Abstract
Agricultural intensification practices involve varying degrees of disturbance to the soil ecosystem. This study evaluated six agricultural management regimes with increasing levels of topsoil disturbance, on the composition and abundance of surface-active invertebrates on Vertisols at a sub-catchment scale. Two grazing (native and introduced pastures), and four cropping (combining short and long fallow, with zero and conventional tillage) management regimes were examined. Surface-active invertebrates were collected seasonally with pitfall traps over 2 years (8 seasons), and identified to order, while ants (Formicidae) that comprised 47% of total invertebrates collected, were identified to genera. Season had a significant effect on ant abundance and number of genera recorded with higher abundance and twice the number of genera in summer than all other seasons. Ants, particularly Iridomyrmex, were mainly active in summer, while other invertebrates especially Coleoptera, were more active in winter. Surface-active invertebrates were 30% more abundant in grazing than cropping land use types. Native pasture, with little surface soil disturbance, recorded the highest number of invertebrates, mainly ants, compared to other agricultural management regimes. Coleoptera and Dermaptera were higher in abundance under conventional tillage compared with those agricultural management regimes that disturb the topsoil less. Optimizing surface-active invertebrate activity on Vertisols for most taxa will require reducing topsoil disturbance. However, the research findings also suggest that the impact of agricultural management regimes on invertebrate activity was difficult to predict with any certainty as the three main ant genera, and most abundant invertebrate collected, did not respond in a consistent manner.
Highlights
Soil health decline and invertebrate biodiversity loss are common symptoms of unsustainable soil management practices, especially under conventional agriculture with high inputs involving heavy use of agrochemicals, and frequent disturbance of the surface soil layer [1,2,3]
The results focus on the three research questions in sequence and examine them in order of total invertebrate abundance, followed by those invertebrate taxa that recorded greater than 1% of the pitfall trap collection, and with soil interactions and the most dominant invertebrate order collected—Ants
Total abundance of invertebrate taxa recorded over the eight sampling periods in two calendar years was dominated by a few taxa, with ants constituting the dominant invertebrate from all the sites, followed by Diptera and Coleoptera (Table 2)
Summary
Soil health decline and invertebrate biodiversity loss are common symptoms of unsustainable soil management practices, especially under conventional agriculture with high inputs involving heavy use of agrochemicals, and frequent disturbance of the surface soil layer (top 0–20 cm) [1,2,3]. The lack of consideration of collateral impacts, due to agricultural intensification, on biota constitutes a serious risk to sustainability of the system and potential loss of ecosystem functioning [4,5,6]. The need to examine more closely the agricultural management practices and their impacts on invertebrate composition and activity in order to determine which taxa are able to persist in an agricultural system. While invertebrates may be regarded as pests or vectors of diseases to crops and animals [13,14], there is compelling evidence of their role in the productivity and sustainability of the soil system [12,15,16,17,18,19,20], especially in ecosystem processes such as nutrient cycling, and soil bioturbation [21,22,23,24]
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