The study looked at how different amounts of phosphorus fertilizer affect the growth and yield of dryland wheat in years with varying rainfall. They found that applying phosphorus increased root growth, water use, and grain phosphate levels. Higher phosphorus levels led to more spikes, higher yields, and better water use efficiency. In dry years, using more phosphorus improved root growth, water use, and grain phosphate levels even more. Overall, applying 150 kg of phosphorus per hectare gave the best results in terms of root growth, yield, and phosphorus use efficiency.