The influence of the soil matrix on nitrogen mineralisation and nitrification V. Microporosity and manganese

Soil Research ◽  
1999 ◽  
Vol 37 (2) ◽  
pp. 345 ◽  
Author(s):  
D. T. Strong ◽  
P. W. G. Sale ◽  
K. R. Helyar
Keyword(s):  
Linear Models ◽  
Positive Influence ◽  
Important Variable ◽  
N Mineralisation ◽  
Mineral N ◽  
Soil Matrix ◽  
Drying And Rewetting ◽  
O2 Diffusion ◽  
O2 Supply ◽  
Mn Oxides

Small soil cubes of dimensions 12 by 12 by 12 mm were collected from the surface of a red earth. Treatments were addition of clover substrate or urea, drying and rewetting, or no amendment, after which soils were incubated at either –10 or –30 kPa. Each soil cube was analysed for NO-3 -N, NH+4 -N, total soil N (%N), volumetric water content (θv), microporosity (volume of pores <0·6 µm), and Mn 2+ concentration. Multiple regression analysis was used to determine if microporosity and Mn 2+ contributed uniquely to linear models in which %N and qv were also used to predict N mineralisation and nitrification. In soils incubated at –10 kPa, both microporosity and Mn 2+ had a strong positive influence on N mineralisation and nitrification, whereas in soils incubated at –30 kPa no such influence could be observed. These and other observations suggest that when soils with high microporosity were incubated at –10 kPa, O2 supply to the microbial biomass was limited and the reduction of Mn oxides to divalent Mn was enhanced. Increased substitution of Mn oxides for O2 as terminal electron acceptors in the microbially mediated oxidation of carbon substrates considerably increases H+ consumption. We propose that in the wetter soil (–10 kPa), this process relieves pH stress experienced by N mineralising and nitrifying organisms, thereby increasing their activity, but that in the drier soil (–30 kPa), O2 diffusion is less restricted and this mechanism does not operate appreciably. The influence of microporosity on clover-amended soils was to decrease levels of mineral N and this was attributed to greater denitrification in soils with high microporosity. Neither microporosity nor Mn2+ was an important variable in the prediction of mineral N in the urea-treated soils. This work highlights the interaction of physical, chemical, and biological components of the soil which give rise to microbial microsites and diffusion gradients which are important determinants of soil function.

The influence of the soil matrix on nitrogen mineralisation and nitrification. I. Spatial variation and a hierarchy of soil properties

Soil Research ◽  
1998 ◽  
Vol 36 (3) ◽  
pp. 429 ◽  
Author(s):  
D. T. Strong ◽  
P. W. G. Sale ◽  
K. R. Helyar
Keyword(s):  
Soil Properties ◽  
Water Content ◽  
Organic N ◽  
Small Field ◽  
N Mineralisation ◽  
Mineral N ◽  
Conceptual Tool ◽  
Soil Matrix ◽  
Total N ◽  
Soil Variables

Natural heterogeneity of soil properties was used to explore their influence on nitrogen (N) mineralisation and nitrification in undisturbed small soil volumes (soil cells; c. 1 · 7 cm3 ) sampled from a small field plot (2 m by 3 m). Soil cells (840) were randomly ascribed to 1 of 6 treatments in which soils were retained continuously moist (M10 and M30 treatments) and amended with organic N from clover (Cl10 and Cl30 treatments), dried and rewetted (DW10), or treated with urea (Ur10) (subscripts indicate soil incubation at matric potential - 10 or - 30 kPa). After 20 days of incubation at 24C, each soil cell was analysed for NO-3 -N, NH + 4 -N, pH, bulk density (BD), volumetric water content (θv), water content at - 490 kPa (θv490), and pH buffer capacity (pHBC). On 25 soil cells from each treatment, % clay, % silt, % sand, total N (% N), organic carbon (% C), and 7 cations and anions were also determined. Net N mineralisation and net nitrification occurred in all treatments, and the total mineral N at the end of the incubation was 497, 81, 73, 31, 27, and 31 µg N/g in the Ur10 Cl10, Cl30, M10, M30, and DW10 treatments, respectively. Net N mineralisation in the M30 treatment was 84% of that in the M10 treatment, and net N mineralisation in the Cl30 treatment was 86% of that in the Cl10 treatment. Fluctuations in soil pH varied markedly between treatments and over time, and it was apparent that alkaline processes were occurring in all soil cells. The heterogeneity between soil samples was substantial for all of the soil variables. Soil variables were classified in a hierarchy from the least to the most fundamental based on their stability through time. This ranking provides a conceptual tool for understanding interrelationships between soil properties and for interpreting results of regression analyses. The sampling approach adopted in this study was designed to harness the natural heterogeneity of soil properties in the small field site while keeping other properties and environmental factors, that usually vary over larger distances, constant. Both the extent of heterogeneity of soil properties and the nature of their correlations with NO-3 -N suggested that this technique would be useful in the exploration of how soil properties influence N mineralisation and nitrification.

The influence of the soil matrix on nitrogen mineralisation and nitrification III. Predictive utility of traditional variables and process location within the pore system

Soil Research ◽  
1999 ◽  
Vol 37 (1) ◽  
pp. 137 ◽  
Author(s):  
D. T. Strong ◽  
P. W. G. Sale ◽  
K. R. Helyar
Keyword(s):  
Soil Ph ◽  
Organic N ◽  
Organic Substrates ◽  
Small Field ◽  
N Mineralisation ◽  
Field Plot ◽  
Pore System ◽  
Undisturbed Soil ◽  
Soil Matrix ◽  
Drying And Rewetting

Regression analysis was used to examine the importance of organic nitrogen (%N), soil water content (θv), soil pH, and C: N ratio for predicting N mineralisation in a small field plot. Undisturbed soil cubes (c. 1·7 cm3) were collected from the soil surface and received treatments of drying and rewetting, urea, substrate derived from clover leachate, or no amendment, and were incubated at either –10 or –30 kPa for 20 days. The data confirm the hypothesis that within a small field plot, θv and %N explain most of the variation in net N mineralisation and nitrification. The pore size classes of 0·6–10 and 10–30 µm made disproportionately small and large contributions to N mineralisation, respectively, apparently due to non-uniform distribution of organic N through the pore system. When soluble N substrate was added to the soils, both these pore classes appeared to support mineralisation. We concluded that prior to sampling, the microbial biomass had been more active in the pores 0·6–10 µm, and had nearly exhausted the organic substrates in this pore class, whereas this was not so for the 10–30 µm pore class. Drying and rewetting increased the importance of %N as a predictor of N mineralisation, probably because this treatment disrupted physical protective mechanisms of organic N. Soil pH was generally not a useful predictor of N mineralisation and often seemed to be a dependent rather than an independent variable in relation to nitrification. Neither was C: N ratio a useful predictor of N transformation processes, and this was probably related to physical regulatory mechanisms in the soil.

scholarly journals Shift in the Spatio-Temporal Natural Fruiting of Boletes in West African Woodlands: the Key Role of the Soil Moisture

2020 ◽  
Author(s):  
Akotchayé Sylvestre Badou ◽  
Roel D. Houdanon ◽  
Kassim I. Tchan ◽  
D.M.T. Apollon Hègbè ◽  
Nourou Soulemane Yorou
Keyword(s):  
Species Richness ◽  
Soil Moisture ◽  
Ectomycorrhizal Fungi ◽  
Linear Models ◽  
Positive Influence ◽  
Permanent Plots ◽  
Data Logger ◽  
Fresh Biomass ◽  
Natural Production ◽  
Spatio Temporal

Abstract Background: The ectomycorrhizal fungi display strong fluctuations during the mycological season. However, how abiotic parameters affect the fruiting sequences of ectomycorrhizal fungi and also the direction and extent of this effect are not yet tapped adequately. The present study seeks to assess the microclimate effect on the natural production of boletes. Nine permanent plots of 2500 m2 (50m x 50m) split into 25 subplots of 100 m2 (10m x 10m) were installed in three different vegetation dominated respectively by Isoberlinia doka, Isoberlinia tomentosa and Uapaca togoensis. Microclimatic parameters were recorded each 30 minutes throughout by mean of a Micro Station Data Logger - H21-002 the mycological seasons. Each plot was surveyed twice a week (from May to October) over three years (2015, 2016 and 2017) to record the presence/absence of fruit bodies and fresh biomass of boletes. To evaluate the effect of time and microclimate variables on natural production, we used mixed effects and generalized linear models using R version 3.5.3. Results: In total, during the three years (2015, 2016 and 2017), we recorded 14 species of boletes. Species richness does not change over time (P > 0.05). In addition, fresh biomass varies within years and vegetation (P < 0.05). The combination of year and month of collection has a significant effect on the number of fruit bodies (P < 0.05). Only the soil moisture has a significant positive influence on the species richness of boletes (P > 0.05). Conclusions: When the soil moisture decreases by four units, the number of fruit bodies of ectomycorrhizal fungi is significantly reduced by one unit. Therefore, above 0.25 m3 / m3 and below 0.05 m3 / m3 there is a decrease in the number of fruit bodies.

Productivity and nitrogen use of three different wheat-based rotations in North West Syria

1998 ◽  
Vol 49 (3) ◽  
pp. 451 ◽  
Author(s):  
M. Wood ◽  
C. J. Pilbeam ◽  
H. C. Harris ◽  
J. Tuladhar
Keyword(s):  
Crop Residues ◽  
Wheat Crop ◽  
N Mineralisation ◽  
Soil N ◽  
N Budget ◽  
Mineral N ◽  
North West ◽  
System A ◽  
To Come ◽  
C 50

Productivity of 3 different 2-year crop rotations, namely continuous wheat, wheat-chickpea, and wheat-fallow, was measured over 4 consecutive seasons beginning in 1991-92 at the ICARDA station, Tel Hadya, Syria. Nitrogen (N) fertiliser (30 kg N/ha at sowing) was broadcast every other year in the continuous wheat only. 15N-labelled fertiliser was used to quantify the amount of nitrogen supplied to the crops through current and past applications of fertiliser and by N2 fixation. The remaining N in the crop was assumed to come from the soil. In any single season, wheat yields were unaffected by rotation or N level. However, 2-year biomass production was significantly greater (32%, on average) in the continuously cropped plots than in the wheat-fallow rotation. On average, <10% of the N in the wheat crop came from fertiliser in the season of application, and <1·2 kg N/ha of the residual fertiliser was recovered by a subsequent wheat crop. Chickpea fixed 16-48 kg N/ha, depending on the season, but a negative soil N budget was still likely because the amount of N removed in the grain was usually greater than the amount of atmospheric N2 fixed. Uptake of soil N was similar in the cereal phase of all 3 rotations (38 kg N/ha, on average), but over the whole rotation at least 33% more soil N was removed from continuously cropped plots than from the wheat-fallow rotation, suggesting that the latter is a more sustainable system. A laboratory study showed that although wheat and chickpea residues enhanced the gross rate of N mineralisation by c. 50%, net rates of N mineralisation were usually negative. Given the high C/N ratio of the residue, immobilisation, rather than loss processes, is the likely cause of the decline in the mineral N content of the soil. Consequently, decomposition of crop residues in the field may in the short term reduce rather than increase the availability of N for crop growth.

Intracellular oxygen supply during hypoxia

1982 ◽  
Vol 243 (5) ◽  
pp. C247-C253 ◽  
Author(s):  
D. P. Jones ◽  
F. G. Kennedy
Keyword(s):  
Diffusion Coefficient ◽  
Critical Factor ◽  
Rat Hepatocytes ◽  
Cell Suspensions ◽  
Isolated Mitochondria ◽  
Hypoxic Conditions ◽  
O2 Diffusion ◽  
Absorbance Changes ◽  
O2 Supply

The intracellular supply of O2 to mitochondria was studied in single-cell suspensions of rat hepatocytes by measuring the O2 dependence of oxidation of cytochromes. Values were obtained by adding standardized O2-containing solutions to anaerobic cell suspensions and observing absorbance changes at wavelength pairs specific for cytochromes a + a3, c + c1, and b561 + b566. Half-maximal oxidation, calculated relative to aerobic cells, occurred at 3.5, 6.2, and 4.9 microM O2, respectively. These values are similar to those for changes in cellular ATP/ADP, lactate/pyruvate, and NADH/NAD+ but are much higher than corresponding values for isolated mitochondria. Analysis of these data indicate that the diffusion coefficient in the region of mitochondria in situ is considerably smaller than the extracellular diffusion coefficient and suggests that a significant O2 gradient in the vicinity of mitochondria occurs under hypoxic conditions. These results suggest that the rate of O2 diffusion may be a critical factor for intracellular O2 supply to mitochondria during hypoxia.

Biological and chemical assays to estimate nitrogen supplying power of soils with contrasting management histories

Soil Research ◽  
2004 ◽  
Vol 42 (7) ◽  
pp. 737 ◽  
Author(s):  
D. Curtin ◽  
F. M. McCallum
Keyword(s):  
Best Management Practices ◽  
Management Practices ◽  
N Uptake ◽  
N Mineralisation ◽  
Aerobic Incubation ◽  
Arable Soils ◽  
Mineral N ◽  
Mineralisation Potential ◽  
N Fertility

Nitrogen (N) mineralised from soil organic matter can be an important source of N for crop uptake, particularly following cultivation of pastures. Difficulty in predicting the contribution of mineralisation continues to be a serious obstacle to implementating best management practices for fertiliser N. We evaluated biological tests (i.e. net N mineralised in a 28-day aerobic incubation and anaerobically mineralisable N, AMN) and chemical tests (ammonium-N hydrolysis in hot 2 m KCl) as predictors of N supply to a glasshouse-grown oat (Avena sativa L.) crop. The oat plants were grown to maturity without added N on 30 soils representing a range of management histories, including soils collected from long-term pastures and intensive arable cropping sites. The majority (average 83%) of the N accumulated in grain and straw was mineralised N. Plant N derived from mineralisation (PNDM), estimated by subtracting soil mineral N at sowing from N uptake, was generally higher for long-term pasture soils (mean 82 mg/kg, n = 9) than for long-term arable soils (mean 48 mg/kg, n = 9). The 2 measures of N mineralisation were not closely related [R2 = 0.11 (0.37*** when one outlying observation was omitted)], indicating that aerobic and anaerobic assays can give quite different N fertility rankings. Aerobically mineralisable N was the best predictor of PNDM (R2 = 0.79***). The ratio of CO2-C evolved to net N mineralised in the aerobic incubation was highly variable (e.g. mean of 13.6 for pasture soils v. 7.5 for long-term arable soils), likely due to differences in N immobilisation. The correlations of AMN (R2 = 0.32**) and hot KCl N (R2 = 0.24**) with PNDM were not much better than that between total soil N and PNDM (R2 = 0.16*), suggesting that these tests would not provide reliable estimates of N mineralisation potential in soils with diverse management histories.

scholarly journals Modeling depth of drainage ditches in forested peatlands in Finland

2020 ◽  
Vol 26 (2) ◽  
Author(s):  
Hannu Hökkä ◽  
Leena Stenberg ◽  
Ari Laurén
Keyword(s):  
Linear Models ◽  
Bank Erosion ◽  
Important Variable ◽  
Forest Growth ◽  
Drainage Ditches ◽  
Inventory Data ◽  
Mixed Linear Models ◽  
Bed Slope ◽  
Ditch Cleaning ◽  
Average Development

Drainage ditches have been dug in peatlands and paludified forests in order to enhance forest growth in an area of 4.7 M ha in Finland. Because of peat subsidence, bank erosion, sedimentation, and ingrowth of vegetation ditches deteriorate with time. In this study the shallowing of ditch depth over time was investigated on the basis of country-wide peatland inventory data measured repeatedly up to four times. Mixed linear models were constructed separately for original ditches and maintained ditches (cleaned once or twice). After 20 years the ditches were 20-30 cm shallower than right after the digging. Time since digging was the most important variable explaining the shallowing for both original and maintained ditches. Other variables explaining the ditch shallowing were the digging method (excavator, plow), ditch bed slope, location, and peat layer thickness. The average development of maintained and original excavator ditches was very similar. The results can be used in assessing decision making concerning ditch cleaning.

scholarly journals Effect of cotton - cowpea intercropping on C and N mineralisation patterns of residue mixtures and soil

Soil Research ◽  
2009 ◽  
Vol 47 (2) ◽  
pp. 190 ◽  
Author(s):  
L. Rusinamhodzi ◽  
H. K. Murwira ◽  
J. Nyamangara
Keyword(s):  
Rate Constant ◽  
Crop Residues ◽  
Nutrient Use Efficiency ◽  
Field Capacity ◽  
C Sequestration ◽  
N Mineralisation ◽  
N Losses ◽  
Mineral N ◽  
C Mineralisation ◽  
C And N

Carbon and nitrogen mineralisation potential of mixed cotton (Gossypium hirsutum L.) and cowpea (Vigna unguiculata (L.) Walp) crop residues produced under intercropping, as well as a reddish-brown soil classified by FAO as Ferralic Cambisol previously under intercrops, were studied over a 10-week incubation period under controlled conditions (25°C and moisture content of 70% field capacity, 125 mm) in the laboratory. Treatments consisted of cotton residues (100 : 0), cowpea residues (0 : 100), and cotton–cowpea residues (50 : 50, 70 : 30, and 30 : 70). These ratios were based on yields obtained in different cotton–cowpea intercrop treatments from a field study. Cowpea residues (0 : 100) released the highest amount of mineral N of 36.4 mg/kg soil, and cotton residues (100 : 0) least, 19.2 mg/kg soil, while the other mixtures were in between. All treatments except for cowpea residues (0 : 100) and the 30 : 70 mixture showed immobilisation of soil N during the first 2 weeks of incubation. The trend for C mineralisation was similar to that of N, and cowpea residues (0 : 100) released the highest amount, 492 mg C/kg soil, while cotton residues (100 : 0) recorded the least, 315 mg C/kg soil. The C mineralisation patterns of cowpea residues (0 : 100) and 30 : 70 treatments were exponential and were well described by the equation: where CE is exponentially mineralisable C fraction, k is the rate constant, and t is time in days. The mineralisation patterns for other treatments were sigmoidal and were well described by the equation: where CS is sigmoidally mineralisable C fraction; t 0 is time in days required for complete mineralisation of CS , while k is rate constant. The amount of N released from soil previously under cotton–cowpea intercrops and sole crops was approximately one-third of the amount released when the residues were incorporated. The highest amount of N released (12.2 mg/kg soil) was from soil previously under sole cowpea, while soil from the 1 : 1 cotton–cowpea intercrop released 9.9 mg/kg soil and soil from sole cotton released 5.9 mg/kg soil. There was no significant effect (P > 0.05) of previous crop on C mineralisation patterns of the soil. Mixtures slow down N losses and increase nutrient use efficiency of legume residues, especially in the short-term. When cotton is grown as a sole crop, starter N to offset negative effects of initial N-immobilisation at the start of season is required. A better understanding of controlling parameters of decomposition can make it possible to predict C and N mineralisation patterns in mixtures. Reduced C mineralisation in cotton–cowpea mixtures may result in more C sequestration and, hence, SOM build-up and improved sustainability in the long term in intercropping systems.

Myoglobin content and oxygen diffusion: model analysis of horse and steer muscle

1996 ◽  
Vol 271 (6) ◽  
pp. C2027-C2036 ◽  
Author(s):  
K. E. Conley ◽  
C. Jones
Keyword(s):  
Consumption Rate ◽  
Oxidative Capacity ◽  
Capillary Blood ◽  
Diffusion Limitation ◽  
Tissue Samples ◽  
The Core ◽  
Model Combining ◽  
O2 Diffusion ◽  
O2 Supply ◽  
Tissue Diffusion

We test the hypothesis that myoglobin is important for O2 supply near the oxidative capacity of muscle. This hypothesis is evaluated with a simple model that incorporates the properties of heart and skeletal muscle tissue taken from steers and horses exercising at their maximum O2 consumption rate. These tissue samples allowed us to set the bounds on oxidative demand and O2 flux from red blood cells to the core of the muscle fiber, to estimate the blood and tissue capacities for O2 diffusion, and to define the capillary blood PO2 driving this O2 flux. A model combining blood convection with tissue diffusion indicates that O2 diffusion alone is insufficient to achieve the measured O2 fluxes in many samples. The myoglobin content of these fibers is significantly correlated with this O2 diffusion limitation and provides sufficient additional O2 flux to meet muscle O2 demand. The presence of myoglobin maintains the PO2 in the fiber core above anoxic levels for the majority of muscles. Thus myoglobin is critical to O2 supply at fluxes near the maximum and prevents anoxia by maintaining PO2 above levels needed to support mitochondrial function.

scholarly journals Effects of enhanced hydrological connectivity on Mediterranean salt marsh fish assemblages with emphasis on the endangered Spanish toothcarp (Aphanius iberus)

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3009 ◽  
Author(s):  
Patricia Prado ◽  
Carles Alcaraz ◽  
Lluis Jornet ◽  
Nuno Caiola ◽  
Carles Ibáñez
Keyword(s):  
Salt Marsh ◽  
Fish Community ◽  
Linear Models ◽  
Fish Assemblages ◽  
Marine Species ◽  
Fish Population ◽  
Important Variable ◽  
Hydrological Connectivity ◽  
Local Diversity ◽  
Negative Effect

The hydrological connectivity between the salt marsh and the sea was partially restored in a Mediterranean wetland containing isolated ponds resulting from former salt extraction and aquaculture activities. A preliminary assessment provided evidence that ponds farther from the sea hosted very large numbers of the endangered Spanish toothcarp,Aphanius iberus, suggesting that individuals had been trapped and consequently reach unnaturally high densities. In order to achieve both habitat rehabilitation and toothcarp conservation, efforts were made to create a gradient of hydrologically connected areas, including isolated fish reservoirs, semi-isolated, and connected salt marsh-sea areas that could allow migratory movements of fish and provide some protection forA. iberus. The fish community was monitored prior to, and for three years after rehabilitation. Results showed an increase in the number of fish species within semi-isolated areas (Zone A), whereas areas adjacent to the sea (Zone B) increased the number of marine species and decreased that of estuarine species (ES). Yet overall differences in fish assemblages were much higher between zones than among study years. Generalized linear models (GLMs) evidenced that distance to the sea was the most important variable explaining the local diversity of the fish community after restoration, with occasional influence of other factors such as temperature, and depth. The abundance ofA. iberuswas consistently higher in semi-isolated areas at greater distances from the sea, but a decline occurred in both zones and in isolated reservoir ponds after restoration efforts, which may be attributable to interannual differences in recruitment success and, to a lesser extent, to dispersal into adjacent habitats. A negative effect of restoration works on fish population cannot be excluded, but the final outcome of the intervention likely needs a longer period.

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