Decomposition of plant material in Australian soils. III. Residual organic and microbial biomass C and N from isotope-labelled legume material and soil organic matter, decomposing under field conditions

Soil Research ◽  
1985 ◽  
Vol 23 (4) ◽  
pp. 603 ◽  
Author(s):  
JN Ladd ◽  
M Amato ◽  
JM Oades
Keyword(s):  
Microbial Biomass ◽  
South Australia ◽  
Experimental Period ◽  
Decay Rates ◽  
Microbial Biomass C ◽  
Plant Residues ◽  
Total Biomass ◽  
Organic C ◽  
Air Temperatures ◽  
C And N

After eight years decomposition of 14C, 15N-labelled legume (Medicago littoralis) material previously mixed into topsoils (0-10 cm) at four field sites in South Australia, residual organic 14C and 15N to 30 cm depth accounted for respectively 11-13% of input 14C, and 31-38% of input 15N. About 90% of the residual organic 14C and 70-80% of the residual l15N was recovered in topsoils. For sites in similar rainfall areas, soils of heavier texture retained slightly greater amounts of 14C and15N-labelled residues. Throughout the eight-year experimental period, the rates of decline of residual organic 14C and 15N exceeded those of native soil organic C and N. A comparison of the decline of organic 14C in topsoils, averaged for the four South Australian sites, with the average decline reported for 14C-labelled plant residues in soils at English and Nigerian field sites, suggests that net decomposition rates doubled approximately for an 8-9�C rise in mean annual air temperatures. Microbial biomass 14C and 15N of topsoils with time accounted for decreasing proportions of total biomass C and N, and of residual organic I4C and I5N. The relatively greater retention after eight years of biomass 14C and 15N in soils of heavier texture is consistent with the concept that the net decay of C and N in soils is dependent upon the turnover of biomass C and N, and that decay rates are decreased in soils which have the greater capacity to protect decomposer populations.

Seasonal trends in selected soil biochemical attributes: Effects of crop rotation in the semiarid prairie

1999 ◽  
Vol 79 (1) ◽  
pp. 73-84 ◽  
Author(s):  
C. A. Campbell ◽  
V. O. Biederbeck ◽  
G. Wen ◽  
R. P. Zentner ◽  
J. Schoenau ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Microbial Biomass ◽  
Microbial Biomass Carbon ◽  
Light Fraction ◽  
Water Soluble ◽  
Microbial Biomass C ◽  
Weather Variables ◽  
Total N ◽  
Organic C ◽  
C And N

Measurements of seasonal changes in soil biochemical attributes can provide valuable information on how crop management and weather variables influence soil quality. We sampled soil from the 0- to 7.5-cm depth of two long-term crop rotations [continuous wheat (Cont W) and both phases of fallow-wheat (F–W)] at Swift Current, Saskatchewan, from early May to mid-October, 11 times in 1995 and 9 times in 1996. The soil is a silt loam, Orthic Brown Chernozem with pH 6.0, in dilute CaCl2. We monitored changes in organic C (OC) and total N (TN), microbial biomass C (MBC), light fraction C and N (LFC and LFN), mineralizable C (Cmin) and N (Nmin), and water-soluble organic C (WSOC). All biochemical attributes, except MBC, showed higher values for Cont W than for F–W, reflecting the historically higher crop residue inputs, less frequent tillage, and drier conditions of Cont W. Based on the seasonal mean values for 1996, we concluded that, after 29 yr, F–W has degraded soil organic C and total N by about 15% compared to Cont W. In the same period it has degraded the labile attributes, except MBC, much more. For example, WSOC is degraded by 22%, Cmin and Nmin by 45% and LFC and LFN by 60–75%. Organic C and TN were constant during the season because one year's C and N inputs are small compared to the total soil C or N. All the labile attributes varied markedly throughout the seasons. We explained most of the seasonal variability in soil biochemical attributes in terms of C and N inputs from crop residues and rhizodeposition, and the influences of soil moisture, precipitation and temperature. Using multiple regression, we related the biochemical attributes to soil moisture and the weather variables, accounting for 20% of the variability in MBC, 27% of that of Nmin, 29% for LFC, 52% for Cmin, and 66% for WSOC. In all cases the biochemical attributes were negatively related to precipitation, soil moisture, temperature and their interactions. We interpreted this to mean that conditions favouring decomposition of organic matter in situ result in decreases in these attributes when they are measured subsequently under laboratory conditions. We concluded that when assessing changes in OC or TN over years, measurements can be made at any time during a year. However, if assessing changes in the labile soil attributes, several measurements should be made during a season or, measurements be made near the same time each year. Key words: Microbial biomass, carbon, nitrogen, mineralization, water-soluble-C, light fraction, weather variables

Effect of crop rotations and cultural practices on soil organic matter, microbial biomass and respiration in a thin Black Chernozem

1991 ◽  
Vol 71 (3) ◽  
pp. 363-376 ◽  
Author(s):  
C. A. Campbell ◽  
V. O. Biederbeck ◽  
R. P. Zentner ◽  
G. P. Lafond
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
Cultural Practices ◽  
Respiratory Activity ◽  
Crop Rotations ◽  
Microbial Biomass C ◽  
Soil Organic C ◽  
Organic C ◽  
C And N

The effects of crop rotations and various cultural practices on soil organic matter quantity and quality in a Rego, Black Chernozem with a thin A horizon were determined in a long-term study at Indian Head, Saskatchewan. Variables examined included: fertilization, cropping frequency, green manuring, and inclusion of grass-legume hay crop in predominantly spring wheat (Triticum aestivum L.) production systems. Generally, fertilizer increased soil organic C and microbial biomass in continuous wheat cropping but not in fallow-wheat or fallow-wheat-wheat rotations. Soil organic C, C mineralization (respiration) and microbial biomass C and N increased (especially in the 7.5- to 15-cm depth) with increasing frequency of cropping and with the inclusion of legumes as green manure or hay crop in the rotation. The influence of treatments on soil microbial biomass C (BC) was less pronounced than on microbial biomass N. Carbon mineralization was a good index for delineating treatment effects. Analysis of the microbial biomass C/N ratio indicated that the microbial suite may have been modified by the treatments that increased soil organic matter significantly. The treatments had no effect on specific respiratory activity (CO2-C/BC). However, it appeared that the microbial activity, in terms of respiration, was greater for systems with smaller microbial biomass. Changes in amount and quality of the soil organic matter were associated with estimated amount and C and N content of plant residues returned to the soil. Key words: Specific respiratory activity, crop residues, soil quality, crop rotations

scholarly journals ORGANIC C DYNAMICS IN GRASSLAND SOILS. 2. MODEL VALIDATION AND SIMULATION OF THE LONG-TERM EFFECTS OF CULTIVATION AND RAINFALL EROSION

1981 ◽  
Vol 61 (2) ◽  
pp. 211-224 ◽  
Author(s):  
R. P. VORONEY ◽  
J. A. VAN VEEN ◽  
E. A. PAUL
Keyword(s):  
Organic Matter ◽  
Microbial Biomass ◽  
Management Practices ◽  
State Level ◽  
Microbial Biomass C ◽  
Organic C ◽  
Native Prairie ◽  
Cropping Sequence ◽  
C And N ◽  
Rainfall Erosion

The amounts of organic matter in native prairie and in an adjacent cultivated field were compared with the output from a simulation model describing organic matter dynamics. The effects of past and possible future soil management practices, and the loss of organic C through rainfall erosion were incorporated into the simulation study. Seventy years of cultivation increased the bulk density of the A horizon by an average of 16% along the catena of a Black Chernozemic soil. Organic C had decreased by 36% in the soil profile at the mid-slope position. Losses of organic N were 5–10% less. Depletion of organic C and N from the Ah horizon accounted for > 90% of the total loss from the soil profile. Therefore, extrapolation of data from surface soil, based solely on changes in the concentration of organic C and N, could result in an overestimation of organic matter losses from soils. Microbial biomass in the Ap horizon of the crop-summer-fallow site was 30% less than in the Ah horizon of the native prairie. The model predicted an immediate rise in microbial biomass C upon cultivation of the native prairie due to a large initial input of grassland litter and roots. Subsequently, the microbial biomass C decreased and approached a steady-state level which was 25% less than in the native prairie. The model indicates that large quantities of N released during the initial years of cultivation would not have been totally utilized by the cultivated crops, therefore resulting in major losses to the environment. However, now the organic matter is reaching a steady-state level and only small net release of N can be expected; external N sources are required for optimum crop production. Management practices such as straw removal and cropping sequence have short-term effects on the rate of depletion of soil organic C. Similar equilibrium levels of soil organic matter were predicted after 100 yr of cultivation in simulation studies that did not consider erosion losses. The inclusion of rainfall erosion losses indicated that major organic C and other nutrient losses will occur in management practices that include significant portions of fallow in the cropping sequence.

scholarly journals Assessment of Microbial Biomass Carbon and Nitrogen in Some Tea Soils of Bangladesh

1970 ◽  
Vol 25 (1) ◽  
pp. 21-25
Author(s):  
SM Abdur Rahman ◽  
ARM Solaiman
Keyword(s):  
Microbial Biomass ◽  
Organic Carbon ◽  
Microbial Biomass Carbon ◽  
Microbial Biomass C ◽  
Biomass Carbon ◽  
Total N ◽  
Organic C ◽  
Biomass N ◽  
C And N ◽  
Tea Garden

Microbial biomass carbon (C) and nitrogen (N) and their contribution to soil organic carbon and total N contents were assessed in soils collected from Bilashchara Tea Estate under Bangladesh Tea Research Institute (BTRI), Srimangal of Moulavibazar district, and Sripur Tea Garden under Jaintapur of Sylhet district. Microbial biomass C and N in Bila shchara Tea Estate soils varied from 90.4-144.0 and 20.5-29.0 mg/kg soil, and that of Sripur Tea Garden soils varied from 120.7-362.0 and 26.6-59.5 mg/kg soil, respectively. Within the two tea growing areas biomass C/N ratios ranged from 3.35-6.12. Relationships between biomass C and organic carbon and biomass N and total N were positively correlated. The contribution of biomass C to soil organic C was 1.23%, ranging from 0.9-1.55% and the contribution of biomass N to total N content of the soils ranged from 1.19-2.89%. Keywords: Biomass carbon (C); Biomass nitrogen (N); Organic C; Total N; Tea soilDOI: http://dx.doi.org/10.3329/bjm.v25i1.4850 Bangladesh J Microbiol, Volume 25, Number 1, June 2008, pp 21-25

Changes in microbial biomass and structural stability at the surface of a duplex soil under direct drilling and stubble retention in north-eastern Victoria

Soil Research ◽  
1992 ◽  
Vol 30 (4) ◽  
pp. 493 ◽  
Author(s):  
MR Carter ◽  
PM Mele
Keyword(s):  
Microbial Biomass ◽  
Soil Depth ◽  
Cropping Systems ◽  
Aggregate Stability ◽  
Microbial Biomass C ◽  
Organic C ◽  
Stubble Retention ◽  
C And N ◽  
Direct Drilling ◽  
Wet Sieving

Changes and relationships for organic C, microbial biomass C and N, and soil structural stability indices were determined at the soil surface after 10 years of direct drilling stubble retained (DDR) and stubble burnt (DDB), and cultivation with stubble burnt (CCB) for cropping systems on a sandy clay loam, duplex soil (calcic luvisol) in south-eastern Australia. Direct drilling caused a slight but significant increase in soil organic C at the 0-25 mm soil depth compared to the cultivated treatment. Microbial biomass C and N increases over the 0-100 mm soil depths were seasonal and generally greater for the DDR in comparison with DDB and CCB systems. Use of short duration wet sieving for the 0-25 mm soil depth showed a significant increase in aggregate stability for the DDR, especially for 2-10 mm sized aggregates, compared with the other tillage treatments. Such differences were reduced by standard wet sieving or use of a dispersion test illustrating the fragile nature of these unstable aggregates developed under cropping systems. Soil structural indices (water stable aggregates >2.00 mm, and >0.25 mm; mean weight diameter) were weakly correlated with increases in microbial biomass (r = 0.45, P < 0.01) and to total organic C (r = 0.35, P < 0.05). For these tillage systems, microbial biomass tended to be a poor predictor of changes in soil organic C. Overall, the long term effect of direct drilling and stubble retention in these cropping systems provided only relatively minor increases in organic C and, consequently, aggregate stability.

scholarly journals Long term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland .VII. Dynamics of nitrogen mineralization potentials and microbial biomass

Soil Research ◽  
1987 ◽  
Vol 25 (4) ◽  
pp. 461 ◽  
Author(s):  
RC Dalal ◽  
RJ Mayer
Keyword(s):  
Microbial Biomass ◽  
Nitrogen Mineralization ◽  
Continuous Cultivation ◽  
Microbial Biomass C ◽  
Total N ◽  
Organic C ◽  
Mineralizable N ◽  
Biomass N ◽  
Potentially Mineralizable N ◽  
C And N

The dynamics of nitrogen mineralization potential (N0) and mineralization rate constant (k) were studied in six major soils which had been used for cereal cropping for up to 20-70 years. In the top 0.1 m layer of virgin soils, N0 varied from 110 � 22 mg kg-1 soil (Riverview) to 217 � 55 mg kg-1 soil (Langlands-Logie), representing about 13% and 11%, respectively, of total N in these soils. Upon cultivation and cropping, N0 declined by 1 7 � 0.5 mg kg-1 yr-1 (Riverview) to 4.8 � 2.0 mg kg -1 yr -1 (Billa Billa). This represented < 20% of total N lost annually from the top layer (0-0.1 m depth) of these soils. The k values varied less than the N0 values, both within and among soils, and were also less affected by cultivation than N0. The mineralizable N in cultivated soil during cropping for periods up to 70 years can be estimated from N0 and k values, taking No as 5% of total N for soils of <40% clay and 15% of total N for soils of >40% clay and k as 0.066 week-1 at 40�C (0.027 week-1 and 0.054 week-1 at 25�C and 35�C, respectively). Organic C and N contained in the 'stabilized' microbial biomass (determined after 30 weeks' pre-incubation) accounted for 1.7-38% of total organic C and 2.0-5.1% of total N in the six soils studied. The microbial biomass C and N declined with cultivation in most soils, biomass N representing 10-23% of the total annual loss of N0. The microbial biomass, urease activity and total N, in addition to a number of other soil properties [e.g. light-fraction (<2 Mg m-3) C, sand-size C, CEC and ESP], were significantly correlated with N0 and k, thus indicating the existence of a myriad of environments for the activity, association and stability of microbial biomass and potentially mineralizable N in soil.

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