Soil Electrical Conductivity Research Articles

How to remediate sulfate-nitrate salinized greenhouse soil? An optimal combination of organic amendment, fertilizer and irrigation

Greenhouse soil secondary salinization is a widespread problem along the lower-middle reaches of the Yangtze River basin, which seriously deteriorates the yield and quality of vegetables. High multiple-cropping index of the greenhouse management needs intensive application of agrochemicals and frequent irrigation which led to significant soil salinization in this area. In this study, we investigated how to remediate the salinized plastic shed soils and improve the yield and quality of vegetables using various measures, including two types of irrigation (intermittent irrigation and 80% water-holding capacity), four types of organic matter (cow manure, mushroom residue, fermented sawdust, and half-fermented sawdust) with two application rates (2 g C kg−1 soil and 8 g C kg−1 soil), and two types of inorganic fertilizers (compound fertilizer with and without sulfate). Results showed that intermittent irrigation decreased either soil electrical conductivity from 1.55 to 0.36 mS cm−1 or the concentrations of soil nitrate from 507 mg kg−1 to 31 mg kg−1 and sulfate from 664 mg kg−1 to 114 mg kg−1 in the incubation period. This effect continued to the next two periods (before seed sowing and after the first harvest). After the second harvest, all these parameters had a recover trend but remained lower than those of the original soil. Half-fermented sawdust had the best effect for soil amelioration among the four organic amendments whilst the effects were not enhanced at higher application rate. Across the two continuous growing seasons (pak choi (Brassica rapa subsp. chinensis) in first season, cherry radish (Raphanus sativus L.) in second season), especially the second harvest season, the compound fertilizer without sulfates ameliorated soil degradation and maintained greater yield compared with sulfate-containing fertilizer. Therefore, application of 2 g C kg−1 half-fermented sawdust with intermittent irrigation and use fertilizer without sulfate was optimum for the degraded greenhouse soil remediation and vegetable yield improvement. This treatment could either decreased soil EC from 1.55 to 0.325 mS cm−1 or the concentration of soil nitrate from 507 to 89 mg kg−1 and sulfate from 664 to 266 mg kg−1 after continuous two growing seasons while the radish yield in second growing season was 71% higher than CK. These findings provided an economical and practical method to remediate sulfate-nitrate salinized greenhouse soil in a short period and designed a field management mode to maintain the efficacy.

Analysis of Tea Plantation Suitability Using Geostatistical and Machine Learning Techniques: A Case of Darjeeling Himalaya, India

This study aimed to identify suitable sites for tea cultivation using both random forest and logistic regression models. The study utilized 2770 sample points to map the tea plantation suitability zones (TPSZs), considering 12 important conditioning factors, such as temperature, rainfall, elevation, slope, soil depth, soil drainability, soil electrical conductivity, base saturation, soil texture, soil pH, the normalized difference vegetation index (NDVI), and land use land cover (LULC). The data were normalized using ArcGIS 10.2 and the models were calibrated using 70% of the total data, while the remaining 30% of the data were used for validation. The final TPSZ map was classified into four different categories: highly suitable zones, moderately suitable zones, marginally suitable zones, and not-suitable zones. The study revealed that the random forest (RF) model was more precise than the logistic regression model, with areas under the curve (AUCs) of 85.2% and 83.3%, respectively. The results indicated that well-drained soil with a pH range between 5.6 and 6.0 is ideal for tea farming, highlighting the importance of climate and soil properties in tea cultivation. Furthermore, the study emphasized the need to balance economic and environmental considerations when considering tea plantation expansion. The findings of this study provide important insights into tea cultivation site selection and can aid tea farmers, policymakers, and other stakeholders in making informed decisions regarding tea plantation expansion.

Impacts of repeated coastal flooding on soil and groundwater following managed dike realignment

Coastal defense structures (e.g., dikes, seawalls) protect vulnerable communities along marine coastlines and estuaries from the physical and chemical influences of adjacent water bodies. These structures are susceptible to overtopping or breaching by tides and waves, with risks amplified by climate change-induced sea-level rise. Repeated inundation by saline water can contaminate freshwater resources and salinize soil, impacting land-use activities, including agricultural productivity. Managed ecosystem-based dike realignment and salt marsh restoration can provide alternatives to traditional coastal adaptation approaches. We assess the changes to soil salinity at a managed dike realignment project prior to the transformation from a diked terrestrial environment to an estuarine environment. Baseline data are compared to conditions following 8–10 months of intermittent flooding at spring tides.Results show that an increase in salinity occurred over the entire site in the shallow subsurface, with the most significant contamination occurring in low-lying areas. Bulk soil electrical conductivity (salinity proxy) measured from geophysical surveys increased from the previous freshwater condition of ∼300 μS/cm to over 6000 μS/cm following <20 flood events, while successive flooding resulted in increased soil moisture as infiltrated floodwater propagated to greater depths. Sediment deposition occurred at high rates, with up to 4 cm of sediment deposited per flood, converting much of the previously cultivated land into tidal mudflats. Deeper sediments and groundwater (i.e., >1.8 m depth) were not impacted over the time scale of this research. This study demonstrates that intermittent shallow flooding can rapidly increase moisture content and soil salinity in surficial sediments and, in turn, adversely impact conditions suitable for agricultural crop production. The realignment zone serves as an engineered analog of coastal flooding, presenting an opportunity to investigate how low-lying coastal environments may experience regular flooding in the future due to sea-level rise and intensifying coastal storms.

Filling the maize yield gap based on precision agriculture – A MaxEnt approach

Precision agriculture (PA) and yield gap (Yg) analysis are promising strategies to achieve the desired sustainable intensification of agricultural production systems. Current crop Yg approaches do not consider the internal field yield variability caused by soil properties. Topographic and edaphic characteristics causing consistent high and low yield patterns in time and space can be interpreted as an ecological niche and used as proxies for potential yield (Yp) and Yg. Ecological niche models (ENMs) are statistical models originally developed to forecast a species’ niche. However, its application to analyse crop yield spatio-temporal variability has never been made. This study aimed to fill this void by developing a novel approach: i) to quantify the magnitude and spatio-temporal distribution of Yp and Yg, ii) to identify the main factors that cause the Yg, and iii) to provide statistical and agronomical interpretation of the data to reduce the Yg. We performed this work using high-resolution maize yield maps from three seasons, with an ancillary dataset composed of soil electrical conductivity, soil properties and digital elevation models provided by “Quinta da Cholda”, Portugal. The yield maps were averaged, resulting in a standardised multiyear yield map. The 90th and 10th yield percentiles were interpreted as proxies for Yp and Yg, and analysed by an ENM machine learning algorithm – maximum entropy (MaxEnt). The average Yg and Yp were quantified as 1.5 and 19.1 ton/ha. Yp was characterised by having silty, richer soils and lower elevations, with several nutritional factors above the critical limits to maintain higher yields. Yg had loam soils coupled with higher relative elevations and lower nutrition content. This innovative modelling approach can efficiently manage high-dimensional spatio-temporal data to support advanced PA solutions, allowing detailed support for narrowing the Yg.

Predicting Dynamics of Soil Salinity and Sodicity Using Remote Sensing Techniques: A Landscape-Scale Assessment in the Northeastern Egypt

Traditional mapping of salt affected soils (SAS) is very costly and cannot precisely depict the space–time dynamics of soil salts over landscapes. Therefore, we tested the capacity of Landsat 8 Operational Land Imager (OLI) data to retrieve soil salinity and sodicity during the wet and dry seasons in an arid landscape. Seventy geo-referenced soil samples (0–30 cm) were collected during March (wet period) and September to be analyzed for pH, electrical conductivity (EC), and exchangeable sodium percentage (ESP). Using 70% of soil and band reflectance data, stepwise linear regression models were constructed to estimate soil pH, EC, and ESP. The models were validated using the remaining 30% in terms of the determination coefficient (R2) and residual prediction deviation (RPD). Results revealed the weak variability of soil pH, while EC and ESP had large variabilities. The three indicators (pH, EC, and ESP) increased from the wet to dry period. During the two seasons, the OLI bands had weak associations with soil pH, while the near-infrared (NIR) band could effectively discriminate soil salinity and sodicity levels. The EC and ESP predictive models in the wet period were developed with the NIR band, achieving adequate outcomes (an R2 of 0.65 and 0.61 and an RPD of 1.44 and 1.43, respectively). In the dry period, the best-fitted models were constructed with deep blue and NIR bands, yielding an R2 of 0.59 and 0.60 and an RPD of 1.49 and 1.50, respectively. The SAS covered 50% of the study area during the wet period, of which 14 and 36% were saline and saline-sodic soils, respectively. The extent increased up to 59% during the dry period, including saline soils (12%) and saline-sodic soils (47%). Our findings would facilitate precise, rapid, and cost-effective monitoring of soil salinity and sodicity over large areas.

New insights into the role of soil properties in driving cadmium-induced hormesis in soil alkaline phosphatase under vegetation cover change

This study investigated the hormetic responses of soil alkaline phosphatase (ALP) to exogenous Cd under five different vegetation cover types in a typical coastal wetland, including mudflat (Mud), Phragmites australis (PA), Spartina alterniflora (SA), Metasequoia glyptostroboides (MG), and Cinnamomum camphora (CC). The results showed that the activity of soil ALP was significantly enhanced by exogenous 0.3–1.0, 0.2–0.8, 0.05–0.3, 0.05–0.6, and 0.05–0.60 mg Cd /kg in Mud, PA, SA, MG, and CC, respectively. Moreover, the Horzone (an integrated indicator of the stimulation phase) of Mud and PA was significantly higher than that of SA, MG, and CC. Multiple factor analysis revealed that soil chemical properties and soil bacteria community play an important role in the hormetic effect of soil ALP to Cd stress. Soil electric conductivity (EC) and the relative abundance of Gammaproteobacteria were also identified as key drivers of the hormetic effects of Cd on soil ALP under five vegetation cover types. These findings suggest that the soil ecosystem had better resistance to exogenous Cd stress under mudflat and native species (PA) than invasive species (SA), and artificial forests (MG and CC) when soil ALP activity was the test endpoint. Consequently, this study is beneficial for future ecological risk assessment of soil Cd contamination under divergent vegetation covers.

Biofertilizer based on halotolerant microorganisms promotes the growth of rice plants and alleviates the effects of saline stress.

Long-term soil salinization easily contributes to soil hardness, soil nutrient imbalance, and soil microbial diversity reduction, resulting in low rice yields in the salinized fields, and microbial remediation is one of the important measures to improve salinized soil. To verify the effect of biofertilizer based on halotolerant microorganisms on promoting rice growth and alleviating saline stress, this study discussed the effects of biofertilizer on soil microbial diversity and community structure and analyzed the correlation between the formation of microbial community structure and soil nutrient factors in the salinized field. The result, in comparison with applying inorganic fertilizer (referred to as CK), showed that notably increased soil available nitrogen, available phosphorus, available potassium, and rice paddy yield (p < 0.05) and significantly decreased soil electrical conductivity (p < 0.05) were achieved via biofertilizer (referred to as G2). Additionally, the application of biofertilizer contributes to the increase in soil microbial diversity and reorganization of microbial community structure, and through the analysis of linear discriminant analysis effect size, a notable difference in relative abundance was found in 13 genera, 6 families, and 3 orders between the control group and experimental groups (p < 0.05), and by linear discriminant analysis, Desulfomonas was further identified as the differentiated indicator. The redundancy analysis showed that available phosphorus and cation exchange capacity were the key environmental factors that affected microbial community structure and composition. Through bacterial functional prediction, increased rhizosphere soil bacterial metabolism, enzyme activity, membrane transport, and other potential functions were achieved by applying biofertilizer. Therefore, the application of biofertilizer could significantly alleviate rice growth stress and increase nutrient supply capacity in saline soil. These findings provide theoretical support for soil microbial improvement technology in the salinized field.

MORPHOLOGY OF PILA GLOBOSA (GASTROPOD MOLLUSCA: AMPULLARIIDAE) WITHIN ENVIRONMENTAL VARIATION OF SOUTH-WESTERN BANGLADESH

Owing to the community engagement of the gastropod collection in the south western ecosystems in Bangladesh, the gastropod molluscs are getting important attention in terms of edible and non-edible purposes while detailed morphological information about the gastropods is scarce in this area. The present research has investigated the morphological variability of the gastropod molluscs (Pila globosa) in the six localities of south-western coastal Bangladesh (such as, Khulna, Bagerhat, Satkhira, Gopalganj, Pirojpur and Jessore). A total of 2160 gastropod samples (Pila globosa) were collected from July to December monthly over the two consecutive years of 2013 and 2014. The results of the analyses revealed that the maximum monthly mean values of the dry shell mass and the dry body mass were found in November, indicating the complete growth and development of the gastropods in the coastal environment. One-way ANOVA and ANCOVA show that there is a significant morphological variability of Pila globosa among different localities in the south-west coastal Bangladesh, while the covariate of water salinity significantly affects the aperture length of it; the covariate of electrical conductivity of soil significantly affects both the height and aperture length; the covariate of sodium contents of the soil significantly affects the aperture length of the gastropod mollusc. The results also revealed that the morphological variability of the mollusc P. globosa is linked to complex ecological systems and habitat variation.

Variation in Certain Soil Properties Based on Land Use Type, and Elevation in Arhavi Sub-Basin, Artvin, Turkiye

Knowledge of soil properties such as texture, bulk density, organic matter, soil reaction, soil electrical conductivity, and soil erodibility factor is fundamental to the sustainable management of soil resources. This study aimed to determine the changes in certain soil properties including texture, bulk density, organic matter, pH, electrical conductivity, and soil erodibility factor with different land uses, elevation zones and soil depths in the Arhavi Sub-basin, Artvin, Turkiye. For these purposes, a total of 618 soil samples (309 disturbed and 309 undisturbed) were taken from 155 sampling points located in areas with different land uses, including tea (33 sampling points), hazelnut (33 sampling points), forest (67 sampling points), and grassland (22 sampling points). The results of the statistical analysis revealed that the soils at depths of 0–15 cm and 15–30 cm showed significant differences according to the land use in terms of sand, clay, silt, bulk density, organic matter, and pH. There were significant positive correlations between elevation and soil bulk density (r = 0.495) at a soil depth of 0–15 cm in the tea areas. In the grassland areas, there were significant positive correlations between elevation and silt, bulk density, and the soil erodibility factor (r = 0.485, r = 0.794, and r = 0.442, respectively) at depths of 0–15 cm, and significant positive correlations between elevation and both silt and bulk density (r = 0.468 and r = 0.691, respectively) at depths of 15–30 cm. Similarly, there were significant positive correlations between elevation and both sand and organic matter at soil depths of 0–15 cm and 15–30 cm (sand: r = 0.351 and r = 0.638, respectively; organic matter: r = 0.277 and r = 0.587, respectively). On the other hand, significant negative correlations were found between elevation and silt, bulk density, pH, and the soil erodibility factor at depths of 0–15 cm and 15–30 cm (silt: r = −0.400 and r = −0.461, respectively; bulk density: r = −0.593 and r = −0.545, respectively; pH: r = −0.354 and r = −0.309, respectively; soil erodibility factor: r = −0.443 and r = −520, respectively). Soil acidity was found to be the most important problem threatening soil fertility in all land uses. The use of soil acidity-increasing fertilizers, such as ammonium sulfate, in tea gardens in the region should be eliminated to protect the fertility of soils in the future. The knowledge that this study provides might help farmers and foresters in the region in the proper management and fertilization of their lands. Moreover, this study will provide data to future studies related to soil acidification, soil erosion, and land use that are planned for the Arhavi Sub-basin.

Composition of plant growth promoting rhizobacteria in forest and systematic plantations of tasar silkworm food plants and their relationship with soil and leaf nutrients

Aim: To investigate the status of bacterial load and number of isolates of plant growth promoting rhizobacteria in forest and systematic plantation of Terminalia tomentosa and T. arjuna, and their relationship with soil and leaf nutrient levels. Methodology: Soil samples were collected from the rhizosphere of food plants in four tasar silkworm rearing regions of India. Bacterial load of total bacteria, Nitrogen fixing bacteria (NFB), Phosphate Solubilizing Bacteria (PSB) and bacteria grown on King's B media (KBB) was enumerated on specific media by employing serial dilution technique. Based on the colony morphology and cell type, distinct colonies on specific media were counted as isolate. Nutrient levels in soil and leaf samples collected from different plantations were analyzed. Multivariate correlation analysis was performed between PGPR microbial load and isolates with soil physio-chemical parameters and leaf nutrients. Results: The rhizosphere of forest plants possessed the highest total bacterial load, the systematic plantation possessed the highest NFB load, whereas PSB and KBB load was equal in both the plantations. Forest plantations of Keonjhar and Sundergarh regions had the highest number of NFB isolates per rhizosphere soil sample and systematic plantations possessed the highest number of KBB (Keonjhar and Sundergarh regions) and PSB isolates (West Singhbhum region). Positive correlation was observed between PSB load and the number of isolates with soil organic carbon, KBB load with soil electrical conductivity and available potassium, PSB load and KBB isolates with soil available sulphur. NFB and KBB load and their isolates showed positive correlation with leaf N and K content. Interpretation: Results suggest the possibility of improving leaf nutrient quality of tasar silkworm food plants by enriching PGPR microbial load through biofertilizer application. Key words: Rhizobacteria composition, Soil nutrients, Silkworm, Terminalia tomentosa, Terminalia arjuna

Responses of soil nutrient and enzyme activities to long-term mulched drip irrigation (MDI) after the conversion of wasteland to cropland

Soil nutrients and enzymes are essential indicators of ecological functions in terrestrial ecosystem and are also sensitive to land-use change. However, the response of soil nutrients and enzymes to long-term mulched drip irrigation (MDI) in the conversion of agroecosystems is still limited. In this study, we analyzed soil nutrient concentrations and enzyme activities at a soil depth of 0–40 cm in four typical cotton fields with different durations of MDI (8, 12, 16, and 22 years) and a wasteland (CK) as control. After the conversion of saline-alkali wasteland into cotton fields, we found that soil electrical conductivity (EC) and pH significantly decreased, but the concentrations of available soil phosphorus (AP), total carbon (TC), soil organic carbon (SOC) and total nitrogen (TN) significantly increased with increasing years of MDI application. Soil enzymes, such as polyphenol oxidase, catalase, urease, alkaline phosphatase, and cellulase were more active in the subsoil than in the topsoil. Compared to the wasteland, a significant reduction of soil enzyme activities (polyphenol oxidase, catalase, and cellulase) appeared in the young cotton field, which gradually reestablished after practicing long-term MDI. Based on redundancy analysis, the variations of the enzyme activities were obtained by pH (38.7 %), C/N (27.6 %), EC (20.9 %), TN (4.9 %), and NO3−-N (3.1 %) at 0–20 cm depth; and by AP (43.7 %), SWC (18.4 %), pH (12.6 %), and TN (12.5 %) at 20–40 cm depth. Long-term MDI has a positive effect on reducing soil salinity, increasing nutrient content in cotton fields, and can accelerate the activities of nutrient-releasing enzymes, which partly confirm the sustainability of MDI in oasis agroecosystems.

Soil Fertility Evaluation and Mapping of Burugamaradoddi Microwatershed of Ramanagara Taluk, Ramanagara District, Karnataka

The present investigation was conducted to know the soil fertility status of Burugamaradoddi microwatershed of Ramanagara district. The soil samples were collected from 0-15 cm soil depth from 70 locations. Soil fertility maps were prepared for pH, electrical conductivity, organic carbon, available nitrogen, available phosphorous, available potassium and available sulphur, exchangeable calcium and magnesium, available boron and available micronutrients viz., iron, manganese, zinc, copper and zinc. Results revealed that the soils were slightly acidic (pH: 5.35-8.32) to moderately alkaline and electrical conductivity of soil were non- saline to slightly saline. The organic carbon status ranged from low to high (0.15-0.90%), and available nitrogen was mostly low. The soil available phosphorus was low to medium; available potassium was in low to medium range and exchangeable calcium and magnesium were found in sufficient range, available sulphur was in low to high range. Regarding available micronutrients, boron and zinc were in low category and level of copper, iron and manganese were in sufficient range. The assessment of soil fertility in Burugamaradoddi micro-watershed revealed that, watershed had better soil fertility status in soil.

Synthetic bacterial communities reshape microbial communities and enhance nutrient supply in desertified land of Northwest China

Climate change and human disturbance have led to widespread soil degradation worldwide. The problem of desertification is gradually destroying soil carbon accumulation. Synthetic bacterial communities (SynComs) are a healthy solution capable of improving the microbiome for plant growth. However, the effect of SynCom on nutrient functions in desertified land remains poorly understood. Here, two years of different treatments (control, chemical fertilizer, SynCom, combined SynCom-Chemical fertilizer) were conducted on desertified land in the Loess Plateau, and we aimed to reveal the effects of introducing SynCom on bacterial communities and nutrient multifunctionality. The SynCom enriched more beneficial bacteria as key microorganisms and increased biodiversity. At the same time, the bacterial community structure of the desertified land shifted significantly and remained stable at the soil surface (0–10 cm). We found that SynCom enhanced the complexity of the bacterial network with higher modularity. Our results also revealed the influence of biotic and abiotic factors on nutrient availability. Bacterial diversity and soil electrical conductivity (EC) were the significant influencing factors for chemical and combined fertilizers. However, SynCom exhibited stronger bacterial effects, and soil organic matter significantly affected the biodiversity-ecosystem function (BEF) relationships. Overall, this study illustrates the impact of microbial amendment on nutrient function in desertified land and provides insights into SynCom application to enhance ecosystem restoration and carbon sinks.

Detection of the Spatial Variability of Soil Salinity East of the Bitter Lake of the Suez Canal, Egypt, as a Basis for Management Zones Using Sentinel-2 Multispectral Imagery

ABSTRACT Soil salinity is one of the more serious problems that cause soil degradation, particularly in semi-arid and arid regions. In agricultural lands, it threatens plant growth and productivity, which requires specific management decisions for various inputs, such as fertilizers. Accurate prediction and mapping of soil salinity have become possible through remote sensing techniques. The focus of this research is to derive soil salinity from spectral indices measured from different bands of sentinel-2 satellite in order to delineate management zones (MZs). Four spectral salinity indices were used for the purpose of this study, using blue, green, red, and NIR bands in different combinations. Exponential regression best describes the relationship between salinity indices and soil electrical conductivity (EC) through groundtruthing. The results indicate that salinity indices 2 () and 4 () (SI2 and SI4) outperformed the other indices and could describe 70% and 71% of the variability in soil EC with prediction models of: and , respectively. The generated models were validated by normalized root mean square error and the d coefficient of agreement. The results of the best-fit models were 16.5% and 0.86 for SI2 and 16.7% and 0.84 for SI4, respectively. The box-and-whiskers diagram proposed that the field can be divided into four soil EC-dependent groups, which are considered MZs to support a variety of management decisions. This study shows that through sentinel-2 multispectral imagery, the spatial variability of soil salinity can be mapped and used as a basis for MZs within the studied region.

Mixed Consortium of Salt-Tolerant Phosphate Solubilizing Bacteria Improves Maize (Zea mays) Plant Growth and Soil Health Under Saline Conditions.

The rhizobacterial isolate SP-167 exhibited considerable phosphate solubilization, IAA production, exo-polysaccharides, proline, APX, and CAT at a concentration of 6% NaCl (w/v). 16S rDNA sequencing and BLAST analysis showed that isolate SP-167 was Klebsiella sp. In this study, T2 and T8 consortium was developed on the basis of the compatibility of isolate SP-167 with Kluyvera sp. and Enterobacter sp. At 6% NaCl (w/v) concentration, T2 and T8 showed increased PGP properties such as phosphate solubilization, IAA, Proline activity, CAT, POD, and EPS than isolate SP-167. The maximum increase in shoot length was recorded in T2-treated maize plants as compared to the control after 60days in 1% NaCl stress. The N, P, and K content of leaves were significantly increased in maize plants with the inoculation of both the T2 and T8 consortium. The electrical conductivity of soil was decreased significantly in the T2 inoculated 1% NaCl (w/v) treated pot after 30, 60, and 90days. In this study, soil enzymes DHA and PPO were significantly increased in both T2 and T8 treated combinations. The Na concentration in root and shoot were significantly decreased in T8 inoculated plant than in T2, as confirmed by the translocation factor study.

Comparison of single vs composite soil electrical apparent conductivity-directed samples of irrigated soils for inorganic nitrogen estimation with electromagnetic induction sensors

The management of soil can be improved by precision agriculture. A way to achieve this is by quantifying NH4+–N and NO3−–N in soil. The sampling of soil for quantifying these N species is a laborious task. Electromagnetic induction (EMI) sensors could ease the task, providing a large quantity of data. The correlation of inorganic N with soil electrical apparent conductivity (ECa) in either single or composite samples is essential to accomplish this. Using an ECa-directed sampling approach, suitable sampling points were identified at four centre pivots. Single and composite samples were collected in 300 mm increments to 600 mm at Hofmeyr and 1500 mm at Douglas, Luckhoff and Empangeni. The samples were analysed for NH4+–N and NO3−–N from which total inorganic N (TIN) was calculated. All three inorganic N fractions were correlated insignificantly to in-field readings of ECa, implicating that EMI sensors are not suitable for inorganic N estimations in these irrigated soils. A comparison between single and composite samples, however, showed a good agreement of NH4+–N concentrations which was not true for NO3−–N or TIN concentrations. Composite samples are recommended for inorganic N measurements with an EMI sensor. Single samples could be used when only NH4+–N is analysed.

Soil Nutrient, Salinity, and Alkalinity Responses of Dendrocalamopsis oldhami in High-Latitude Greenhouses Depending on Planting Year and Nitrogen Application

This study explored the viability of greenhouse cultivation of Dendrocalamopsis oldhami under the “South Bamboo North Transplanting” initiative. In this study, the effects of planting year and nitrogen application on changes in soil nutrient levels, salinity, and alkalinity over the plant growth period were explored. After the introduction and planting of bamboo in 2017, a soil layer with a thickness of 0–40 cm was sampled at the end of the shooting stage in the greenhouse between 2017 and 2019 (late August), and the bamboo shoot yield and standing culm density were measured. Following the application of nitrogen to the bamboo groves in 2019, three nitrogen levels were established: no nitrogen (N1:0 g grove−1), medium nitrogen (N2:540 g grove−1), and high nitrogen (N3:1080 g grove−1). Soil layers at depths of 0–20 and 20–40 cm were sampled during the shoot elongation stage (late May) and at the end of the shooting stage (late August). The yield and nutrient content of bamboo shoots under different nitrogen treatments were also investigated. The results showed that Ca2+ and HCO3− were the main salt ions in greenhouse soil. With later planting years, the total number of cations (Ca2+, Na+, Mg2+, and K+) decreased, whereas the total number of anions (HCO3−, SO42−, NO3−, and Cl−) increased, resulting in a decrease in the percentage of exchangeable sodium (ESP), pH, and electrical conductivity (EC). The diameter at breast height, individual weight, and quantity of bamboo shoots increased annually, and the standing culm density increased by 1.4 times. Each year, the total nitrogen content decreased, whereas the alkali-hydrolyzed nitrogen, available phosphorus, and available potassium contents increased. Nitrogen application resulted in a significant decrease in ESP and pH and an increase in the total anion, cation, and EC values. It also reduced soil organic carbon, total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium. Nitrogen application increased the number of bamboo shoots, total yield, and accumulation of N and P; however, there was no significant difference between N2 and N3. In conclusion, the salinization of calcareous soil was alleviated, and the available nutrients were activated following the introduction of D. oldhami from south to north. The mineralization rates of organic matter and soil fertility increased. Soil acidification and EC decreased at the end of the shoot stage. Nitrogen application acidified the soil, and the yield and soil salt accumulation increased with increasing nitrogen levels. The nutrient uptake efficiencies of nutrients at high nitrogen levels were lower than those at medium nitrogen levels. Therefore, soil salt concentrations with values 0.26 &lt; EC &lt; 0.42 hindered the nutrient uptake of D. oldhami.

Effects of plastic film mulching and legume rotation on soil nutrients and microbial communities in the Loess Plateau of China

BackgroundPotato (Solanum tuberosum L.) continuous cropping causes the decrease of tuber yield, deterioration of quality and soil degradation in the semi-arid area. These negative effects can generally be mitigated by legume rotation and mulching. However, little is known about how can mulching and legume rotation alleviate the above damage through altering soil environment.MethodsA field experiment was conducted to investigate changes in soil properties and microbial community in response to legume rotation and mulching under six planting patterns: potato continuous cropping without film mulching (PC), potato continuous cropping with film mulching (PCF), potato–broad bean rotation without film mulching (R1), potato–broad bean rotation with film mulching (R1F), potato–pea rotation without film mulching (R2) and potato–pea rotation with film mulching (R2F).ResultsCompared with the PC, the R1F and R2F had significantly enhanced the contents of alkaline nitrogen (AN), available phosphorus (AP), available potassium (AK), total carbon (TC) and total nitrogen (TN), but reduced soil pH and electrical conductivity (EC). The Shannon index of fungi in R1F and R2 was significantly higher than other treatments. The dominant bacterial and fungal phyla of each treatment was Proteobacteria and Ascomycota. R1, R1F, R2 and R2F enhanced the relative abundance of metabolic fungi and altered key differential microbial species. Soil EC, AN and AK were major factors influencing the soil bacterial and fungal communities.ConclusionOverall, the study demonstrated that potato-broad bean/pea rotation with mulching can be adopted as the preferred cropping systems to alleviate potato continuous cropping obstacles through enhancing soil fertility and regulating soil microbial communities in the semi-arid of Loess Plateau, China.Graphical

A novel method for detecting soil salinity using AVIRIS-NG imaging spectroscopy and ensemble machine learning

Soil salinization is one of the major land degradation processes spread over millions of hectares of global land. Hyperspectral Remote Sensing (HRS) coupled with modern data mining approaches help in real-time and cost-effective assessment or monitoring of salt-affected soils. This study aimed at predicting soil salinity across five sites in India using the Airborne Visible-Infrared Imaging Spectrometer - Next Generation (AVIRIS-NG) data in low to moderately salt-affected cropland soils. We have identified four unique spectral absorption features having sensitivity towards soil salinity through a hybrid feature selection algorithm. Soil electrical conductivity (EC) was estimated using different machine learning (ML) based models such as random forest (RF), gradient boosting machines (GBM), and deep learning (DL). An ensemble of RF and DL models showed the best performance with the coefficient of determination (R2) of 0.89 and 0.55 and normalized root-mean-squared error of 0.15 and 0.16 in training and test datasets, respectively. We also proposed a new hyperspectral soil salinity index using Shannon entropy-based aggregation of selected absorption features. The newly proposed index outperformed other majorly used remote sensing-based salinity indices. It also showed a strong correlation with measured EC (r = 0.68) and ML-predicted soil EC (r = 0.78), both being significant at 1% level of significance. The index was effective in classifying HRS images into six distinct salinity classes. We also assessed the feasibility of applying the proposed salinity index for future hyperspectral missions through the simulation of various spectral-spatial resampling scenarios and estimated the optimal spectral and spatial resolution for salinity prediction. The hyperspectral salinity index can be directly estimated from HRS data without the need for time-consuming and expensive field samplings and used as a proxy to evaluate soil salinity status under field conditions.

Ammonia oxidizing archaea and bacteria respond to different manure application rates during organic vegetable cultivation in Northwest China

Ammonia oxidization is a critical process in nitrogen cycling that involves ammonia oxidizing archaea (AOA) and bacteria (AOB). However, the effects of different manure amounts on ammonia-oxidizing microorganisms (AOMs) over the course of organic vegetables production remains unclear. We used the amoA gene to evaluated AOMs abundance and community structure in organic vegetable fields. Quantitative PCR revealed that AOB were more abundant than AOA. Among them, the amoA copy number of AOB treated with 900 kgN ha−1 was 21.3 times that of AOA. The potential nitrification rate was significantly correlated with AOB abundance (P < 0.0001) but not with AOA, suggesting that AOB might contribute more to nitrification than AOA. AOB sequences were classified into Nitrosomonas and Nitrosospira, and AOA into Nitrosopumilus and Nitrososphaera. Nitrosomonas and Nitrosopumilus were predominant in treatments that received manure nitrogen at ≥ 900 kg ha−1 (52.7–56.5%) and when manure was added (72.7–99.8%), respectively, whereas Nitrosospira and Nitrososphaera occupied more than a half percentage in those that received ≤ 600 kg ha−1 (58.4–84.9%) and no manure (59.6%). A similar manure rate resulted in more identical AOMs’ community structures than greater difference manure rate. The bacterial amoA gene abundances and ratios of AOB and AOA showed significantly positive correlations with soil electrical conductivity, total carbon and nitrogen, nitrate, phosphorus, potassium, and organic carbon, indicating that these were potential key factors influencing AOMs. This study explored the AOMs’ variation in organic vegetable fields in Northwest China and provided a theoretical basis and reference for the subsequent formulation of proper manure management.