Effects of different management regimes on aquatic macroinvertebrate diversity in Australian rice fields

Abstract

The maintenance of invertebrate diversity within agricultural environments can enhance a number of agronomically important processes, such as nutrient cycling and biological pest control. However, few Australian studies have been undertaken which specifically address the effects of commercial management regimes on rice field biodiversity. In this study, we compared aquatic macroinvertebrate communities within Australian rice fields cultivated under three commercial management regimes: conventional-aerial (agrochemicals applied, aerially sown), conventional-drill (agrochemicals applied, directly drill-sown) and organic-drill (agrochemical-free, directly drill-sown). These comparisons were undertaken using a combination of community assessment approaches, including morphospecies richness, abundance, diversity and community composition. In general, greater biodiversity existed within macroinvertebrate communities that developed under organic management regimes than under conventional regimes (i.e., higher morphospecies richness and Shannon diversity). Although there were significant differences in several parameters across management regimes early in the rice-growing season, as the growing season progressed the invertebrate communities that developed in the different management regimes became more similar. Only community composition analyses showed significant differences late in the growing season, with functional differences across aquatic faunal assemblages suggested by increased predator abundance in communities sampled from the organic management regime. In order to improve biodiversity within these aquatic environments, management techniques need to be examined individually and the most disruptive processes identified. Alternative management procedures can then be developed that minimise biodiversity loss whilst still delivering required agronomic outcomes.

Benthic macroinvertebrates and degradation of phytomass as indicators of ecosystem functions in flooded rice cropping

“…However, the diversity index for the organic systems did not differ from that in the other sampled sites. The results were different from those observed in rice fields in Australia, where the organic cultivation showed higher diversity indices throughout the experimental period (Wilson et al, 2008). Keeping diversity is a feature of more sustainable systems (Thrupp, 2000), which increases redundancy of microorganisms performing the same systemic functions (for example, more organisms of a single trophic group); this allows of organisms to carry out the processes, and ensure maintenance of the ecosystem functions, even if some of these organisms decrease, due to their sensitivity to some environmental factors.…”

“…In the present work, abundancy in the site of the organic farming was higher (p<0.05) than in the conventional one, in accordance with the results obtained by Wilson et al (2008) during the crop season.…”

“…Electric conductivity showed a great variation, and the highest values were observed in the conventional farming (Table 2). Chemical inputs used in conventional management may have affected this difference; the organic farming does not make use of these inputs (Wilson et al, 2008). No correlation was observed between the physicochemical and biotic parameters (p>0.05) (Figure 2).…”

“…Chemicals cause ecological risks to different organisms, and the use of conjugate products, which is common in cultural practices, results in additive actions between them, even for less toxic ones (Nakagome et al, 2007). This technicalization arises from conventional rice growing systems, in contrast to organic production systems of irrigated rice, which not only are performed without the use of pesticides and synthetic fertilizers, but also are based on crop rotation (Wilson et al, 2008).…”

Ocorrência de agrotóxicos em águas usadas com irrigação de arroz no sul de Santa Catarina

“…Áreas cultivadas com arroz irrigado tem sido alvo de especulações quanto aos efeitos deletérios dessa cultura sobre a qualidade das águas superficiais (POLEZA et al, 2008;WILSON;WATTS;STEVENS, 2008;GASPA-RINI & VIEIRA, 2010;SILVA et al, 2011). Segundo Poleza et al (2008), dependendo das condições de precipitação pluviométrica e manejo inadequado da água de irrigação da lavoura, existe o risco dos resíduos dos agroquímicos serem carreados para fora da lavoura, podendo provocar alterações na qualidade da água a jusante desses agroecossistemas.…”