Variation In Soil pH Research Articles

Regulating soil bacterial diversity, community structure and enzyme activity using residues from golden apple snails

It has been shown that the golden apple snail (GAS, Pomacea canaliculata), which is a serious agricultural pest in Southeast Asia, can provide a soil amendment for the reversal of soil acidification and degradation. However, the impact of GAS residue (i.e., crushed, whole GAS) on soil bacterial diversity and community structure remains largely unknown. Here, a greenhouse pot experiment was conducted and 16S rRNA gene sequencing was used to measure bacterial abundance and community structure in soils amended with GAS residue and lime. The results suggest that adding GAS residue resulted in a significant variation in soil pH and nutrients (all P < 0.05), and resulted in a slightly alkaline (pH = 7.28–7.75) and nutrient-enriched soil, with amendment of 2.5–100 g kg−1 GAS residue. Soil nutrients (i.e., NO3-N and TN) and TOC contents were increased (by 132–912%), and some soil exocellular enzyme activities were enhanced (by 2–98%) in GAS residue amended soil, with amendment of 1.0–100 g kg−1 GAS residue. Bacterial OTU richness was 19% greater at the 2.5 g kg−1 GAS residue treatment than the control, while it was 40% and 53% lower at 100 g kg−1 of GAS residue and 50 g kg−1 of lime amended soils, respectively. Firmicutes (15–35%) was the most abundant phylum while Bacterioidetes (1–6%) was the lowest abundant one in GAS residue amended soils. RDA results suggest that the contents of soil nutrients (i.e., NO3-N and TN) and soil TOC explained much more of the variations of bacterial community than pH in GAS residue amended soil. Overuse of GAS residue would induce an anaerobic soil environment and reduce bacterial OTU richness. Soil nutrients and TOC rather than pH might be the main factors that are responsible for the changes of bacterial OTU richness and bacterial community structure in GAS residue amended soil.

Response of soil faunal communities to tea tree cultivars in the hilly region of western Sichuan, China

Soil fauna is vitally important to all soil ecosystems due to its significant role in humification and mineralization of plant residues, cycling of nutrients, improvement of soil porosity and structure, etc. Soil fauna is sensitive to land-use changes, fertilizer use, tillage, and land degradation. Tea production is one of the most important agricultural industries in China. However, very few studies have investigated the responses of soil fauna to tea tree (Camellia sinensis L.) cultivars; understanding these responses is crucial to maintaining soil health and biological diversity stability in such agricultural ecosystems. This paper concentrates on the impacts of tea trees on soil faunal community composition and diversity, forming the background of an evaluation of the land-use sustainability associated with various cultivars. Soil samples were collected at a depth of 0−20 cm from four major tea plantations in western Sichuan, China, with different cultivars (“Chuannong Huangyazao” - CH, “Fuding Dabai” - FD; “Chuanmu No.217” - CM, and “Chuancha No.3” - CC). The results showed that different tea tree cultivars in this study had significant (p < 0.05) influences on soil chemical properties. The soil at the FD plantation had the lowest pH, total nitrogen (TN), and available phosphorus (AP) but the highest available nitrogen (AN), while the soil at the CM plantation had the highest pH, AP and available potassium (AK). The highest soil faunal abundance (as indicated by the number of individuals per unit area) and community diversity (as indicated by Shannon and Margalef indices) occurred at the CC plantation. This result illustrated that compared to the other plantations, the CC plantation provided a more habitable environment and more nutrient resources for the soil faunal community development. The diversity of the soil faunal community was highly associated (p < 0.05) with variations in soil pH, organic carbon (OC), TN, AP and AK. The effects of tea tree cultivars on the rare soil faunal composition differed among the four tea plantations, but no significant difference in the composition of dominant and common taxa was observed. The relative abundance of the top ten soil faunal taxa was strongly associated with environmental variables. The two most important environmental factors (AP and AN) accounted for 57 % of the changes in soil faunal composition. This study highlighted cultivation and land-use management practices to promote soil health sustainability and soil faunal stability on land degraded by tea tree cultivars in western Sichuan, China.

Significant dose effects of fertilizers on soil diazotrophic diversity, community composition, and assembly processes in a long‐term paddy field fertilization experiment

AbstractAlthough diazotrophs are major participants in biological nitrogen fixation (BNF) processes, the variations in community structure and assembly processes in response to long‐term fertilization with different fertilizer application are still ambiguous, especially under various doses with balance or not. Using nifH amplicon sequencing, we investigated the soil diazotrophic communities in a paddy field which received 20‐year fertilization including control (CK), balanced fertilization (three doses of nitrogen (N), phosphorus (P), and potassium (K) at same ratio (NPK, 2(NPK), and 3(NPK)), unbalanced fertilization (three ratios, (2 N)PK, N(2P)K, and NP(2K)), and manure (M). Our results showed that the diazotrophic diversity increased with the long‐term fertilization, but it was tapering‐off with doses increment. However, the community dissimilarities increased with fertilizer doses. These variations were attributed to the trade‐off between the variation of soil pH and nutrients. The increasing of fertilizer doses induced the transformation of community assembly processes, which changed from mainly dominated by deterministic processes in CK, NPK, NP(2K) and M to stochastic processes in the other treatments. Our findings suggest that the long‐term fertilization, especially different fertilizer doses, strongly affect soil diazotrophic diversity, community structure, and assembly processes, which could help to improve the sustainable agricultural management in the future.

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.

Application of Waste Lemon Extract to Toxic Metal Removal through Gravitational Soil Flushing and Composting Stabilization

The present study aims to investigate the treatment efficiency of soil flushing using waste lemon extract for samples collected from contaminated farmland, in which the copper concentration was measured as 2487 ± 139 mg/kg. The flushing solution, containing 9.9 g/L citric acid, was prepared from the waste lemon extraction process. The soil-flushing treatment using a solution containing commercial citric acids of 10 g/L was also conducted for comparison. Additionally, the collected soil was mixed with crushed waste lemons and the mixture was subjected to a composting process for subsequent stabilization study. After 120-min batch experiments, the desorbed copper concentration for waste lemon-extract experiment was 36.9 mg/L, which was higher than that (28.6 mg/L) for commercial citric solution experiment. The reduction in soil copper concentration (1504 mg/kg) treated by waste lemon-extract flushing was more than that treated by commercial citric solution (1256 mg/kg) at the comparable citric acid concentration. More metals were removed by waste lemon-extract flushing. This is because the waste lemon-extract solution contains additional co-dissolved organic substances with a longer flushing time, which allows more exchange reactions between adsorbed metals and flushing solution. For the treatment with waste lemon extract, the soil pH values were 4.56, 5.70 and 6.29 before, after flushing and after compost treatment, respectively. The observed variation in soil pH also showed that waste lemon extract might be a better flushing agent, while flushing with commercial citric solution decreased the pH in the soil environment. The plant copper availability dropped from 677 mg/kg to 156 mg/kg after waste lemon-extract flushing and stabilization with composted waste lemon. Therefore, the use of waste lemon extract for soil flushing not only removed toxic metals from the soil but also prevented the occurrence of soil acidification, an often-observed phenomenon using an acidic solution in conventional soil flushing. After soil flushing, the application of composted waste lemon could stabilize the toxic metals and increase the pH to a range suitable for plant growth.

Effects of fertilization and stand age on N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O and NO emissions from tea plantations: a site-scale study in a subtropical region using a modified biogeochemical model

Abstract. To meet increasing demands, tea plantations are rapidly expanding in China. Although the emissions of nitrous oxide (N2O) and nitric oxide (NO) from tea plantations may be substantially influenced by soil pH reduction and intensive nitrogen fertilization, process model-based studies on this issue are still rare. In this study, the process-oriented biogeochemical model, Catchment Nutrient Management Model – DeNitrification-DeComposition (CNMM-DNDC), was modified by adding tea-growth-related processes that may induce a soil pH reduction. Using a dataset for intensively managed tea plantations at a subtropical site, the performances of the original and modified models for simulating the emissions of both gases subject to different fertilization alternatives and stand ages were evaluated. Compared with the observations in the early stage of a tea plantation, the original and modified models showed comparable performances for simulating the daily gas fluxes (with a Nash–Sutcliffe index (NSI) of 0.10 versus 0.18 for N2O and 0.32 versus 0.33 for NO), annual emissions (with an NSI of 0.81 versus 0.94 for N2O and 0.92 versus 0.94 for NO) and annual direct emission factors (EFds). For the modified model, the observations and simulations demonstrated that the short-term replacement of urea with oil cake stimulated N2O emissions by ∼62 % and ∼36 % and mitigated NO emissions by ∼25 % and ∼14 %, respectively. The model simulations resulted in a positive dependence of EFds of either gas on nitrogen doses, implicating the importance of model-based quantification of this key parameter for inventory purposes. In addition, the modified model with pH-related scientific processes showed overall inhibitory effects on the gases' emissions in the middle to late stages during a full tea plant lifetime. In conclusion, the modified CNMM-DNDC exhibits the potential for quantifying N2O and NO emissions from tea plantations under various conditions. Nevertheless, wider validation is still required for simulation of long-term soil pH variations and emissions of both gases from tea plantations.

The effects of the soil environment on soil organic carbon in tea plantations in Xishuangbanna, southwestern China

Increasing soil organic carbon (SOC) reserves in agricultural land is important for mitigating global climate change. The soil environmental factors that affect SOC storage in agricultural cultivation are relatively easy to manage, but the effects of these factors on SOC have not been studied systematically, especially the relative weight of each factor is still unclear. In this study, more than 30 soil environmental factors including SOC, soil physical and chemical properties, mineral types, and microorganisms present in the 0–140 cm soil layer were determined hierarchically within tea plantations. The main and secondary factors affecting SOC storage were then analyzed quantitatively using a structural equation model. The most important factors affecting SOC storage in tea plantations included water content (18.9 %), total nitrogen (N, 18.8 %), oxalate-extractable iron (active iron, poorly crystalline iron, Feox, 16.3 %), sulfur (S, 13.1 %), total phosphorus (P, 8.6 %), calcium (6.1 %), oxidation reduction potential (5.4 %), clay (4.5 %), bromine (4.3 %), and manganese (4.0 %). Variations in soil temperature and pH on this small scale were small and thus these factors had negligible effects on SOC storage in this study. Organic fertilizer application increased C, N, S, and P concentrations, which can contribute to SOC storage. Appropriate irrigation can also improve SOC storage. We identified a set of Fe-N-S-P coupling mechanisms that promoted SOC storage. Soils with high Fe, N, and S concentrations, high water content, and high oxidation reduction potential relate to an increased Feox concentration, which is important for enhancing SOC stability. Therefore, the application of magnetic (iron oxide) fertilizer to increase Feox in soil promotes SOC storage.

Geostatistical Analysis on Spatial Variability of Soil Nutrients in Vertisols of Deccan Plateau Region of North Karnataka, India

Different methods of land use and management have a significant effect on soil properties distribution. Understanding of variations in soil nutrients in agricultural land use is important. An increase in extraction of nutrients, soil degradation, and management of nutrients is leading to a decline in quality of vertisols across the Deccan plateau of India. Though there are studies on spatial variability of vertisols macronutrients, studies on available calcium (Ca) and available magnesium (Mg) are rare. This study is conducted in Gulbarga taluk, north Karnataka, India, to evaluate the variability of soil pH, Ca, Mg, and Zinc (Zn). A total of 78 samples of soils are collected at 0 to 15 cm depth based on the accessibility and distribution of field patterns. Four subsamples represent a single composite sample. Agilent 4200 MP-AES (Microwave Plasma-Atomic. Emission Spectrometer) was used for determining the concentration of soil nutrients. The soil nutrients represent wide variation in coefficient of variation (CV) with a value of 6 % (for pH) to 70.9 % (for Zn). The soil pH showed a significantly positive correlation to Ca and a negative correlation to Mg. Geostatistical investigation indicates spherical model is the best fit for all nutrients. Except for Ca, all nutrients showed moderate spatial dependence. Ordinary kriging is used to generate spatial variability maps. The maps of spatial variability are highly variable in nutrients content and indicate that site-specific management needs to be taken by local authorities and improve the livelihood of marginal farmers and also for sustainable agriculture.

Variations in Soil Chemical Parameters of Long Term Sugarcane Growing Alfisols under Contrasting Cropping Conditions at Sevanagala, Sri Lanka

This study was conducted to determine the variability of soil pH, macronutrients and Na contents in long term sugarcanegrowing Alfisols at Sevanagala, South-East of Sri Lanka. The study site included the entire sugarcane-growing area covering its contrasting cropping systems namely, irrigated and rain-fed cultivation on low humic gley (LHG) and reddish brown earth (RBE) soils, and adjacent undisturbed soils. The mean pH of the two soil types was significantly different and ranged from 4.5 to 9.3. Except some soils under rain-fed cultivation with a pH less than 5.5 in RBE soil and a pH greater than 7.5 in LHG soils, pH in all other soils favoured sugarcane growth. Plant available P content of soils were not significantly different among cropping conditions due to its wide variation. In both cropping systems and soil types there were areas with very low to nondetectable P levels. Exchangeable K content was significantly different between LHG and RBE soils with the latter having a mean concentration of 257 mg/ kg that is favourable for sugarcane cultivation. Though, the mean values are higher than the optimum range, there were K deficient patches in the studied area. Soil exchangeable Ca, Mg and Na contents were low in the study area but were significantly higher in LHG soils than in RBE soils contributing to alkalinity in the former soils especially under rain-fed conditions. The sugarcane-growing soils except LHG under rain-fed conditions showed chemical properties similar to undisturbed soils in the area highlighting their buffered nature despite long-term sugarcane cultivation. This study also emphasised the need for site-specific soil fertility management strategies for the Sevanagala sugarcane growing areas.

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.

Standardization of potting media and nutrition protocol for raising acid lime seedling in containerized nursery

The study was carried out on acid lime (Citrus aurantifolia) to investigate nutritional requirements vis-avis potting media i.e. potting mixture and cocopeat in primary and secondary protected citrus nursery with regard to nutrient availability and growth behaviour to shorten time required for production of seedlings. Three types of potting media viz., potting mixture (PM), sole cocopeat (CP) and mixture of PM and CP were used. Nutrient application treatments (NPK in g) for primary nursery were 60+25+25, 40+25+25 and 20+10+10, and for secondary nursery were 10+5+5, 8+4+4, 6+3+3, 4+2+2 and control. The results revealed that in primary nursery, seedling emergence and survival was maximum in PM + CP mixture. Plant height and leaf chlorophyll content was highest with the application of 40+20+20 in PM + CP media while number of leaves were highest in 20+10+10 g NPK in the same media. The highest dry weight of all the plant parts was obtained in PM + 20+10+10 g NPK. Extreme variation in soil pH (4.27–7.12), electrical conductivity (0.46–2.06 dS/m), organic carbon (2.19 23.6%) as well as available N (180.6 - 1679.8 kg/ha), P (7.8 - 39.8 kg/ha) and K (1253.2 - 4894.5 kg/ha) was recorded under different treatments at the end of the experiment. In secondary nursery application of lowest dose of fertilizer i.e. 4+2+2 g NPK in PM + CP mixture recorded maximum plant height, number of leaves and chlorophyll content while stem girth was maximum in same dose applied with PM. Application of 4+2+2 g NPK in PM also had similar results without any plant mortality. Presented results showed that cocopeat, if cheaply available, can be used by mixing it with nursery potting mixture (50%) with supplementation of minimal dose of fertilizers for producing both types of nursery plants.

Impact of urban green spaces, native tree species and seasons on soil pH in Kaunas, Lithuania

Tree growth is sensitive to soil pH in urban areas and is often higher than in rural forest. However, there are knowledge gaps on how soil pH and alkalization are affected by urban environments and seasonal climate as well as the cascading effects on tree species. In order to fulfill these gaps, we analyzed the soil pHCaCl of four common native deciduous tree species: Acer platanoides, Tilia cordata, Quercus robur and Betula pendula in five different types of urban green spaces in Kaunas city municipality (Lithuania). The results show that soil pH in urban environments with Betula pendula sites were most alkaline (pH 7.04), whereas the soil pH of urban environments with Acer platanoides (pH 6.7) and Tilia cordata (pH 6.8) were most acidic. The soil pH of street tree greeneries was alkaline, while soils of peri-urban forests and large urban parks were acidic. Differently to natural conditions in peri urban forests the soil pH level drop down by 0.5 is observed during spring-autumn period in broad street greeneries with largest urban pressure. The variation in soil pH of the different types of green space and tree species shows that city planner should consider the unique conditions of all green space to maximize their potential for human well-being.

Critical Limits of Deficiency of Nickel in Intensively Cultivated Alluvial Soils

Although nickel (Ni) has been studied a lot as a pollutant, a very few studies have been conducted with this element as a plant nutrient. Present study was undertaken to evaluate the crop response of applied Ni and suitability of the chemical extractants for assessing the available Ni in soil using soybean as a test crop. Fifteen bulk surface (0–15 cm) soil samples with wide variation in physicochemical properties were collected from the cultivated fields of various locations. A greenhouse experiment was conducted to assess the response of soybean to applied Ni (0 and 5 mg kg− 1). There was 16.5 to 26.6% increase in the biomass yield of soybean to the applied Ni (5 mg kg− 1) over control. Effectiveness of diethylene triamine pentaacetic acid (DTPA) soil test for predicting the Ni content in plant improved, when the variation in soil pH was taken into account. Critical limit of deficiency of the DTPA-extractable Ni in soil was 0.17 mg kg− 1, and critical plant Ni concentration of deficiency for soybean was worked out as 0.20 mg kg− 1.

Spatial prediction and mapping of soil pH across a tropical afro-montane landscape

Soil pH is an indispensable part of the soil bionetwork, but so vulnerable to the dynamics of land-use change. Understanding the spatial and temporal distribution of soil pH is thus important for sustainable land use planning and management. In this study, we developed an approach based on geographically weighted regression-kriging (GWRK) to predict the continuous variation of soil pH up to 15 cm depth. The approach is compared to multiple linear regression-kriging (MLRK) using a total of 220 soil observations and 28 candidate auxiliary data, including climatic, topographic, and remotely sensed data. Results revealed that organic matter, sand, silt, temperature, and Landsat 8 operational land imager band 7 can explain the spatial variability of soil pH. GWR-based (local) models remarkably improved the prediction accuracy of soil pH compared to the MLR-based (global) models considering the root mean square error (i.e., 0.33 vs. 0.15; 0.37 vs. 0.17, respectively) and the coefficient of multiple determination (R2) (i.e., 0.59 vs. 0.74; 0.43 vs. 0.55, respectively). In conclusion, the use of GWR-based models revealed that the correlations between soil pH and environmental covariates were not stationary in space. Forested areas tended to be very strongly to moderately acidic, while croplands were slightly acidic to neutral. The GWR-based models demonstrated their utility in improving predictive soil mapping. These findings will support spatially-targeted soil pH management for improved food security and ecosystem health.

Responses of ground-active arthropod community in Caragana shrub plantations to grazing management in desertified region.

We investigated the community structure of ground-active arthropods as well as vegetation and soil properties in Caragana shrub plantations under grazing and exclosure management across spring, summer and autumn in Yanchi County of Ningxia in northern China. The aim of this study was to uncover the responses of ground-active arthropods in shrub plantations to grazing management in desertified regions. The results showed that: 1) plant height, soil fine sand content, and soil electrical conductivity were significantly lower, whereas soil bulk density and coarse sand were significantly higher in shrub plantations under grazing than exclosure. 2) There were 40 families from 13 orders captured. The dominant groups included Formicidae and Tenebrionidae families, which comprised 68.75% of the total individuals. There were four common groups occupying 20.82% of the total individuals. The remaining 34 groups were relatively rare, only accounting for 10.44% of the total. Across the three seasons, the composition of ground-active arthropod community was significantly different between grazing and exclosure, which indicates the sensitivity and adaptability of ground-active arthropods to environmental changes including grazing management and seasonal changes. 3) There was a significant effect of grazing on total abundance of ground-active arthropods in shrub plantations, with significantly higher values under grazing than under exclosure. There was no significant effect of grazing management on group richness and diversity of ground-active arthropods in shrub plantations. 4) There was a correlation of total abundance, evenness index and the Simpson index with plant abundance, vegetation height, soil moisture, soil pH and electrical conductivity. There was a significant correlation of the Shannon index with vegetation height, soil moisture and soil fine sand. Plant density, and soil pH, soil moisture and soil temperature were the key factors driving the structure of ground-active arthropod communities in shrub plantations under gra-zing management across seasons based on the partial RDA results. It was concluded that the variations of plant height, soil pH, soil moisture and soil temperature under grazing management could result in different ground-active arthropod taxon to changing habitats. The conservation effect of shrub on ground-active arthropod could reduce the negative impacts of grazing. Spring grazing could enhance ground-active arthropod abundances in shrub plantations. It was necessary to pay attention to prevention of insects which are caused by spring grazing in shrub plantations.

Electrokinetic remediation of contaminants of emergent concern in clay soil: Effect of operating parameters

The potential of electrokinetic (EK) remediation to remove from soils one particular group of contaminants - contaminants of emergent concern (CECs), remains largely overlooked. The present study aimed to evaluate the efficiency of the EK process for the remediation of an agricultural clay soil containing CECs. The soil was spiked with four CECs - sulfamethoxazole, ibuprofen, triclosan and caffeine - and their status (i.e. residual amounts and spatial distribution) evaluated at the seventh day of EK treatment at a defined current intensity, directionality and duration of void period. The characterization of the soil physicochemical properties was also undertaken. The results showed similar degradation trends in all applied EK strategies, which were suchlike to that of the natural attenuation (biotic control): sulfamethoxazole > ibuprofen ≥ triclosan ≥ caffeine. The removal of the CECs was higher under a 10 mA constant current application than in the natural attenuation (up to 2.8 times higher; from 13 to 85%). Caffeine was the exception with its best removal efficiency being achieved when the ON/OFF switch mode with a void period duration of 12 h was used (36%). The use of electro-polarization reversal mode did not favour the remediation. The soil pH variations resulting from EK application were determinant for triclosan remediation, which increased with soil pH increase. The only EK condition that promoted the removal of all CECs was the ON/OFF switch mode of 12 h (removals between 36 and 72%), in which only minor physicochemical disturbances of the soil were observed. This is in accordance with a potential application of EK in-situ. The last is reinforced by the low estimated electrical cost of the best EK technology - 2.33 €/m3 for the 7 days. Overall the EK remediation processes are a promising technology to stimulate in situ the removal of CECs from agricultural soils.

Factors affecting variations of soil pH in different horizons in hilly regions.

Soil pH is a key factor that controls soil nutrient availability, soil microbial activities, and crop growth and development. However, studies on the soil pH variations of cultivated lands in different horizons at the regional scale remain limited. In this work, 348 soil samples were collected from three soil horizons (A, B, and C) at 120 sites over the hilly region of Chongqing, southwestern China. Six topographic indicators, four climate parameters, and parent material were considered. Classification and regression trees (CARTs) were applied to investigate the relationships between soil pH and the variables in the A, B, and C horizons. Model performances were evaluated by root mean square error (RMSE), relative root mean square error (RRMSE), and coefficient of determination (R2). Results showed that soil pH increased obviously from the A to C horizons. Soil pH was predicted well by the forcing factors with the CART models in all horizons. RMSE, RRMSE, and R2 varied between 0.37 and 0.435, between 5.93 and 7.23%, and between 0.71 and 0.80, respectively. The relative importance of the studied variables to soil pH differed with the horizons. Annual temperature range (ATR), terrain wetness index (TWI), and Melton ruggedness number were critical factors that controlled soil pH variability in the A horizon. Parent material, precipitation of warmest quarter (PWQ), ATR, and TWI were important variables in the B horizon. Parent material, PWQ, ATR, and precipitation were key factors in the C horizon. The results are expected to provide valuable information for designing appropriate measurements for agricultural practices and preventing soil acidification.

Status of Sulphur and Boron in Soils of North Gujarat Region of India

The soils of North Gujarat region's were assessed for its Sulphur and Boron status due to its visible deficiency in plants. Study was conducted in three districts viz., Sabarkantha, Mehsana and Patan from which 60, 110 and 52 villages were selected and soils samples were collected with geo-tagging. A total of 1332 surface soil samples (Sabarkantha 360, Mehsana 660 and Patan 312) were collected from these respective districts. Analysis of these soil samples showed a wide variation in soil pH (6.04-9.72) from slightly acidic to alkaline. Organic carbon (OC) content ranged from 1.0 to 7.1 g kg-1, about 90, 65 and 74% of soil samples were found to be under the low OC in Mehsana, Sabarkantha and Patan districts, respectively. Available S content ranged from 1.7 to 68.5 mg kg-1 with a mean value of 15.6, 14.7 and 14.9 mg kg-1 in Mehsana, Sabarkantha and Patan districts, respectively. S deficiency in soils of all three districts was 18.1, 25.5 and 16.9 per cent, which appeared in medium-fertility class level as per Nutrient Index Value (NIV). The high magnitude of S deficiency was noticed in soils of Idar taluka (43.9 %) followed by Khedbrahma taluka (40.9%) of Sabarkantha district, showing medium-fertility class. Further, these samples were also found deficient in hot water-soluble boron (HWS-B) and it ranged from 0.06 to 3.12 mg kg-1 with a mean value of 0.44, 0.45 and 0.44 mg kg-1 in districts of Mehsana, Sabarkantha and Patan, respectively. The NIV indicated B fertility level of low to high. Per cent deficiency of B recorded about 29.4, 17.9 and 19.2 per cent in all three districts. A large scale of B deficiency was noticed in Satlasna taluka (52.4 %) of Mehsana district, which showed low fertility class.

Soil acidification and P, K, Ca and Mg budget as affected by sheep grazing and crop rotation in a long-term integrated crop-livestock system in southern Brazil

The insertion of the animal component into the crop production system can alter the nutrient dynamics and, consequently, the soil fertility status over time. This change occurs differently according to the arrangement adopted, depending on both, the intensity and frequency of animal grazing, as well as the crop rotation system. This study was carried out aiming to evaluate the effect of sheep grazing intensity and frequency during the winter period and the crop rotation in the summer period on the (i) temporal evolution and vertical distribution of soil chemical properties, and (ii) on the nutrient (phosphorus – P, potassium – K, calcium – Ca, and magnesium – Mg) budget. The experiment was established in 2003, in a subtropical Acrisol in southern Brazil, arranged in a randomized block design with split plots. The treatments were two grazing intensities (moderate and low), two stocking methods (continuous and rotational), subdivided into two crop rotation systems (monoculture - soybean/soybean and crop rotation soybean/maize). Temporal variation of soil pH, exchangeable aluminum (Al), Ca and Mg, available P and K, base saturation, Al saturation, and cation exchange capacity (CEC) were evaluated in samples collected in 2003, 2010, 2015 and 2017, corresponding to 0, 7, 12 and 14-years after the beginning of the experiment. The vertical distribution (0–5, 5–10, 10–20, 20–30 and 30–40 cm) of these chemical properties were also evaluated 14-years after the beginning of the experiment (2017). The nutrient budget in the soil was calculated based on the initial and final available/exchangeable contents in the 0–10 cm soil layer and the inputs (fertilizers) and outputs (exportation by grain and meat) of nutrients. >95% of P, K, Ca and Mg were exported by grains and <5% by sheep meat. There was an intense acidification of the soil over the 14-years of experiment as shown by the decrease of soil pH and base saturation, and the increase of Al saturation. Crop rotation with soybean/maize increased CEC up to 5 cm soil depth and increased the available K content up to 40 cm soil depth. The available K budget was more negative in soybean monoculture due to higher grain exportation. Integrated crop-livestock system involving low grazing intensities and rotational stocking methods, coupled with crop rotation in the summer, was more efficient in the use of nutrients.

Spatial variability of soil pH sampled by two methodologies used in precision agriculture in farms under crop rotation

This study aimed to characterize the spatial variability of pH in soils of two farms in the state of Paraná, Brazil, based on two different sampling methods used in precision agriculture, by means of geostatistical analyzes. The first method of sampling the pH grid consisted in the collection of soil samples by the traditional method (1 point / ha). The second method of pH determination was by on-the-go soil sensor (200 points / ha). The spherical model was better suited to most semivariograms, regardless of the sampling method. After adjusting the semivariograms for soil pH determination methods, thematic maps were made using normal kriging. The best spatial distribution of pH was obtained where the attribute was sampled by the on-the-go sensor. The number of pH samples collected and the sampling method influenced the visual representation of pH variability.