The Role of Net Assimilation Rate and Nitrogen Management in Optimizing Rice (Oryza sativa L.) Yield

Abstract

Background: The net assimilation rate (NAR) is a physiological parameter related to leaf area and dry weight per unit of time. It is used to figure out how much grain a plant will produce. This study aims to explain the net assimilation rate of several types of rice at different doses and nitrogen application times. Methods: The research was conducted from December 2021 to April 2022. The experimental design was a split-plot design consisting of two treatment factors: the variety (main plot) and the time and dose of fertilization N (subplot). The variety factor consists of four varieties: IPB 3S (new type varieties), Inpari 33 (new high-yielding varieties), Hipa 21 (hybrids) and Mentik Wangi (local) at nitrogen 4 levels, namely 0 kg ha-1 (N0), 45 kg ha-1 applied when planting (N1), 90 kg ha-1 applied twice [45 kg at planting and 45 kg at panicle initiation (N2)] and 90 kg ha-1 applied three times, namely 45 kg at planting, 22.5 kg at the age of panicle initiation and 22.5 kg at heading (N3). Result: Results demonstrated that applying 90 kg ha-1 nitrogen fertilizer in three split applications (N3) improved agronomic performance by increasing tiller number, leaf area, dry matter accumulation, leaf nitrogen content and grain yield compared to other nitrogen regimes. Our findings newly highlight the vital influence of net assimilation rate (NAR) on panicle development, as NAR was positively correlated with panicle length. Uniquely, among all four varieties tested, the local cultivar Mentik Wangi recorded the highest NAR across N treatments.