Abstract
In situ measurements with visible and near-infrared spectroscopy (vis-NIR) provide an efficient way for acquiring soil information of paddy soils in the short time gap between the harvest and following rotation. The aim of this study was to evaluate its feasibility to predict a series of soil properties including organic matter (OM), organic carbon (OC), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK) and pH of paddy soils in Zhejiang province, China. Firstly, the linear partial least squares regression (PLSR) was performed on the in situ spectra and the predictions were compared to those with laboratory-based recorded spectra. Then, the non-linear least-square support vector machine (LS-SVM) algorithm was carried out aiming to extract more useful information from the in situ spectra and improve predictions. Results show that in terms of OC, OM, TN, AN and pH, (i) the predictions were worse using in situ spectra compared to laboratory-based spectra with PLSR algorithm (ii) the prediction accuracy using LS-SVM (R2>0.75, RPD>1.90) was obviously improved with in situ vis-NIR spectra compared to PLSR algorithm, and comparable or even better than results generated using laboratory-based spectra with PLSR; (iii) in terms of AP and AK, poor predictions were obtained with in situ spectra (R2<0.5, RPD<1.50) either using PLSR or LS-SVM. The results highlight the use of LS-SVM for in situ vis-NIR spectroscopic estimation of soil properties of paddy soils.
Highlights
Paddy soil is one of the most important soil resources for humans because more than half of the world’s population takes rice, the typical farming product of paddy soils, as staple food
The aims of this study were to evaluate the feasibility of in situ visible and nearinfrared (vis-Near Infrared (NIR)) sensing for prediction of soil properties in paddy soils by (i) predicting various soil properties of paddy soils (i.e. organic carbon (OC), organic matter (OM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK) and pH using in situ vis-NIR spectroscopy; (ii) comparing the prediction accuracy between in situ vis-NIR spectra and laboratory-based spectra for paddy soils; (iii) evaluating the prediction accuracy of in situ vis-NIR measurements of soil properties by implementing a multivariate calibration algorithm, i.e., linear partial least square regression (PLSR), and a data-mining algorithm, i.e., least-square support vector machine (LS-Support vector machine (SVM))
Near Infrared (NIR) spectra are dominated by weak overtones and combinations of fundamental vibration which occurs in the MIR region, while visible spectra mainly comprise of electronic transitions [22]
Summary
Paddy soil is one of the most important soil resources for humans because more than half of the world’s population takes rice, the typical farming product of paddy soils, as staple food. In the past 30 years, due to over-fertilization, significantly declined soil pH has been found in major crop production areas and enhanced nitrogen deposition has been identified in terrestrial and aquatic ecosystems as well as in rice [2,3]. Visible and nearinfrared (vis-NIR) spectroscopy has received popularity because it is fast, less labor-intensive and cost-effective compared to conventional chemistry experiments and enables rapid measurements of various soil physical and chemical properties. Despite the success of predicting various soil properties using laboratory-based measurement with vis-NIR spectra, the pretreatment of samples (e.g. air-drying, grinding and sieving) is still tedious and time-consuming. With its faster and more effective characteristics compared to the laboratory-based spectroscopic measurement, in situ vis-NIR is a promising method in measuring and mapping soil properties of paddy fields [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
