Nitrogen Management Strategies to Improve Crop Performance, Recovery Efficiency and Their Relationship with Physiological Indices in Dry Direct-Seeded Rice

Nitrogen (N) recovery efficiency in dry-direct seeded rice (DSR) is less than 30%, hence, requires special consideration. Nitrogen management strategies such as splitting N in appropriate dose and application time synchronize with crop demand to improve nitrogen use efficiency (NUE). This two-year field study compared two- and three- N splits top-dressed at different crop stages using 80, 120 and 160 kg ha^{− 1} with 0 kg ha^{− 1} as control in dry DSR. Results showed that two N- splits performed similar as three-splits for agronomic, quality and NUE traits including SPAD-chlorophyll and normalized difference vegetation index (NDVI). Similar and higher straw and grain yields including harvest index was found for 120 and 160 kg N ha^{− 1} that was attributed to reduced spikelet sterility (24–29%), improved filled kernels (16–19%) and productive tillers (21–31%). Two- N splits at 160 kg ha^{− 1} resulted in higher net income and benefit: cost ratio (BCR) of dry DSR. Improved plant N status reduced kernel chalkiness and improved kernel length, proteins contents and water absorption ratio. Agronomic and physiological efficiency reduced with increasing N application while recovery efficiency (31–58%) was improved. Strong association of NDVI with leaf N, and total N uptake with sufficiency index (SI) and grain yield indicated that rice crop achieved optimal N concentration to support growth during active tillering period. Thus, additional N applied in three splits might be reduced to economize N use and SI can be used to predict and optimize the N schedule during panicle initiation or heading stages to reduce the sink limitation.