Evaluation of Near Infrared Spectroscopy (NIRS) for Estimating Soil Organic Matter and Phosphorus in Mediterranean Montado Ecosystem

Francisco Moral,Marjan Jongen,João Serrano,Shakib Shahidian,José Marques Da Silva,Tiago Domingos,Julio Nogales-Bueno,Ricardo F.M Teixeira,Ana Elisa Rato,Mário De Carvalho,Luís Paixão

doi:10.3390/su13052734

Abstract

The Montado is an agro-silvo-pastoral ecosystem characteristic of the Mediterranean region. Pasture productivity and, consequently, the possibilities for intensifying livestock production depend on soil fertility. Soil organic matter (SOM) and phosphorus (P2O5) are two indicators of the evolution of soil fertility in this ecosystem. However, their conventional analytical determination by reference laboratory methods is costly, time consuming, and laborious and, thus, does not meet the needs of current production systems. The aim of this study was to evaluate an alternative approach to estimate SOM and soil P2O5 based on near infrared spectroscopy (NIRS) combined with multivariate data analysis. For this purpose, 242 topsoil samples were collected in 2019 in eleven fields. These samples were subjected to reference laboratory analysis and NIRS analysis. For NIRS, 165 samples were used during the calibration phase and 77 samples were used during the external validation phase. The results of this study showed significant correlation between NIRS calibration models and reference methods for quantification of these soil parameters. The coefficient of determination (R2, 0.85 for SOM and 0.76 for P2O5) and the residual predictive deviation (RPD, 2.7 for SOM and 2.2 for P2O5) obtained in external validation indicated the potential of NIRS to estimate SOM and P2O5, which can facilitate farm managers’ decision making in terms of dynamic management of animal grazing and differential fertilizer application.

Highlights

The Montado is an agro-silvo-pastoral ecosystem typical of the temperate Mediterranean climate (“Csa: hot-summer Mediterranean climate” according to Köppen–Geiger climate classification)
Of phosphorus, (ii) an important variability between fields, (iii) and an important spatial variability of both parameters within each experimental field
The soils in this study showed the same sensitive spectral regions for soil organic matter (SOM) and phosphorus; both calibration models used the spectral bands between 7500–7000 cm−1 (1333–1429 nm) and

Summary

Introduction

The Montado is an agro-silvo-pastoral ecosystem typical of the temperate Mediterranean climate (“Csa: hot-summer Mediterranean climate” according to Köppen–Geiger climate classification). This ecosystem covers 3.5–4.0 Mha in Portugal and Spain and is usually associated with poor soils [1]. It is estimated that 16% of cultivated land in Europe is vulnerable to desertification, this proportion may be even higher in areas with harsh climates such as the Mediterranean, which experiences frequent summer droughts [2] In this scenario, ensuring permanent land cover has been an effective strategy in management land degradation through the reduction of water, soil, and nutrient losses and increase of soil fertility [2].

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Conclusion