Measured Soil pH Research Articles

Rapid colorimetric methods for analysis of pH, extractable aluminium and Colwell phosphorus in soils

Context Analytical procedures and technologies for soil analyses can be prohibitively expensive for small laboratories and researchers in developing countries. There is a need for low cost and high-throughput methods for assaying pH, extractable aluminium and phosphorus when conducting field trials on acid soils. Aims We investigated methods to develop rapid yet inexpensive colorimetric assays for the assay of pH, extractable aluminium and Colwell phosphorus in soil extracts. Methods We developed a colorimetric method to measure soil pH enabling pH to be quantified in a high-throughput assay. Similarly, two existing methods for extractable aluminium and Colwell P were modified for high throughput assays also using microtiter plates. Key results All three methods yielded linear relationships when using absorbance to quantify the parameters with the high throughput methods. Furthermore, there was a strong correlation between pH values of the soil samples obtained with the colorimetric assay and pH values measured with a glass electrode. Conclusions We demonstrated that the rapid assays for all three methods can be implemented to characterise field sites through the mapping of distributions for extractable Al, Colwell P and pH. Implications The high-throughput methods described here will be useful for researchers who conduct field trials to map variations in soil pH, soluble Al and Colwell P. Although the focus of the current work was on acid soils, the colorimetric pH and Colwell P methods can also be applied to non-acid soils.

Оцінка вимірювання pH водного розчину та електролітними методами в окультурених ґрунтах Непалу

Soil pH is most routinely measured parameter among all others in soil chemistry laboratory. There are various methods developed for pH measurement, although we using only distilled water from the beginning. In Nepal, there do not have database for showing performance of the methods. The three methods namely; H2O, KCl and CaCl2 with their soil:solution ratios (1:1, 1:2 and 1:2.5) were used. The total 115 samples were collected randomly at a depth of 0-20 cm from the hill and terai regions of Nepal. The collected samples were analyzed following mentioned methods, separately. The various statistical tests (F-test, mean separation, correlation, and regression model) were performed for comparison. Moreover, model validation parameters were also calculated for relating H2O with electrolyte method. The three models linear, quadratic and cubic were used for this task. The result revealed the effect of methods on pH measurement was significantly different in the entire ratio. The pHH2O was 0.57, 0.56 and 0.67 units higher than pHCaCl2 in 1:1, 1:2 and 1:2.5 ratios, respectively. Whereas, 1.24, 0.99 and 0.95 units higher than pHKCl in respective ratio. Moreover, regarding timing to reach stable during measurement were in the order pHH2O (89.44 sec) > pHCaCl2 (54.29 sec) > pHKCl (33.08 sec). Similarly, relating modeling quadratic and cubic model showed nearly equal performance (lower RMSE, MAE and higher R2 and d) for predicting pHCaCl2 and pHKCl from the pHH2O in each soil solution ratio. The determined database can be useful for comparing used three different methods of soil pH measurement under Nepalese context.

Nitrapyrin-based nitrification inhibitors shaped the soil microbial community via controls on soil pH and inorganic N composition

Nitrate is a major source of N nutrition for plant production, but it is prone to loss from an arable soil via leaching and denitrification. Chemicals that inhibit biological NO3− production, known as nitrification inhibitors or N stabilizers, have been widely applied to slow nitrification and therefore minimize soil NO3− accumulation. However, the impacts of nitrification inhibitors on microbes other than nitrifying bacteria and archaea are largely unknown. Here we examined the diversity, abundance, and composition of the soil microbial community following the addition of two nitrification inhibitors, both containing nitrapyrin as the active ingredient but different solvents or emulsifying agents. Two silt loam soils of different acidities were used for a two-month microcosm incubation. Each soil was subjected to six treatments of soil alone, soil with the addition of each nitrification inhibitor at 4 μg nitrapyrin g−1 soil, soil with the addition of ammonium sulfate at 60 μg N g−1 soil, and soil with the addition of both ammonium sulfate and each nitrification inhibitor. Periodically during the incubation, soil NH4+ and NO3− were quantified. In addition to measurements of soil pH and potential rate of nitrification at the end of incubation, 16S rRNA and ITS marker gene libraries were prepared for high throughput sequencing. Our data showed clear targeted effects of nitrapyrin-based nitrification inhibitors on nitrification as well as ammonia oxidizing bacteria and archaea; and these effects were little affected by different solvents for dissolving or emulsifying nitrapyrin. However, the use of a nitrification inhibitor generated some non-target effects on the soil microbial community. Microbes of copiotrophic life strategy, e.g., Alphaproteobacteria, Betaproteobacteria, and Ascomycota were promoted, whereas microbes of oligotrophic life strategy, e.g., Acidobacteria, Planctomycetes, and Basidiomycota were suppressed. The degree of non-target effects appeared to be soil and microbial domain specific, with stronger effects in the acidic soil than neutral soil on the bacterial community and yet comparable effects on the fungal community between the two soils. Spearman's rank correlations suggested that non-target effects of nitrification inhibitors were primarily attributed to changes in soil pH as well as soil inorganic N composition, i.e., the percentage of ammonium (or nitrate) in inorganic N. Further research is needed for better understanding soil microbial ecology under high NH4+ concentrations so that the management practice of keeping more NH4+ in soil can be well adopted to improve crop N use efficiency and soil sustainability.

Impacts of land use and salinization on soil inorganic and organic carbon in the middle-lower Yellow River Delta

Soil inorganic carbon (SIC) is an important reservoir of carbon (C) in arid, semi-arid, and semi-humid regions. However, knowledge is incomplete on the dynamics of SIC and its relationship with soil organic C (SOC) under different land use types in the semi-humid region, particularly in coastal zones impacted by soil salinization. We collected 170 soil samples from 34 profiles across various land use types (maize-wheat, cotton, paddy, and reed) in the middle-lower Yellow River Delta (YRD), China. We measured soil pH, electrical conductivity (EC), water-soluble salts, and SOC and SIC contents. Our results showed significant differences in both SOC and SIC among land use types. The dry cropland (maize-wheat and cotton) soils had significantly higher SOC and SIC densities (4.71 and 15.46 kg C m–2, respectively) than the paddy soils (3.28 and 14.09 kg C m–2, respectively) in the 0–100 cm layer. Compared with paddy soils, reed soils contained significantly higher SOC (4.68 kg C m–2) and similar SIC (15.02 kg C m–2) densities. There was a significant positive correlation between SOC and SIC densities over a 0–100 cm soil depth in dry cropland soils, but a negative relationship in the paddy soils. On average, SOC and SIC densities under maize-wheat cropping were 15% and 4% lower, respectively, in the salt-affected soils in the middle-lower YRD than the upper YRD. This study indicated that land use types had great influences on both SOC and SIC and their relationship, and salinization had adverse effect on soil C storage in the YRD.

Microplastics Increase Soil pH and Decrease Microbial Activities as a Function of Microplastic Shape, Polymer Type, and Exposure Time

Microplastic pollution is a topic of increasing concern, especially since this issue was first addressed in soils. Results have so far been variable in terms of effects, suggesting that there is substantial context-dependency in microplastic effects in soil. To better define conditions that may affect microplastic-related impacts, we here examined effects as a function of microplastic shape and polymer type, and we tested if effects on soil properties and soil microbial activities change with incubation time. In our laboratory study, we evaluated twelve different secondary microplastics representing four microplastic shapes: fibers, films, foams and fragments; and eight polymer types: polyamide (PA), polycarbonate (PC), polyethylene (PE), polyester (PES), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyurethane (PU). We mixed the microplastics with a sandy soil (0.4% w/w) and incubated at 25°C for 31 days. Then, we collected soil samples on the 3rd, 11th, and 31st day, and measured soil pH, respiration and four enzyme activities (soil enzymatic activities). Our results showed that microplastics could affect soil pH, respiration and enzymatic activities depending on microplastic shape and polymer type, effects that were altered with incubation time. Soil pH increased with foams and fragments and overall decreased in the first days of incubation and then increased. Soil respiration increased with PE foams and was affected by the incubation time, declining over time. Overall, acid phosphatase activity was not affected by shape or polymer type. β-D-glucosidase activity decreased with foams, cellobiosidase activity decreased with fibers, films and foams while N-acetyl-β-glucosaminidase activities decreased with fibers and fragments. Enzymatic activities fluctuated during the incubation time, except N-acetyl-β-glucosaminidase, which showed a declining trend with incubation time. Enzymatic activities were negatively correlated with soil pH and this relationship was less strong when microplastics were added to the soil. Our study adds to the evidence that research should embrace the complexity and diversity of microplastics, highlighting the role of microplastic shape and polymer type in influencing effects; additionally, we show that incubation time is also a parameter to consider, as effects are dynamic even in the short term.

Design and development of an Irrigation Mobile Robot

Water plays a significant role among other existing natural resources. The daily demand for water supplies is increasingly on the rise as the population grows. To minimize the consumption of water in irrigation, several proposals were suggested. The currently existing system known as the automated irrigation system for effective water resource use with the prediction of the weather (AISWP) functions with a single farm that lacks the reliability in the precision of weather forecasting. So, a robot-based irrigation system has been proposed to improve the performance of the system. To minimize the water usage for crops, an automated irrigation system has been developed which irrigates the field in acres. An additional characteristic of the system has also been given for the soil pH measurement to allow the use of fertilizers accordingly. The solar-powered robot is managed wirelessly by a designated application. The robot is attached with various sensors and with a highresolution camera that tests crop conditions and senses the soil state. The application has been created to provide information about the soil’s condition such as temperature level, humidity level, water level, and level of nutrients to the PC/Laptop with the real-time values via the GSM module.

Dissection of the Contributing Factors to the Variable Response of Crop Yield to Surface Applied Lime in Australia

Modern agricultural farming systems acidify the soil profile due to application of fertilisers with acidifying properties. In most parts of Australia, lime has been used to improve agricultural soil conditions and restore its productive potential. The observed response of crop yield to applied lime often varies with soil type, acidity profile and seasonal conditions, so it is difficult to specify the expected yield response in a given situation. We conducted a meta-analysis of 86 agricultural field trials from Western Australia (WA), New South Wales (NSW) and Victoria (VIC) where various rates of lime had been applied to the soil surface and crop yield (wheat, barley, canola, lupin or field pea) measured for a number of years after the initial application. Information from the meta-analysis was then paired with output from a crop simulation model, where the water-limited yield potential was estimated for both a neutral and acidified soil profile. The average increase in yield to applied lime across all locations and crops was 12%, but the response ranged from 0 to 185%. A trend was observed, where sites with topsoil pH (CaCl2) < 5 and subsoil pH < 4.5 had the greater benefit to liming. Soil type had little effect on the percentage yield increase. Overall, responses to applied lime were most likely when the yield of the trial site was at 50% of water-limited yield potential (or less), the quantity of lime applied was greater than 2.5 t ha−1 and the time since lime had been applied was greater than three years (with the maximum response occurring from four and sometimes up to eight years after liming). Therefore, soil pH measurements, combined with an assessment of actual yield relative to potential yield, provide the best guide to the response to surface applied lime and this response is likely to take more than four years to be realised.

Pemetaan Status pH Tanah dan C-Organik Tanah Sawah Tadah Hujan di Kecamatan Panai Tengah Kabupaten Labuhanbatu

<p>The production center for lowland rice in Labuhanbatu Regency in the last three years, precisely in Panai Tengah District, North Sumatra Province, has decreased production since 2018. One of the causes is a decrease in production because the nutrient content in the soil has decreased and added by fertilizer application by farmers. Lowland rice is still common due to limited data on land resources. This study aims to evaluate the land through the identification of classes, distribution and status of soil pH and C-Organic nutrients as well as organic matter in agricultural land in Central Panai District, and to determine the level of soil damage in each Land Mapping Unit. This research was carried out in Central Panai District with elevation. place 11 meters above sea level. Soil analysis was carried out in the integrated science laboratory of the Faculty of Science and Technology, Labuhanbatu University from January 2021 to March 2021, while the method in this study was a semi-detailed grid survey with the density of observation of 1 sample per 250 meters. Soil pH measurements used the pH-H<sub>2</sub>O and C-organic methods of soil using the Walkley and Black method. Furthermore, the results of the analysis of nutrient rainfed lowland soils are interpreted into a nutrient status map. The results showed that the pH content of rainfed lowland soil in Panai Tengah District, Labuhanbatu Regency was classified as very acidic and slightly acidic, while based on the soil nutrient status, namely C-organic and organic matter in the low category, so as to increase the productivity of rainfed lowland soil with soil organic matter content.up to 3% required organic fertilizer in the Central Panai District, Labuhanbatu Regency.</p>

Long-term effects of atmospheric deposition on British plant species richness

The effects of atmospheric pollution on plant species richness (nsp) are of widespread concern. We carried out a modelling exercise to estimate how nsp in British semi-natural ecosystems responded to atmospheric deposition of nitrogen (Ndep) and sulphur (Sdep) between 1800 and 2010. We derived a simple four-parameter equation relating nsp to measured soil pH, and to net primary productivity (NPP), calculated with the N14CP ecosystem model. Parameters were estimated from a large data set (n = 1156) of species richness in four vegetation classes, unimproved grassland, dwarf shrub heath, peatland, and broadleaved woodland, obtained in 2007. The equation performed reasonably well in comparisons with independent observations of nsp. We used the equation, in combination with modelled estimates of NPP (from N14CP) and soil pH (from the CHUM-AM hydrochemical model), to calculate changes in average nsp over time at seven sites across Britain, assuming that variations in nsp were due only to variations in atmospheric deposition. At two of the sites, two vegetation classes were present, making a total of nine site/vegetation combinations. In four cases, nsp was affected about equally by pH and NPP, while in another four the effect of pH was dominant. The ninth site, a chalk grassland, was affected only by NPP, since soil pH was assumed constant. Our analysis suggests that the combination of increased NPP, due to fertilization by Ndep, and decreased soil pH, primarily due to Sdep, caused an average species loss of 39% (range 23–100%) between 1800 and the late 20th Century. The modelling suggests that in recent years nsp has begun to increase, almost entirely due to reductions in Sdep and consequent increases in soil pH, but there are also indications of recent slight recovery from the eutrophying effects of Ndep.

The complexity of wood ash fertilization disentangled: Effects on soil pH, nutrient status, plant growth and cadmium accumulation

Wood ash is a by-product from energy production that can be recycled to forests to regain nutrients and prevent acidification. However, low concentrations of nitrogen (N) in wood ash may reduce its potential positive effect on plant growth. In addition, wood ash can have a high content of toxic heavy metals such as Cd, thus there are concerns that it may increase Cd accumulation in plants.We grew Deschampsia flexuosa (Wavy hair-grass) in pots in acidic nutrient poor forest soil fertilized with different concentrations of wood ash (corresponding to field application of 0, 1.1, 3.3, 11 and 33 t ha−1). Additionally, to disentangle the pH and nutrient effects of wood ash application, we included treatments with either CaO, to simulate pH effects of wood ash, or potassium (K) + phosphorus (P) fertilizer to mimic the nutrient effects. After 4.5 months of growth, we measured soil pH, plant biomass, Cd accumulation in shoots and N concentration in the various compartments of the system.Wood ash addition stimulated plant growth, whereas CaO and K + P addition resulted in more moderate increases in biomass. Despite the low concentration of N in the wood ash, plant uptake of N increased in wood ash amendments, probably because wood ash stimulated mineralization of soil organic N. Plant Cd content significantly increased at the highest dose of wood ash.Our results suggest that addition of wood ash significantly stimulates plant growth due to the combined effect of increased pH, elevated nutrient levels and increased N mineralization. Furthermore, despite the rather high Cd content in used wood ash (16.3 mg kg−1), wood ash amendments up to 11 t ha−1 did not result in significantly increased plant uptake of Cd.

Spatial and Temporal Variability of Soil Redox Potential, pH and Electrical Conductivity across a Toposequence in the Savanna of West Africa

Soil redox potential is an important factor affecting soil functioning. Yet, very few agronomy studies included soil redox potential in relation to soil processes. The objective of this study was to evaluate the spatial and temporal variation in soil redox potential and to determine the soil parameters affecting its variation. Soil redox potential, soil moisture, soil temperature, pH and bulk electrical conductivity were measured in upland rice fields during two growing seasons at six positions along an upland–lowland continuum, including two positions at the upland, two at the fringe and two at the lowlands in central Côte d’Ivoire (West Africa). The measurements were made at the following soil depths: 3, 8, 20 and 35 cm. Soil redox potential varied between 500 and 700 mV at the upland positions, 400 and 700 mV at the fringe positions and 100 and 750 mV at the lowland positions, and increased with soil depth. Variations in soil redox potential were driven by soil moisture, bulk electrical conductivity and soil organic carbon. We concluded that for proper interpretation of soil redox potential, sampling protocols should systematically include soil pH, moisture and bulk electrical conductivity measurements.

National Scale 3D Mapping of Soil pH Using a Data Augmentation Approach

Understanding the spatial variation of soil pH is critical for many different stakeholders across different fields of science, because it is a master variable that plays a central role in many soil processes. This study documents the first attempt to map soil pH (1:5 H2O) at high resolution (100 m) in New Zealand. The regression framework used follows the paradigm of digital soil mapping, and a limited number of environmental covariates were selected using variable selection, before calibration of a quantile regression forest model. In order to adapt the outcomes of this work to a wide range of different depth supports, a new approach, which includes depth of sampling as a covariate, is proposed. It relies on data augmentation, a process where virtual observations are drawn from statistical populations constructed using the observed data, based on the top and bottom depth of sampling, and including the uncertainty surrounding the soil pH measurement. A single model can then be calibrated and deployed to estimate pH a various depths. Results showed that the data augmentation routine had a beneficial effect on prediction uncertainties, in particular when reference measurement uncertainties are taken into account. Further testing found that the optimal rate of augmentation for this dataset was 3-fold. Inspection of the final model revealed that the most important variables for predicting soil pH distribution in New Zealand were related to land cover and climate, in particular to soil water balance. The evaluation of this approach on those validation sites set aside before modelling showed very good results (R2=0.65, CCC=0.79, RMSE=0.54), that significantly out-performed existing soil pH information for the country.

Influence of natural factors on the biodegradation of simple and composite bioplastics based on cassava starch and corn starch

The massive use of petrochemical plastics has become a real problem for health and the environment. This problem is related to the non-biodegradable character of a great majority of these plastics and to the presence of certain chemical substances sometimes toxic in their internal structures. The development of biodegradable and less dangerous plastics thus represents an alternative to the petrochemical plastics. Two types of bioplastics were elaborated from cassava starch and corn starch. The simple bioplastics were obtained from starch only. The composite bioplastics were obtained by adding a natural ingredient extracted from the species Cola cordifolia to the starch. The biodegradability was assessed through burial tests in soil. The biodegradation was confirmed by the burial soil pH measurement. The burials in soil were also carried out taking into account the influence of abiotic (humidity, temperature) and biotic (enrichment in microorganisms) factors. The study showed that biodegradability of bioplastics is linked to the nature of the starch used. The simple cassava-based bioplastic degraded faster than those based on corn. The addition of the Cola cordifolia's natural ingredient, significantly improves the biodegradability of composite bioplastics compared to simple bioplastics. However, variability of environmental factors can improve or disadvantage biodegradability. Humidity promotes the biodegradability of bioplastics, especially composite bioplastics, up to a maximum rate of 15%. Enrichment in microorganisms is unfavourable beyond 10% enrichment for simple corn bioplastic and beyond 20% enrichment for composite and simple cassava-based bioplastics. The burial temperatures above 30 °C lead to a decrease in the biodegradability of bioplastics.

Predicting soil pH changes in response to application of urea and sheep urine.

Volatilization of NH3 following urea application or livestock urine deposition can result in significant loss of N to the environment. Urea hydrolysis to NH4 + results in an increase in pH, which in turn promotes transformation of NH4 + to NH3 . Accurately predicting changes in soil pH following urea (or urine) application will allow successful simulation of NH3 volatilization. The magnitude of the pH change depends on the soil's pH buffering capacity (pHBC). However, as actual pHBC values are not generally available, pHBC proxies (e.g., cation exchange capacity) have been used in modeling studies. In a 34-d laboratory incubation study, we measured soil pH and mineral N (NH4 + and NO3 - ) following a large application of urea (800mg N kg-1 soil) to four soils with a range of pHBC values. In a second incubation, pH changes and mineral N dynamics were monitored in soil treated with sheep urine (773mg N kg-1 soil) in the absence and presence of the nitrification inhibitor dicyandiamide. In both incubations, pH changes associated with urea hydrolysis and subsequent nitrification of NH4 + were predicted well using measured pHBC data. Our results confirmed that pHBC is base-type dependent (values greater when measured using KOH than NH4 OH). Soil pHBC is easily measured, and the use of a measured value (determined using NH4 OH) can improve model simulations of pH in the field and, potentially, lead to improved estimates of NH3 loss from animal-deposited urine patches and urea-treated soil.

The effects of land degradation on plant community assembly: Implications for the restoration of the Tibetan Plateau

AbstractUnderstanding how biotic and abiotic filters drive plant distributions is critical for informing restoration efforts of degraded lands. However, it remains unclear whether or not it is possible to develop efficient restoration strategies that are based on field investigations? Here, we conducted a field‐based investigation along a land degradation gradient on the Tibetan Plateau. Along this gradient, we compared species composition, Pianka's niche overlap, and total aboveground biomass among grasses, sedges, legumes, and forbs. We also used Faith's (1992) phylogenetic diversity index (PD) and the net relatedness index (NRI) to measure community phylogenetic patterns. To understand the effects of abiotic filtering, we measured soil pH, moisture, electrical conductivity, total soil organic carbon, microbial biomass carbon, and microbial biomass nitrogen. Our results show that grasses replaced sedges and mesoxerophytes replaced mesohydrophytes with increasing land degradation. We also found that niche overlap declined with increasing degradation intensity. Furthermore, grass biomass increased, while sedges and legumes decreased, and forb biomass showed a hump‐shaped relationship with degradation intensity. In addition, the communities transitioned from a clustered to a more random phylogenetic pattern. Soil conditions changed from acidic to alkaline and from fertile to harsh (p < .05). High niche overlap indicates a high biotic filtering at lightly degraded land where abiotic filtering is less stressful. However, when degradation is intense, abiotic filtering is apparent, as indicated by low levels of niche overlap. Overall, we suggest that distantly related, arid tolerant and hardy plants, and soil reclamation should be considered in degraded alpine lands restoration.

Evaluation of bacterial glycerol dialkyl glycerol tetraether and <sup>2</sup>H–<sup>18</sup>O biomarker proxies along a central European topsoil transect

Abstract. Molecular fossils, like bacterial branched glycerol dialkyl glycerol tetraethers (brGDGTs), and the stable isotopic composition of biomarkers, such as δ2H of leaf wax-derived n-alkanes (δ2Hn-alkane) or δ18O of hemicellulose-derived sugars (δ18Osugar), are increasingly used for the reconstruction of past climate and environmental conditions. Plant-derived δ2Hn-alkane and δ18Osugar values record the isotopic composition of plant source water (δ2Hsource-water and δ18Osource-water), which usually reflects mean annual precipitation (δ2Hprecipiation and δ18Oprecipiation), modulated by evapotranspirative leaf water enrichment and biosynthetic fractionation (εbio). Accuracy and precision of respective proxies should be ideally evaluated at a regional scale. For this study, we analysed topsoils below coniferous and deciduous forests as well as grassland soils along a central European transect in order to investigate the variability and robustness of various proxies and to identify effects related to vegetation. Soil pH values derived from brGDGTs correlate reasonably well with measured soil pH values but are systematically overestimated (ΔpH = 0.6±0.6). The branched vs. isoprenoid tetraether index (BIT) can give some indication whether the pH reconstruction is reliable. Temperatures derived from brGDGTs overestimate mean annual air temperatures slightly (ΔTMA=0.5 ∘C ± 2.4). Apparent isotopic fractionation (εn-alkane/precipitation and εsugar∕precipitation) is lower for grassland sites than for forest sites due to signal damping; i.e. grass biomarkers do not record the full evapotranspirative leaf water enrichment. Coupling δ2Hn-alkane with δ18Osugar allows us to reconstruct the stable isotopic composition of the source water more accurately than without the coupled approach (Δδ2H = ∼-21 ‰ ± 22 ‰ and Δδ18O = ∼-2.9 ‰ ± 2.8 ‰). Similarly, relative humidity during daytime and the vegetation period (RHMDV) can be reconstructed using the coupled isotope approach (ΔRHMDV=∼-17±12). Especially for coniferous sites, reconstructed RHMDV values as well as source water isotope composition underestimate the measured values. This can likely be explained by understorey grass vegetation at the coniferous sites contributing significantly to the n-alkane pool but only marginally to the sugar pool in the topsoils. Vegetation-dependent variable signal damping and εbio (regarding 2H between n-alkanes and leaf water) along our European transect are difficult to quantify but likely contribute to the observed underestimation in the source water isotope composition and RH reconstructions. Microclimate variability could cause the rather large uncertainties. Vegetation-related effects do, by contrast, not affect the brGDGT-derived reconstructions. Overall, GDGTs and the coupled δ2Hn-alkane–δ18Osugar approach have great potential for more quantitative paleoclimate reconstructions.

The within-field spatial variation in rice grain Cd concentration is determined by soil redox status and pH during grain filling

Rice is a major dietary source of the toxic trace metal Cd. Large variation in Cd concentration in rice grain was documented by global and regional surveys, with this variation difficult to predict from soil tests. Even within individual fields, a large spatial variation is often observed but the factors controlling this within-field spatial variation are still poorly understood. In the present study, we used field- and laboratory-based experiments to investigate the effects of a gentle slope gradient within paddy fields (a common farmers’ practice to facilitate water flow from the inlet to the outlet) on Cd availability and grain Cd concentrations in unlimed and limed soils. In our field experiments, a gentle slope resulted in large spatial variations in soil redox potential (Eh) and pH upon soil drainage during rice grain filling. As a result of these variations in Eh and pH, there was a 6- to 7-fold spatial within-field variation in grain Cd concentrations, which were the highest in the irrigation inlet area associated with higher Eh values and the lowest in the outlet area with lower Eh values. Our results highlight that soil Eh, and more importantly, field-moist soil pH during grain filling determine grain Cd concentration and accordingly, incorporating measurements of soil redox status (or water content) and pH of field moist soils (rather than air-dried soils) during grain filling may improve the prediction of grain Cd concentrations. Delaying drainage during grain filling or increasing soil pH by liming is effective in reducing grain Cd accumulation.

Soil PH Measurement Based on Compressive Sensing and Deep Image Prior

Soil quality is vital in agriculture. People often use sensor networks to obtain the soil data of a piece of land. Sometimes, people detect soil data by using one-dimensional (1-D) ultrawideband (UWB) signals, which is too energy consuming. Hence, we want an energy-saving model for this condition. Compressed sensing (CS) is a feasible model to save energy. As soon as CS was put forward, it attracted wide attention. However, how to design a suitable sparse dictionary is still a problem until now. Aiming at different situations, designers should change their sparse dictionary. Unfortunately, soil data are always changing because of the variance of weather and environment. Therefore, if there is a computational intelligent CS algorithm which is suitable for variant signals, the problem is solved. In this paper, we proposed a deep learning model of CS, which can avoid designing a sparse dictionary. We combine deep learning and CS together and regard the output of networks as the recovery signals, because deep learning's end-to-end structure solves the above-mentioned problem. We use deep image prior, which is derived from deep convolutional generative adversarial networks to recover 1-D signals of soil data. Meanwhile, we used the mean square error between the recovery signals and the original signals of soil echoes to verify our algorithm. Finally, we classified PH values with recovery signals based on Xgboost because of its excellent classification ability. The experiment results show that our model's accuracy is much higher than those by traditional CS algorithms with a relatively small number of sensors. Also, our model has a better robustness.

Cost Effective Soil pH Sensor Using Carbon-Based Screen-Printed Electrodes

This paper for the first time demonstrates a low cost, easy to make, disposable and paper-based soil pH sensor. The measurement of soil pH is performed using three electrode based electrochemical platform. The sensor is printed using screen-printing technique on a non-tearable hydrophobic paper. Carbon paste is modified with pH sensitive quinone moiety, alizarin, which shows 2e−/2H+ redox process. The detection is carried out using square wave voltammetry at 25 ± 1°C. Eleven different kinds of soil have been collected from three different provinces in India. Samples are prepared using the standard protocol viz . 1M KCl and 0.01M CaCl2. The sensitivity is 60.61 mV/pH and 65.16 mV/pH for buffer solution containing 1M KCl and 0.01M CaCl2, respectively. Two consecutive scans are taken for accurately measuring the soil pH. The first scan shows two peaks which correspond to different types of redox behaviour of alizarin. The second scan shows the actual pH behavior which is demonstrated for the first time. Soil samples prepared using KCl solution show the relative error within 4.9%. For CaCl2 samples the relative error is within 2.9% for soil pH less than 7.3 and within 7.9% for pH greater than 7.3.

The Role of Different Earthworm Species (Metaphire Hilgendorfi and Eisenia Fetida) on CO2 Emissions and Microbial Biomass during Barley Decomposition

Earthworms are commonly known as essential modifiers of soil carbon (C) and nitrogen (N) cycles, but the effects of their species on nutrient cycles and interaction with soil microbial activities during the decomposition of organic materials remain unclear. We conducted an incubation experiment to investigate the effect of two different epigeic earthworms (M. hilgendorfi and E. fetida) on C and N concentrations and related enzyme activities in agricultural soils with added barley residues (ground barley powder). To achieve this, four treatments were included; (1) M. hilgendorfi and barley, (2) E. fetida and barley, (3) barley without earthworms, and (4) without earthworms and without barley. After 32 days incubation, we measured soil pH, inorganic N, microbial biomass C (MBC), water or hot-water soluble C, and soil enzyme activities. We also measured CO2 emissions during the incubation. Our results indicated the earthworm activity in soils had no effect on the cumulative CO2 emissions. However, M. hilgendorfi had a potential to accumulate MBC (2.9 g kg−1 soil) and nitrate-N (39 mg kg−1 soil), compared to E. fetida (2.5 g kg−1 soil and 14 mg kg−1 soil, respectively). In conclusion, the interaction between soil microbes and earthworm is influenced by earthworm species, consequently influencing the soil C and N dynamics.