Respiration from soil and litter in a sown perennial grass pasture

Soil Research ◽  
1995 ◽  
Vol 33 (1) ◽  
pp. 167 ◽  
Author(s):  
FA Robertson ◽  
RJK Myers ◽  
PG Saffigna
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Perennial Grass ◽  
Bare Soil ◽  
Plant Residues ◽  
Root Pruning ◽  
Panicum Maximum ◽  
Co2 Evolution ◽  
Litter Addition ◽  
Alkali Absorption

The severe nitrogen (N) deficiency which occurs in many sown grass pastures in Queensland is believed to be exacerbated by large and continuous inputs of carbon (C) from decomposing plant residues. In this study we attempted to quantify the importance of surface litter, roots and soil organic matter as sources of respiration in an established green panic (Panicum maximum var. trichoglume) pasture in south-east and Queensland. Intact pasture cores were taken from the field and the surface litter was removed before applying the following treatments: (i) surface litter added, (ii) roots pruned to kill approximately 60% of roots but not kill the plant, and (iii) plant shoots removed. Cores from bare soil between green panic plants were also included. The cores were kept in a glasshouse and CO2 evolution measured continuously for 117 days using an alkali absorption method. Respiration from the various components of the system was estimated. Evolution of CO2 from the cores was increased by litter addition and decreased by shoot removal. Root pruning stimulated CO2 evolution in litter-removed treatments but had no effect in litter-added treatments. Root respiration and microbial respiration of root-derived C accounted for an average of 53% of the total evolved CO2. Surface litter, soil organic matter and dead roots accounted for an average of 40%, 4% and 3% respectively. The importance of a particular C source to microorganisms varied depending on the availability of other C sources. Cores were destructively sampled on five occasions and the soils incubated at 25�C for 10 days to measure CO2 evolution with surface litter and roots removed. Evolution of CO2 in incubated soils was increased by litter and, to a lesser extent, by live roots, demonstrating that some of the labile C from these plant components was soluble or well incorporated into the soil.

Effects of modifying plant carbon inputs on nitrogen distribution in intact cores of a perennial grass pasture

Soil Research ◽  
1995 ◽  
Vol 33 (2) ◽  
pp. 297 ◽  
Author(s):  
FA Robertson ◽  
RJK Myers ◽  
PG Saffigna
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
N Uptake ◽  
Organic N ◽  
Root Pruning ◽  
Panicum Maximum ◽  
15N Recovery ◽  
N Availability ◽  
Plant Shoots

Perennial pastures can accumulate large quantities of roots and surface litter of high C:N ratio, which may reduce N availability to the plant by stimulating microbial immobilization. We studied the effects of modifying carbon inputs from roots and litter on the distribution of nitrogen (N) in plant and soil fractions of an old N-deficient green panic (Panicum maximum var. trichoglume) pasture. Intact pasture cores were taken from the field to a glasshouse, and the surface litter was removed before applying the following treatments: (i) surface litter added, (ii) roots pruned to kill approximately 60% of roots, and (iii) plant shoots removed. A small pulse of 15N as ammonium sulfate was added to the soil surface, and the cores were destructively sampled on several occasions over the following 4 months. Litter addition had little effect on N uptake by uncut plants. When plant shoots were removed, litter markedly reduced plant N uptake. Litter increased N and 15N in microbial biomass and N and 15N stabilized in non-biomass soil organic matter, and reduced loss of N from the cores. Root pruning had little effect on N distribution, except for an initial reduction in plant uptake. Removal of pasture shoots markedly increased soil nitrate and loss of 15N, and decreased non-biomass organic N and 15N. Recovery of 15N in non-biomass organic matter was around three times greater than 15N in microbial biomass, and was closely associated with microbial CO2 production. There was evidence that 15N entered the non-biomass organic matter by both abiotic and microbially mediated processes. In these pastures, the non-biomass soil organic matter may be a more important sink for N than the microbial biomass.

Nitrogen cycling in brigalow clay soils under pasture and cropping

Soil Research ◽  
1997 ◽  
Vol 35 (6) ◽  
pp. 1323 ◽  
Author(s):  
F. A. Robertson ◽  
R. J. K. Myers ◽  
P. G. Saffigna
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
Plant Uptake ◽  
Significant Proportion ◽  
Clay Soils ◽  
Plant Residues ◽  
Panicum Maximum ◽  
N Availability ◽  
Soil Inorganic

Clay soils previously under native brigalow (Acacia harpophylla) forest are highly productive under annual cropping in central and southern Queensland. Grass pastures sown on these soils are initially productive, but deteriorate after several years because of N-stress (rundown). The aim of this work was to compare the patterns of N cycling in these pasture and cropping systems, in order to understand the rundown of the pastures. A small pulse of 15N-labelled ammonium sulfate was applied in the field to sites cropped with sorghum (Sorghum bicolor) and under green panic (Panicum maximum var. trichoglume) pasture, and its movement through the soil and plant pools was followed over 2 growing seasons. There were large differences in the cycling of 15N in the cropping and pasture systems. Under sorghum, 60% of the applied 15N was immobilised by microorganisms after 4 days, after which it was re-mineralised. Plant uptake and stabilisation in soil organic matter and clay were relatively slow. The first sorghum crop assimilated 14% of the applied 15N. During the second season, most of the 15N was stabilised in soil organic matter and clay (maximum 42%). A significant proportion of the 15N remained in the soil inorganic pool over the 2 seasons. Under green panic, 82% of the 15N left the soil inorganic pool within 4 days and entered the microbial biomass, soil organic matter, and the plant. Uptake and re-release of 15N were most rapid in the microbial biomass (maximum uptake 34% of applied after 4 days). Microbial immobilisation and re-mineralisation were, however, slower under green panic than under sorghum. The pasture plant accumulated 32% of the applied 15N, two-thirds of which was re-released in the second season. Stabilised N represented up to 62% of the applied 15N, and was consistently greater under green panic than under sorghum. After 2 seasons, 15N was released from the stabilised N pool in both systems, at approximately the same rate as it had been stabilised. At the end of the experiment, 40% of the applied 15N was unaccounted for in the pasture system, and 66% in the crop system. The reduced N availability in the pasture system was attributed to immobilisation of N in soil organic matter and clay, plant material, and, to a lesser extent, soil microbial biomass. This immobilisation resulted from the large accumulation of carbonaceous plant residues.

scholarly journals Organic matter quality in a soil cultivated with perennial herbaceous legumes

2004 ◽  
Vol 61 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Luciano Pasqualoto Canellas ◽  
José Antonio Azevedo Espindola ◽  
Carlos Eduardo Rezende ◽  
Plínio Barbosa de Camargo ◽  
Daniel Basílio Zandonadi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Humic Acids ◽  
Soil Layer ◽  
C3 Plants ◽  
Plant Residues ◽  
Panicum Maximum ◽  
Organic Matter Quality ◽  
Herbaceous Legumes ◽  
Soil Organic Matter Quality

Using herbaceous legumes in agricultural systems yields great quantities of plant residues, allowing changes in soil organic matter quality and content over the years. This study was conducted on an Ultisol, at Seropédica, RJ, Brazil, to evaluate the effects of different perennial herbaceous legumes on soil organic matter quality. A factorial scheme with three replications was used to evaluate the species: forage groundnut cv. BR-14951 (Arachis pintoi), tropical kudzu (Pueraria phaseoloides), and siratro (Macroptilium atropurpureum). After the first cut, each plot was divided into two subplots; plants were cut and left on the soil surface or cut and removed. Soil samples of a closed area covered by spontaneous vegetation (mainly C3 plants) or by Panicum maximum were also analysed. Samples were collected from two layers (0-5 and 5-10 cm), processed for the fractionation of organic matter and the evaluation of structural characteristics of humic acids (HA). Evaluated legumes did not change total organic carbon contents, but promoted HA accumulation in the superficial soil layer. Humic acids may be used as indicators of the management effects on soil organic fractions, because there was significant incorporation of carbon and nitrogen derived from the legume residues, even for the short experimentation time (28 months). Residue management did not modify quantitative aspects of the distribution of the humified organic matter, but promoted, however, a higher condensation degree of humic acids evaluated by the elementary composition, IR and fluorescence spectroscopy.

scholarly journals ORGANIC CARBON DYNAMICS IN GRASSLAND SOILS. 1. BACKGROUND INFORMATION AND COMPUTER SIMULATION

1981 ◽  
Vol 61 (2) ◽  
pp. 185-201 ◽  
Author(s):  
J. A. VAN VEEN ◽  
E. A. PAUL
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Experimental Studies ◽  
Decay Rates ◽  
Background Information ◽  
Plant Residues ◽  
Decomposition Rates ◽  
Straw Decomposition ◽  
Soil Biomass ◽  
The World

The decomposition rates of 14C-labelled plant residues in different parts of the world were characterized and mathematically simulated. The easily decomposable materials, cellulose and hemicellulose, were described as being decomposed directly by the soil biomass; the lignin fraction of aboveground residues and the resistant portion of the roots entered a decomposable native soil organic matter. Here it could be decomposed by the soil biomass or react with other soil constituents in the formation of more recalcitrant soil organic matter. The transformation rates were considered to be independent of biomass size (first–order). Data from 14C plant residue incorporation studies which yielded net decomposition rates of added materials and from carbon dating of the recalcitrant soil organic matter were transformed to gross decomposition rate constants for three soil depths. The model adequately described soil organic matter transformations under native grassland and the effect of cultivation on organic matter levels. Correction for microbial growth and moisture and temperature variations showed that the rate of wheat straw decomposition, based on a full year in the field in southern Saskatchewan, was 0.05 that under optimal laboratory conditions. The relative decay rates for plant residues during the summer months of the North American Great Plains was 0.1 times that of the laboratory. Comparison with data from other parts of the world showed an annual relative rate of 0.12 for straw decomposition in England, whereas gross decomposition rates in Nigeria were 0.5 those of laboratory rates. Both the decomposable and recalcitrant organic matter were found to be affected by the extent of physical protection within the soil. The extent of protection was simulated and compared to data from experimental studies on the persistence of 14C-labelled amino acids in soil. The extent of protection influenced the steady-state levels of soil carbon upon cultivation more than did the original decomposition rates of the plant residues.

Tillage effects on the dynamics of total and corn-residue-derived soil organic matter in two southern Ontario soils

1999 ◽  
Vol 79 (3) ◽  
pp. 473-480 ◽  
Author(s):  
S. D. Wanniarachchi ◽  
R. P. Voroney ◽  
T. J. Vyn ◽  
R. P. Beyaert ◽  
A. F. MacKenzie
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Field Experiments ◽  
Soil Depth ◽  
Reduced Tillage ◽  
Plant Residues ◽  
Organic C ◽  
Tillage Practices ◽  
Loam Soil

Agricultural management practices affect the dynamics of soil organic matter (SOM) by influencing the amount of plant residues returned to the soil and rate of residue and SOM decomposition. Total organic C and δ13C of soil were measured in two field experiments involving corn cropping to determine the effect of tillage practices on SOM dynamics. Minimum tillage (MT) and no tillage (NT) had no significant impact on the soil C compared with conventional tillage (CT) in the 0- to 50-cm soil depth sampled at both sites. Continuous corn under MT and CT for 29 yr in a silt loam soil sequestered 61–65 g m−2 yr−1 of corn-derived C (C4-C), and it accounted for 25–26% of the total C in the 0- to 50-cm depth. In a sandy loam soil cropped to corn for 6 yr, SOM contained 10 and 8.4% C4-C under CT and NT, respectively. Reduced tillage practices altered the distribution of C4-C in soil, causing the surface (0–5 cm) soil of reduced tillage (MT and NT) plots to have higher amounts of C4-C compared to CT. Tillage practices did not affect the turnover of C3-C in soil. Key words: Soil organic matter, 13C natural abundance, tillage practices

scholarly journals Mapping Soil Organic Matter and Analyzing the Prediction Accuracy of Typical Cropland Soil Types on the Northern Songnen Plain

2021 ◽  
Vol 13 (24) ◽  
pp. 5162
Author(s):  
Meiwei Zhang ◽  
Huanjun Liu ◽  
Meinan Zhang ◽  
Haoxuan Yang ◽  
Yuanliang Jin ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Mean Squared Error ◽  
Critical Role ◽  
Absolute Error ◽  
Bare Soil ◽  
Soil Types ◽  
Coefficient Of Determination ◽  
Songnen Plain ◽  
Type Data

Soil organic matter (SOM) plays a critical role in agroecosystems and the terrestrial carbon cycle. Thus, accurately mapping SOM promotes sustainable agriculture and estimations of soil carbon pools. However, few studies have analyzed the changing trends in multi-period SOM prediction accuracies for single cropland soil types and mapped their spatial SOM patterns. Using time series 7 MOD09A1 images during the bare soil period, we combined the pixel dates of training samples and precipitation data to explore the variation in SOM accuracy for two typical cropland soil types. The advantage of using single soil type data versus the total dataset was evaluated, and SOM maps were drawn for the northern Songnen Plain. When almost no precipitation occurred on or near the optimal pixel date, the accuracies increased, and vice versa. SOM models of the two soil types achieved a lower root mean squared error (RMSE = 0.55%, 0.79%) and mean absolute error (MAE = 0.39%, 0.58%) and a higher coefficient of determination (R2 = 0.65, 0.75) than the model using the total dataset and resulted in a mean relative improvement (RI) of 30.21%. The SOM decreased from northeast to southwest. The results provide reference data for the accurate management of cultivated soil and determining carbon sequestration.

Microbial necromass as a source for soil organic matter formation - implications for soil processes

2020 ◽  
Author(s):  
Anja Miltner ◽  
Tiantian Zheng ◽  
Chao Liang ◽  
Matthias Kästner
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
Surface Properties ◽  
Soil Microorganisms ◽  
Plant Litter ◽  
Plant Residues ◽  
Elemental Stoichiometry ◽  
Stress Changes ◽  
Cell Envelopes

<p>The vital role of soil microorganisms as catalysts for soil organic matter (SOM) formation has long been recognised. Plant residues are now considered to be transformed by soil microorganisms who use the plant litter as a carbon source for microbial biomass formation. How much carbon is retained as microbial biomass during transformation of plant material, critically depends on substrate availability, carbon use efficiency of the microorganisms, and maximum microbial growth. In addition, microorganisms presumably recycle biomass building blocks from plant or microbial material to avoid energy expenditure for biomass synthesis. After cell death, a part of the microbial necromass is cycling through the microbial food web; the other part is stabilised in soil (Miltner et al., 2012). Potential stabilisation mechanisms are similar to those for SOM in general, with organo-mineral interactions, in particular encapsulation and physical isolation, being important mechanisms. Independent of which pathway the plant-derived carbon goes, SOM constitutes a continuum of plant and microbial necromass at various stages of decay. The contribution of microbial necromass to the topsoil organic matter pool has recently been estimated to range from 30 to 60% (Liang et al., 2019). Such high contributions of microbial necromass have a number of important implications for understanding SOM transformation and sequestration processes. Most obviously, the chemical identity of the organic material changes. For example, while retaining a substantial part of the carbon, the elemental stoichiometry changes substantially. Some microbial necromass materials are rather long-lasting in soil. In general, cell envelope residues have a higher stability than bulk biomass carbon. Proteins have also been shown to be rather persistent in soil, presumably due to conformational changes and the spatial arrangement of microbial necromass material, e.g. fragments of cell envelopes presumably pile up in multiple layers and the material forms clusters of macromolecular size. Residual electron-shuttle biomolecules (e.g. oxidoreductases, Fe-S-cluster, quinoid complexes of respiratory chains) may persist and retain some activity and thus contribute to redox reactions in soil. In addition, the necromass is expected to cover soil particle surfaces and thus determine the surface properties of these particles. In particular, these materials contribute to the water storage potential. They affect water retention and nutrient diffusion as well as microbial motility. Adaption of microbes to water stress changes their cell surface properties and molecular composition and thus may determine overall soil wettability. Knowledge on the contribution of microbial necromass to SOM would thus be essential for modelling SOM formation and optimising soil management practices for maintaining soil functions.</p><p> </p><p>References:</p><p>Miltner A, Bombach P, Schmidt-Brücken B, Kästner M (2012) SOM genesis: Microbial biomass as a significant source. Biogeochemistry 111: 41-55.</p><p>Liang C, Amelung W, Lehmann J, Kästner M (2019) Quantitative assessment of microbial necromass contribution to soil organic matter. Global Change Biology 25: 3578-3590.</p>

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