关键词: 水稻, 冠层叶片, SPAD读数, 影响因素

Abstract: SPAD meter can be used to determine the nitrogen rates in rice production， but it is easily influenced by many factors. This paper studied the effects of nitrogen rates， cultivars and light on the SPAD readings in rice canopy. SPAD reading in the rice canopy changed regularly and showed three “up-down” stages during the rice growth period， and was influenced by nitrogen rates and rice cultivars. With the growth of rice canopy， the difference in SPAD reading between the upper and lower leaf became greater， especially between the first and other position leaf. The difference between the upper and lower position leaf decreased as the N rates increased. SPAD reading in rice canopy differed in rice cultivars responding to the light gradient. Therefore， when the SPAD meter was applied to determine the nitrogen fertilizer amount and percent in rice growth period， different SPAD thresholds should be used on the basis of rice cultivars. In addition， the difference of SPAD reading between the upper and lower leaf could also be used as an indicator to guide the application of nitrogen fertilizer.

Key words: rice, canopy, SPAD reading, influencing factors