"Molybdenum is required for growth of legumes and by rhizobia in root nodules. It is often deficient in acid soils and legume growth responses to small applications of Mo are well documented. Molybdenum deficiency in legumes is usually denoted by inward cupping of leaflets of young fully expanded leaves. If a legume is totally dependent on its Rhizobium symbiosis for nitrogen, the symptoms of molybdenum deficiency and nitrogen deficiency are similar." http://www.fao.org/ag/agp/AGPC/doc/publicat/FAOBUL4/FAOBUL4/B402.htm 

Folks, nitrates do accumulate in plants when molybdenum is low. The enzyme, nitrate reductase requires molybdenum to begin the protein making process. When nitrates accumulate, aphids, mites, and other issues follow. Grape growers notice nematode issues go away. Consider soil testing for molybdenum so your nitrogen goes to make protein, not toxic nitrates.