Microbial nitrogen immobilization as a tool to manage weeds in agroecosystems

Harnessing the activity of soil microorganisms is currently underutilized in sustainable agricultural management. One such underutilized microbial approach, referred to as reverse fertilization, is a practice that involves introducing substantial quantities of high carbon:nitrogen (C:N) amendments into the soil. The surplus of carbon stimulates the growth of soil microorganisms and triggers microbial scavenging of soil nitrogen, resulting in nitrogen immobilization within microbial cells. Immobilized nitrogen becomes temporarily unavailable for plant uptake, affecting plant competitive interactions. Most applied research using this technique focuses on controlling invasive plants in disturbed habitats to help reestablish native plant communities, which are often sensitive to high-nitrogen soils. However, reverse fertilization is not currently a standard practice in agricultural systems, hence this review explores the feasibility of adopting this management strategy in cropping systems. An analysis of the restoration ecology literature suggested that perennials, legumes and plants with higher root: shoot ratios were more resilient in nitrogen immobilized soils than annuals, non-nitrogen-fixing plants and plants with lower root:shoot ratios. Based on these contrasting responses, there is potential to improve and increase the use of reverse fertilization as a weed management tool in agroecosystems. This tool, along with other ecologically-based methods, can be incorporated into farm-scale prescriptive management programs to improve the sustainability and productivity of cropping systems.