<![CDATA[Nitrogen is an essential nutrient that plays a key role in regulating growth, physiological processes, and yield formation in lowland rice, primarily through its influence on the source-sink balance. Yield variation among upland rice varieties is closely related to differences in photosynthetic capacity, assimilation efficiency, and grain filling during the generative phase. Therefore, understanding the response of source and sink morphophysiological traits and upland rice yield components to nitrogen application under dryland conditions is crucial. This study aimed to evaluate the morphophysiological characteristics of sources and sinks and to assess the effect of various nitrogen doses on source (g) and sink (g) size in several lowland rice varieties. The study was conducted in a dryland area using a split-plot design in a randomized block design. Nitrogen dose treatments consisted of 30 kg N ha⁻¹ (62.5 kg ha⁻¹ urea equivalent) and 115 kg N ha⁻¹ (250 kg ha⁻¹ urea equivalent) as the main plot, while upland rice varieties IPB 9G, IPB 10G, Inpago 8, and Situpatenggang were used as subplots. The results showed significant varietal differences in physiological traits, yield components, and source-sink balance in response to nitrogen application. Among the tested varieties, IPB 9G showed the most stable performance, characterized by high source and sink sizes, optimal yield components, and a relatively stable harvest index. Increasing nitrogen application to 115 kg N ha⁻¹ improved physiological indicators and sink capacity, contributing to increased yield potential. These findings highlight that nitrogen response is strongly influenced by varietal characteristics and assimilation utilization efficiency, emphasizing the importance of determining variety-specific optimal nitrogen levels for dryland rice under dryland conditions.]]>
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