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Soil Bacteria's Role in Overall Turf Quality & Survival

By: Achille Correggia BSc. (Agri.), Agronomy, CCA-ON

The world’s nitrogen supply can be divided into three major pools: the atmospheric pool, the soil pool, and nitrogen contained within the biomass. The complex interaction between these three pools is known as the nitrogen cycle. This process is highly dependent on the microorganisms that populate our soils. Without these vital microscopic creatures the majority of the processes (fixation, mineralization, nitrification, and denitrification) involved in the nitrogen cycle could be hindered dramatically. To provide a better understanding of these important components, the following will discuss each process in more detail.

Nitrogen fixation includes any process that converts nitrogen gas from the air to ammonium (NH₄+) or nitrate (NO₃-). Nitrogen fixation can occur naturally through biological fixation (eg. by bacteria) and lightning or artificially through industrial nitrogen fertilizer production. Bacteria that are involved in the fixation process can be classified into two groups, free living (independent) or symbiotic (associated with another species, example soybeans). Azotobacter bacteria are an example of free living nitrogen fixating bacteria, while Bradyrhizobium japonicum is a symbiotic nitrogen fixating bacteria primarily associated with soybeans. Although free living bacteria are widespread, they multiply fairly slowly and are confined to specific habitats.

Mineralization of nitrogen can be described as a process where mineral forms of nitrogen are released into the soil through organic matter degradation by microorganisms. The nitrogen is released initially as ammonium, which is rapidly converted to nitrate by nitrifying bacteria in the nitrification process.

Nitrogen fixation, mineralization and nitrification can be classified as a process that supplies soil nitrate in either small or large amounts for turf uptake. Denitrification on the other hand can be described as a process that removes nitrate from the soil. Denitrification occurs in soils with low levels of oxygen (ex. water logged and highly compacted). Nitrate (NO₃-) ions are converted to atmospheric nitrogen by a series of widely occurring biochemical reactions that include bacteria from the Psedomonas, Baillius and Micrococcus genera.

Due to turf’s inability to convert atmospheric nitrogen into a useful biological form, the presence of both Nitrosomonas and Nitrobacter play a critical role in its survival. Products that affect the concentration levels of both of these bacteria in the soil could potentially affect the overall quality of turf. A reduction of Nitrosomonas levels could cause ammonium to be lost to the atmosphere as ammonia. This could result in reduced fertilizer efficiency, repeated applications and higher operational costs. A reduction in the Nitrobacter population could create higher soil nitrite levels that are potentially harmful to both turf and mammals. Without the presence of these two bacteria in the soil the overall turf quality and consequently, the enjoyment that comes with the recreational activities it supports could be diminished.

Reference:

• Ministry of Agriculture, Food and Rural Affairs Publication 611 (1998). Soil Fertility Handbook. Toronto, Ontario, Canada: Queen’s Printer for Ontario.
• Hopkins, W.G, (1995). Introduction to Plant Physiology. Toronto, Ontario, Canada: John Wiley & Sons Inc.
• Brady, N.C., Weil, R.R. (1996). The Nature and Properties of Soils. (11 th Edition). Upper Saddle River, New Jersey, USA: Prentice Hall.

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