Recent Advances in Chemical Sensors for Soil Analysis: A Review

The continuously rising interest in chemical sensors’ applications in environmental monitoring, for soil analysis in particular, is owed to the sufficient sensitivity and selectivity of these analytical devices, their low costs, their simple measurement setups, and the possibility to perform online and in-field analyses with them. In this review the recent advances in chemical sensors for soil analysis are summarized. The working principles of chemical sensors involved in soil analysis; their benefits and drawbacks; and select applications of both the single selective sensors and multisensor systems for assessments of main plant nutrition components, pollutants, and other important soil parameters (pH, moisture content, salinity, exhaled gases, etc.) of the past two decades with a focus on the last 5 years (from 2017 to 2021) are overviewed.

Assessment of soil quality for guided fertilization in 7 barley agro-ecological areas of China

Soil quality is the basis for the development of sustainable agriculture and may be used for evaluating the sustainability of soil management practices. Soil quality status and integrated soil quality index (SQI) in sampled 97 farmlands distributed in 7 barley agro-ecological areas of China were analyzed by using 13 soil chemical parameters. The results showed six principal components totally explained 72% variability for the 13 parameters and identified 9 parameters (includes pH, NH4+-N, NO3--N, available P, available K, exchangeable Mg, DTPA-Fe, DTPA-Cu and Cl-) with high factor loading values as the minimum data set (MDS) for assessing soil quality. Average soil quality of all farmlands is moderate (SQI = 0.62). The SQI of barley farmlands in 7 agro-ecological areas showed the following order: Inner Mongolia Plateau (0.75 ± 0.02) > Yunnan-Kweichow Plateau (0.72 ± 0.06) > Qinghai-Tibet Plateau (0.63 ± 0.08) > Yangtze Plain (0.62 ± 0.10) > Huanghuai Region (0.58 ± 0.09) > Northeast China Plain (0.56 ± 0.07) > Xinjiang Province (0.54 ± 0.07). Total 29 out of 97 farmlands in 7 areas have low SQI level (< 0.55). Hence, these farmlands require urgent attention for soil quality improvement through modification of the soil parameters in the MDS.

Assessment of the early growth of agarwood (Aquilaria crassna) seedlings under different sources of nutrients

The effect of different sources of nutrients on the growth of Aquilaria crassna seedlings was assessed by raising seedlings in polybags treated with inorganic fertilizer (IF), organic fertilizer (OF) and biofertilizer (BF) either alone or in combinations. The pots were established following a completely randomized block design with eight treatments: (T1) soil without IF, OF or BF ‒ control; (T2) soil + IF; (T3) soil + OF; (T4) soil + BF; (T5) soil + IF + OF; (T6) soil + IF + BF; (T7) soil + OF + BF; (T8) soil + IF + OF + BF each replicated five times. Plant height, stem diameter, dry weight of shoots and roots, leaf area and chlorophyll index were measured six months after planting. Soil pH (H₂O) and available soil P content were measured as soil parameters. The best growth performances (54.30 cm, 6.48 mm, 7.10 and 5.92 g·plant^–1, 435.33 cm² and 58 for plant height, stem diameter, shoot and root dry weight, leaf area and chlorophyll index, respectively) were recorded in T8, which also resulted in the highest available P content (18.96 mg·kg–1 soil). The lowest soil pH (H₂O) value (6.02) was recorded in T7 followed by T6 (6.17). The application of IF, OF and BF as a combination could be recommended to promote the growth of Aquilaria seedlings.

Evaluating Slow Pyrolysis of Parthenium hysterophorus Biochar: Perspectives to Acidic Soil Amelioration and Growth of Selected Wheat (Triticum aestivum) Varieties

Application of biochar on acidic soils may improve soil fertility and crop productivity. This study aimed to explore the relevance of parthenium biochar-induced changes in the physicochemical properties and agronomic performance of the selected wheat varieties in acidic soils. A pot trial was used in determining the effect of slow pyrolysis parthenium biochar on acidic soils and the agronomic performance of wheat varieties. A general linear model (GLM) of multivariate analysis and principal component analysis (PCA) was used to compare functional variation among soil assayed parameters with biochar dosages and years. Biochar-treated acidic soils did not show significant differences in their physical properties. However, a significant incremental trend was observed in the soil moisture content. The biochar-amended acidic soils showed noticeable differences in the soil pH, available phosphorous, and exchangeable bases (Ca, K, and Na) compared to the control. In all soil samples, a decreasing trend in the soil micronutrients was observed with an increase in the biochar amounts. The analysis also unveiled significant changes in root length, root and shoot dry biomass, and plant height of wheat varieties in response to the biochar amendments. The application of 19.5 t/ha and 23 t/ha dosages of biochar gave the maximum changes in the agronomic performance of Kekeba and Ogolcha varieties, while the minimum was obtained in the 26.5 t/ha and the control. Furthermore, PCA axis 1 accounted for 74.34% of the total variance within a higher eigenvector value (10.4076), and most of the soil parameters were positively correlated with CEC (0.29), available phosphorous (0.29), and soil pH (0.28); however, the micronutrients were negatively correlated. In conclusion, Parthenium hysterophorus biochar has the potential to amend acidic soils, and thus, the application of 16.0, 19.5, and 23 t·ha−1 biochar dosages are considered suitable to reduce the soil acidity level and improve the agronomic performance of wheat varieties. However, extensive research will be needed to determine the effects of biochar on soil properties and crop production in field conditions.

A Hybrid Bulk Algorithm to Predict Turbulent Fluxes over Dry and Wet Bare Soils

Measurements made in the Columbia River Basin (Oregon) in an area of irregular terrain during the second Wind Forecast Improvement Project (WFIP 2) field campaign are used to develop an optimized hybrid bulk algorithm to predict the surface turbulent fluxes from readily measured or modelled quantities over dry and wet bare or lightly vegetated soil surfaces. The hybrid (synthetic) algorithm combines (i) an aerodynamic method for turbulent flow which is based on the transfer coefficients (drag coefficient and Stanton number), roughness lengths, and Monin-Obukhov similarity and (ii) a modified Priestley-Taylor (P-T) algorithm with physically based ecophysiological constraints which is essentially based on the surface energy budget (SEB) equation. Soil heat flux in the latter case was estimated from measurements of soil temperature and soil moisture. In the framework of the hybrid algorithm, bulk estimates of the momentum flux and the sensible heat flux are derived from a traditional aerodynamic approach, whereas the latent heat flux (or moisture flux) is evaluated from a modified P-T model. Direct measurements of the surface fluxes (turbulent and radiative) and other ancillary atmospheric/soil parameters made during WFIP 2 for different soil conditions (dry and wet) are used to optimize and tune the hybrid bulk algorithm. The bulk flux estimates are validated against the measured eddy-covariance fluxes. We also discuss the SEB closure over dry and wet surfaces at various timescales based on the modelled and measured fluxes. Although this bulk flux algorithm is optimized for the data collected during the WFIP 2, a hybrid approach can be used for similar flux-tower sites and field campaigns.

Applying biostimulants boosts forage productivity without affecting soil biotic and abiotic parameters on a Central Coast California rangeland

There is increasing interest in using biostimulant products, such as microbial inoculants and humic substances, to help manage rangelands regeneratively. Understanding how plant and soil communities on rangelands respond to these products is therefore important. In this study, we examined the combined effects of a commercial inoculant and humic product that are currently on the market, and asked whether they influenced rangeland forage productivity and quality, soil microbial biomass and community composition, and abiotic soil parameters in Central Coastal California. We found that forage productivity and some metrics of forage quality responded positively to the foliar application of a commercial microbial inoculant and humic product, but that these benefits were not mirrored by changes belowground in the microbial community or abiotic parameters. Depending on the goals of using the products, this could be seen as a winning scenario and suggests microbial inoculants and humic products could warrant attention as a potential tool for regenerative stewardship of rangelands. While our study derives from one ranch and therefore requires confirmation of its ubiquity prior to broadscale adoption, our results provide new insights into the usefulness of this approach for managing rangeland productivity in California's Central Coast.