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Soil interactions

Soil microbiota can suppress both disease and beneficial root symbionts (mycorrhizal fungi are easier to establish in sterile soil). Inoculation with soil bacteria can increase internode extension, yield and quicken flowering. The migration of bacteria along the root varies with natural soil conditions. For example, research has found that the root systems of wheat seeds inoculated with Azotobacter showed higher populations in soils favorable to Azotobacter growth. Some studies have been unsuccessful in increasing the levels of certain microbes (such as P. fluorescens) in natural soil without prior sterilization.

Grass root systems are beneficial at reducing soil erosion by holding the soil together. Perennial grasses that grow wild in rangelands contribute organic matter to the soil when their old roots decay after attacks by beneficial fungi, protozoa, bacteria, insects and worms release nutrients.

Scientists have observed significant diversity of the microbial cover of roots at around 10 percent of three week old root segments covered. On younger roots there was even low coverage, but even on 3-month-old roots the coverage was only around 37%. Before the 1970s, scientists believed that the majority of the root surface was covered by microorganisms.