Soil restoration under pasture after topsoil removal: Some factors influencing C and N mineralization and measurements of microbial biomass |
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Authors: | D J Ross P B S Hart G P Sparling J A August |
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Institution: | (1) DSIR Land Resources, Private Bag, Lower Hutt, New Zealand |
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Abstract: | Factors influencing rates of C and N mineralization of soil and plant materials, and the reliability of different procedures
for estimating microbial biomass, were measured in a soil (Typic Dystrochrept) that had been restored under grazed pasture
in a temperate environment for 10–11 years after 20 cm of the original topsoil had been removed by stripping.
Rates of net N mineralization were appreciably lower, but CO2-C production higher, in the stripped than in the unstripped soil. These activities were not influenced directly by levels
of soil mineral-N, but they were influenced by differences in plant composition. Herbage and litter, and roots, from the stripped
plots were generally mineralized more readily to CO2-C, but more slowly to net mineral-N, than were the corresponding materials from the unstripped plots. Rates of mineralization
of herbage and litter, or roots, were mainly indistinguishable in stripped and unstripped soil, whereas rates of mineralization
of all standing dead material were lower in stripped soil.
Measurements of extractable-C flush, and of CO2-C flush (using a fumigated soil control) and mineral-N flush by fumigation-incubation procedures, indicated that microbial
biomass in stripped soil had recovered to at least 88 percent of the levels in unstripped soil. Substrate-induced respiration
also generally indicated high levels of recovery of microbial biomass. The fumigation-incubation procedure appeared to under-estimate
microbial biomass markedly in stripped soil when unfumigated soil controls were used; the used of a large soil inoculum (20
percent w/w) only sometimes overcame this problem. Possible reasons for apparent anomalies in estimation of microbial C are
discussed. |
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Keywords: | microbial biomass mineral-N flush nitrogen mineralization pasture plants soil respiration soil restoration |
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