Measurements of Microbial Biomass C and N in Paddy Soils by the Fumigation-Extraction Method

During a 3-year study, soil microbial biomass C and N, length of the fungal hyphae, soil respiration, and the percent mass loss of needle litter were recorded in coniferous forest soil humus layers following a prescribed burning (PB) treatment or a forest fire simulation (FF) treatment (five plots per treatment). Unburned humus from adjacent plots served as controls (PC and FC, respectively). Prescribed burning was more intensive than the forest fire, and this was reflected in all the measurements taken. The amounts of microbial biomass C and N, length of fungal hyphae, and soil respiration in the PB area did not recover to their controls levels, whereas unchanged microbial biomass N and recovery of the length of the fungal hyphae to control levels were observed in the FF area. The mean microbial C/N ratio was approximately 7 in all the areas, which reflected the C/N ratio of the soil microbial community. Deviation from this mean value, as observed during the first three samplings from the PB area (3, 18, and 35 days after fire treatment), suggested a change in the composition of the microbial community. Of the two treated areas, the decrease in soil respiration (laboratory measurements) was much more pronounced in the PB area. However, when the humus samples from both areas were adjusted to 60% water holding capacity, no differences in respiration capacity were observed. The drier humus, due to higher soil temperatures, of the PB area is a likely explanation for the low soil respiration. Lower soil respiration was not reflected in lower litter decomposition rates of the PB area, since there was a significantly higher needle litter mass loss during the first year in the PB area followed by a decline to the control level during the second year. Consistently higher mass losses were recorded in the FC area than in the FF area.

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Carbon and nitrogen mineralization in cultivated and grassland soils in subtropical Queensland

Soil Research ◽

10.1071/sr9930611 ◽

1993 ◽

Vol 31 (5) ◽

pp. 611 ◽

Cited By ~ 24

Author(s):

FA Robertson ◽

RJK Myers ◽

PG Saffigna

Keyword(s):

Microbial Biomass ◽

Specific Activity ◽

Continuous Cultivation ◽

Microbial Biomass C ◽

N Availability ◽

Grassland Soils ◽

Prolonged Incubation ◽

Cultivated Soil ◽

C And N ◽

Cultivated Soils

Availability of N in the clay soils of the brigalow region of Queensland declines rapidly under sown pasture, but under continuous cultivation and cropping, it remains high enough to supply the needs of cereal crops for at least 20 years. The aim of this work was to determine whether the low availability of N under pasture was due to low microbial activity or to rapid re-immobilization of mineralized N. Microbial biomass C and N (0-28 cm) were 420 and 68 �g g-1 respectively in pasture soil but only 214 and 41 �g g-1 respectively in cultivated soil. Pasture soils respired more CO2 (Cresp) and mineralized less N (Nmin) than cultivated soils (219 and 93 �g C g-1 and 3.1 and 5.9 �g N g-1 respectively) during 10-day incubations over 2 years. Increased Crop under pasture was due to an increase in the amount rather than the specific activity of the microbial biomass. The smaller Nmin in grassland soils was due to more rapid immobilization rather than reduced gross mineralization of N, as the ratio Cresp : Nmin was larger and the ratio Nmin :biomass N was smaller in the grassland than in the cultivated soil. On prolonged incubation. with progressive loss of CO2 through respiration, Nmin increased and N immobilization decreased in the grassland soils. Prolonged incubation of the cultivated soils reduced Nmin because of C limitation. The above patterns of C and N mineralization in the grassland and cultivated soils helped to explain the differences in N availability in the two systems.

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

Canadian Journal of Soil Science ◽

10.4141/s98-008 ◽

1999 ◽

Vol 79 (1) ◽

pp. 73-84 ◽

Cited By ~ 38

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

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