Interactions between compost, vermicompost and earthworms influence plant growth and yield: A one-year greenhouse experiment

The aim of the present study was to examine the interactions between an endogeic earthworm species, Metaphire posthuma , and purely mineral (control) or mineral plus organic (compost vs. vermicompost) amendments in terms of soil chemical properties and plant growth and yield. A one-year experiment was carried out in a greenhouse with a maize–tomato–maize cycle. Compost and vermicompost modified soil chemical properties leading to higher C and N, higher pH and CEC, and lower available P, NH 4 + and NO 3 − than in the control. Although no significant difference in plant growth was observed for the first maize planting, tomato and maize growth were then highest for the mineral and vermicompost treatments and lowest for compost. Overall plant yields were always highest in mineral fertilizer alone and lowest for the compost treatments. The application of vermicompost led to a similar yield as the control treatment for the first maize planting. However, its beneficial influence decreased during the experiment until it was similar to that of the compost treatment. The presence of earthworms reduced the C content in soil mixed with compost and vermicompost but only influenced plant growth and yield in the compost treatment. The effect of earthworms was initially null (i.e. for the first maize crop), positive (i.e. for tomato planting) and finally negative (i.e. for the second maize planting), thereby underpinning the complexity of the interactions between the quality of organic matter in soil, earthworm activity and plant growth.