Abstract
Nitrogen ( N ) fertilizers are critical in today's agriculture especially in the United States. Leaching, methane and nitrous oxide emissions from N fertilizer use and the implications for global climate and water pollution raised serious concerns among environmentalists and agronomists. Prices of N fertilizers increased geometrically over the past few years. The projected increase in maize ( Zea mays L .) ethanol production is expected to increase N fertilizer demand and prices. Hay prices are, however, staggering and producers are looking for alternatives to N fertilizers. This review paper assessed trends in fertilizer use and prices as well as factors affecting fixation and transfer of dinitrogen ( N 2 ) in forage production systems. Additionally, economic implications of using N fertilizers and grass‐legume mixtures are discussed. From the review, it was apparent that legumes have the potential to replace N fertilizers or at least complement the use of N fertilizers in forage production systems. However, N transfer in forage production systems is low. A lot more research is needed to answer the question “Why legumes fix so much N 2 and transfer just a small proportion to other crops.” Similarly, identifying compatible grass‐legume species that enhance N 2 fixation will be a giant step towards reduced N fertilizer use and ensuring environmental sustainability. With the sharp increase in N fertilizer prices, the use of legumes in forage production systems seems promising.