عنوان مقاله [English]
One of the main objectives of organic agriculture is low negative effect on the environment and according to this issue, maintaining biodiversity is one of the key responsibilities of this agriculture system. Disuse of chemical fertilizers and using mechanization with less intensity caused significant increase in biodiversity in organic agriculture. Insect's diversity can help in biological control of pests, pollination and biological control of weeds and diseases. This study was performed based on the key role of insects in ecosystem function, especially in organic agro-ecosystems and effective factors for biodiversity of them and also with respect to the high potential for progressing of organic agriculture in Iran. The purpose of the study was to identify different families of insects in conventional and organic fields for wheat and potato crops in Fariman city.
Material and Methods
The study was carried out in wheat and potato fields at Fariman city in 2012. In order to collect insects, we used a sweet net with a diameter of 50 cm in 10 different regions of the fields. Sampling was performed after 45, 75 and 105 days after planting. Sampling was conducted which it covers total farm area. Shannon-weaver index, Simpsons reciprocal and Margalef indexes were used to calculate the insect’s biodiversity and Pielou and Simpson were used to calculate the species evenness. Relative frequency (pi) was used to determination of dominant species in each agro-ecosystem and the species with the highest relative frequency was considered as dominant species. In order to compare the alpha and beta diversity between two organic and conventional systems, we fitted the power function for species richness as a dependent variable and sampling number as an independent variable.
Results and Discussion
The results of the wheat farm showed that the total number of collected insects’ families during the growing season in the organic farm was higher than the conventional farm (2047 number of insects from 41 families vs. 1928 from 34 families, respectively). From total families, 32 families were the same in both organic and conventional wheat systems and 9 families were collected from the only organic farm. Two families were observed only on the conventional farm. Species richness was the same in both organic and conventional at first stage of sampling, but in the organic system, it was higher at the second and third stage of sampling. Insects’ diversity in the conventional farm was higher than organic based on obtained values for alpha diversity. Calculated beta diversity in the organic system was higher than conventional. In fact, beta diversity is the increasing rate of the species richness per increasing of sampling number and the high value of beta diversity in the organic system indicates that species richness and biodiversity of the organic system were higher than conventional at total farm area. In potato organic and conventional farms, 435 insects (from 18 families) and 787 insects (from 22 families) were collected, respectively. From total trapped families, 15 families were the same in both organic and conventional systems, 7 families only were in conventional farm and three families observed only in the organic farm. Therefore, species diversity in conventional system was higher in comparison with the organic system in the potato crop. Two families were introduced as dominant species in the organic farm with a relative frequency of 17% and 15.6%, respectively and Miridae family was dominant species in the conventional farm as 27.8% of relative frequency. Alpha diversity in conventional system was higher than organic. Beta diversity in conventional system was higher in 45 and 75 days after planting, but it was lower in 105 days after planting than organic. In total, the results showed that alpha and beta diversity were higher in conventional than organic. It seems that the reason for higher biodiversity in conventional compared to organic was related to failure to comply with the organic principles in potato farm.
It can be concluded that the move towards organic agriculture, in addition to preserving and enhancing biodiversity in agricultural ecosystems, has led to a reduction in using chemical pesticides and, as a result, the reduction of environmental pollution will be followed by the sustainability of agricultural production.