基于无人机多光谱植被指数的生菜全氮含量预测

Prediction of Total Nitrogen Content of Lettuce Based on UAV Multi-Spectral Vegetation Index

我国露地蔬菜种植规模庞大,生产方式高度集约化,但过量施肥等导致的水氮利用效率低下的问题较为严重。为实现露地蔬菜规模化种植中精准施肥、高效生产的目标,以露地生菜为研究对象,设无氮(N0)、低氮(N1)、高氮(N2)三个处理,通过无人机搭载多光谱相机,建立3种多光谱植被指数(NDVI、RVI和SAVI)与生菜叶绿素、生物量、吸氮量、全氮含量数据集,并构建单生育期和多生育期氮素诊断模型。结果表明:(1)在莲座期和结球期,生菜各处理NDVI、RVI和SAVI值表现出随施氮量的增加而增大,但在收获期,N1处理达到最大值。(2)在生菜结球期,NDVI与生菜的产量、吸氮量、叶绿素均存在显著相关性,其中生菜全氮含量与叶绿素在p≤0.01水平下显著相关,相关系数(R)为0.51;综合生菜多生育期,NDVI值与生菜的产量、叶绿素、吸氮量和全氮含量均在p≤0.001水平下达到极显著相关,相关系数分别为0.85、0.82、0.81和0.71。(3)通过相应数据集拟合出指数、线性、对数和幂函数4种模型关系,建立生菜多生育期植株全氮最佳预测模型:全氮=16.52ln(NDVI)+73.514;应用生菜全氮估层模型反演基地生产田块,其平均相对误差为3.22%、RMSE=0.5566、NRMSE=0.0108,说明模型估算效果均较好,通过无人机多光谱遥感对蔬菜氮素诊断具有一定的可行性。

China has a huge and intensive open-field vegetable production system.However,serious issues such as low water and nitrogen use efficiencies,as well as excessive fertilizer application,limit the sustainability of the system.To improve the efficiency of production and enhance accurate fertilization in large-scale vegetable cultivation systems,this study was conducted with open-field lettuce.Three treatments of no nitrogen(N0),low nitrogen(N1)and high nitrogen(N2)were established.An unmanned aerial vehicle(UAV)equipped with a multi-spectral camera was used to establish correlations between three multi-spectral vegetation indices(NDVI,RVI,and SAVI)and lettuce chlorophyll content,biomass,crop nitrogen uptake,and total nitrogen content.Models to predict total nitrogen content for single growth stage and multiple growth stages were developed.The results showed that:(1)during rosette and heading stages,NDVI,RVI and SAVI values increased with the amount of applied nitrogen,but that during harvest stage,maximum values occurred with the N1 treatment;(2)NDVI showed a significant correlation with lettuce yield,nitrogen uptake and chlorophyll content during heading stage;and the total nitrogen content of lettuce was significantly correlated with chlorophyll content at p<0.01 level,with a correlation coefficient(R)of 0.51.When considering multiple growth stages together,NDVI values showed a significant correlation with lettuce yield,chlorophyll content,nitrogen uptake,and total nitrogen content at p<0.001 level,with correlation coefficients of 0.85,0.82,0.81,and 0.71,respectively.(3)Relationships of exponential,linear,logarithmic and power functions were fitted to the corresponding datasets,and the best prediction model of total nitrogen content for lettuce(N%=16.52ln(NDVI)+73.514)was established in the multiple growth stages.Using the lettuce total nitrogen content prediction model to obtain modeled values of total nitrogen content for the area of a commercial production field on the same farm,the average relative error was 3.2%,RMSE=0.5566,NRMSE=0.0108,showing accurate estimation of total nitrogen content.The results show that the model had good accuracy and that it is feasible to diagnose vegetable nitrogen content using unmanned aerial vehicle multi-spectral remote sensing.