Effects Of Light And Nitrogen Levels On The Dis-tribution Of Canopy SPAD Values And The Diagnosis Of Nitrogen Nutrition In Rice Leaf

The application of real-time, site-specific nitrogen management can guarantee the high yield of rice, and improve the utilization rate of nitrogen. The management pointed out that SPAD value could be an index for nitrogen application precise precision, namely using chlorophyll meter as a nitrogen nutrition diagnosis tools on rice. Previous studies had looked at the effects of cultivars, growth stage, leaf position and other factors on SPAD value, while research on the influence of light and nitrogen on rice canopy SPAD value is few in our country. Therefore, it is necessary to study the distribution characteristics of SPAD value under low light conditions. And investigate the feasibility of applying chlorophyll meter on nitrogen nutrition diagnosis.Pot experiments were conducted to study the distributing characteristics of canopy SPAD and the distributional difference at tillering, booting and heading stages. There were three levels of sheltering and five levels of nitrogen supply in the experiment.This article studied methods to optimize nitrogen nutrition diagnosis of rice leaves under low-light stress condition with SPAD meter. There exists a law that the greenness of rice leaf was regularly changed as black-yellow alternation ways through the whole growth period of rice despite of the effect of light deficiency. But the fluctuation was significantly suppressed under shading conditions. The decrease of SPAD value resulted from laCKing light. Improving nitrogen level had positive effect on increasing the SPAD value of functional leaves. However, less-light condition made an inhibitory effect on the positive role of nitrogen. Shading treatment promoted the increment of lower leaf SPAD value. The fourth leaf (L4) has an instruction function for nitrogen nutrition status during the key growing periods under the interaction of grow light density and nitrogen supply, and it may be a better leaf indicator for rice N status.Shading had significant effect on leaf area, plant height, yield, etc. This resulted in the difference of parallel factors(such as plant mutual shading) among treatments. In this case, using the difference of rice plant itself to eliminate the influence of non-parallel factors is very necessary. At different growth stages and nitrogen levels, SPADL3-L2and SPADL4-L3were remarkably correlated linearly with nitrogen application (in full sunlight, R2L3-L2=0.87～0.97. When shading, R2L4-L3=0.85-0.97) without considering the influence from the growing stages and N rates. For Hang43, SPAD value of the top four leaves on main stem could be used as an indicator for diagnosis of nitrogen status and nitrogenous fertilizer application in rice under shading. Under natural ultraviolet radiation condition, SPAL3-L2will be a better one for nutrition diagnosis. When light intensity is low and less(Dificient sunshine or light attenuation by mutual shading during the growing period of rice), SPADL4-L3may perform better for N status diagnosis.