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Improper fertilization or excessive nitrogen input may cause serious environmental problems and affect soil health. This is particularly the case in saline agroecosystems, as soil salinization alters nitrogen cycling and contributes to substantial nitrogen losses. However, the impact of amendment materials on the combined processes of nitrogen transformation and migration in salt-affected soil has not yet been explicitly clarified. Here, soil column and incubation experiments on biochar (BC)- and potassium humate (PH)-amended salt-affected soil were conducted. The transport and redistribution characteristics of soil water, salt and mineral nitrogen under drip fertigation (urea as fertilizer) were investigated, and the responses of urea hydrolysis and nitrification to BC and PH addition under soil salinity gradients were elucidated. The results showed that BC application increased the migration and redistribution ranges of soil water, salt and mineral nitrogen by improving soil macropores and infiltration and diffusion rates. PH addition maintained higher contents of soil water, salt and mineral nitrogen in the wetting pattern by enhancing the soil water-holding capacity. Both BC and PH addition shifted not only the transport and redistribution but also the morphological conversion of urea-N. BC and PH addition delayed the rise and decline of ammonium nitrogen (NH4+-N) content and postponed the rise of nitrate-nitrogen (NO3−-N) content in the wetting pattern. The results of the incubation experiment corroborated those of the column experiment. Both BC and PH aggravated the inhibitory effect of soil salinity on urea hydrolysis and nitrification by prolonging the duration by 2–7 days and postponing the time when the maximum NH4+-N and NO3−-N concentrations were reached. PH showed a stronger inhibitory effect on nitrification than BC. The redistribution of urea-N in soil under drip fertigation was primarily dominated by water migration and diffusion, as physically mediated by BC and PH addition, and by the morphological conversion biochemically affected by the interactions of soil salt and BC and PH addition. It was concluded that morphological conversion played an important role in soil nitrogen transport and redistribution, and it is essential to consider the interactive impact of amendment materials and soil salinity level on nitrogen transformation for efficient and sustainable management of fertilizer nitrogen in salt-affected soil. [ABSTRACT FROM AUTHOR]

Understanding the impacts of tillage on soil microflora, especially functional microbes related to nitrogen conversion, is essential for ensuring the sustainable production, biodiversity and function of agroecosystems in salinized soils. Based on a two-year field plot experiment in a salt-affected farmland, the effects of three tillage methods, namely, CT (conventional rotary tillage, depth 25 cm), VRT (vertical rotary tillage, depth 25 cm) and DVRT (deep vertical rotary tillage, depth 50 cm), on soil physicochemical properties and ammonia-oxidizing archaea (AOA), bacteria (AOB) and comammox bacteria (CAOB) communities were investigated. Soil samples over the sunflower (Helianthus annuus L.) growing season were collected on three dates, i.e., April 28, July 6, and September 6, 2020. The results indicated that CT, VRT and DVRT had the lowest EC 1:5 values (0.75–1.23 dS/m) and the highest OC (organic carbon, 14.50–19.32 g/kg), WSA1 (> 2 mm water-stable aggregates, 31.05–37.88 g/kg), and WSA2 (2–0.25 mm water-stable aggregates, 69.51–83.70 g/kg) values on the middle sampling date. The average number of OTUs was 51.2 ± 3.3, 43.2 ± 3.8 and 42.8 ± 6.2 (mean ± SD) per soil sample for AOA, AOB and CAOB, respectively. DVRT significantly affected the community richness indices (Sobs, ACE and Chao1) of AOA and AOB, whereas sampling dates shifted almost all the soil physicochemical properties and diversity indices (Shannon and Simpson) of AOA and AOB but not those of CAOB. Phyla Crenarchaeota , unclassified_d_Unclassified , Unclassified_k_norank_d_Archaea and Thaumarchaeota were the most common taxa (with relative abundances >5 %) of AOA under all the treatments. For AOB, >92 % of the taxa were categorized into the phylum Proteobacteria , and CT had a greater frequency of the phylum Proteobacteria than did VRT and DVRT on all sampling dates. For CAOB, approximately 90 % of the taxa were classified into the phylum Nitrospirae , and the relative abundance of Nitrospirae did not differ among the tillage practices, whereas VRT and DVRT had the highest relative abundance of Nitrospirae on the middle sampling date. A total of 88.69 % of the variation in the genus compositions of AOA, AOB and CAOB was explained by EC 1:5 , pH, OC, ρ b (bulk density), WSA1 and WSA2. In conclusion, tillage practices and sampling dates can diversely affect soil physicochemical properties, microbial richness and diversity indices of AOA, AOB and CAOB, and seasonal changes overwhelm tillage practices in shaping AOA, AOB and CAOB communities across the sunflower growing season in salinized irrigated farmland. • Tillage and sampling date dominated richness and diversity, respectively, for AOA and AOB. • Community richness and diversity of CAOB were only responsive to sampling date. • Tillage and seasons affected microbial communities by changing EC 1:5 , pH, OC, ρ b , WSA1 and WSA2. • Seasons overwhelmed tillage in shaping AOA, AOB and CAOB communities in sunflower growing season. [ABSTRACT FROM AUTHOR]

Aims: Soil fungal communities play pivotal roles in promoting ecosystem carbon (C) and nitrogen (N) cycling, stimulating disease resistance and enhancing tolerance against salt stress of host plants. However, the impact of anthropogenic management practices on the soil fungal community structure has not yet been clarified. Methods: Using a four-consecutive-year field experiment and the quantitative polymerase chain reaction (qPCR) and Illumina MiSeq DNA sequencing methods, the single and interactive impacts of crop cultivation (CK), N fertilization (N) and fulvic acid (F) on soil fungal diversity, abundance, composition and functional groups were investigated. Results: Consecutive crop cultivation improved soil chemical and microbial properties by reducing soil electrical conductivity (ECe) and enhancing soil organic carbon (SOC), microbial biomass carbon (MNC), and microbial biomass nitrogen (MBN). Crop cultivation had larger contribution to fungal richness and diversity than N fertilization and fulvic acid. Crop cultivation enriched mycorrhizal fungi and N fertilization enriched endophytic, saprophytic and pathogenic fungi. Structural equation modeling (SEM) revealed that soil ECe and pH indirectly influenced MBN through their adverse direct impact on OTUs, Shannon index and abundance of predominant fungal taxa. N input exhibited a positive indirect influence on MBN through enhancing abundance of Funneliformis at the genus level. Conclusions: Crop cultivation, N input, and fulvic acid addition in saline soil environment changed the environmental niches and drove the evolution of soil fungal community. In return, the shifts in soil fungal community composition and functional groups greatly affected soil C and N transformation with potential feedback on soil microbial activity. [ABSTRACT FROM AUTHOR]

Reliable and real-time information on soil and crop properties is important for the development of management practices in accordance with the requirements of a specific soil and crop within individual field units. This is particularly the case in salt-affected agricultural landscape where managing the spatial variability of soil salinity is essential to minimize salinization and maximize crop output. The primary objectives were to use linear mixed-effects model for soil salinity and crop yield calibration with horizontal and vertical electromagnetic induction (EMI) measurements as ancillary data, to characterize the spatial distribution of soil salinity and crop yield and to verify the accuracy of spatial estimation. Horizontal and vertical EMI (type EM38) measurements at 252 locations were made during each survey, and root zone soil samples and crop samples at 64 sampling sites were collected. This work was periodically conducted on eight dates from June 2012 to May 2013 in a coastal salt-affected mud farmland. Multiple linear regression (MLR) and restricted maximum likelihood (REML) were applied to calibrate root zone soil salinity (ECe) and crop annual output (CAO) using ancillary data, and spatial distribution of soil ECe and CAO was generated using digital soil mapping (DSM) and the precision of spatial estimation was examined using the collected meteorological and groundwater data. Results indicated that a reduced model with EMh as a predictor was satisfactory for root zone ECe calibration, whereas a full model with both EMh and EMv as predictors met the requirement of CAO calibration. The obtained distribution maps of ECe showed consistency with those of EMI measurements at the corresponding time, and the spatial distribution of CAO generated from ancillary data showed agreement with that derived from raw crop data. Statistics of jackknifing procedure confirmed that the spatial estimation of ECe and CAO exhibited reliability and high accuracy. A general increasing trend of ECe was observed and moderately saline and very saline soils were predominant during the survey period. The temporal dynamics of root zone ECe coincided with those of daily rainfall, water table and groundwater data. Long-range EMI surveys and data collection are needed to capture the spatial and temporal variability of soil and crop parameters. Such results allowed us to conclude that, cost-effective and efficient EMI surveys, as one part of multi-source data for DSM, could be successfully used to characterize the spatial variability of soil salinity, to monitor the spatial and temporal dynamics of soil salinity, and to spatially estimate potential crop yield. [ABSTRACT FROM AUTHOR]

Biochar has been globally recognized as a novel and eco-friendly soil ameliorant to mitigate hazardous effects of salinization on soil health, and mediate carbon and nitrogen (N) nutrient cycling in agricultural ecosystems. However, knowledge pertaining to the regulatory mechanism of biochar application on nitrification in the salt-affected soil is limited. In this study, field plot experiment for three consecutive years and an aerobic incubation experiment with three biochar application rates (7.5, 15, and 30 ton ha−1) and N fertilizer (225 kg N ha−1 yr−1) were conducted. We investigated the effect of combined application of biochar and N fertilizer on soil chemical and microbial properties, nitrification kinetic parameters, and the abundance of ammonia monooxygenase (subunit A, amoA) gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Our results showed that biochar addition increased soil pH, cation exchange capacity, available potassium, and microbial biomass carbon, and decreased the numbers of amoA -AOB gene in the salt-affected soil applied with N fertilizer. The nitrification process and fitted kinetic parameters were negatively responsive to the combined application of biochar and N fertilizer, which reduced the nitrification potential and potential nitrification rate, and prolonged the duration of nitrification. The nitrification rate and abundance of amoA -AOB and amoA -AOA genes decreased under biochar and N fertilizer addition, and biochar played the predominant role in the inhibiting effect, which aggravated with the increase of biochar rate. The AOB dominated the autotrophic nitrification with the nitrification rate having higher positive correlation with abundance of amoA -AOB gene than with that of amoA -AOA gene. The abundance of both amoA -AOB and amoA -AOA genes showed significantly negative correlation with nitrate nitrogen (NO 3 −-N) concentration. In conclusion, biochar and N fertilizer addition inhibited the autotrophic nitrification rate mainly by greatly reducing the abundance of amoA -AOB gene, which was adaptive to the changing soil microhabitat traits induced by biochar application and N fertilization. • Biochar and N fertilizer addition inhibited nitrification and shifted kinetic parameters. • Biochar and N fertilizer addition decreased the nitrification rate and abundance of amoA gene. • Biochar dominated nitrification inhibition and increase of biochar rate aggravated inhibition. • Biochar and N fertilizer inhibited nitrification rate by reducing the abundance of amoA -AOB gene. [ABSTRACT FROM AUTHOR]

Abstract: The need for understanding and assessing soil quality is getting increasingly important because of growing public interest in determining the effect of management practices on the sustainability of the soil resource base. Our objectives were to investigate the effect of consecutive cultivation and different rotation systems on potential soil quality indicators, to identify effective soil quality indicators and to establish a minimum data set that discriminate different rotation systems. This study was conducted in a typical coastal salt-affected farmland in north Jiangsu Province, China. A pool of 22 measured variables representing soil chemical and physical properties (0–10cm) and groundwater features at 60 sampling sites and 10 representative soil profiles were used. A specific emphasis was given to the impact of crop rotation systems on measured soil and groundwater properties because of the importance of cultivation to the sustainability of soil quality. One-way analysis of variance (ANOVA) showed that measured variables of SOM, SOCD, TN, AP, CEC, AK, ECe, Na and Cl were positively impacted by cultivation. In contrast to cotton–barley rotation, rice–rape rotation had significantly positive influence on SOM and SOCD, but adverse impact on AK, pH, ρ b , K s , WTg and ECg. Factor analysis grouped all measured variables into seven principal components explaining 78.5% of total variance: salinity (PC1), organic matter (PC2), water permeability (PC3), soil texture (PC4), ion exchange (PC5), soil alkalinity (PC6) and available nutrients (PC7). Discriminant analysis indicated that PC1 (Cl, Na and ECg), PC2 (SOM and SOCD) and PC7 (WTg) were the most powerful factors (indicators) to distinguish the two rotation systems. SOCD (SOM) and Cl offered the greatest potential for monitoring soil quality under different management practices. SOM not only had the strongest positive influence on crop biomass, but also contributed the greatest to distinguishing the effect of rotation systems on soil quality. Our study suggested that SOM may be considered as an indispensable factor to determine the sustainability of soil productivity for the salt-affected farmlands in coastal reclamation area. [Copyright &y& Elsevier]

Abstract: In the Lower Yellow River Delta, soil salinity is a problem due to the presence of a shallow, saline water table and marine sediments. Spatial information on soil salinity at the field level is increasingly needed, particularly for better soil management and crop allocation in this area. In this paper, a mobile electromagnetic induction (EMI) system including EM38 and EM31 is employed to perform field electromagnetic (EM) survey, and fast determination and quantitative evaluation of the spatial pattern of soil salinity is discussed using the field EM survey data. Optimal operation modes of EM38 and EM31 are determined to establish multiple linear regression models for estimating salinity from apparent soil electrical conductivity (ECa). Spatial trend and semivariogram are illustrated and spatial distribution of field salinity status is further visualized and quantitatified. The results suggest that ECa (EM38 and EM31) data is highly correlated with salinity, and that the interpretation precision of soil salinity at various layers can be improved using EM38h and EM31h (where h represents the horizontal mode of EM measurement). Both EM38h and EM31h exhibit significant geographic trend. Nested spherical models fit the semivariance of EM38h and EM31h better than single spherical models. Spatial autocorrelation of EM31h is stronger than that of EM38h, and short-range variation is the chief constitute of spatial heterogeneity for both EM38h and EM31h. Quantitative classification shows that soil salinity exhibits the trend of accumulation in the root zone. In 0–1.0m solum, heavy salinized and saline soils are the predominant soil types, accounting for 54% and 41% of total survey area, respectively. The area of light and moderate salinized soils is comparatively small, which accounts for only 0.4% and 4.6%, respectively. [ABSTRACT FROM AUTHOR]

• Field data showed groundwater salinity increase after beach nourishment. • Beach nourishment of heterogeneous aquifers creates complex fresh-saline interface movement. • Beach nourishment can merge layered heterogeneity and cause severe groundwater salinization. Beach nourishment is a widespread coastal management technique, which can not only counteract coastal erosion, but also changes coastal groundwater dynamics. Understanding mechanisms and drivers of this subsurface flow and transport processes is key to predicting future groundwater resources to beach nourishment. We implemented a monitoring network of specific conductivity (SC) sensors in wells at different aquifers layers before and after beach nourishment. Recorded SC show that groundwater salinity increased differently after beach nourishment at multiple depths. We used a series of variable-density groundwater flow and salt transport models with both homogeneous and layered heterogeneous cases to illustrate characteristics of groundwater salinity after beach nourishments. Simulations showed that in homogeneous aquifers, salinization patterns were simple and linear related to the beach depth and width, with a relief effect on seawater intrusion. In heterogeneous aquifers, salinity patterns were much more complicated, and the resulting effects on seawater intrusion were determined by the breakdown of original layered system. The analysis provides new insights into the effect of beach nourishment on seawater intrusion. Consideration of aquifer heterogeneity can be a starting point for more sophisticated groundwater management, including vulnerability assessment and optimization of beach nourishment. [ABSTRACT FROM AUTHOR]

Climate events, such as drought and rainfall, can lead to a cycle of drying and wetting that may cause changes in soil structure, leading to deteriorations in the health of saline soils. However, little is known about the extent and behavior of soil structure degradation under the combined influences of salinity and drying–wetting (D‐W) cycles. Thus, we systematically investigated the effects of salinity (0, 5, 30, and 100 g/L, labeled as CK, T5, T30, and T100) and D‐W cycles on soil structure by determining soil volume, shrinkage, and swelling potentials along with soil pore character obtained from soil shrinkage characteristics curve, intending to explore how D‐W cycles and salinity affect soil structure. The results showed that soil deformation behaviors in saline and non‐saline soils varied with the number of D‐W cycles. Irreversible deformation of the soil was observed during continual D‐W cycles. The soil volume increased by 3.75%–15.73% after three D‐W cycles. In vertical direction, the maximum expansion magnitude for each treatment was reached with the value of 29.03%, 23.42%, 34.23%, and 35.87% in CK, T5, T30, and T100, respectively. The magnitudes of shrinkage and expansion were equal in the horizontal direction since the soil samples consistently returned to their original dimensions. Furthermore, the decrease was observed in the micropores and capillary pores affected by salinity, with values of 50%, 58.6%, and 70.4% in CK, T5, T30, and T100, respectively. However, the D‐W cycles primarily affected large pores. High salinity levels enhanced swelling potential and inhabit shrinkage potential, prolonging the water processes required for the soil structure to achieve stability. The results of this study underscore the necessity of understanding the hysteresis of soil volume change and elucidate the mechanisms of soil structure deterioration driven by salinity and D‐W cycles. These findings provide a valuable reference for healthier soil management. [ABSTRACT FROM AUTHOR]

The improvement effect of willow (Salix matsudana cv. zhuliu) cultivation on coastal saline soil and the main factors affecting soil properties were studied. Three treatments were designed: willow seeding site (SS), willow afforestation site (AS) and natural control site (CK). The results showed that soil pH and ECe decreased from 8.50 to 7.43 and from 6.8 dS/m to 0.8 dS/m at 0–20 cm layer, respectively. Willow cultivation significantly increased soil organic matter both in SS (3.64 g kg−1 – 4.05 g kg −1) and AS (2.82 g kg−1 – 3.92 g kg −1) treatments. The soil total nitrogen and available potassium of different treatments were increased with time and ranked AS > SS > CK. The AS16 treatment has a higher soil enzyme activity (soil urease, catalase, sucrase and phosphatase) and soil microbial population (bacteria, fungi and actinomycetes). Redundancy analysis suggested that soil pH and salinity were the key factors (85.4%) determining soil microbial quantities. Principal component analysis showed that the soil improvement by willow cultivation was significantly affected by soil enzyme activity, and AS16 had a better effect on costal saline soil especially in reducing soil salinity and improving microbial environment [ABSTRACT FROM AUTHOR]

Paddy cultivation in saline soil can rapidly reduce soil salinity, which is an important approach for managing, utilizing, and improving such soils. However, the high salinity of saline soil severely limits the sustainability of paddy production. Adding exogenic organic material to improve soil fertility in saline soil is a key measure for obtaining high-yield, efficient and sustainable cultivation of paddy. This study used a field experiment to explore the influences of different organic materials application on soil desalination and fertility improvement in saline paddy soil. The results showed that the application of dairy manure (DM), sludge vermicompost (SV), and vinegar residue (VR) reduced soil barrier factors, including electrical conductivity (EC) and pH, increased soil fertility, including soil organic carbon (SOC), nitrogen (N), and phosphorus (P), and promoted paddy growth in saline soil. Specifically, soil EC decreased by 29.0%, 32.9% and 49.4% and paddy biomass increased by 27.7%, 63.7% and 107.6% in DM, SV, and VR-treated soils with the highest application rates, respectively, compared to the control. At an equal carbon application rate, VR was more conducive to decreasing soil EC and pH and increasing paddy biomass. Compared to DM and SV, VR addition resulted in an average decrease of 20.7% and 19.1% in soil EC, respectively, and an average increase of 57.3% and 29.5% in paddy biomass. In addition, soil water-stable aggregates (WSA), SOC, N, and P contents in VR-treated soil were lower than those in DM and SV-treated soils. Correlation and path analysis revealed that there was a significant negative correlation between paddy biomass and soil barrier factors. However, EC in VR-treated soil had a direct negative effect on paddy biomass, while EC in DM and SV-treated soils had an indirect negative effect on paddy biomass. Additionally, the direct contribution of soil pH to paddy biomass was higher with VR (−1.49) than that with DM (−0.21) and SV (0.89). In contrast to DM and SV, the effect of soil WSA on paddy biomass in VR-treated soil was mainly an indirect positive effect, and the direct effect was negative. The corresponding results provided new options and ideas for the efficient utilization of saline soils and high-yield cultivation of paddy. [ABSTRACT FROM AUTHOR]

The Yellow River Delta is an important grain production base in China, and it is a typical Yellow River irrigated area. Chemical fertilizer overuse has seriously affected grain production safety, and understanding the fertilizer application situation is useful for scientific agronomy management. In this study, we collected the data of the N, P, K fertilizers for crop cultivation in Donging City from 2011 to 2020, and we collected 185 investigating questionnaires to gather information on the fertilizer application rate for small farmers. The results showed that the amount of total fertilizer used has decreased from the year 2015, but the macro element fertilizer rate for crop cultivation exceeded the recommended dosage. The application of compound fertilizer increased during the investigated 10 years, and its proportion in 2020 was 1.65 times higher than in 2011. For obtaining an ideal grain yield, the N and P2O5 had relative reduction rates of 67.8% and 69.6% for wheat planting. Furthermore, the relative reduction rates of N, P2O5, and K2O were 25.9%, 69.6%, and 59.7%, respectively, for maize cultivation when compared to the recommended dosage. During wheat growth, the potassium fertilizer was needed to increase the dosage, although the K element content in the soil was high. Furthermore, the medium and trace elements are all important nutrients for improving crop yield and quality which need to be studied. More scientific measurements should be conducted to match chemical fertilizer reduction to constructing healthy and sustainable agriculture in the Yellow River irrigated area. [ABSTRACT FROM AUTHOR]

Irrigation is the primary agricultural utilization of water resources worldwide, and it produces 36% of the food. The quality of irrigation water influences crop growth and food safety. The coastal river delta region supplies huge area lands for developing agriculture, and the irrigation in this area is composed of many resources for its special location. This study investigated the agricultural water with different resources and evaluated its quality in the Yellow River Delta. The water samples included irrigation water, underground water, and drainage water. The sampling points were designed in the typical areas of Kenli county and Guangrao county in Dongying city, which is the core area of the Yellow River Delta. Through testing the ions composition and the parameters of electrical conductivity (EC), pH, and so on, six evaluation methods were conducted to assess the water quality. The results suggested that the Yellow River water has good quality for irrigation or unconventional water utilization. The high concentration of Na+ and Cl− was the primary problem of the water resource. The rainfall was also another water resource supplement in this region. Therefore, developing saline water irrigation incorporated with salt-tolerant crop cultivation is a rational measure for improving coastal agriculture in the Yellow River Delta. [ABSTRACT FROM AUTHOR]

Soil salinization and water shortage restrict the utilization of saline soil resources in the Yellow River Delta, China (YRD). As such, soil water and salt management are two methods for the saline soil reclamation in this area. In this study, a two-year field experiment was conducted to investigate the effects of compound control on the rules of water and salt movement in salt-affected field, and their effect on cotton yield, which were combined by plastic film mulch and buried wood fibre layer (FM+BL). Hydrus-2D was used to analyse their spatial and temporal change. Results showed that soil water at different observation positions were maintained above 0.15 cm3 cm−3 under film mulch, which was higher than that in bare ground (BG), and the closer to the topsoil the greater difference between FM+BL and BG, especially in 2020. FM+BL controlled soil water stress and improved water use efficiency during the whole growing season both in 2019 and 2020. FM+BL invariably and significantly controlled the salt content of the upper 60 cm depth, which was lower than 2.00 g kg−1 during the whole growing season. Furthermore, soil salt contents under film mulch in the upper 30 cm depths were significantly reduced for the high soil water contents. Thus, soil salt content of 0–60 cm layer responded to the heavy rainfall events positively, soil salinity decreased as a whole along with the process of rainfall under the effect of FM+BL. FM+BL has a significant effect on crop growth and yield improvement, the average yields were 1163.7 and 1301.7 kg ka−1 in 2019 and 2020, respectively. Therefore, FM+BL could be an efficient way for soil water conservation, salt accumulation interruption and cotton yield increasing in the YRD. • Hydrus-2D well used in the Yellow River Delta, China. • Buried wood fibre layer plus film mulch improve soil water content. • Salt accumulation was well controlled by the buried layer and film mulch. • Buried wood fibre layer plus film mulch would improve cotton yield. [ABSTRACT FROM AUTHOR]

Soil salinity and the shortage of fresh water resource are the major factors to limit sustainable development of agriculture industry in the newly reclaimed coastal tidal flat soil in northern Jiangsu Province. The results from previous investigation demonstrate that this area has saline water resources with a shallow groundwater table. Rice as a moderate salt-tolerant crop is cultivated widely in this area. Thus, an experiment has been conducted to evaluate the effects of irrigation water with different salt concentration on soil salinity, grain yield and water use efficiency in the region. Field experiments always are time-consuming and expensive. Whereas, simulation models play an increasingly important role in predicting long-term effects of saline water irrigation on soil salinity and crop production. The objective of this paper was to use SWAP model to evaluate the effects of irrigation water with different salt concentration on rice water use efficiency and the dynamic of soil salt concentration in a paddy field based on a field experiment results. Rice was grown on a sandy loam soil and surfaced irrigated with three water quantities (V1, V2 and V3) and five different salt concentrations (C, M1, M2, M3, Ma and Mb), respectively. SWAP model was calibrated and validated based on the field experiments. Model simulation results agreed well with the observed values. For example, the root mean squared error (RMSE) for the salt concentration were 0.60 mg cm-3 from simulation and 0.50 mg/cm3 from the experiment, and the simulated and observed values distributed along the 1:1 line. For the grain yield, most of the relativity error (RE) values were less than 10%. Furthermore, the water use efficiency (WUE) and dynamics of soil water and salt for rice were analyzed based on SWAP simulation results. The results showed that the grain yield and WUE increased with the increase of irrigation water quantity, but the effect of irrigation quality on grain yield and WUE was not as obvious as irrigation quantity. And the high rice yield and WUE were obtained under sufficient irrigation amount with 1.5 mg/cm3 salt concentration, i.e. MaV3 treatment. The soil salt was accumulated at 60- 90 cm soil depth for all the irrigation treatments, and the depth for soil salt accumulation was related to irrigation water quantity and quality. The highest salt concentration was 8.94 mg/cm3 occurred at 85 cm soil depth for M3V3 treatment. Even so, the soil still was considered as non-salinized soil based on the saline soil classification standard for coastal regions in China. The degree of soil salinity was not increased after the brackish water irrigation and the main outflow of soil salt was through deep percolation. Finally, the validated model was used to predict the soil salt concentration distribution characteristics under optimal irrigation treatment for long-term brackish water irrigation. Ten-year simulation showed that the with 1.5 mg/cm3 salt concentration, the water irrigation would not result in soil secondary salinization for 0-100 cm soil depth. The study provided useful information for utilization of local slight saline water. [ABSTRACT FROM AUTHOR]

Soil salt-water dynamics in the Yangtze River Estuary (YRE) is complex and soil salinity is an obstacle to regional agricultural production and the ecological environment in the YRE. Runoff into the sea is reduced during the impoundment period as the result of the water-storing process of the Three Gorges Reservoir (TGR) in the upper reaches of the Yangtze River, which causes serious seawater intrusion. Soil salinity is a problem due to shallow and saline groundwater under serious seawater intrusion in the YRE. In this research, we focused on the temporal variation and spatial distribution characteristics of soil salinity in the YRE using geostatistics combined with proximally sensed information obtained by an electromagnetic induction (EM) survey method in typical years under the impoundment of the TGR. The EM survey with proximal sensing method was applied to perform soil salinity survey in field in the Yangtze River Estuary, allowing quick determination and quantitative assessment of spatial and temporal variation of soil salinity from 2006 to 2017. We developed regional soil salinity survey and mapping by coupling limited laboratory data with proximal sensed data obtained from EM. We interpreted the soil electrical conductivity by constructing a linear model between the apparent electrical conductivity data measured by an EM 38 device and the soil electrical conductivity (EC) of soil samples measured in laboratory. Then, soil electrical conductivity was converted to soil salt content (soil salinity g kg−1) through established linear regression model based on the laboratory data of soil salinity and soil EC. Semivariograms of regional soil salinity in the survey years were fitted and ordinary kriging interpolation was applied in interpolation and mapping of regional soil salinity. The cross-validation results showed that the prediction results were acceptable. The soil salinity distribution under different survey years was presented and the area of salt affected soil was calculated using geostatistics method. The results of spatial distribution of soil salinity showed that soil salinity near the riverbanks and coastlines was higher than that of inland. The spatial distribution of groundwater depth and salinity revealed that shallow groundwater and high groundwater salinity influenced the spatial distribution characteristics of soil salinity. Under long-term impoundment of the Three Gorges Reservoir, the variation of soil salinity in different hydrological years was analyzed. Results showed that the area affected by soil salinity gradually increased in different hydrological year types under the impoundment of the TGR. [ABSTRACT FROM AUTHOR]

• Soil salinity increases NH 3 volatilization. • Urea shows the highest NH 3 volatilization, followed by MAP, and then manure. • Low biochar addition rate can avoid aggravating NH 3 volatilization in saline soil. • Gypsum decreases NH 3 volatilization in saline soil regardless of the gypsum amount. Ammonia (NH 3) volatilization is a major route of nitrogen (N) loss from soil, especially in saline soil. Biochar and gypsum are two important soil amendments that are widely used in coastal saline farmland. However, little is known about the interactive effects of soil amendments and salinity on NH 3 volatilization. In this study, five soil salinity levels, three N sources (urea, monoammonium phosphate (MAP), and manure) and two soil amendments (biochar and gypsum, both applied at two rates) were selected to conduct incubation experiments. Nitrogen transformation experiments were conducted simultaneously with NH 3 volatilization experiments. The results showed that cumulative NH 3 volatilization increased with salinity due to the accumulation of ammonium, which resulted from the inhibition of nitrification by salinity, and also the effect of salinity on soil properties related to NH 3 volatilization. Among the tested N sources, the highest NH 3 volatilization was observed for urea, followed by MAP and manure, in soils with three different salinity levels. Biochar application increased NH 3 volatilization in saline soil, as salt ions constrained the NH 3 / NH 4 + adsorption capacity of biochar, and the inhibition of nitrification by biochar was aggravated in saline soil. Overall, NH 3 volatilization increased with the biochar application rate in saline soil, whereas the effect of a low rate of biochar application on NH 3 volatilization was not significant. Gypsum decreased NH 3 volatilization in saline soil, whereas the contribution of different gypsum rates to NH 3 volatilization showed no difference. The conclusion could be drawn from the above results that low rates of biochar and gypsum may prevent or reduce NH 3 volatilization and nitrogen losses in coastal saline soil. [ABSTRACT FROM AUTHOR]

Core IdeasMore salts were distributed in liquid water than saline ice during the saline water freeze‐thaw process.Leaching with saline ice melt‐water was better than leaching with saline water at reducing soil EC and SAR.Gypsum application could improve the soil Ks when leached by the saline ice melt‐water.The addition of gypsum could eliminate the soil alkalinity hazards post leaching. Saline‐alkali soils adversely affect both the construction of ecological landscapes and crop production in coastal areas. This study aimed to investigate the effects of freeze‐thaw process on purifying saline water, and evaluate the potential of combining saline ice melt‐water leaching and gypsum addition for remediating coastal saline‐alkali soil. Saline water with a salinity of 10 g L−1 was tested in this study, and the leaching experiment included four treatments: saline water direct leaching (S), saline water direct leaching combined with gypsum application (SG), saline ice melt‐water leaching (SI), and saline ice melt‐water leaching combined with gypsum application (SIG). The results showed that more salts were concentrated in the bottom ice layer than in the other ice layers after the saline water was completely frozen. The salinity of the melt‐water decreased during the melting process, and the mean salinity of melt‐water during the second half of the melting process was significantly lower than the salinity of source water samples. During the leaching phase, the cumulative leachate losses of Na+, Ca2+ and Mg2+ were significantly greater for the SI treatment than that for the S treatment. After leaching, the soil electrical conductivity (EC) significantly decreased, and the SI treatment exhibited better performance than the S treatment in terms of reducing the soil EC and sodium adsorption ratio (SAR). The application of gypsum improved the soil saturated hydraulic conductivity (Ks) and decreased both the soil pH and alkalinity when the coastal saline soil was leached by the saline ice melt‐water. [ABSTRACT FROM AUTHOR]

Numerical simulation is an efficient approach for investigating the salt and water movement through soil profile and predicting of crop response to soil water deficit and salinity. In this study a coupled model that describes the soil water and solute transport by means of HYDRUS-1D model and crop growth process by means of growth module of EPIC was used. The model was calibrated and validated against field data, collected during two growing seasons in field plots of winter wheat irrigated with four levels of irrigation amount and water salinity of 5 ds m −1 at the Fengqiu State Key Agro-Ecological Experimental Station, in North China Plain. The model was also used to evaluate the salinity stress on evapotranspiration (ET), grain yield and water use efficiency (WUE) and long-term use of saline water on grain yield and salt accumulation. Visual inspection and the obtained statistical parameters values showed that good agreement between measured and simulated data of soil water content, salt concentration, ET and grain yield. Evapotranspiration values of winter wheat were reduced under salinity stress conditions, mainly by reducing crop transpiration. The grain yields were reduced due to salinity stress, but the change trend of WUE was associated with precipitation amount. Increasing per saline water irrigation amount is an effective way to reduce the WUE decline rate under the low rainfall growing season as like that in simulation year. The average of ten years grain yield confirmed that a yield potential exceeding 86% could be maintained by saline water with 5 ds m −1 when per irrigation volume more than 0.8 E, E denotes evaporation from an uncovered, 20 cm diameter pan positioned 0–5 cm above the crop canopy. There has a slight salt build-up after ten years simulation, and the quantity of salt accumulation decreased with the increase of irrigation volume. Thus, more attention should be paid to the sustainability of irrigated agriculture with low irrigation volume when using saline water irrigation. On the whole, field observations combined with the coupled model could be used to evaluate different agricultural managements on grain yield and soil salinity. [ABSTRACT FROM AUTHOR]

Sustainable development of agriculture in the North China Plain is severely restricted by a shortage of fresh water. Saline water used for irrigation can increase crop yields as well as the risk of soil salinization. Therefore, to identify safe and simple ways of using saline water in this region, field experiments were conducted from 2011 to 2013 to evaluate the effect of irrigation volume and water salinity on winter wheat productivity and soil salinity distribution. A total of twelve treatments including four levels of irrigation volume (0.8 E , 1.0 E , 1.2 E and 1.4 E ) and three levels of water salinity (3.3, 5, and 6.8 dS m −1 ) (S1, S2 and S3), were arranged in a randomized split-plot design with three replicates of each treatment. E is the total net pan evaporation that occurred after the irrigation. The results indicated that soil salinity increased at the harvest time of winter wheat under all of the treatments compared with initial conditions, particularly in the upper soil layers (0–40 cm). However, these impacts were eliminated by rainfall in summer and autumn. The effect of irrigation water salinity on yield was significant in the 2011/2012 growing season and non-significant in the 2012/2013 growing season ( p < 0.05). Quadratic relationships were found between grain yield and irrigation volume for three water salinity levels in both growing seasons. The effects of irrigation volume on total water use (TWU), water productivity (WP) and irrigation water productivity (WP irrig ) were significant. The interaction effects of irrigation volume and water salinity on grain yield, TWU, WP, WP irrig and soil salinity were statistically non-significant. The optimal irrigation volume per application was 0.98 E , 0.98 E and 0.92 E for water salinities of S1, S2 and S3, respectively, by which more than 96% of the maximum yield and WP can be achieved. [ABSTRACT FROM AUTHOR]

The study conducted a detailed analysis of the modeling processes and performances of 2 types of different neural network models including back propagation artificial neural network (BP-ANN) and neuro-fuzzy (NF), in the groundwater salinity dynamics forecasting. Firstly, the classical statistical analysis was used to determine the dominant driving factors of groundwater salinity dynamics and to reveal the available model inputs combinations. Then, the optimal neural network model structures were determined by the trial-and-error method and used to effectively forecast the mid-long term groundwater salinity dynamics. By our research, the idea of necessity in selecting the optimal NF model parameters of transfer functions, rule numbers and iteration steps was innovatively proposed, and the mechanism of differences involved in the model inputs for different groundwater salinity dynamics forecasts was demonstrated. At estuarine Yinyang site, the optimal NF forecast model structure was NF(5-gbellmf-160) with 1 input of the precipitation dynamics, which denotes the optimal rule numbers of 5, the bell type transfer function and the iteration steps of 160. The optimal BP-ANN forecast model structure was ANN(2-2-1), which denotes 2 inputs of precipitation and river water EC dynamics, 2 hidden layers and 1 output. As for estuarine Daxing site, the optimal NF forecast model structure was NF(4-gaussmf-100) with 2 inputs of precipitation and inland water EC dynamics, which denotes the optimal rule numbers of 4, the gauss type transfer function and the iteration steps of 100. The optimal BP-ANN forecast model structure was BP-ANN(1-3-1), which denotes 1 input of inland river EC dynamics, 3 hidden layers and 1 output. As the dominant groundwater recharge resource, the precipitation dynamics was the major impact factor on estuarine groundwater salinity dynamics. On the other hand, the groundwater salinity dynamics at Yinyang site was also affected by the high river water salinity, while at Daxing site was influenced by the inland water salinity, because Yinyang site was much closer to the sea than Daxing site and the shallower groundwater table at Yinyang site made the groundwater salinity dynamics be more directly influenced by the river water salinity. In addition, different models have different abilities to extract the dominant impact factors on the groundwater salinity dynamics. Results showed that the forecast performances of the neural network models (NF and BP-ANN) were better than the conventional linear model that simply combined all the impact factors and added their correlations with dependent variable to forecast groundwater salinity. For Yinyang site's forecast, the predicted r values of NF, BP-ANN and liner models were 0.565, 0.445 and 0.261, respectively. For Daxing site's forecast, the predicted r values of NF, BP-ANN and liner models were 0.886, 0.784 and 0.543, respectively. In particularly, the NF algorithm showed prominent capabilities in simulating and error correcting, which consequently led the NF model to perfectly extract the dominant impact factors affecting the groundwater salinity dynamics and effectively simulate the small-scale details and extreme values of groundwater salinity dynamics. Compared with the BP-ANN and liner models, the prediction errors using NF models could be decreased by more than 30% and 50% at Yinyang and Daxing sites, respectively. The presented ideas in constructing the optimal NF model and using it to forecast the regional groundwater salinity dynamics provide a new and practical approach for studies on regional water-salt system health. [ABSTRACT FROM AUTHOR]

Establishing better nitrogen (N) management strategies is of great significance for sustaining crop production and reducing environmental pollution. However, there is limited knowledge about N fertilizer management practices with soil nutrient supply, N leaching, crop productivity and nutrient use efficiency (NUE) reaching the desired level simultaneously. In this study, pot experiment was conducted to evaluate the effects of N fertilizer and in combination with fulvic acid (FA) on NUE and nutrient supply in a moderate-salinized soil (with total salt content 3.30 g kg−1 and EC 1:5 1.18 dS m−1). Ten treatments were included: treatment without any addition (CK); 100%, 85% and 70% of the conventional inorganic N fertilizer addition rate (100% CF, 85% CF and 70% CF); 100% CF, 85% CF and 70% CF combined with 75 kg ha−1 FA (100% CF + F1, 85% CF + F1, and 70% CF + F1), respectively; and 100% CF, 85% CF and 70% CF combined with 150 kg ha−1 FA (100% CF + F2, 85% CF + F2, and 70% CF + F2), respectively. In order to further investigate the effects of combining N fertilizer and FA applications on soil N leaching losses, part of the fertilizer management practices were selected to conduct a soil leaching experiment. The results demonstrated that the Olsen-P for the upper 20 cm of soil was significantly affected by N fertilization (P ≤ 0.01). In the treatments with inorganic fertilization alone, the concentration of soil mineral N at 0–10 cm soil depth decreased with decreasing level of fertilizer N, while Olsen-P content and alkaline phosphatase activity decreased with increasing N fertilizer application rate. The application of FA significantly increased alkaline phosphatase activity. Overall, the total mineral N leaching losses increased exponentially with increasing annual fertilizer N application rates, while the addition of FA decreased the total mineral N leaching factor (TLF N). Furthermore, the results of multiple regression analysis revealed that wheat grain yield, plant P uptake, plant N uptake, harvest index of applied fertilizer N (HI N), partial factor productivity of applied fertilizer P (PFP P), recovery efficiency of P (RE P) and recovery efficiency of N (RE N) reached ≥85% of their maximum concurrently, when the application amounts of N fertilizer and FA varied from 300 to 370 kg ha−1 and from 164 to 250 kg ha−1, respectively. These results of this study provide a basis for appropriate nitrogen (N) management in salt-affected soils and for the improvement of the sustainability of agricultural development in China. • Olsen-P content decreased with increasing nitrogen (N) application rate. • Fulvic acid addition decreased the total mineral nitrogen leaching factor (TLF N). • Combined application of fulvic acid with optimum N fertilization could improve wheat grain yield and nutrient use efficiency. • The recommended application rates of N fertilizer and fulvic acid were 300–370 kg ha−1 and 164–250 kg ha−1, respectively. [ABSTRACT FROM AUTHOR]