Development of SPAD Values of Medium- and Long-duration Rice Variety for Site-specific Nitrogen Management

Nitrogen fertilizer application in rice either in excess or deficit dose, causing environmental pollution and yield loss can be avoided through Site-Specific Management using a chlorophyll meter (SPAD 502). A field experiment was conducted with two rice varieties of varying duration at varying N application levels (0, 50, 100 and 150 kg N ha-1) during wets season (June-November) of the year 2006 to 2008 at the Research farm of Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur to determine the crop growth stage specific optimum SPAD value for higher grain yield. The rice varieties were Lalat of medium duration (120 days) type and Swarna of long duration (150 days) type. Correlation between N application levels and grain yield determined the optimum grain yield of the variety Lalat and Swrana as 5024 and 6427 kg ha-1, respectively, under the corresponding N application levels of 105 and 155 kg N ha-1. A significant and positive correlation was observed between flag leaf N content and SPAD value (R2≈0.80) and SPAD value at different growth stages and grain yield for both the varieties. The average SPAD value for optimum grain yield production was 35.4 and 40.1 for Lalat and Swarna, respectively. The desired SPAD values at critical growth stages were determined for optimum grain yield production of both the varieties.