Effects of Organic and Inorganic Fertilizers on Earthworm (Lumbricus terrestris) Population and Soil Properties for Cowpea (Vigna unguiculata) Cultivation

An experiment was conducted at the Rivers State University research farm to investigate the effects of organic and inorganic fertilizers on earthworms (Lumbricus terrestris) population and soil properties under cowpea (Vigna unguiculata) cultivation. Top soil was collected from the research farm and 3 kg of the soils were bagged in perforated bags and a total of 240 earthworms of different species were introduced into the soil at 5 per pot in 12 pots before planting the cowpea and additional 15 earthworms were added to each plot 3 weeks after planting. Four treatments PM (poultry manure) NPK (20:10:10), NPK+ PM and Control) were laid out in a Completely Randomized Design (CRD) and replicated three times. Treatments were applied 14 days before planting. Soil samples were collected from experimental pots after harvest and a total of 12 samples which were analyzed for physical and chemical properties using standard methods of analysis. Bags were also torn at the end of experiment to determine earthworm population. Results showed that the earthworms’ population of the poultry manure bag increased to (64) followed by NPK+PM (35), control (31) and the least earthworm count was found in NPK (11). Physical and chemical properties of soil revealed that pH ranged from 4.75 at the control to 5.83 in the pot treated with NPK+ PM, OC ranged from 0.92 g kg-1 in the control and the pot treated with NPK to 20.0 g kg-1 in the pot treated with poultry manure (PM). Organic matter (OM), Available phosphorus (AP) and Total Nitrogen (TN) values were the highest with the application of poultry manure. The textural class of the soil was determined to be loamy soil whose properties reduced with the application of Poultry manure (PM) to an average of (100.1) with clay soil having the lowest percentage increase (8.32), next to silt (11.39) and sand (80.3) had highest percentage, while in the control, particle size increased with sand having the highest percentage increase (81.63), next to clay (9.65) and silt (8.72) having the least percentage increase. Therefore, the study concludes that the use of organic fertilizer by farmers is cost effective, less harmful to soil health and soil dwelling useful organism like earthworm and improved soil nutrient fortification.