Source : Soil and Tillage Research, 194(2019) 104345. https://doi.org/10.1016/j.still.2019.104345 

Abstract

[Near infrared spectroscopy (NIRS) has been widely used as a rapid, cost-effective and nondestructive technique to predict many soil properties, including soil water content (SWC). Few studies, however, use NIRS to assess how variations in soil physical properties affect those in SWR. In this study, we explored the ability of NIRS to assess effects of soil tillage and fertilization on SWR properties. The study was performed on silty soil samples with 10.4 g kg-1 of organic carbon content and pH of 5-6.5. Undisturbed soil blocks were collected from an experimental station located in Brittany, France. In 2012, the field was designed as a split-plot by combining two tillage practices (conventional tillage (CT) and shallow tillage (ST)) with two types of fertilization (mineral and organic). Six undisturbed soil blocks were sampled from each of two depths (0-15 cm and 15-25 cm) and each agricultural practice. Soil was sampled on two dates: before starting the treatment (2012) and after 5 years of tillage (2017). From each soil block, four aggregates 3-4 cm in wide and 5-6 cm long were collected. The whole aggregates were set at a number of matric potentials, from saturation up to permanent wilting point (pF=4.2). At given pressure head, soil samples were scanned in triplicate to acquire reflectance spectra from 400-2500 nm using a handheld spectrometer (ASD Fieldspec®). We focused on the absorption band near 1920 nm and used a new NIRS index based on the full width at half maximum of this band, called SWSI. Our results showed a linear relation between SWSI and SWC (R² > 0.99), regardless of the soil sample. Moreover, the slope and intercept of this linear relation were significantly correlated with water holding capacity (WHC) and soil physical quality. Using these parameters, we found that SWR properties were significantly greater under CT than under ST. This significant effect was observed only from 15-25 cm. Overall, soil physical quality was greater under CT than under ST but neither differed significantly from that at the initial state. Fertilization had no significant effect on SWR properties. Nevertheless, cattle manure improved the physical quality of soils under CT. The results obtained with the NIRS approach agreed with those of conventional approaches. More importantly, our results show that the slope and intercept of the linear relation between the NIRS index SWSI and SWC offer a way to summarize and assess effects of agricultural practices on SWR properties and soil structural quality.]

Keywords: NIRS, NIRS index, SWSI, soil water retention, soil physical quality, tillage, fertilization.

Projection dans le plan, d’abscisse l’ordonnée à l’origine et d’ordonnée la valeur absolue de la pente (AvS), des valeurs moyennes de l’état initial (T0) et des différentes combinaisons de fertilisation et de travail du sol après 5 années d’exercice.  Copyright Soltani et al. (2019)