Influence of summer irrigation on soil invertebrate populations in a long-term sheep irrigation trial at Winchmore (Canterbury)

Abstract

Soil invertebrates have limited defences against moisture stress but little is understood of how irrigation influences their community. This paper investigates the influence of five summer irrigation schedules on earthworms over a 15-month period in a long-term pasture irrigation study. The influence of the two extreme rates of irrigation on other soil invertebrates was also examined. The effects of frequent drought periods under dryland pasture favoured small and short-lived nematodes and oribatids. During wetter months, earthworm abundances were similar between dryland and irrigated treatments, while earthworms tended to migrate down the soil profile and aestivate in response to soil water deficits during summer. The higher abundance of earthworms in the summer months under irrigation may partly explain the lower soil carbon found under irrigation, due to enhanced rates of soil organic matter turnover, despite higher primary production and inputs of carbon. It is thus important to consider irrigation schedules not only to optimise plant growth, but also to optimise the invertebrate community and its activity.

Effects of stock type, irrigation and effluent dispersal on earthworm species composition, densities and biomasses in New Zealand pastures

“…Furthermore, since the effluent was applied as slurry containing considerable amounts of water, effects of the effluent only treatment may mimic those resulting from irrigation. This increase in density and biomass with intensification is consistent with other studies (Muldowney et al, 2003;Fraser et al, 2012).…”

“…studied. A. caliginosa dominancy is in agreement with other earthworm studies in New Zealand (Riley et al, 2008;Schon et al, 2011a;Fraser et al, 2012). The low earthworm species richness we encountered may reflect elements of biogeography, especially the long period of geographic isolation of the island ecosystems without ecological disturbance by humans, such as agricultural activities.…”

“…recorded in an irrigated sheep farm in the Canterbury region of New Zealand (Fraser et al, 2012), 523 individuals m À2 in irrigated pastures in South Australia (Baker et al, 1992), and 904 m À2 in the Netherlands (Zorn et al, 2005). Other records of earthworm density in unirrigated New Zealand pastures are very disparate: Fraser et al (1996) ; while Lee (1985) considered 200-1000 individuals m À2 as a normal range.…”

“…Many studies have focused on earthworm responses to factors such as tillage, chemical additions, temperature, and land use change or as soil quality indicators and drivers of ecosystem processes (Callaham et al, 2006;Briones et al, 2009;Malmström et al, 2009;Rossi et al, 2010). Studies of earthworm populations under normal farm paddock conditions in New Zealand are scarce (Schon et al, 2008;Schon et al, 2011a;Fraser et al, 2012;Manono, 2014), and only two have investigated the effects of effluent dispersal (Yeates, 1976;Degens et al, 2000). None have investigated the effects of converting sheep farms to dairy, or separated the effects of adding irrigation water to pastoral soils in combination with dairy effluent.…”

The Winchmore Trials

“…Hitherto, the irrigation trial has received much less attention than the fertiliser trial, but nevertheless has been a valuable resource, for instance, in the field of soil biology. Fraser et al (2012) outline the changes in biotic communities that have occurred in the irrigation trial. They conclude that irrigation to optimise plant growth also optimises (or selects) the invertebrate community.…”