Allocation and Microbial Utilization of C in Two Soils Cropped to Barley

Abstract

C in two soils cropped to barley. Can. J. Soil This study was undertaken to compare some aspects of carbon cycling in a Gray Luvisol at Breton and a Black soil at Ellerslie, Alberta cropped to barley. Comparisons of the above and below-ground allocation of carbon, distribution of carbon in soil, and microbial use of carbon were made between sites. Shoot C. root C, microbial biomass C, soil organic C, water soluble organic C, and polysaccharide C were measured on four dates between 31 July and 20 Oct. 1986. The total quantity ofcarbon in the soilplantsystematEllerslie (l7.2kgcm-2)wasgreaterthanatBreton(6.6kgCm-2).On average shoot C at Ellerslie Qa7 gC m-2) was greater than at Breton (147 gm 2).The quantity of root C (avg. 21 g C m-2) was the same at both sites resulting in higher shoot C:root C ratios at Ellerslie than Breton. Microbial biomass (expressed as g C m-2 or g C g-lroot C) was one to two times lower at Breton than at Ellerslie but respiration (g CO'-C g I microbial biomass C) during a lO-d laboratory incubation was two to four times greater. Microbial biomass C, soluble C and polysaccharide C expressed as mg C g-r of soil were less at Breton than Ellerslie. However when these data were compared on a relative basis in terms of soil C (g C g-t soil C), microbial biomass C and soluble C were higher at Breton than Ellerslie. Polysaccharide C was the same at both sites. Although the microbial biomass was smaller at Breton than at Ellerslie, more carbon was lost from the system by microbial respiration and a greater proportion of the carbon in the soil was in microbial and soluble C pools. Soil characteristics, and cropping history affected the amount ofcarbon stabilized in soil. (Friedemann et al. 1962). Statistical AnalysesThe design was a factorial splirptot with three replicates per site. The data were analyzed using the UANOVA multivariate analysis of covariance program developed at the University of Alberta (T. Taerum, pers. commun.). This procedure gives the usual F-ratio found in an ANOVA table as well as an F-ratio which has been adjusted for unequal variances of the means by the Greenhouse-Geisser adjustment (Greenhouse and Geisser 1959). Probabilities derived from the Greenhouse-Geisser adjusted F-ratios have been used in the following results. When a significant F-ratio was found, the sums of squares for that source of variation were partitioned into single degree of freedom effects as recommended in Mize and Schultz (1985). RESULTSDifferences in the carbon content of shoots, roots, microbial biomass, and soil over the four sampling dates were not significant (Table 2). Shoot C at Ellerslie was up to 2.8 times greater than at Breton (P:0.0431).Root C did not differ between sites but decreased with depth (P:0.0001). Microbial biomass C was 1.5-2.5 times greater at Ellerslie than at Breton (P:0.0020) and varied with depth (P:0.0060) with more microbial C in the 0-to 10-and l0-to 20-cm depths than the 20* cm depth. Soil C was 2.5-3.5 times higher at Ellerslie than Breton (P:0.0001) and changed wit...

Microbial biomass C and N dynamics, and 15N incorporation into microbial biomass under faba bean, canola, barley, and summer fal- low in a Gray Luvisol

“…Statistical analysis was conducted for ANOVA (P3V), multiregression (P2R) and principal component analyses (P2R) on NH + 4 , NO − 3 in soils before fumigation and soils fumigated and nonfumigated after 10 days incubation using BMDP statistical software (Dixon, 1983). Three crops together with summer fallow were categorized as treatment whereas four sampling dates were considered as another treatment.…”

“…Lynch and Panting (1980a) had observed that correlation exist between soil microbial biomass and root growth and rooting density of the crop. Foster and Rovira (1976) found that older roots of wheat at the flowering stage showed consistent development of microorganisms both in the rhizosphere and in the outer cortical cells and cell walls.…”

“…If assume an average of microbial biomass 300 µg C/g soil as in barley and canola plots, 10.7 mg C/g soil /h is needed for maintenance only. In contrast, water-soluble C in soil was only 20 µg/g soil (Dinwoodie, 1988). It should be kept in mind that maintenance energy of soil microorganisms was not quantified yet and it is only the general concept applied here for further consideration.…”

“…Nannipier et al(1978) showed that using one or two indices to estimate microbial biomass activity is too simplistic and not sufficient for interpretating the microorganisms in the soils. Results of Dinwoodie (1988) had reported 43% of the microorganisms in the Gray Luvisol cropped to barley was active. Root exudates stimulates population increase but most of these organisms are either dormant or starved due to lack of available energy supply (Lynch and Panting, 1980a, b).…”

Simulation of protozoa-induced mineralization of bacterial carbon and nitrogen

“…Soluble C was not measured in the laboratory incubation; however, the initial pool size was estimated from previous work on similar soils (Dinwoodie and Juma 1988 The active C and N pools represent rapid cycling insoluble organic matter pools, consisting of microbial metabolic products and recently stabilized materials (Paul and Juma 1981). Campbell and Souster (1982) half-life of > 600 yr (Campbell et al 1967 Rate of bacterial CO2-C evolution (Rb) (pg C g-l soil d-l) was calculated using growth and maintenance components (Hunt et al 1984 the active C pool (Hunt et al 1984).…”