Effects of Sowing Dates and Phosphorus Application on Seed Yield and Yield Components of Alfalfa

Background: Alfalfa (Medicago sativa L.) is a globally important cool-season forage grass for semiarid regions and the demand for seeds is increasing with the increase of alfalfa planting area. However, its seed yield is often low or inconsistent. Methods: A field experiment was conducted to investigate the response of seed yield and yield components of alfalfa to different sowing dates and phosphorus (P) fertilization levels from 2020 to 2022. This research was conducted using a split-plot design in a randomized complete block, with four replications. The main plots were three sowing dates (20 July, 5 and 20 August) and subplots were five different rates (0, 40, 70, 100 and 130 kg P2O5 ha-1). Result: Our results revealed that delaying the sowing dates reduced seed yield, by influencing its yield components, except for the 1000-seed weight, but P fertilization enhanced the seed yield components affected by late sowing and increased seed yield, it is recommended to apply P fertilizer at 77.6~144.8 kg ha-1. Stem density and seeds per pod were the primary factors determining seed yield and they may be useful to consider in developing traits for high-seed-yield alfalfa.