Abstract: To understand the growth responses of dryland wheat to different application rates of phosphorus fertilizer in different rainfall years, we examined root characteristics, spike number, yield and phosphate utilization. Results would help improve phosphate fertilizer use in dryland wheat production. We carried out a field experiment at the research station of Shanxi Agricultural University from 2012 to 2016. We examined the effects of four application rates of phosphorus (0, 75, 150 and 225 kg·hm^-2 on root growth, phosphate utilization and yield formation of dryland wheat in different years with contrasting rainfall pattern. Compared with the treatment without phosphorus fertilization, phosphate application increased root surface area at all growth stages and root weight density in the 0-80 cm soil layer at jointing, anthesis, and maturity stages. Phosphate application significantly increased soil water consumption from jointing to anthesis, and total soil water consumption in the growing season. Phosphate application enhanced the amount of pre-anthesis phosphate translocation and phosphate accumulation of grain. Spike number, yield and water use efficiency were increased with 75, 150 and 225 kg P·hm^-2 by 9.2% to 22.5%, 11.8% to 30.0%, and 2.1% to 12.1%, respectively. In the dry years, the application rates of 150 and 225 kg P·hm^-2 in comparison to 75 kg P·hm^-2 significantly increased root weight density and root surface area at all stages, soil water consumption from sowing to jointing and from jointing to anthesis, and total water consumption in the growing season. In comparison to the rate of 75 kg P·hm^-2, 150 and 225 kg P·hm^-2 increased soil water consumption from sowing to jointing by 7.3-8.7 mm, soil water consumption from jointing to anthesis by 15.6-18.1 mm, and total water consumption by 15.6-18.1 mm. Significant increase in the pre-anthesis phosphate translocation and phosphate accumulation in grain was higher under 150 and 225 kg P·hm^-2 than that under 75 kg P·hm^-2 in dry years. Furthermore, the two rates (150 and 225 kg P·hm^-2) in dry years increased spike number by 9.3%-10.7% and yield by 11.9%-14.6%. The application rate of 150 kg P·hm^-2 significantly improved phosphorus use efficiency by 20%-82% in comparison to other rates. In normal years, the rates of 150 and 225 kg P·hm^-2 increased root surface area, root weight density at both anthesis and maturity compared with 75 kg P·hm^-2. Soil water consumption from anthesis to maturity and total soil water consumption in the growing season were also increased by 1.2-15.0 and 3.8-23.1 mm, respectively. In addition, phosphorus accumulation in post-anthesis and phosphate accumulation in grain were increased in both 150 and 225 kg P·hm^-2, which increased spike number by 1.4%-9.6% and yield by 3.5%-10.4%. The effects of phosphate application at the rate of 150 kg P·hm^-2 were significantly different from 75 and 225 kg P·hm^-2. In conclusion, phosphorus fertilizer application enhanced uptake of water and phosphate in dryland wheat at early and middle growth stages in dry years and at the late growth stage in normal years. Phosphorus application increased wheat yield mainly due to the increases of spike number. The application of 150 kg P·hm^-2 is the best choice for high water and phosphorus fertilizer use efficiency and high yield in both dry and normal years.

Key words: yearly rainfall pattern, dryland wheat, phosphate fertilizer, soil water consumption, root weight density, root surface area, yield