Abstract

Vermicomposting is a process where worms are used to transform organic waste products into fertilizers for agricultural use and as soil amendments to improve soil health. Vermicompost is used in agriculture as both an organic fertilizer and a soil amendment due to its large biological component and abundant nutrient concentrations, in particular nitrogen (N). Vermicomposts promote soil microbial biodiversity by inoculating the soil with a wide array of beneficial microbes, which can enhance plant growth by the production of plant growth-regulating hormones and enzymes while also controlling plant pathogens and nematodes, all of which can minimize crop yield losses. Current and historical studies have evaluated many vermicompost types for their ability to increase crop growth, development, and fruit quality across a wide range of field and greenhouse crops. Many of these studies conclude that crop response to vermicompost can meet or exceed crop response to conventional rates of synthetic fertilizers. Vermicompost use has therefore been increasingly considered in conventional and organic agricultural systems as an alternative to synthetic fertilizers to decrease N losses. However, it is difficult to determine the short and long-term effects to soil N cycling with increased vermicompost use in agriculture. Here, we summarize the current state of knowledge regarding the influence of vermicompost on N dynamics in laboratory and agricultural settings. In particular, the physical, chemical and biological means of N cycle alteration following vermicompost use is examined, with emphasis on the ability of vermicomposts to influence N leaching. We find conflicting results regarding the influence of vermicomposts on soil N dynamics, in particular the influence of vermicompost on soil N flux over short and long time scales. We find evidence for both soil N retention and leaching with vermicompost use, largely contingent on rate of application and vermicompost type.  The differences in chemical, biological and physical properties between vermicompost types along with a wide range of recommended rates of application may pose problems for large-scale adaptation of vermicompost use in commercial agriculture. It is important to determine a proper “goldilocks” rate of vermicompost amendment for crop systems that supports high crop yield while minimizing N leaching. We conclude that much research still needs to be performed in laboratory and field settings to study N dynamics with vermicomposts.

Key words: Organic fertilizer, organic matter, nitrate sorption, nitrification, nitrogen immobilization, nitrate leaching.