Soybeans Will Have Several Hundred Rhizobium Nodules

Soybeans will have several hundred Rhizobium nodules.A study in Minnesota found that soybeans grown without P₂O₅ fertilizer produced 23.0 bushels per acre,while adding 23 lbs of P₂O₅ per acre gave a yield of 37 bushels per acre.What is the best explanation for this observation?

A) Rhizobium cannot produce PO₄, so you need to add P containing fertilizer
B) Rhizobium produces NH₄, so you don't need N containing fertilizer
C) Rhizobium produces PO₄ and NH₄, so you don't need any fertilizer
D) Rhizobium produces PO₄, so you don't need P containing fertilizer
E) Rhizobium cannot produce NH₄, so you need to add N containing fertilizer