A New Coupled Elimination Method of Soil Moisture and Particle Size Interferences on Predicting Soil Total Nitrogen Concentration through Discrete NIR Spectral Band Data

Wei Yang,Weichao Wang,Minzan Li,Peng Zhou

doi:10.3390/rs13040762

Abstract

Rapid and accurate measurement of high-resolution soil total nitrogen (TN) information can promote variable rate fertilization, protect the environment, and ensure crop yields. Many scholars focus on exploring the rapid TN detection methods and corresponding soil sensors based on spectral technology. However, soil spectra are easily disturbed by many factors, especially soil moisture and particle size. Real-time elimination of the interferences of these factors is necessary to improve the accuracy and efficiency of measuring TN concentration in farmlands. Although, many methods can be used to eliminate soil moisture and particle size effects on the estimation of soil parameters using continuum spectra. However, the discrete NIR spectral band data can be completely different in the band attribution with continuum spectra, that is, it does not have continuity in the sense of spectra. Thus, relevant elimination methods of soil moisture and particle size effects on continuum spectra do not apply to the discrete NIR spectral band data. To solve this problem, in this study, moisture absorption correction index (MACI) and particle size correction index (PSCI) methods were proposed to eliminate the interferences of soil moisture and particle size, respectively. Soil moisture interference was decreased by normalizing the original spectral band data into standard spectral band data, on the basis of the strong soil moisture absorption band at 1450 nm. For the PSCI method, characteristic bands of soil particle size were identified to be 1361 and 1870 nm firstly. Next, normalized index Np, which calculated wavelengths of 1631 and 1870 nm, was proposed to eliminate soil particle size interference on discrete NIR spectral band data. Finally, a new coupled elimination method of soil moisture and particle size interferences on predicting TN concentration through discrete NIR spectral band data was proposed and evaluated. The six discrete spectral bands (1070, 1130, 1245, 1375, 1550, and 1680 nm) used in the on-the-go detector of TN concentration were selected to verify the new method. Field tests showed that the new coupled method had good effects on eliminating interferences of soil moisture and soil particle size.

Highlights

In order to research the effect of soil moisture on discrete NIR spectral band data, the soil particle size was eliminated by artificial sieving
Taking the soil absorbance at 1450 nm as an example, when the soil moisture content increased from 3.18% to 14.16%, the soil absorbance increased from 0.79 to 1.11, and the soil spectral absorbance increased by 40.51%
The results showed that the new coupled elimination method could effectively reduce the interferences of soil particle size and moisture on the prediction of total nitrogen (TN) concentration

Summary

Introduction

Excessive application of commercial fertilizers has been cited as a source of contamination of surface and groundwater [1,2,3,4]. As one of the important parts of precision agriculture (PA), based on the needs of the plant and the soil nutrients state, variable rate (VR) fertilization can reduce the overuse of manure in the farmlands to protect the soil and environment [5,6,7,8]. Real-time, and accurate acquisition of high-resolution soil parameter information is the basis of applying VR fertilization operation [9]. As the main nutrient for plant and soil, soil total nitrogen (TN) is one of the key factors that determine plant nutrient levels and soil fertility [10,11]. The estimation of TN concentration status is crucial from agricultural and environmental points of view [12,13,14]

Objectives

Methods

Results

Discussion

Conclusion