西北旱区不同覆膜和灌溉水平下的玉米冠层氮含量垂直分布及高光谱反演

为探究不同覆膜和灌溉水平下玉米叶片氮含量垂直分布特征及其遥感反演规律，2020年在甘肃省武威绿洲农业高效用水国家野外科学观测研究站进行大田试验，设置3种灌水量水平(春玉米灌溉需水量的100%(W₁₀₀)、70%(W₇₀)和40%(W₄₀))和3种覆膜处理(不覆膜(M₀)、普通塑料膜(M₁)和生物可降解膜(M₂))，测定春玉米在不同灌水量和覆膜条件下叶片氮含量垂直分布、冠层反射特征和反射率与叶片氮含量等指标，并采用随机森林法构建氮含量估测模型分析垂直分布的叶片氮含量。结果表明，相同灌水处理的玉米冠层叶片中氮含量由高到低为M₀>M₂>M₁，M₀比M₂的上、中、下部位叶片氮含量分别增加6.78%、5.11%、2.55%，M₂比M₁的上、中、下部位叶片氮含量分别增加7.14%、5.24%、5.39%。相同覆膜条件下玉米冠层叶片氮含量由高到低为W₁₀₀>W₇₀>W₄₀，W₁₀₀比W₇₀的上、中、下部位叶片氮含量分别增加6.84%、6.23%、7.74%，W₇₀比W₄₀的上、中、下部位叶片氮含量分别增加4.41%、3.32%、9.49%。在M₀W₁₀₀处理中，玉米冠层叶片氮含量从上到下依次减小，上部比中部叶片氮含量增加7.44%，中部比下部叶片氮含量增加7.60%。在相同覆膜条件下，在可见光波段范围内，冠层反射率随着灌水量的增加而降低；在近红外波段范围内，冠层反射率随着灌水量的增加而增加。综上，基于随机森林的春玉米不同垂直部位叶片中氮含量估算模型均与实测结果相吻合(验证的R²>0.5)，上部叶片中氮含量估算精度最高(R²为0.63，RMSE为1.66 g/kg，RPD为1.57)，其次为中部叶片(R²为0.73，RMSE为1.66 g/kg，RPD为1.30)，精度最低的下部叶片(R²为0.00)。

Vertical distribution of nitrogen content in spring maize leaves and its hyperspectral inversion under different film mulching and irrigation levels in northwest arid region

In order to explore the vertical distribution characteristics and remote sensing inversion of nitrogen content in maize leaves under different film mulching and irrigation levels, a field experiment was carried out at the National Field Scientific National Field Scientific Observation and Research Station on Efficient Water Use of Oasis Agriculture in Wuwei of Gansu Province in 2020. A total of three irrigation levels(100%(W₁₀₀), 70%(W₇₀)and 40%(W₄₀))of spring maize irrigation requirement and three mulching treatments(non-mulching(M₀), ordinary plastic film(M₁)and degradable film(M₂))were designed. The vertical distribution of leaf nitrogen content, canopy reflectance and leaf nitrogen content of spring maize under different irrigation and film mulching conditions were measured by Kjeldahl method and hand-held ground object spectrometer. The results showed that: Under different mulching treatments, the nitrogen content in maize canopy leaves of non-mulching treatment was in the order of non-mulching treatment(M₀)>biodegradable film(M₂)>ordinary plastic film(M₁). Under the same mulching condition, the more irrigation amount, the higher leaf nitrogen content. Under the same treatment, nitrogen content in different vertical parts of maize canopy decreased from top to bottom. Under the same mulching condition, canopy reflectance decreased with the increase of irrigation amount in the range of visible light band. Within the near infrared band range, canopy reflectance increases with the increase of irrigation amount. The estimation model of leaf nitrogen content in different vertical parts of spring maize based on random forest was consistent with the actual measurement. The estimation accuracy of nitrogen content in the upper leaves were the highest, followed by the middle leaves, and the lowest in the lower leaves.