The Impact of Land Cover on the Population Growth and Diversity of Earthworms at MUARIK, Central Uganda
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A field research was conducted at Makerere University Agricultural Research Institute Kabanyolo (MUARIK) located in Kyadondo North, Wakiso district, central Uganda to determine the impact of land cover and method of extraction of earthworms on population density, growth parameters and diversity of earthworms. Six land covers: BA- Banana cover, SB- Soybean cover, FA- Fallowed, MZ- Maize cover, GL- Native pasture (with local pastures) and IP- Improved pasture. Earthworms were sampled from three randomly selected sampling spots within each cover for determination of the parameters investigated in mid-January 2021. Detergent and Onion solutions were used as vermifuges or method of expulsion of the earthworms from the soil for collection. The earthworms collected were hand sorted and recorded. Land cover greatly affected the number of earthworms where soy bean field had the highest population (24±2.54)/0.16 m2 and the fallowed field had the least (1.3±2.54) /0.16m-2. Detergent vermifuge was generally more effective in expulsion of earthworms on average from the soil (38.3±3.59) in shorter time than the onion solution ((1±3.59). There was a significant interaction between land cover and method of earthworm extraction where detergent was recommended as vermifuge for Soybean, maize and Improved pastures, Onion for Banana, both Detergent and onion for Native pasture and Fallow. The earthworm species obtained were the 3-4 inch light red surface dwellers Eisenia fetida (epigeics), the 8-10 inch dark red vertical burrowers, Eudrilus Eugenia (anecics) and the 5-6inch pale grey or pink horizontal burrowers, Allolobophora chlorotica (endogeics). Endogeics were the highest number of species obtained (159/0.16m2) per earthworm count. Epigeics thrived in banana, maize, soybean, native pastures, improved pastures and fallow, Endogeics in soybean, maize, native pastures, improved pastures, banana except fallow while Anecics were found in banana, maize, improved pastures, native pastures, fallow but not in soybean. The diversity index for all the earthworm species was 0.38 indicating a low diversity according to Simpson’s Diversity index. The distribution of earthworms was diverse and their population fluctuated in relation to the different land cover, land use patterns and to a lesser extent the physico-chemical properties of the soil. The method of earthworm collection had no effect on the number of earthworms collected, their body length, weight, clitellum length nor the earthworm species. Soil organic matter in and upon the soil surface influenced earthworm distribution and abundance but the quality, quantity, position in soil profile and particle size determined the earthworm species present in the land covers. Epigeic and endogeic species exhibited greater dispersal and fecundity rates enabling them to adapt to more unstable habitats like disturbed soils hence they can stay in same habitat whereas anecics are sensitive to soil disturbance with low growth rates and fecundity that predisposes them to more stable environments like in the Banana, Fallow and Native pasture. Earthworm number and diversity was not limited by pH and prefer silty soils than clay and sandy soils.