The soil invertebrate contribution to nitrogen mineralisation differs between soils under organic and conventional dairy management |
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Authors: | Nicole L Schon Alec D Mackay Mike J Hedley Maria A Minor |
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Institution: | (1) Ecology, Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand;(2) AgResearch Grasslands, Private Bag 11008, Palmerston North, 4442, New Zealand;(3) Soil and Earth Science, Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand |
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Abstract: | Organic management aims to promote soil biological activity. To test whether organic management stimulates soil biological
activity, invertebrates (macrofauna, mesofauna and microfauna) were collected from four paired commercial organically and
conventionally managed dairy farms on different soil types (Allophanic, Pallic, Recent and flooded Recent). Food webs were
constructed and rates of invertebrate-mediated N mineralisation calculated. The organic dairy operations used fewer nutrient
inputs and had lower stocking rates than their paired conventional farms. This translated into lower calculated pasture production
and less available plant litter entering the soil food web. Despite the lower plant litter inputs into the organic system,
earthworm biomass was higher (particularly in the Recent and flooded Recent soils), suggesting that under conventional management
the physical condition of the soil, as influenced by stock treading pressures, was more important for invertebrate activity
and their influence on N mineralisation than was food supply. Nitrogen mineralisation was higher in organic systems, with
earthworms contributing the most (24–98 kg N/ha/year). As the physical loading on the soil increased under conventional management,
the ability of the soil to provide soil services (i.e. N mineralisation and litter decomposition) became compromised. Organic
management on four soils stimulated biological activity by reducing the treading pressure on the soil and highlights the need
to consider the influence of management practices on the faunal environment (food availability and physical condition) to
understand the impacts of organic management and the role of fauna in N mineralisation. |
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