In an experiment in which three levels of P and five levels of N fertilizer were applied, it was found that at the highest levels of fertilization the hay yields were increased fourfold, the percentage of crude protein was doubled, the crude‐protein yield increased sevenfold, and the P uptake increased five times over those of the control. This increased production was mainly a result of the use of N fertilizer, although significant PxN interactions were obtained at the higher levels of N fertilizer. By itself, P fertilizer had little effect on any of the above increased yields. It would appear that very much higher production, especially of CP and P, might be attained, if even higher levels of fertilizer were applied.Basing income on hay yields and expenditure on fertilizer costs, the greatest profit was obtained from the higher levels of fertilization. This applied especially to N fertilize