A novel approach for nitrogen diagnosis of wheat canopies digital images by mobile phones based on histogram

Xin Qi,Wei Qin,Yufang Huang,Wen Fu,Yanan Zhao,Youliang Ye,Yulong Guo,Yang Wang

doi:10.1038/s41598-021-92431-5

Abstract

The accurate and nondestructive assessment of leaf nitrogen (N) is very important for N management in winter wheat fields. Mobile phones are now being used as an additional N diagnostic tool. To overcome the drawbacks of traditional digital camera diagnostic methods, a histogram-based method was proposed and compared with the traditional methods. Here, the field N level of six different wheat cultivars was assessed to obtain canopy images, leaf N content, and yield. The stability and accuracy of the index histogram and index mean value of the canopy images in different wheat cultivars were compared based on their correlation with leaf N and yield, following which the best diagnosis and prediction model was selected using the neural network model. The results showed that N application significantly affected the leaf N content and yield of wheat, as well as the hue of the canopy images and plant coverage. Compared with the mean value of the canopy image color parameters, the histogram could reflect both the crop coverage and the overall color information. The histogram thus had a high linear correlation with leaf N content and yield and a relatively stable correlation across different growth stages. Peak b of the histogram changed with the increase in leaf N content during the reviving stage of wheat. The histogram of the canopy image color parameters had a good correlation with leaf N content and yield. Through the neural network training and estimation model, the root mean square error (RMSE) and the mean absolute percentage error (MAPE) of the estimated and measured values of leaf N content and yield were smaller for the index histogram (0.465, 9.65%, and 465.12, 5.5% respectively) than the index mean value of the canopy images (0.526, 12.53% and 593.52, 7.83% respectively), suggesting a good fit for the index histogram image color and robustness in estimating N content and yield. Hence, the use of the histogram model with a smartphone has great potential application in N diagnosis and prediction for wheat and other cereal crops.

Highlights

The accurate and nondestructive assessment of leaf nitrogen (N) is very important for N management in winter wheat fields
There were some minor differences between the yield responses of the plants of some cultivars, i.e., the plants of ‘Huayu 198 (HY198)’ performed well even without additional N, while those of Zhongmai 1 (ZM1) and Ping’an 8 (PA8) had maximal yields at N240 and N360, respectively
The mean absolute percentage error (MAPE) and root mean square error (RMSE) of index image histogram (IIH) were lower than those of index image mean value (IIMV), and the results showed that IIH had a better application effect for different wheat cultivars

Summary

Introduction

The accurate and nondestructive assessment of leaf nitrogen (N) is very important for N management in winter wheat fields. The stability and accuracy of the index histogram and index mean value of the canopy images in different wheat cultivars were compared based on their correlation with leaf N and yield, following which the best diagnosis and prediction model was selected using the neural network model. The histogram of the canopy image color parameters had a good correlation with leaf N content and yield. Xiao et al.[25] found that the R/(R + G + B) of digital images of wheat could be highly correlated with conventional nutritional diagnostic indicators, such as chlorophyll, nitrate concentration at the base of the stem, and total N content of the plant at the jointing stage. The normalized redness intensity (NRI) and CMI (color mix index, a*R + b*G + C*b) were suitable as characteristic parameters of wheat N nutrition d iagnosis[26]

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Conclusion