To Determine The Physiological Basis For Diagnose Of Nitrogen Status By Reflectance Measurement

Two field experiments were conducted respectively in the year of 1999 and 2000 to study the response of individual leaf spectral reflectance to five levels of nitrogen fertilizer treatments in rice (Oriza sativa L.) plant. Sampling was combined through a rice canopy at upper, medium and low levels for total nitrogen content, protein-N content and leaf pigments (chlorophyll a, b and carotenoid) concentrations with spectral signals from the leaves. The spectral data were correlated with the leaf parameters by regression analysis. Nitrogen deficiency caused the leaf reflectance increased in the visible region and decreased in rear infrared region in all leaf levels, which were associated with the decreased pigment concentration.Reflectance from upper level leaf were greater than that from the low level leaf, and reflectance from lower surface were greater than that from upper surface in the visible and infrared region at tillering, booting and flowering stages.Results of regression analysis showed the spectral data were strongly correlated with leaf parameters (mainly leaf pigment concentrations and N contents) and the spectral reflectance could be used to diagnose nitrogen status in rice plants. The defined N level applied and increased with the growth stage progressing, which may be attributed to N remobilization caused by N deficiency and theshading and senescence in lower leaves caused by plant development. The results suggested N gradient could be used as a better indicator of N status in comparison with N content in plant or individual leaves.