施氮对半湿润农田夏玉米冠层氮素及叶绿素相对值(SPAD值)垂直分布的影响

Effect of nitrogen on vertical distribution of canopy nitrogen and chlorophyll relative value (SPAD value) of summer maize in sub-humid areas

以半湿润地区土垫旱耕人为土为供试土壤,采用田间试验,研究了不同施氮水平下夏玉米(Zeamays L.)拔节期、灌浆期和成熟期3个生育期冠层叶片氮素、叶绿素相对值(SPAD值)的垂直分布规律及其差异;同时对各层叶片含氮量、SPAD值与施氮量进行相关分析。结果表明,在各生育期不同叶层叶片含氮量按上、中、下层顺序呈明显递减规律,从全生育期不同施氮处理看,上层比中层增加6.64%,中层比下层增加5.18%。随施氮量增加,中上层叶片含氮量差异增大,中下层叶片含氮量差异减小。冠层内叶片SPAD值垂直分布规律与叶片含氮量分布规律相类似。相关分析表明,全生育期各层叶片SPAD值与叶片含氮量呈极显著线性正相关关系(R=0.503**)。进一步分析发现,各层叶片SPAD值、叶片含氮量与施氮量的相关性以上层叶关系最为密切,揭示了夏玉米氮素营养诊断的较好叶片是上层叶位。

A field experiment was carried out in sub-humid area using Eum Orthic Authrosols as sample soil type. The experiment analyzed the vertical distribution pattern of canopy leaf nitrogen and leaf chlorophyll relative value （SPAD value）, differences in different layer-leaves for different nitrogen levels in summer-maize （Zeamays L.） at three growth stages （jointing, grain filling and maturity） and correlation for layer-leaf nitrogen content, leaf SPAD value and applied N. The results show that different layer-leaves have different nitrogen content which obviously diminishes from the upper to middle, then the lower leaf canopy. Based on the average of different leaf layers for the entire growth stage, upper leaf layer is 6.64% higher than middle leaf layer, which in turn is 5.18% higher than the lower leaf layer. With increasing application of nitrogen, the difference between upper and middle leaf layers increases. However, the difference between middle and lower leaf layers decreases with increasing nitrogen application. The vertically changing trend of canopy leaf chlorophyll relative value is similar to that of nitrogen content of leaves. Correlation analysis indicates a significant （R = 0.503＊＊） linear correlation between chlorophyll relative value and leaf nitrogen content throughout the growth stage. Further analysis indicates that the upper leaf layer has the most closed correlation of leaf nitrogen content, chlorophyll relative value with applied nitrogen. So the best diagnosis of nitrogen nutrition for summer-maize is in the upper leaf layer.