Biomass C Research Articles

Biochemical indicators of soil fertility in vineyards with different conservative management systems

Biochemical parameters are particularly suited to evaluate soil fertility because soil microorganisms play a pivotal role in determining soil quality and functionand are very sensitive to changes in soil management and environmental conditions. For such reasons, in this work, we used several biochemical indexes to assess the effect on soil fertility of 3 different conservative management systems of vineyards. The managements compared were chemical weed control vs permanent grass (CWC/MWC), land levelling vs undisturbed soil (LL/US), conventional farming vs organic farming (CON/ORG). The following parameters were determined in 2014 and 2015 on soil samples: total organic C (TOC), extractable N (EN), soil basal respiration (SBR), microbial biomass C (BC), microbial quotient (BC/TOC) and metabolic quotient (qCO2 = SBR/BC). Results showed that biochemical indicators were effective in detecting changes in soil fertility between compared systems. In particular, conservative systems (MWC, US and ORG) showed a larger and more efficient microbial biomass and enhanced EN content in comparison to the relative conventional systems. Furthermore BC/TOC and qCO2indicated higher C use efficiency in conservative systems. Results as a whole indicate that conservative management systems aimed to maintain and enhance soil organic matter displayed a higher level of soil fertility.

Arylesterase activity in trace element contaminated soils

Arylesterase activity was measured along with microbial biomass C (BC) and respiration, and H2O-soluble and NH4NO3-exchangeable trace elements (TE), in contaminated soils (TECS) from three long-term field trials. The AGIR (AG) soils were contaminated only by inorganic Cd, whereas the Ambarès (AM) and Louis Fargue (LF) soils were contaminated mainly by Mn and Zn, and Cd and Ni, respectively, from past sludge application at different rates. In the AG soils, the arylesterase activity decreased with increasing Cd total concentration and solubility. In the AM soils, the arylesterase activity decreased with increased contamination, whereas in the LF soils the arylesterase activity was increased by sludge additions, with the higher values detected in soils with lower sludge incorporation rates. In the AG and AM soils, arylesterase activity was significantly and negatively correlated with H2O-soluble and NH4NO3-exchangeable TE, whereas in the LF soils it showed a ‘hump’-shaped trend with sludge additions and could not be modelled. Multiple regression analysis showed significant interactions between TE, soil pH value and TOC with this enzyme activity. Respiration values of the AG soils generally increased while the BC generally decreased with Cd contamination, while different trends were observed in the AM and LF soils. No trends in the enzyme activity-to-BC ratios were found in relation to soil contamination. Information regarding the inhibition of arylesterase activity in TECS can be important for the management of soils co-contaminated by TE and organic pollutants, in which the detoxification action of arylesterase may be reduced.

Fluorescein diacetate hydrolysis, respiration and microbial biomass in freshly amended soils

The hydrolysis of the fluorescein diacetate (FDA), related to several soil hydrolases, has been utilised to estimate the potential microbial activity of soil freshly amended with a wide range of organic amendments and compared to the size and activity of soil microflora, measured by the microbial biomass C (B C) and CO2 evolution, respectively. Three different composting mixtures at different phases of the composting process were added to a semi-arid soil and incubated for 2 months under laboratory conditions. The addition of the organic amendment immediately increased B C and both measures of microbial activity (FDA and CO2 evolution). Highly significant correlations were found between FDA hydrolysis and B C for soil amended with the three composting mixtures (r = 0.81–0.96; P < 0.01), regardless of the origin, composition and degree of stability of the organic amendments. FDA hydrolysis, conversely to CO2 evolution, was unaffected by the disturbance caused by the soil amendment, indicating that the two parameters probably reflect different aspects of soil microbial activity. FDA hydrolysis could serve as an alternative estimation of the microbial biomass in freshly amended soils, despite the disturbance caused by the exogenous organic matter.

Microbial C and N dynamics during composting process of urban solid waste

Microbial characterization of composting is of importance for the optimization of the process and the quality of the end product. The aim of this work was to follow microbial biomass C and N dynamics during the composting process of urban solid waste. Microbial biomass C (B(C)) ranged from 4.06 to 1 microg kg(-1) of dry compost from day 5 to day 62 and decreased to reach 0.44 mg kg(-1) in mature compost. Microbial biomass N (B(N)) showed the same trend as B(C), ranging from 1.472 to 0.443 microg kg(-1) of dry compost from day 5 to day 62. This behaviour is probably related to the decreasing availability of readily decomposable substrates with the ongoing of the process. B(C) and B(N) showed a strong correlation (r = 0.78). The dynamics of the B(C)/B(N) ratio, index of the chemical composition of the whole microbial population suggested a shift in the composition of microbial populations during the process from prevailing bacteria and actinomycetes to prevailing fungi.

Dynamics in microbial immobilization and transformations of phosphorus in highly weathered subtropical soil following organic amendments

To improve knowledge on the role of microbial processes in phosphorus (P) transformations in highly weathered subtropical soil, dynamics in microbial biomass C (BC) and P (BP), and Olsen-P in a subtropical Ultisol following amendments with glucose at 2 g C kg−1 soil (G2) and rice straw at 2 and 4 g C kg−1 soil (RS2 and RS4) was studied during a 43-day incubation period at 25°C and 45% of soil water-holding capacity. By 3 days, the amount of soil BC had increased about 3.2, 1.7, and 2.6 times for G2, RS2, and RS4, respectively. The amount of soil BC significantly decreased between 3 and 7 days for G2 and 3 and 14 days for RS4, and thereafter remained almost steady throughout the 43-day incubation period, at levels about 1.6–2.4 times larger than for the control (no organic amendment; CK). The amount of soil BP for G2 and RS4 almost doubled by 3 or 7 days, then remained relatively steady, and for RS2, maintained relatively constant (6.7–8.2 mg kg−1 soil) throughout 43-day incubation period, whereas it declined by about 50% for CK. A significant decrease (3.5 mg kg−1 soil) in Olsen-P occurred in G2 by 3 days; indicating a close response of available P to microbial immobilization. Also, the amounts of Al- and Fe-bound P in G2 and Fe-bound-P in RS4 decreased significantly, as determined at 43 days. In conclusion, organic amendment enhances microbial immobilization and transformations of P, but the turnover of BP behaves in different patterns as BC in highly weathered subtropical soil.

Effects of Cd, Zn, or both on soil microbial biomass and activity in a clay loam soil

We investigated Cd, Zn, and Cd + Zn toxicity to soil microbial biomass and activity, and indigenous Rhizobium leguminosarum biovar trifolii, in two near neutral pH clay loam soils, under long-term arable and grassland management, in a 6-month laboratory incubation, with a view to determining the causative metal. Both soils were amended with Cd- or Zn-enriched sewage sludge, to produce soils with total Cd concentrations at four times (12 mg Cd g−1 soil), and total Zn concentrations (300 mg Zn kg−1 soil) at the EU upper permitted limit. The additive effects of Cd plus Zn at these soil concentrations were also investigated. There were no significant differences in microbial biomass C (BC), biomass ninhydrin N (BN), ATP, or microbial respiration between the different treatments. Microbial metabolic quotient (defined as qCO2 = units of CO2–C evolved unit−1 biomass C unit−1 time) also did not differ significantly between treatments. However, the microbial maintenance energy (in this study defined as qCO2-to-μ ratio value, where μ is the growth rate) indicated that more energy was required for microbial synthesis in metal-rich sludge-treated soils (especially Zn) than in control sludge-treated soils. Indigenous R.leguminosarum bv. trifolii numbers were not significantly different between untreated and sludge-treated grassland soils after 24 weeks regardless of metal or metal concentrations. However, rhizobial numbers in the arable soils treated with metal-contaminated sludges decreased significantly (P Cd > Cd + Zn.

Fate of 14C-labeled pyrene in a creosote- and octadecane in an oil-contaminated soil

The disappearance of dichloromethane-extractable organic C (DEO-C) from hydrocarbon-contaminated soil is seldom fully accounted for by the evolution of CO 2. An oil-contaminated soil was spiked with 14C n-octadecane and a creosote-contaminated soil with 14C[4,5,9,10]pyrene to test the hypothesis that contaminant C is redistributed among soil C fractions during bioremediation. The soils were incubated for 12 months and destructively analyzed at one week, two weeks, one month, and thereafter monthly. The soil fractions examined were biomass-C (BC), humic-C (HC), and water soluble-C (WSC). Humin-C (HNC) was calculated as 14C total minus the sum of direct measurements of the other C fractions. Labeled CO 2 and volatile organic C (VOC) were collected and measured. The data provide a series of ‘snapshots’ of the transformations of contaminant-C in each soil. VOC was insignificant and for both soils 47–50% of the applied 14C was recovered in the evolved CO 2 only after three months incubation. The primary fate of C from the labeled organic compounds in both soils was into the humic-C and humin-C fractions; in some cases as much as 50% of the applied 14C was recovered from these fractions. Neither BC nor WSC were significant fates of the 14C during this incubation, and in combination did not exceed 12% of the total 14C applied in each soil. Enrichment of the humic-C and humin-C with contaminant-derived C poses interesting questions regarding the end point of bioremediation, traditionally total removal of the contaminant. Metabolism of the C to other fractions is clearly an alternate possibility. Furthermore, the fractions enriched may actually be those considered beneficial to soil quality, such as humic and humin-C.

Sensitive Indicators of Soil Organic Matter Sustainability in Orchard Floors of Organic, Conventional and Integrated Apple Orchards in New Zealand

ABSTRACT Major objectives of this study were to evaluate the effects of organic, conventional and integrated orchard fruit production systems on the quality and quantity of soil organic matter in orchard floors and to identify sensitive soil organic matter indicators. Seventeen different soil organic matter parameters were studied. These were soil aggregate stability (AS), total nitrogen (TN), total carbon (TC), carbon/nitrogen ratio, microbial biomass N (BN), microbial biomass C (BC), BC:BN; BC:TC; BN:TN; hot-water extractable C (HC), hot-water extractable carbohydrate (HCA), HCA:HC; humin N (hum N), humin C (hum C), hum C:TC; hum N:TN and potentially mineralizable N (Pot N). They were based largely on soil organic matter characteristics and fractions extracted sequentially by different extractants from soils collected from the alleys and treelines of organic, conventional, and integrated grassed-down apple orchard types from both commercial and experimental sites in Canterbury, New Zealand. A total of 12 apple orchards were investigated. Soil samples collected from these orchards (0–75 mm depth) were analysed for TC, TN, BC, BN, Pot N, AS and also sequentially extracted for labile and stable soil organic matter fractions using cold and hot water, acid mixtures (hydrochloric:hydroflouric acids, HC1:HF) and alkalis (sodium pyrophosphate and sodium hydroxide, Na4P207 and NaOH). Only TN, BN, and BN:TN showed significant interaction effects and all these were associated with soil N. Overall, combining orchards according to similar management systems, results obtained showed no significant differences between experimental and commercial orchards. However, sensitive indicators capable of distinguishing significant differences between different orchard management systems were BC, BC:TC and HCA:HC while HCA:HC distinguished significantly between treelines and alleys within each group of the same orchard type.

Effects of cropping systems on soil organic matter in a pair of conventional and biodynamic mixed cropping farms in Canterbury, New Zealand

Effects of cropping systems on soil organic matter (SOM) in a pair of conventional and biodynamic mixed cropping farms were investigated. Soil samples (0–75 and 75–150-mm depths) were analysed for total carbon (TC), total nitrogen (TN), microbial biomass C (BC) and microbial biomass N (BN), and sequentially extracted for labile and stable SOM using cold water, hot water, acid mixtures and alkalis. In the biodynamic farm, TC and TN decreased with increasing period of cropping but the reverse occurred under pastures. These were not shown in soils from the conventional farm, probably due to N fertilizer additions. Under pastures, increases in SOM were attributed to greater biological N2 fixation and the return of plant residues and excreta from grazing animals. Overall, sensitive SOM quality indicators found for labile SOM were BN, BN:TN and HC:TC, and for stable SOM were HCl/HFC, HCl/HFC:TC, humin C, humin N, humin C:TC and humin N:TN. The BN and BN:TN were better indicators than BC and BC:TC. The humin fraction was strongly related to both labile and stable SOM fractions suggesting that humin contained non-extractable strongly complexed SOM components with mineral matter and also non-extractable plant and microbial residual components.

The effects of long‐term superphosphate application on soil organic matter content and composition from an intensively managed New Zealand pasture

SummaryChanges in quantity and composition of soil organic matter (SOM) in pasture receiving annual superphosphate (SP) applications for 41 years at 0 (control), 188 and 376 kg SP ha−1a−1 were investigated in soil samples collected from 0–75 and 75–150 mm depths by determining total carbon (TC), total nitrogen (TN), biomass C (BC), biomass N (BN) and subjecting the soils to sequential extraction using cold water, hot water, a mixture of hydrochloric (0.1 M HC1) and hydrofluoric (0.3 M HF) acids (HCl/HF), and sodium pyrophosphate (Na4P2O7) followed by sodium hydroxide (NaOH) for extracting labile and stable SOM fractions. There were significant differences in some SOM fractions between control (0) and SP treatments (188 and 376), especially in the topsoil (0–75 mm) but these were not observed between the two SP treatments. Soil TN (0–75 mm), BN and BN: TN ratio (0–75 and 75–150 mm depths) and the proportion of hot–water–extractable C (HC) in soil TC (HC:TC) (0–75 mm) were significantly greater in the SP treatments than in the control. HC1/HF extractable C and the proportions of soil TC as HC1/HF extractable C (HC1/HF extractable C: TC) were smaller in the topsoil of SP treatments than in the control. Similar results were observed in humin N: TN ratio and the proportions of soil TC as cold–water–extractable carbohydrate (CWcC: TC) and of soil HC as hot–water–extractable carbohydrate (HWcC : HC). Increases in the proportion of labile fraction in SOM were reflected in values of BN, BC: BN, BN: TN, HWcC : HC and HC: TC whereas decreases in the proportion of stable fraction in SOM were found in humin N: TN and HCl/HF–extractable C: TC ratios. Increases in labile SOM (BN and N–containing compounds such as amino acids and amino sugars, which were extractable by hot water but were not present as carbohydrate) and decreases in stable SOM (HC1/ HF–extractable C and humin fraction) in soils under pastures treated with annual SP applications compared with the control were attributed to pasture improvement and the amelioration of P and S deficiency, resulting in a greater return of plant residues and animal excreta and also an increase in clover growth and associated biological N2 fixation. The additional labile SOM in SP treatments compared with that of the control was not associated with the soil mineral Al and Fe components.

Effect of crop rotations on microbial biomass, specific respiratory activity and mineralizable nitrogen in a Black Chernozemic soil

The effects of crop rotations, fertilization, cropping frequency, green manuring, and inclusion of grass-legume hay crops in predominantly spring wheat (Triticum aestivum L.) rotations, on some biochemical characteristics of a fine-textured Orthic Black Chernozemic soil were determined at Melfort, Saskatchewan. Thirty-one years after establishment of this experiment, soil samples were taken from the upper 7.5 and the 7.5- to 15-cm layers in mid-September, 2 wk after cereal harvest and 2 mo after hay harvest and plow-down. Results showed that fertilizer had no effect on the total amount of CO2-C respired, microbial biomass C (BC), and the specific respiratory activity (ratio of CO2-C/BC), but it decreased microbial biomass N (BN), widened BC/BN ratio, and increased the initial potential rate of N mineralization (Nok). The BN was inversely related to straw yields of the most recent crop grown on these plots. When a legume-grass hay crop was underseeded into wheat grown on stubble in a 6-yr rotation, the young growing forage crop decreased BC but increased CO2-C, BN and CO2-C/BC. Reducing fallow frequency in monoculture wheat systems increased CO2-C/BC and Nok. Sweet clover [Melilotus officinalis (L.)] green manure did not increase yields of the subsequent wheat crop, consequently, this treatment did not influence soil biochemical characteristics. The BC appeared to be less sensitive to crop management effects than BN or CO2-C/BC. The BC/BN ratio was wider for systems that received more fertilizer, those that were being fallowed and for the lower soil depths, indicating a possible change in microbial ecology in these situations. This aspect may require further research. In contrast to our earlier conclusions for this fertile Black Chernozemic soil, our results indicate that there are several soil biochemical characteristics that allow identification of short- and long-term treatment effects on soil organic matter. Key words: N mineralization, microbial biomass, C respiration, legumes, fertilization

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

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