World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt
Abstract
The present study aimed to screen the effect of overuse of the
insecticide Dimethoate and its residues within 0 -15 cm soil layer on
the soil micro-arthropods population, which play a very important role
in maintenance of the fertility of the soil. The valley of Zendan is
located in Arhab Destrict, Sana'a Governorate, Yemen. The valley is
about 50 km north-east of Sana'a city and this geographical area is a
large producer of Qat (Catha edulis Forsk); the plant which most of the
people in the country chew. In this study the valley divided into three
stations, each station contained three treated substations and three
control substations. The control substations selected from the farms,
which are historically free from pesticides. Due care has been taken to
insure that the treated sub-stations were from the closest area to the
control substations. The average use of Dimethoate 40% E.C is 1-2 ml/L
water. The treatment replication was 1-3 times within the period of 2-3
weeks. In this study also, we analyzed the total concentration of
Dimethoate, and its metabolite; Omethoate in the soil layer of 0-15 cm.
The analysis of Dimethoate and Omethoate residues from representative
soil samples covered the major part of the Zendan valley was done by
the technique of LC-MS, and the results revealed that the detected
levels ranged from 0.914 to 5.180 mg/kg air-dried soil for Dimethoate
residues and 0.001 to 0.067 mg/kg air-dried soil for Omethoate
residues. For studying the effect of Dimethoate residues on the soil
micro-arthropods population, soil samples from each substation were
collected with core sampler. The soil micro-arthropods were extracted
for 48 hours and collected in vials containing 70% alcohol by using the
extraction funnels technique. The number and type of soil
micro-arthropods extracted from each substation were separated and
recorded and the data obtained was analyzed. The outcomes of the study
revealed that Dimethoate and Omethoate residues are beyond the Total
Threshold Limit Concentration (TTLC) and significantly reduced the
population of the non-target soil micro-arthropods that included mainly
mites, collembolans, beetle larvae, trips, cutworms, symphyla and seed
corn maggot. Mites and collembolans were the most affected
micro-arthropods by Dimethoate and Omethoate residues. The reduction in
the soil micro-arthropods population varied from 59% to 69% as compared
to its population in control substations. The maximum decline of soil
microarthropods was found to be in substations where the highest
residues of Dimethoate and Omethoate were recorded. Thus indiscriminate
use of pesticides such as Dimethoate will definitely affect the soil
fertility in the area and that will reduce the crop yield in future.
@JASE