Soil characteristics,belowground diversity and rates of simazine mineralisation of a New Zealand Gley Soil in a chronosequence under horticultural use |
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| Authors: | G Sparling L A Schipper G W Yeates J Aislabie M Vojvodic-Vukovic J Ryburn H J Di A E Hewitt |
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| Institution: | (1) Landcare Research, Private Bag 3127, Hamilton, 3240, New Zealand;(2) Landcare Research, Private Bag 11 052, Palmerston North, 4442, New Zealand;(3) Centre for Soil and Environmental Quality, Lincoln University, P.O. Box 84, Lincoln, 7647, New Zealand;(4) Landcare Research, P.O. Box 40, Lincoln, 7640, New Zealand;(5) Department Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, 3240, New Zealand |
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| Abstract: | The chemical, physical and biological conditions of a New Zealand Gley Soil was examined on matched sites under long-term
permanent pasture or used to grow blackcurrants (Ribes nigrum) for 2, 8, 10 or 20 years. The chemical and physical conditions of topsoils (0–10 cm) were assessed by soil pH, Olsen P,
total C, total N, mineralisable N, cation exchange, bulk density, porosity and moisture release characteristics. The biological
conditions were assessed from the microbial biomass, soil respiration, catabolic evenness and numbers and diversity of the
soil nematode populations. The ability of the soil populations to degrade the triazine herbicide simazine was tested. The
particle size distribution confirmed all the sites were very well matched, within 2%, in terms of percentage clay, silt and
sand contents, which were 36.5–40.5% clay and 59.5–62.5% silt. Compared with the soil under pasture, that under horticultural
use for 2, 8, 10 and 20 years had lower total C and N, lower mineralisable N, lower cation exchange and lower porosity but
higher bulk density and particle density. The differences were greater the longer the plots had been under blackcurrant production.
Olsen P content was greatest (58 μg P cm−3) under the 20-year blackcurrant plots. Changes in biological characteristics were greater than in physical or chemical characteristics.
Microbial biomass was 1.73 mg C cm−3 under pasture and decreased to 0.87 mg C cm−3 after 20 years of blackcurrants. Total nematode populations deceased from 3.89 million m−2 under pasture to 0.36 million m−2 after 2 years of blackcurrant production and to 108 000 m−2 after 20 years. There were similar proportional decreases in bacterial-feeding, fungal-feeding, plant-feeding and omnivore
nematodes; however, there was comparatively little change in nematode diversity (Shannon–Weiner) or in microbial catabolic
diversity or soil respiration. Despite the decreased microbial biomass, the microbial community under blackcurrant production
had enhanced capacity to degrade simazine, as compared with the pasture soil. That capacity to degrade simazine was similar
in soils that had grown blackcurrants for 2, 8, 10 or 20 years. Yield of blackcurrants had been maintained in the longer-term
sites, despite the marked changes in soil chemical, physical and biological conditions. |
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| Keywords: | Soil quality Blackcurrant cropping Organic matter Microbial diversity Simazine degradation |
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