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Effects of soil compaction on N-mineralization and microbial-C and -N. II. Laboratory simulation |
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| Authors: | L S Jensen D J McQueen D J Ross and K R Tate |
| Institution: | a Section of Soil, Water and Plant Nutrition, Royal Veterinary and Agricultural University, DK-1871 Frederiksberg C, Copenhagen, Denmark b Ecological Research Associates, P.O. Box 48147, Upper Hutt, New Zealand c Manaaki Whenua Landcare Research NZ Ltd., Private Bag 11052, Palmerston North, New Zealand |
| Abstract: | Soil compaction can affect the turnover of C and N (e.g. by changing soil aeration or by changing microbial community structure). In order to study this in greater detail, a laboratory experiment simulating total soil porosities representative of field conditions in cropped and pasture soils was set up. Soils were silty clay loams (Typic Endoaquepts) from a site that had been cropped with cereals continuously for 28 years, a permanent pasture and a site that had been cropped with maize continuously for 10 years. Soils from the three sites were compacted into cores to different total porosities (corresponding bulk densities ranging from 0.88 to 1.30 Mg m?3). The soil cores were equilibrated to different matric potentials (ranging from ?1 to ?100 kPa), yielding values for the fraction of air-filled pores of < 0.01 to 0.53 m3 m?3, and then incubated at 25°C for 21 days. C-mineralization was on average 15, 33 and 21 μg C g?1 day?1 for soils from the cropped, pasture and maize sites, respectively, and was positively correlated with soil water contents. Net N-mineralization showed a similar pattern only for well-aerated, high total porosity cores (corresponding bulk density 0.88 Mg m?3) from the pasture soil. Denitrification at < 0.20 m3 m?3 for the fraction of air-filled pores may have caused the low N-mineralization rates observed in treatments with high water content or low porosity. Microbial biomass estimates decreased significantly with increasing water contents if measured by fumigation-extraction, but were not significantly affected by water content if estimated by the substrate-induced respiration method. The degree of soil compaction did not affect the microbial biomass estimates significantly but did affect microbial activity indirectly by altering aeration status. |
| Keywords: | Author Keywords: Carbon mineralization Cropping Microbial biomass Nitrogen mineralization Pasture Soil compaction |
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