A taxonomical–ecological investigation of the soil mesofauna in the rhizosphere of citrus trees at Zebediela Estates
Olivier, Pieter Gideon
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The purpose of this investigation was to assess the taxanomic - ecologic nature of Zebediela's citrus sol, situated in the eastern part of the Potgietersrus district, Northern Transvaal . Habitat descriptions are given, together with a review of the geology of the estate and surroundings, the chemical composition of habitat soils, as well as the different soil and air conditions. Five plots were selected, viz.: PLOT A, the control plot, which represents the undisturbed natural soil in the near vicinity of the citrus plots. PLOT B, the old citrus plot, which is a replanted routine citrus plot. PLOT C, the new citrus plot, which is a general routine citrus plot. PLOT D, a citrus plot on which complete biological control is practised and which as such receives no pesticides PLOT E, a routine citrus plot of value for comparatory purposes. A specially developed sampler is described, together with the transportation technique. In relation to extraction a description of the specially transformed funnel system is given. Residual extraction was done by means of the grease film apparatus, and its value was emphasized in an annex presented. A complete data reproduction, with details of the identification and occurrences of all the mesofaunal arthropods extracted are submitted in the tables and described in the text. The total mesofaunal investigation reveals an Acari dominated population in the control plot and the old citrus plot, but Collembola attaining the highest numerical and biomass position in the other plots. The biomass comparison reveals a dominant position for the control plot as a result of diplopod concentrations. With the aid of histograms and graphs, the seasonal fluctuations within the five plots are presented. Exactly the same tendencies were recorded for all plots, namely: 1. A decline in mesofaunal numbers from July 1965 to September 1965. 2. A steep increase to the highest mesofaunal recordings in January 1966. 3. A relatively sharp drop in numbers from January 1966 to April 1966. The vertical distribution patterns for the mesofauna of the five investigated plots, as well as those for the most important species are given. The general population distributional pattern for the mesofauna shows a tendency for higher concentrations in the first 1 - 4 cm. of soil. Population peaks, however, also occurred in the second and third subsample levels. A comparison between the citrus soil fauna and the citrus tree fauna, during the sampling period, reveals that both communities are separate entities with little relation to each other. In connection with the influence of citricultural practices on the composition of the soil mesofauna, the effects of the citrus trees, replanting of citrus trees and insecticides are discussed. It is pointed out that certain mesofaunal arthropods, especially some hemi edaphic predatory Trombidiformes, and certain Oribatei and 'Other Arthropod' members were reduced and even exterminated. On the other hand, certain mite and insect species, mostly eu-edaphic in living manner, were promoted by the citrus rhizosphere habitat and general citricultural practices.
- ETD@PUK