Effect of Nitrogen on Nitrogen Content, Pigment, Growth and Spectral Reflectance of Rice

An experiment was conducted in sand culture with rice to determine the effect of nitrogen (N) fertilizer on the spectral reflectance properties. Rice (cv. CO 51) was directly sown in pots of seven kilogram sand and supplied Hogland's nutrient solution at seven days interval. Plant sampling was done to estimate the N content and pigments (chlorophyll _{a, b} and carotinoid) and biometric observations like plant height, number of tillers plant⁻¹, number of leaves tiller⁻¹ to match with spectral measurement. The above observations, sampling and measurements were performed during tillering initiation, maximum tillering, flowering and milky stages of rice crop. During the growth period under different treatments, fully expanded third uppermost leaves were sampled for nutrient content (for important stages only), pigments and canopy reflectance also recorded. Rice leaf nitrogen (%) content recorded high values (2.4% N) in tillering initiation stage than at milky stages (0.43% N). Positive correlation of spectral indices (GNDVI, NDVI and Red Edge) with pigments and N (%) content were recorded during flowering and milky stages. The plant height positively correlated with Red Edge (flowering stage), GNDVI and NDVI (milky stage). The correlation coefficient of NDVI inflection point with Nitrogen content were found positive (0.952) at maximum tillering stage followed by flowering stage 0.817, milky stage 0.587 and the least value noted in tillering initiation 0.225.