Background: The response of boro rice to different phosphorus fertilizer doses is critical for optimizing growth and yield. Understanding the interactions between rice varieties and phosphorus levels can lead to improved agricultural practices and increased productivity. Objective: The experiment aimed to evaluate the response of two boro rice varieties to different phosphorus fertilizer doses, focusing on growth and yield parameters. Methods: The experiment was conducted from January to June 2022 at the Agronomy Field Laboratory, University of Rajshahi. A Randomized Complete Block Design (RCBD) was used to test two rice varieties (BRRI dhan28 and BRRI dhan58) and three phosphorus levels (P1 = 100 kg ha-1, P2 = 150 kg ha-1, P3 = 200 kg ha-1). Results: The study found that BRRI dhan58 (V2) outperformed BRRI dhan28 (V1) in several growth and yield parameters. Specifically, BRRI dhan58 exhibited superior plant height (101.47 cm), a higher number of tillers, and greater chlorophyll content (51.03 SPAD). It also had longer panicle length (23.23 cm), a higher number of grains per panicle (185.66), and greater 1000-grain weight (23.09 g). Additionally, BRRI dhan58 produced a higher grain yield (7.66 t ha-1), straw yield (9.10 t ha-1), and biological yield (16.76 t ha-1), while having fewer non-effective tillers (5.31) and a lower harvest index (45.73%). Regarding phosphorus treatments, the highest dose (P3 = 200 kg ha-1) yielded the best results across various parameters. Plants treated with P3 exhibited the greatest plant height (108.86 cm), the highest total and effective tiller counts, and the highest chlorophyll content (55.37 SPAD). Additionally, P3 treatment resulted in the longest panicle length (24.94 cm), the highest number of grains per panicle (200.70), and the greatest 1000-grain weight (23.18 g). This phosphorus level also produced the highest grain yield (8.26 t ha-1), straw yield (9.81 t ha-1), and biological yield (18.07 t ha-1), although it also resulted in more non-effective tillers (5.58). The interaction of BRRI dhan58 with the highest phosphorus dose (V2P3) produced the best outcomes for nearly all parameters. This combination resulted in the highest grain yield (8.37 t ha-1) and biological yield (18.42 t ha-1), although it also had the highest number of non-effective tillers (6.09). Keywords:Phosphorus fertilizer; Chlorophyll content; Single-photon avalanche diode.
