial level, and thus eliminated sub-surface soil compaction. Despite these advantages of pigeon pea over rice as a preceding crop to wheat, permanent substitution of rice with pigeon pea in rice–wheat system is unlikely, because rice is a staple foodgrain crop in India. Nonetheless, decline in wheat productivity owing to puddling-induced soil constraints that arise on continuous rice–wheat systems could be minimised by introduction of pigeon pea into the system at longer time intervals.

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