Response of soil invertebrates to pastoral management, and their links to soil services : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand
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2010
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Massey University
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Abstract
Sustained pasture production requires soils which are fertile, porous, and can
support invertebrate populations. Soil invertebrates influence soil processes, supporting
soil services (e.g., nutrient and water supply) required in pastoral soils. The hypothesis,
that invertebrates would show some consistent responses to pastoral management was
tested and used in the development of a biological indicator. Specifically, this thesis
explored the response of soil invertebrates (macrofauna, mesofauna and nematodes) to a
diversity of pasture managements (livestock type, stocking rate, fertiliser application,
irrigation), collecting soil samples from nine sheep grazed, 17 dairy grazed and 15
ungrazed long term research and commercial pastures. Focus was on the influence of
management practices on soil physical condition and potential food resources for the
soil food web.
Food resources influenced invertebrates, particularly in soils with lower stock
live weight loading. Nematodes tended to respond positively to increased pasture
production with increases in plant feeding nematodes. The physical disturbance
associated with dairy cow treading was pronounced (compared with that of sheep
treading) and this had consequences for the invertebrate community. Oribatida were low
in abundance in dairy grazed pastures and slow to recover when treading pressures were
removed. Some larger, predatory nematodes were sensitive to treading, but recovered
when treading pressures were removed. Earthworms are capable of creating their own
burrows and were more resistant to stock treading, especially anecic species. The
calculated effect of earthworms on nitrogen mineralisation was greater under organic
than conventional dairy pasture management. The importance of soil invertebrates in
regulating nitrogen supply to plants in a compacted and high nitrogen fertility soil was
demonstrated in a constructed mesocosm.
The influences of management on food resources and soil physical condition,
and their relationships with invertebrates form critical components of a proposed
invertebrate threshold indicator. Habitable pore space appeared to be a reliable indicator
of invertebrate populations, as food may not always limit populations in pastures. The
indicator, based on invertebrates (i.e., Nematode Channel Ratio, Plant Parasitic Index,
abundances of earthworm functional groups, Oribatida, nematodes and herbivorous
macrofauna) was linked to soil services by establishing thresholds at which soil services
might be 'limited' or 'sustained'. Suggestions on how to manipulate invertebrate
abundance are made. The proposed indicator may provide land managers with a tool
linking invertebrates to soil services required for sustained pasture production.
Description
N.L. Schon, A.D. Mackay, G.W. Yeates, M.A. Minor. (2010). Separating the effects of defoliation and
dairy cow treading pressure on the abundance and diversity of soil invertebrates in pastures. Applied Soil
Ecology 46, 209-221.
Published version available from: http://www.sciencedirect.com/science/article/pii/S0929139310001587
http://dx.doi.org/10.1016/j.apsoil.2010.08.011
Keywords
Soil invertebrates, Soil biology, Soils, Pasture, New Zealand, Dairy pasture, Sheep pasture