Effect of soil management on biodiversity of nematode communities as a biological indicator of soil quality in oasis agro-ecosystem of Kebili

Nematode communities were monitored in 26 oases in Kebili under various agricultural systems. Differences between studied oases consisted in tillage frequency, soil amendment type (manure or manure+ mineral fertilizers), cover crops and field age. In addition, this study evaluated the importance of the C-P (Colonizer-Persistent) triangle and the faunal profile (representation of enrichment index vs. structure index) as a biological indicator and monitoring tools in support of soil quality assessment. The results showed that nematode communities were composed by 10 bacterial feeders (Ba), 3 fungal feeders (Fu), 12 plant parasites (PP), 4 omnivores (O), 1 predator (P) with the dominance of (Ba) and (PP) in all surveyed oases. The nematode communities differed slightly depending on oases age. Bacterial feeders and Discolaimium genus were found in both young and old ones. Plectus genus (Ba) was found only in young oases while Xiphinema, Criconema and Trichodorus genera (PP) were absent in these oases. Few nematode taxa were affected by soil amendment type and cover cropsincluding some bacterial and fungal feeders. The highest taxa richness was recorded in bare soils and in field with tillage frequency of 2 or 3 years. The lower MI (Maturity index) value was recorded in old oases. Most of studied oases were characterized either by a high soil disturbance level with a high abundance of cp-1 group (Bacterivore nematodes with c-p value =1)as an indicator of a disturbed food web or by a stressed soil with high abundance of cp-2 group (Bacterivore and fungivore nematodes with c-p value = 2) as an indicator of degraded food web. Only few sites showed a maturing and structured food webs with respectively low to moderate soil disturbance level and undisturbed soil. This study highlighted also that some nematode genera may potentially serve as differential bio-indicators of soil disturbance.