Soil properties under a Pinus radiata – ryegrass silvopastoral system in New Zealand. Part II. C and N of soil microbial biomass, and soil N dynamics |
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| Authors: | G Amatya S X Chang M H Beare D J Mead |
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| Institution: | (1) Soil, Plant and Ecological Sciences Division, Lincoln University, New Zealand;(2) Centre for Enhanced Forest Management, Department of Renewable Resources, University of Alberta, 4–42 Earth Sciences Building, Edmonton, AB, Canada, T6G 2E3 (Author for correspondence;(3) Crop & Food Research Ltd., Lincoln, Canterbury, New Zealand |
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| Abstract: | At present, our understanding of the dynamics of microbial biomass and soil N in silvopastoral systems is very limited. In
this paper, the effects of understorey management on soil microbial C and N, net N mineralization, and net nitrification were
studied in two seven-year-old radiata pine (Pinus radiata D. Don) – pasture systems, consisting of plots with and without ryegrass (Lolium perenne) as an understorey. Mini-plots (1 × 1 m) with animals excluded and herbage repeatedly clipped and removed were used for soil
sampling. Three mini-plots formed a transect at each of two positions: 0.9 and 3.5 m north of the tree rows. Measurements
were taken from July 1997 to June 1998 about once every 40 days. One composite sample was collected from each of two sampling
depths (0–10 and 10–20 cm) at each transect position on each sampling date. Temporal and spatial variability of N mineralization
rates and microbial biomass C and N was large. Net mineralization and nitrification rates were higher in the bare ground than
in the ryegrass plots for a major part of the year, particularly from late spring to early fall. Net N mineralization and
nitrification rates were higher in the 0–10 than in the 10–20 cm soil layers in both the ryegrass and bare ground treatments;
however, the depth effect on microbial biomass C and N was only significant in the ryegrass treatment. In the surface soil
layer, microbial biomass C and N were substantially greater in the ryegrass than in the bare ground plots. Soil microbial
properties and activities were closely linked to pasture root activities, soil depth, and site biophysical conditions.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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| Keywords: | competition interaction Lolium perenne mineralization nitrification radiata pine |
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