Laurent Bock

Near Infrared Reflectance Spectroscopy for Estimating Soil Characteristics Valuable in the Diagnosis of Soil Fertility

Soil fertility diagnostics rely not only upon measurement of available nutrients but also upon the ability of the soil to retain these nutrients. Near infrared (NIR) reflectance spectroscopy is a rapid and non-destructive analytical technique which allows the simultaneous estimation of standard soil characteristics and does not require the use of chemicals. Previous studies showed that NIR spectroscopy could be used in local contexts to predict soil properties. The main goal of our research was to build a methodological framework for the use of NIR spectroscopy on a more global scale. The specific goals of this study were (i) to identify the best spectral treatment and processing—LOCAL versus GLOBAL—regression methods, Nil to compare the performance of NIR to standard chemical protocols and (iii) to evaluate the ability of NIR spectroscopy to predict soil total organic carbon (TOC), total nitrogen (TN), clay content and cationic exchange capacity (CEC) for a wide range of soil conditions. We scanned 1300 samples representative of the main soil types of Wallonia under crop, grassland or forest. Various sample preparations were tested prior to NIR measurement. The most appropriate options were selected according to analysis of variance and multiple means comparisons of the spectra principal components. Fifteen pre-treatments were applied to a calibration set and the prediction accuracy was evaluated for GLOBAL and LOCAL modified partial least square (MPLS) regression models. The LOCAL MPLS calibrations showed very encouraging results for all the characteristics investigated. On average, for crop soil samples, the prediction coefficient of variation (CVp) was close to 15% for TOC content, 7% for TN content and 10% for clay content and CEC. The comparisons of repeatability and reproducibility of both NIR and standard methods showed that NIR spectroscopy is as reliable as reference methods. Prediction accuracy and technique repeatability will allow the use of NIR spectroscopy within the framework of the soil fertility evaluation and its replacement of standard protocols. LOCAL MPLS can be applied within global datasets, such as the International global soil spectral library. However, the performance of LOCAL MPLS is linked to the number of similar spectra in the dataset and more standard measurements are needed to characterise the least widespread soils.

Mobility and distribution of lead, cadmium, copper and zinc in soil profiles in the peri-urban market garden of Kunming, Yunnan Province, China

Five profiles located in the peri-urban market garden of Yunnan Province, China were investigated for the distribution and sequential extraction fractions (SEF) of Pb, Cd, Cu and Zn, and mobility in relation to soil properties. SEF heavy metals included acetic acid extractable (A-fraction), hydroxylamine hydrochloride extractable (B-fraction) and hydrogen peroxide and ammonium acetate extractable fractions (C + D-fraction). The results showed that: (1) Total Pb and Zn contents decreased with soil depth. The accumulation of different fractions of Pb and Zn was due to accumulation of organic carbon and Fe–Mn oxides. (2) Total Cd content increased with soil depth with the ratio of A to C horizons (RAC) < 1.0. Cd was relatively mobile within the A horizon. C + D-Cd contents were consistent with organic carbon accumulation. (3) Total Cu content in profiles 2 and 3 decreased with depth, while in other profiles it increased. A-Cu contents in the B horizon in profiles 1, 2 and 3 were higher than in the A and C horizons, and decreased with depth in profiles 4 and 5 in the transition unit. B-Cu content increased with depth, whereas C + D-Cu contents decreased. The mobility and redistribution of heavy metals in soil profiles were influenced by clay content, organic carbon and Fe–Mn oxides.

Factors affecting trace element content in periurban market garden subsoil in Yunnan Province, China

Field investigations were conducted to measure subsoil trace element content and factors influencing content in an intensive periurban market garden in Chenggong County, Yunnan Province, South-West China. The area was divided into three different geomorphological units: specifically, mountain (M), transition (T) and lacustrine (L). Mean trace element content in subsoil were determined for Pb (58.2 mg/kg), Cd (0.89 mg/kg), Cu (129.2 mg/kg), and Zn (97.0 mg/kg). Strong significant relationships between trace element content in topsoil and subsoil were observed. Both Pb and Zn were accumulated in topsoil (RTS (ratio of mean trace element in topsoil to subsoil) of Pb and Zn > or =1.0) and Cd and Cu in subsoil (RTS of Cd and Cu < or = 1.0). Subsoil trace element content was related to relief, stoniness, soil color, clay content, and cation exchange capacity. Except for 7.5 YR (yellow-red) color, trace element content increased with color intensity from brown to reddish brown. Significant positive relationships were observed between Fe content and that of Pb and Cu. Trace element content in mountain unit subsoil was higher than in transition and lacustrine units (M > T > L), except for Cu (T > M > L). Mean trace element content in calcareous subsoil was higher than in sandstone and shale. Mean trace element content in clay texture subsoil was higher than in sandy and sandy loam subsoil, and higher Cu and Zn content in subsoil with few mottles. It is possible to model Pb, Cd, Cu, and Zn distribution in subsoil physico-chemical characteristics to help improve agricultural practice.

Availability of Trace Elements for Chinese Cabbage Amended with Lime in a Periurban Market Garden in Yunnan Province, China

Pot experiments were conducted in the laboratory with lime applications to decrease trace elements in Chinese cabbage produced on soils contaminated by trace elements in the intensive periurban area in Chenggong County, Yunnan Province, China. Soil was an acidic loam developed from lacustrine-alluvial deposits. Results showed the following: (1) soil pH increased from 5.3 to 6.5, and acetic-acid-extractable trace-element contents and ratio of acetic-acid-extractable trace-element contents in treatments relative to those in the control (RRCT) decreased with increased rate of lime application. (2) Chinese cabbage more easily absorbed acetic-acid-extractable trace elements. Enrichment coefficients related to trace-element availability (AEC) of lead (Pb; mean: 3.3) and zinc (Zn; mean: 5.8) were stable, and the AEC of cadmium (Cd) was 1.8–2.0 with increased lime application rate. (3) Trace-element contents in Chinese cabbage decreased, and biomass of Chinese cabbage increased, with lime application rate. Trace-element contents in soil solution and acetic-acid-extractable trace-element contents can predict trace-element contents in Chinese cabbage, especially for soil solution. Lime quality and trace-element accumulation in Chinese cabbage should be taken into account when amendment is added to in situ soil contaminated with trace elements.

Soil affects on the cadmium and zinc contents of Chinese cabbage in Yunnan Province, China

Chinese cabbage and surface soil samples (0–20 cm) from a periurban market garden in Yunnan Province (P.R. China) were collected to determine variations of cadmium (Cd) and zinc (Zn) contents in Chinese cabbage and the influence of soil factors. Mean Cd content was 0.49 mg kg−1 dry materials (DM) in Chinese cabbage, ranging between 0.23 and 1.34 mg kg−1 DM (n = 21 samples). Mean Zn content was 51.2 mg kg−1 DM, ranging from 34.9 to 157.5 mg kg−1 DM (n = 21 samples). The soil factors best predicting Chinese cabbage Cd and Zn contents were total and available Cd and Zn contents and cation exchange capacity (CEC). Soil samples and corresponding Chinese cabbage samples were divided into two groups: soils with low pH (<6.5, n = 10) and soils with high pH (>6.5, n = 11). Positive correlation between CEC with pH > 6.5 and Cd and Zn contents in Chinese cabbage were observed. Available trace element contents and CEC explained 77% and 69% of variation of Cd and Zn contents in Chinese cabbage, respectively. AEC (enrichment coefficient related to trace element availability) and BCF (bioaccumulation factors) could be used to understand Cd and Zn accumulation in Chinese cabbage.

Looking for a Dialogue between Farmers and Scientific Soil Knowledge: Learnings from an Ethno-Geomorphopedological Study in a Philippine’s Upland Village

ABSTRACT Several ethnopedological studies highlight the plurality of soil knowledge and the complexity of soil knowledge systems. These knowledge systems are specific to social groups or communities and the dialogue between them is not easy. Local soil knowledge is often misrepresented and reduced when correspondences with soil sciences categories are established without due care. This paper results from two field studies in an upland village of Southern Philippines. The sociocultural richness and the high diversity of farming systems characterizing this local context have highlighted the importance of accounting for the diversity of soil knowledge related to local issues and sustainability. Looking for a dialogue among the plurality of perceptions, knowledge system, and typologies regarding soils implies that attention be given to knowledge construction processes. In order to facilitate an egalitarian dialogue it is also essential to explore relations between soil knowledge, farming systems, and sociocultural context. Discussion with farmers about their soils has cast doubt on the practical relevance of soil science knowledge in a context of non-industrial and non-chemical agriculture and revealed the dynamic dimension of farmers’ soil knowledge construction and the practical relevance of contextualized knowledge. In this paper, we propose methodological and epistemological thoughts to help establish a common language between scientists and farmers. We also propose to use the soil groups emerging from field characterization as a practical tool to dialogue with farmers in the field, to build a common understanding of soil heterogeneity. We consider this approach as a critical step to initiate collaborative soil studies from a practical and endogenous perspective.