Promising phosphorus management is critical for improving water and nutrient use in drip-irrigated cotton. This study evaluated layered phosphorus placement under different basal-to-topdressing ratios and placement depths. A two-year field experiment was conducted in 2021–2022. Three basal-to-topdressing ratios (P25: 25:75, P50: 50:50, P75: 75:25) and three placement depths (L1: 5 + 15 cm, L2: 15 + 25 cm, L3: 5 + 15 + 25 cm) were compared with conventional uniform application (CK). We hypothesized that optimized basal-to-topdressing ratios combined with layered placement would improve soil phosphorus distribution, which could stimulate root growth in phosphorus-rich zones and enhance crop phosphorus and water uptake. Results showed that compared with CK, optimized layered placement significantly increased soil available phosphorus (8.72–72.76%) and the phosphorus activation coefficient (13.41–71.25%) in the 20–40 cm soil layer. Root growth significantly increased by 17.89–95.69% at this depth. Seed cotton yield significantly increased by 5.35–18.61%. Water productivity significantly improved by 3.45–12.74%, and phosphorus use efficiency by 11.99–50.60%. Among all treatments, P50L2 provided the most consistent and largest benefits. These results indicate that layered phosphorus placement with a 50:50 basal-to-topdressing ratio at 15 and 25 cm depths aligns soil phosphorus availability with root distribution. This enhances nutrient and water acquisition and improves cotton productivity. Overall, layered phosphorus placement offers a practical strategy for sustainable phosphorus management in arid cotton-growing regions. • Layered phosphorus (p) placement optimized the vertical distribution of soil phosphorus. • Phosphorus placement at appropriate depths increased soil P availability in the 20–40 cm layer. • Improved P availability promoted root growth and enhanced water and P uptake. • Optimized P placement increased water productivity, P use efficiency, and seed cotton yield.
He et al. (Sat,) studied this question.