Zhang, T., Kang, J., Zhao, Z., Guo, W. and Yang, Q. 2014. Frequency, depth and rate of phosphorus fertilizer application effects on alfalfa seed yields. Can. J. Plant Sci. 94: 1149-1156. Efficient phosphorus (P) management is important for alfalfa (Medicago sativa L.) seed production and is necessary in order to alleviate the negative environmental effects of excess P application. The study was conducted on both very low-P and optimum-P soils to evaluate the effects of two frequencies (annual and triennial applications), two depths (7-8 and 15-16 cm), and three rates (15, 30, and 45 kg P ha^-1) of P fertilization on seed yield, total P uptake (TPU), P-use efficiency of applied P (PUE), and recovery of P fertilizer (PR). There was a zero-P control. Under the model of annual application, the highest seed yields were obtained with the rates of 30 or 45 kg P ha^-1. Under the model of triennial application, however, the seed yield decreased linearly with increasing rates in the first year. Averaged across frequency and depth, PUE and PR decreased linearly but TPU increased linearly with increasing P application rate. Triennial application of 45 kg of P led to higher mean seed yield than annual application of 15 kg of P, and its PUE and PR values were higher than triennial application of 90 and 135 kg of P. However, on low-P or optimum-P soil, annual application of 30 or 45 kg of P resulted in the highest mean seed yields compared with low PUE and PR. Thus, triennial application of a low P rate leads to a high alfalfa seed yield and has potential economic and environmental benefits.