Impacts of ground vegetation management strategies in a kiwifruit orchard on the composition and functioning of the soil biota

In production horticulture, it is desirable that ground management strategi es are selected in such a way as to ensure that there are adequate levels o f soil biota present to carry out key ecosystem processes required for long -term crop growth. We established replicated field plots in a New Zealand k iwifruit orchard of each of five ground management treatments, i.e. mainten ance of pasture, planting of a dwarf fescue mulch, sawdust application, cul tivation and repeated use of herbicides, and then monitored the responses o f components of the soil biota to these treatments over a 5-year period. Th ose treatments involving enhancement of basal resource inputs (pasture, fes cue, sawdust) consistently supported higher levels of microbial biomass and activity than did the others. These effects were not consistently propagat ed through higher trophic levels of the decomposer food web, although popul ations of microbe-feeding and predacious nematodes did often differ signifi cantly across treatments. This idiosyncratic response of decomposer food we b components to treatments is believed to be due to the complex interplay o f top-down and bottom-up forces in soil food webs. There were also importan t treatment effects on nematode community structure; ordination analysis re vealed that the sawdust and cultivated plots supported different species as semblages to the pasture and rescue plots. Further, treatments supporting g reater basal resource inputs tended to result in a higher diversity of nema todes: on average the Shannon-Weiner diversity index for the 0-5 cm depth l ayer was 2.80 and 2.64 for the fescue and pasture treatments, and only 2.32 and 2.45 for the cultivation and herbicide treatments. Populations of Coll embola were also generally enhanced in plots with greater basal resource in puts. We utilised litterbag decomposition rates as a measure of the perform ance of ecosystem functioning carried out by the soil biota, and generally found that surface placed litter decomposition rates were greatest in those treatments supporting greater levels of basal resource inputs and microbia l biomass (i.e. greatest for the mulched and fescue plots, least for the he rbicide and cultivated plots), but were generally independent of higher tro phic levels. Most of our results could be explained by the fact that treatm ents differed in the amounts of the basal resources that were likely to be present, rather than other components of agricultural intensification such as direct effects of cultivation-induced disturbance or herbicide toxicity. Finally, our study indicates that in order to gain a more complete picture of how agricultural intensification affects soil biota in the long-term re quires experiments which simultaneously consider several trophic levels and several modes of intensification, and which run for several years. (C) 200 1 Elsevier Science Ltd. All rights reserved.