Rhizosphere microorganisms are the main drivers of turnover of organic C, N, and P and thus recycling of organically bound nutrients, for example by ammonification and nitrification, but may also increase N loss via denitrification.
@ Bayu, greater rhizosphere effect is seen with bacteria ( R:S values ranging from 10 to 20 or sometimes more) than with fungi or actinomycetes. Only negligible changes is noticed with regard to protozoa and algae. The abundance of nitrogen fixing and phosphate solubilizing bacteria in the crop rhizosphere has a natural significance. Extensive studies have been done on induced changes in the rhizosphere microflora by foliar sprays of antibiotics, growth regulators, pesticides and inorganic nutrients for controlling root diseases. However, no definite conclusions or guidelines have emerged from such studies to merit their application under field conditions. Microbial seed inoculation with Azotobacter, Beijerinkia, Rhizobium or P- solubilizing or mobilizing microorganisms may help in the establishment of beneficial microorganisms in the rhizosphere in the immediate vicinity of the growing roots. Many experiments indicate that cellular extract of certain bacteria, fungi and algae increase the growth of other microorganisms, some microorganisms also have some antigonistic activities.
J. C. Tarafdar @, Thank you very much indeed for this scientific discussion. Of course, the uptake of Nitrate is rapid due to high particle mobility. Most plants, therefore, prefer Nitrate over Ammonium and uptake of Ammonium is slower than that of Nitrate because the Ammonium is bound to clay particle in the soil. But, I found one of the findings which concluded that Ammonium is preferentially up taken. Here the conclusion that I found ”Ammonium is preferentially taken up by many plants when supplied in equimolar concentrations with nitrate”. Is it may be, particularly when the N supply is low?
@ Bayu, Nitrates are the preferred nitrogen source under any situation except water logging conditions. Unlike ammonium, nitrate is non-volatile, so there is no need to incorporate it in the soil when applied by top- or side dressing, which makes it a convenient source for application.Nitrate is mobile in the soil , direct uptake by the plant and have highest efficiency. Plants can use ammonia as a nitrogen source. ... Plants absorb ammonium and nitrate during the assimilation process, after which they are converted into nitrogen-containing organic molecules, such as amino acids and DNA. When the plant takes up ammonium (NH4+), it releases a proton (H+) to the soil solution. Increase of protons concentration around the roots, decreases the pH around the roots. Accordingly, when the plant takes up nitrate (NO3-) it releases bicarbonate (HCO3-), which increases the pH around the roots.
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