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  • 1
    ISSN: 1573-5036
    Keywords: C cycling ; climate change ; elevated CO2 ; microbial biomass ; N mineralization ; soil respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Effects of elevated CO2 (700 μL L−1) and a control (350 μL L−1 CO2) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 μL L−1 CO2 and a temperature 6°C higher throughout than in the other treatments, was included. Under the same temperature conditions, overall herbage yields in the ‘700 μL L−1 CO2’ treatment were ca. 7% greater than in the control at the end of the ‘summer’ period. Root mass (to ca 25 cm depth) in the ‘700 μL L−1 CO2’ treatment was then about 50% greater than in the control, but in the ‘700 μL L−1 CO2+6°C’ treatment it was 6% lower than in the control. Based on decomposition results, herbage from the ‘700 μL L−1+6°C’ treatment probably contained the highest proportion of readily decomposable components. Elevated CO2 had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials. Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO2 on the soil C balance.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5036
    Keywords: actinomycetes ; arsenic ; boron ; chromium ; copper ; enzymes ; microbial C ; N mineralization ; nematodes ; nitrification ; respiration ; sawdust ; soil pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects on soil biochemical and biological properties of a soil amended with Cu-, Cr- and As-(CCA)-treated, or boric-treated, sawdust were investigated using soil adjusted to both pH 5 and pH 7. In one experiment, soil samples were analysed before and after a pot trial conducted to assess the effects of these amendments on plant growth and element uptake (Speir et al., 1992). The other experiment was an incubation study conducted without plants and with soil samples taken for analysis after 0, 4, 8 and 14 weeks at 25°C. Amendment with 10% treated sawdust (v/v) increased total soil concentrations of Cu, Cr, As and B by 45, 136, 63 and 32 μg g-1, respectively, in the appropriate treatments. At these levels of soil contamination, there were very few negative effects attributable to the CCA- or boric-sawdust amendments on soil respiration, microbial biomass C, enzyme activities, indices of N mineralization and nitrification, numbers of nematodes, total microbial numbers and numbers of selected actinomycetes. Except for a substantial and significant (p〈0.05) inhibition of sulphatase activity in the boric treatment, the negative effects that did occur were generally small and usually non-significant. These results are discussed and, when considered with those of the plant growth study, warrant a cautious acceptability of CCA-treated sawdust as a mulch or garden amendment.
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  • 3
    ISSN: 1573-5036
    Keywords: C cycling ; elevated CO2 ; microbial biomass ; N mineralization ; plant decomposition ; soil respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Effects of elevated CO2 (525 and 700 μL L−1), and a control (350 μL L−1 CO2), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further ‘spring’ period, half of the turves under 350 and 700 μL L−1 were subjected to ‘summer’ drying and were then re-wetted before a further ‘autumn’ period; the remaining turves were kept continuously moist throughout these additional three consecutive ‘seasons’. The continuously moist turves were then pulse-labelled with 14C-CO2 to follow C pathways in the plant/soil system during 35 days. Growth rates of herbage during the first four ‘seasons’ averaged 4.6 g m−2 day−1 under 700 μL L−1 CO2 and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these ‘seasons’ averaged 465, 800 and 824 g m−2 in the control, 525 and 700 μL L−1 treatments, respectively. in continuously moist soil, elevated CO2 had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO2-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO2 produced h−1 mg−1 microbial C was about 10% higher in the 700 μL L−1 CO2 treatment than in the other two treatments. Elevated CO2 had no clearly defined effects on N availability, or on the net N mineralization of added herbage. In the labelling experiment, relatively more 14C in the plant/soil system occurred below ground under elevated CO2, with enhanced turnover of 14C also being suggested. Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously ‘summer’-dried, CO2 production was again higher, but net N mineralization was lower, under elevated CO2 than in the control after ‘autumn’ pasture growth. Over the trial period of 422 days, elevated CO2 generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.
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