Phosphorus Uptake and Use Efficiencies of Two Upland Rice (Oryza sativa L.) Varieties under Varying Phosphorus Rates and Seasons

Phosphorus (P) is an essential macronutrient for rice (Oryza sativa L.) production, yet its availability is often limited in tropical soils, constraining crop growth and yield. Optimizing phosphorus use efficiency (PUE) is crucial for enhancing rice productivity while minimizing fertilizer input costs. This study evaluates the yield and phosphorus use efficiencies of two upland rice varieties, Nerica 4 and Komboka, under different phosphorus application levels across two growing seasons (short and long rains) in Kenya. The findings provide insights into varietal differences in phosphorus acquisition and utilization, contributing to site-specific fertilizer recommendations for sustainable upland rice production. A field experiment was conducted using a randomized complete block design (RCBD) in a split-plot arrangement. The main plots consisted of two rice varieties, Nerica 4 and Komboka, while the sub-plots comprised four phosphorus application levels (0, 30, 50 and 70 kg P ha?¹), with three replications. Grain and stover yields were measured at harvest, and plant samples were collected for phosphorus analysis. Phosphorus use efficiencies, including agronomic efficiency, physiological efficiency, partial factor productivity, recovery efficiency, and internal utilization efficiency, were calculated. Nerica 4 exhibited significantly higher grain yield and phosphorus-use efficiency than Komboka. During the short rains, grain yield in Nerica 4 ranged from 2.34 t ha?¹ (P0) to 5.75 t ha?¹ (P70), while Komboka recorded yields between 1.97 t ha?¹ (P0) and 3.5 t ha?¹ (P70). In the long rains, grain yield in Nerica 4 ranged from 0.6 to 2.4 t ha?¹, whereas Komboka recorded yields between 0.6 and 1.85 t ha?¹. Additionally, Nerica 4 demonstrated significantly superior agronomic efficiency, partial factor productivity, and recovery efficiency compared to Komboka. Phosphorus application rates, rice variety and seasonal conditions significantly influenced rice yield, phosphorus uptake, efficiency, and overall plant performance. The findings highlight the importance of variety-specific phosphorus management strategies to enhance the productivity and sustainability of upland rice. Based on the results, an application rate of P 70 kg ha-1 is recommended for optimal yield and P 50 kg ha-1 for efficient nutrient use, and a cost-effective option with relatively good yields.