The influence of different management practices on soil faunal activity in vineyard soils

[摘要] ENGLISH ABSTRACT:Food demands for the ever-increasing human population is increasing thepressure on the agricultural sector to produce more food. In order to satisfy thesedemands, farmers are turning to chemical biocides for the control of pest species toproduce greater crop yields. All pesticides must be toxic or poisonous to the targetspecies they intend to control. Unfortunately, most pesticides are toxic or poisonousto non-target organisms as well, with detrimental effects on their health. Organicfarming was developed to enhance the overall health of the farm's natural soilmicrobe-plant-animal biodiversity. No synthetic fertilisers and/or pesticides are usedwhen farming organically. Life in the soil consists of intricate food webs andinteractions between the soil dwelling invertebrates. The soil-organisms are dividedinto three main groups, viz., Micro-organisms (e.g. protozoa, bacteria and fungi)mesofauna (nematodes, Collembola and Acari) and macro-fauna (e.g. millipedes,isopods, insects, molluscs and earthworms). The invertebrates are very susceptible tochemical contamination by chemical biocides in natural and agro-ecosystems. Thesoil invertebrate communities are responsible for the decomposition of organicmaterial in soil, thereby remineralising the soil. The decomposition processes startwith comminution of the large pieces of organic material by meso- and macro-faunaand ends with the micro-fauna and microbial organisms that complete these processesby returning the nutrients in an inorganic form to the soil. The aim of this study wasto investigate whether, and to what extent the soil organisms are influenced bydifferent management practices viz., organic management practices versusconventional management practices. A vineyard on the farm Plaisir de Merle, inSimondium, Western Cape was used for the present study. One half of a one hectarevineyard was managed organically and the other half conventionally. Within eachvineyard block six different treatments were performed. Three of the treatments werestrictly organic and the other three were strictly conventional. Four replicates of eachmanagement treatment were performed. The bait-lamina technique was used to assessthe feeding activity of the soil organisms exposed to the different managementtreatments. In addition to the bait-lamina trials in the vineyard itself, bait-lamina testswere performed in microcosm studies with soil from the organically andconventionally managed vineyard blocks under controlled conditions. In order to assess the impact of the various pesticides that are used in the vineyards in theconventional way, on the soil fauna, standard acute toxicity tests and behavioural testswere performed on Eisenia fetida, the compost worm. The bait-lamina tests in thevineyard revealed that the moisture content of the soil plays an important role in thebiological activity of soil fauna. The different management treatments did affect thebiological activity of the soil fauna, but seasonal changes also proved to be one of theimportant factors governing biological processes in the soil. The acute toxicity testsshowed that the active ingredients (mancozeb, penconazole and trifloxystrobin) ofthree of the pesticides that were tested in this study, had negatively affected E. fetidaat their recommended application concentrations. The remaining two pesticides'active ingredients (glyphosate and N-acetyl salicylic acid) did not affect theearthworms negatively at the recommended application concentrations. Thepreference behavioural trials showed that E. fetida could detect and avoidcontaminated substrates at the LCso-concentrations of the different pesticides. All theearthworms were influenced positively in the preference behaviour experiments.Because of certain limitations of the bait-lamina technique, it was difficult toformulate conclusions on what happens in the soil. A possible explanation for thedifferences in feeding activity of soil fauna could be attributed to the migration of thesoil fauna to more habitable soil horizons during the dry summer conditions, whenmost of the pesticides are applied. The ecological relevance of the acute toxicity testsconducted need to be investigated further. It is clear that the acute toxicity testsprovided important information that should be considered, but care should be takenand the necessary safety factors be determined and considered when doing riskassessment studies. The results of the preference behaviour studies showed that forcertain pesticides E. fetida can be a sensitive bioindicator of acute and/or sub-acutelethal toxicity testing but this might not necessarily be the case for other pesticides.The goal of doing laboratory studies is to gain as much information to make reliableextrapolations to field situations from laboratory data. Laboratory-to-fieldextrapolations are very complicated because of the physico-chemical composition ofsoil, the unpredictable way pesticides behave within soil and the reaction of soilorganisms to the soil and to the chemical biocides that are used. Further studies needto be done in order to fully understand to what extent the soil fauna were affected bythe different management practices applied to the vineyard at Plaisir de Merle.

[发布机构] Stellenbosch University