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 produces PO₄ and NH₄, so you do not need any fertilizer.
B) Rhizobium produces PO₄, so you do not need phosphorus-containing fertilizer.
C) Rhizobium cannot produce PO₄, so you need to add phosphorus-containing fertilizer.
D) Rhizobium cannot produce NH₄, so you need to add nitrogen-containing fertilizer.
E) Rhizobium produces NH₄, so you do not need nitrogen-containing fertilizer.