In some situations , the application of nitrogen fertilizer to crops?

Question

in some situations , the application of nitrogen fertilizer to crops has to be increased each year because the fertilizer decerease the rate of nitrogen fixation in soil. propose a hypothesis to explain this phenomenon . describe a test for your hypothesis.what results would you expect from your test?

please help me.

Answer 1

One could hypothesize that the fertilizer applications are progressively reducing the populations of root nodule forming bacteria (rhizobia) in the soil.  This could be tested by using microbiological techniques to measure these population sizes from year to year.  If the population of rhizobia are depleted they could be augmented by use of commerically available inoculant.  This should increase nitrogen fixation if indeed natural rhizobia populations are limiting.