The Concurrent Effect of Earthworm (Lumbricus terrestris L.) Inoculation and Different Organic Materials on Temporal Changes in Enzyme Activities in a Loamy Calcareous Soil

Earthworms are an important component of soil fauna, and play a crucial role in the improvement of soil properties. However, very little is known of the interactive influence of earthworms and organic materials on soil enzyme activities, particularly in arid and semi-arid soils. The low organic matter content and the significant role of earthworms in stimulating microbiological and biochemical properties of arid and semi-arid soils may justify researches on the interactive effects of organic materials and earthworms on soil enzymes. Thus, the main objective of this study was to identify the interactive effects of an anecic earthworm (Lumbricus terrestris L.) and various organic materials on soil urease, alkaline phosphatase, invertase, β-glucosidase and arylsulphatase activities. The experiment consisted of a 2×5 factorial treatment arranged in a completely randomized design with four replications under controlled greenhouse conditions. The first factor was soils inoculated with and without earthworm, and the second factor was soils amended with alfalfa, compost, cow dung, and a mixture of alfalfa and compost, in addition to a non-amended soil as the control. Potential soil enzyme activities were assayed 30, 60 and 90 days after the initiation of the experiment using the appropriate substrate for each enzyme under standard conditions. Results showed that the activities of most soil enzymes were markedly greater in the presence of earthworms than in the absence of earthworms. The addition of organic materials to soil also resulted in higher enzyme activities compared with the non-amended soils. Nevertheless, the simultaneous effect of earthworm inoculation and organic material additions was much more effective in increasing soil enzyme activities. Yet, the activities of soil enzymes showed fluctuations and varied during the experiment. We found that the averaged increase in soil enzyme activities over 60-90 days in treatments without earthworms was often more remarkable than in treatments with earthworms, indicating that earthworm activity may shorten the time period to attain the maximum enzyme activities (over 30-60 days).