不同氮肥处理下小麦冠层和叶片光谱特征及产量分析

Relationships between Characteristics of Wheat Canopy and Leaf Spectral Reflectance and Yield under Different Nitrogen Treatments

利用遥感光谱无损、快速分析出氮肥的施用时期和施用模式,对于保护环境、产量及氮肥利用率的提高具有重要意义。利用FieldSpec 4Wide-Res Field Spectrum radiometer便携式地物光谱仪,测定了不同氮水平下小麦冠层和叶片两种模式光谱特征及红边参数变化规律;提出一个新指数——归一化差异最大指数(normalized difference maximum index,NDMI),并分析其与叶面积指数(leaf area index,LAI)、SPAD(soil and plant analyzer development)值、MDA(malondialdehyde)含量、旗叶氮含量和产量的相关性。结果表明,小麦叶片原始光谱在开花后26d起800～1 330nm区间的光谱反射率以N3(1/3底施+1/3冬前追肥+1/3拔节期追肥)处理为最高,N1处理(1/2底施+1/2冬前追肥)次之。主要原因是由冬前和拔节期两个时期均施三分之一氮肥,增强了叶片光合能力。小麦冠层原始光谱,在400～700nm波段,N2(1/2底施+1/2拔节期追肥)处理最低;在760～1 368nm波段区间,由于群体结构不同,在开花期至灌浆中期N1处理的光谱反射率最高,N3处理次之;N3处理的冠层光谱反射率在开花后26和33d最高。建议用400～700和760～1 368nm波段的冠层原始光谱数据,分别来辨别小麦旗叶含氮量的高低及施肥模式。叶片模式下一阶微分光谱在500～750nm区间出现两个"峰",通过峰的位置偏移程度和偏移时期来估测施氮的模式。在670～740nm区间冠层一阶微分光谱值在开花期最高,开花后10d的一阶微分光谱值最低。在开花期至开花后10d N1处理的一阶微分光谱值高于N3处理;灌浆中期至开花后33dN3处理的一阶微分光谱值高于N1处理。可以通过一阶微分最大值来推测小麦所处的生育期和施肥的方式及施肥时期。在开花期至灌浆中期,冠层反射率一阶导数最大值(FD-Max)N1处理最高,N3处理次之;在开花后26～33d,N3处理的群体结构较其他处理密,导致其一阶导数最大值一直最高。四个处理叶片一阶导数最大值变化趋势不如冠层显著。四个处理的反射率一阶导数最大值对应的红边位置(REPFD-Max)中,N1和N3冠层REPFD-Max在灌浆中期后偏移显著;在开花后26～33d,N3处理的群体上层结构密,叶片宽且厚,冬前追施氮肥影响REPFD-Max偏移程度。基于NDVI基础上,筛选出一个新指数——归一化差异最大指数。冠层归一化差异最大指数(CNDMI)与农化参数的相关系数高于叶片归一化差异最大指数(LNDMI),且CNDMI与产量的相关性比LNDMI显著。冠层归一化差异最大指数与旗叶氮含量、SPAD值和MDA含量有着显著的相关性,相关系数r分别为0.812 88,0.928 21和-0.722 17。综上所述,借助光谱数据和红边参数可以推测小麦含氮量的高低,所处的生育期和施氮肥的模式,进而为田间施肥管理及施肥诊断提供依据。CNDMI与小麦产量有着更好的相关性,符合我国资源卫星的光谱波段范围,具有可实际操作性。

The use of remote sensing spectroscopy in predicting the application of nitrogen fertilizer is of great importance in protecting the environment and improving f ertilizer use efficiency and grain yiled.In this study,we used the FieldSpec 4 Wide-Res Fie ld Spectrum radiometer to measure the spectral characteristics and red-edge par ameters of wheat canopies and leaves under different nitrogen applications.We proposed a new spectral index-the Normalized Difference Maximum Index.We analyzed the correlations between Normalized Difference Maximum Index and leaf area index(LAI),SPAD(Soil and Plant Analyzer Development)value,MDA(Malon dialdehyde)content,nitrogen content in flag leaf and yield.Twenty six days after flowering,the original spectrum of the spectral reflectance of leaves wa s the highest in the range of 800~1 330 nm for the N3(1/3 starter fertilizer+1/3 pre-winter topdressing+1/3 jointing stage topdressing)treatment,followe d by the N1 treatment(1/2 starter fertilizer+1/2 pre-winter topdressing).The application of one-third of nitrogen fertilizer in both pre-winter and jointi ng stages enhanced the photosynthetic capacity of the leaves.The original spec trum of the spectral reflectance of canopies in the range of 400~700 nm was the lowest for the N2(1/2 starter fertilizer+1/2 jointing stage topdressing)treat ment.The spectral reflectance of the N1 treatment was the highest in the range of 760~1 368 nm followed by the N3 freatment.The canopy spectral reflectance of the N3 treatment was the highest at 26 d and 33 d after flowering.It is recommended to use the canopy r aw spectral data in the ranges of 400~700 nm and 760~1 368 nm to measure flag leaf nitrogen content and to decide fertilizer application model.Two peaks wer e found in the range of 500~750 nm in the first-order differential spectrum of the leaf.The model of nitrogen application could be estimated by the degree of positional shift of the peaks and the offset periods.Of the canopy,the f irst-order differential spectral value in the range of 670~740 nm was the hi ghest in flowering stage,and the lowest at 10th day after flowering.The firs t-order differential spectral value of the N1 treatment was higher than that of the N3 treatment for the first 10 days after flowering,but lower than the N3 treatment at late grain filling stage.Our results indicated that the first-or der differential maximum value can be used to predict the growth stages and effi cient fertilizer application.From flowering stage to mid-grain-filling stage,the highest first-order derivative(FD-Max)of canopy reflectance was the h ighest in the N1 treatment,followed by the N3 treatment 26 to 33d after flowering,the population structure of the N3 treatment is denser than the other treatments,resulting in the highest first-order derivation maximum.Less differences amo ng different treatments were found on the maximum value of the first derivative of leaves.The red boundary position(REP FD-Max)of the N1,N3 canopy s hifted significantly after the mid-grain-filling stage.26 d to 33 d after fl owering,the N3 treatment ended up with a dense upper structure and wide and th ick leaves.Applying nitrogen fertilizer before winter affected the REP FD-Max migration.Based on the NDVI,we have developed a new index-the Normali zed Difference Maximum Index(NDMI).The maximum canopy normalized index(CNDMI)showed a better correlation with agrochemical parameters than the leaf maximum normalized index(LNDMI).Similarly,a better correlation was also found betw een CNDMI and yiled.The maximum index of normalized canopy differences was sig nificantly correlated with nitrogen content(r=0.81),SPAD value(r=0.92)and MDA content(r=-0.72)in flag leaves.In summary,the spectral data and red edge parameters can be used to predict nitrogen levels in leaves,growth stages and the model of nitrogen fertilizer application.It provides a basis for filed fertilization management and fertilization diagnosis.CNDMI has a better correlation with wheat yiled.CNDMI with a sp ectrum band falling into China’s resource satellites can be practically used in the diagnosis and management of fertilizer application.