Research On Using SPAD Value As Diagnostic Index For N Application In Wheat

The experiment was carried out on the experiment field of Jiangsu Provinced Key Lab of Crop Genetics and Physiology,Yangzhou University from 2005 to 2007 to investigate the changes of SPAD values,chlorophyll content,N content of leaves at different growth stages,different positions of leaves under different N application levels,and their relations with grain yield and quantity in different varieties for different end uses.1. The changes of leaf SPAD values differed among gene types,and leaf SPAD values in different varieties changed Significantly with the changes of N application amount.Leaf SPAD value changed also with the leaf positions and the sites on the same leaf.The order of leaf SPAD values at different positions of a plant at elongation stage was the second spread leaf > the first spread leaf >the third spread leaf > the other leaves,the order of leaf SPAD values at booting and anthesis was flag leaf > the penultimate leaf from top > the 3rd leaf from top >the other leaves.SPAD values from the base to the top of a leaf had a quadratic changes,So the mean SPAD values at tip,middle and base sites of a totally spread leaf could be cased to evaluate the growth status of leaves.The ratio of SPAD value of the 3rd spread leaf to SPAD value of the first spread leaf was nearly 1 when suitable amount of N was applied, while it was greater than 1 when excessive amount of N was applied or lower than 1 when insufficient amount of N was applied.2. Leaf SPAD value was positively related to N application amount at a certain range. When excessive amount of N was applied,SPAD value decreased.3. The relation between SPAD value and chlorophyll content in leaves differed significantly with wheat varieties.SPAD values of leaves at different positions of a plant were significantly related with chlorophyll content in leaves.The higher the SPAD values,the greater the N content in leaves.SPAD value could be used to estimated N content in leaves at a certain range.4. Grain yield had a quadratic relation with leaf SPAD value at different stages.5. The suitable leaf SPAD value for weak-gulten wheat Yangmai 15 with high grain yield and good quality was 47-48 at elongation stage,48 at booting, 50-51 at anthesis.The suitable N applicate amount was 20.53-66.8kg/hm~2 at elongation stage, the suitable total N application amount was 125.53-171.8 kg/hm~2.The suitable leaf SPAD value for medium-gulten wheat Yangmai 16 with high grain yield and good quality was 45-47 at elongation stage,47-48 at booting,48-51 at anthesis.The suitable N applicate amount was 86.35-120kg/hm~2 at elongation stage,the suitable total N application amount was 191.35-225 kg/hm~2.