Temporal and Spatial Distribution of Leaf Nitrogen Content and Its Relationship with Plant Nitrogen Status in Winter Wheat

It is very important to elucidate the plant nitrogen status in nitrogen fertilizer management of wheat,but the distribution characteristics of nitrogen in different organs involving in plant nitrogen status prediction is unclear.Field experiment was conducted using two wheat(Triticum aestivum L.) cultivars differing in protein content to investigate the distribution characteristics of leaf nitrogen content affected by different nitrogen application rates and the relationships with plant nitrogen status.The results showed the vertical distribution of leaf nitrogen content in different positions varied with growth stages.Leaf nitrogen content declined as the order of the 1st leaf2nd leaf 3rd leaf 4th leaf from the top at jointing,heading and anthesis stages.At anther connective and booting stages,however,leaf nitrogen content in the 2nd leaf was higher than that in the 1st leaf.Moreover,the effects of nitrogen application rates on leaf nitrogen content varied with cultivars.For Ningmai 9,leaf nitrogen contents in top three leaves were more sensitive to increased nitrogen supply compared with 4th leaf,and the differences of nitrogen content between 4th leaf and top three leaves were enlarged.For Huaimai 20,nitrogen content in top four leaves was enhanced synchronously.Temporal changes of leaf nitrogen content varied with growth processes and nitrogen application rates.Leaf nitrogen content in different leaf positions was the highest at anther connective stage under nitrogen fertilization treatments.Plant nitrogen content increased with increasing nitrogen application rates,but reduced with growth processes.The correlation analysis showed that leaf nitrogen contents in most leaf positions were significantly positively correlated with plant nitrogen content though there were slight differences between two wheat cultivars.The relationships between the leaf nitrogen difference(LND) and plant nitrogen content varied with cultivars and growth stages,but LND_(4-1) and LND_(4-2) exhibited positively significant correlation with plant nitrogen content at jointing stage without any impacts from cultivars.The results suggest that plant nitrogen status in wheat might be predicted by monitoring the differences of leaf nitrogen content between the 4th leaf and 2nd leaf or 1st leaf at jointing stage.