Relationship between index leaf nitrogen and leaf colour chart (LCC) values in direct wet seeded rice (Oryza sativa L.)

Field experiment was conducted at the wetlands, Tamil Nadu Agricultural University, Coimbatore in deep clay soil (Vertic ustochrept) to study the relationship between Leaf Colour Chart critical value (LCC cv.) and index leaf nitrogen in CO 47 rice variety. The study was conducted in factorial randomized block design with three replications. The treatments included three levels of LCC cv. (LCC cv. 3, 4 and 5) with different rates of nitrogen (N) application (20, 25, 30 and 35 kg ha^-1 at a time) along with three checks (control, blanket N (150 kg N ha^-1 in four equal splits) and manage N practices (150 kg N ha^-1 in four unequal splits). LCC readings were measured every week from 21 Days After Sowing (DAS) to 84 DAS and nitrogen fertilizer was applied as per treatment schedule. Index leaf N content was measured from 35 DAS to 84 DAS. There exist a positive correlation between index leaf N and LCC values. The higher leaf N content monitored at 49, 56, 63 and 70 DAS had its positive implications on the LCC values for atleast another two succeeding weeks of observation. The LCC values and index leaf N recorded in control plot during 35-84 DAS indicated that the native N supply of the experimental field itself was sufficient to maintain LCC cv. 3 after 35 DAS. However N fertiliser application is essential to maintain cv. 4 to increase the index leaf N and achieve crop performance similar to blanket N. Thus LCC values give an indirect measurement of index leaf N and serve as a tool for plant based fertiliser application.