Response of soil microarthropods to composite organic amendment materials
Wide spread use of inorganic fertilizers has been greeted with declining soil nutrients in the long run despite immediate bumper harvests in the tropical rain forest of southern Nigeria. There is therefore need to intensify efforts on production of organic fertilizers that are made from selected agricultural wastes since positive impacts on soil microarthropods have been recorded for their use as organic fertilizers. The effects of application of ground maize stover, cow dung, chicken droppings, ostrich droppings and their mixture on soil microarthropods were investigated on three 187m2 adjacent areas of land (A, B and C). In the first study year (2012), soil microarthropods were sampled for four months in the sites without incorporating organic amendment materials in order to know the species composition, richness and their relative abundance. In the second study year (2013), each area of land was divided into six equal plots (5 m x 5 m) separated by a 1 m strip; and five of these were separately treated with the agricultural wastes while the sixth plot was used as control. 10 kg, 20 kg and 30 kg of the dry agricultural wastes were introduced and mixed thoroughly with the topsoil (0-7.5cm) of plots in A, B and C. Four soil samples were taken randomly and monthly from each of the plots thereafter to monitor changes in the abundance of soil-dwelling microarthropods, important indicators of soil health condition.
Forty-seven species of microarthropods that belong to Acarina, Collembola, Formicidea, and Coleoptera were identified in the experimental plots before the application of soil amendment materials. There was no significant difference in the numbers of different groups of microarthropods in the year the plots were treated with amendment materials, but there is a significant increase in the juvenile stages of coprophagous and detritivorous groups, mostly mites and springtails, in the plots treated with cow dung, chicken droppings and mixture. This increase in numbers of juveniles led to an increase in their adult populations one year after treatment (i.e. 2014). Also, the plots in the 20 kg and 30 kg levels of application showed more adult recruitment in the year following soil amendment. Our results indicate that dry cow dung and chicken droppings were more responsible for increase in the populations of mites and springtails, which are bio-indicators of improved soil fertility. This increase is however selective as some taxonomic groups were not affected.