Abstract
<title>Abstract</title> <p>Blanket phosphorus (P) recommendations for lowland rice do not account for the effect of transplanting date on attainable yield. A two-year split-plot experiment was conducted on a P-deficient acidic soil in Meghalaya, India, with four transplanting dates (3 July, 13 July, 23 July and 2 August) combined with four P rates (0, 13.1, 26.2 and 39.3 kg P ha⁻¹). Seedling age was maintained at 23 d by staggered nursery sowing. Delaying transplanting from 3 July to 2 August reduced grain yield by 24.8%, biomass by 23.0% and aboveground P uptake by 38.7%. Effective tillers, panicle weight and grain number were also reduced, while harvest index changed little. Grain yield and P uptake increased with P application up to 26.2 kg P ha⁻¹ and declined at 39.3 kg P ha⁻¹, where post-harvest available soil P was highest, indicating reduced recovery of applied P under later planting. The transplanting date × P interaction was significant for grain yield, tissue P concentration and P uptake. Fitted quadratic response functions placed the agronomic optimum at 25.5 kg P ha⁻¹ (95% bootstrap confidence interval, CI: 24.7–26.2) for 3 July and 21.8 kg P ha⁻¹ (20.5–23.7) for 2 August, a difference of 3.7 kg P ha⁻¹ (95% CI: 2.2–4.5). Delayed transplanting therefore lowered attainable yield, reduced P recovery and shifted the optimum P rate downward. The optima are site-specific and offer a calibrated basis for incorporating transplanting date into P recommendations, with finer P-rate intervals and additional environments enabling further refinement.</p>