Different Approaches to Reduce Salinity in Salt-Affected Soils and Enhancing Salt Stress Tolerance in Plants

Salt stress is one of the most harmful environmental stresses in recent times and represents a significant threat to food security. Soil salinization is caused by spontaneous natural processes of mineral dissolution and human activities such as inappropriate irrigation practices. Natural geological progressions like weathering of rocks, arid climate, and higher evaporation, as well as anthropogenic activities, including the use of brackish water for irrigation, and poor tillage operations, are the foremost causes of soil salinization. Typical characteristics of saline soils are salt stress, high pH, and lack of organic carbon, as well as low availability of nutrients. Disruption of precipitation patterns as well as high average annual temperatures due to climate change additionally negatively affects the process of soil salinization. Productivity and ability to support crop growth are reduced on saline soil. Salinity-induced stress reduces plant growth by modulating the antioxidative system and nutrient orchestration. The aim of this work is to show that the mentioned problems can be alleviated in several ways such as the addition of biochar, exogenous application of several elicitors, seed priming, etc. Research has shown that the addition of biochar can significantly improve the recovery of saline soil. The addition of biochar has no significant effect on soil pH, while the cation exchange capacity of the soil increased by 17%, and the electrical conductivity of the saturated paste extract decreased by 13.2% (depends on the initial salinity and the type of biochar raw material). Moreover, biochar enriched with silicon increases the resistance of bananas to salt stress. In addition, exogenous application of several elicitors helps plants to alleviate stress by inducing stress-related physicochemical and molecular changes (selenium, sulfur, silicon, salicylic acid). Finally, seed priming showed positive effects on metabolomics, proteomics and growth of plants subjected to abiotic stress. Priming usually involves immersing the seed in a solution for a period of time to induce physiological and metabolic progression prior to germination.

Changes in Soil Properties Under the Influences of Cropping and Drip Irrigation During the Reclamation of Severe Salt-Affected Soils

Reclamation of salt-affected land plays an important role in mitigating the pressure of agricultural land due to competition with industry and construction in China. Drip irrigation was found to be an effective method to reclaim salt-affected land. In order to improve the effect of reclamation and sustainability of salt-affected land production, a field experiment （with reclaimed 1-3 yr fields） was carried out to investigate changes in soil physical, chemical, and biological properties during the process of reclamation with cropping maize and drip irrigation. Results showed that soil bulk density in 0-20 cm soil layer decreased from 1.71 g·cm-3 in unreclaimed land to 1.44 g ·cm^-3 in reclaimed 3 yr fields, and saturated soil water content of 0-10 cm layer increased correspondingly from 20.3 to 30.2%. Both soil salinity and pH value in 0-40 cm soil layer dropped markedly after reclaiming 3 yr. Soil organic matter content reduced, while total nitrogen, total phosphorus, and total potassium all tended to increase after cropping and drip irrigation. The quantities of bacteria, actinomycete, and fungi in 0-40 cm soil layer all greatly increased with increase of reclaimed years, and they tended to distribute homogeneously in 0-40 cm soil profile. The urease activity and alkaline phosphatase activity in 0-40 cm soil layers were also enhanced, but the sucrase activity was not greatly changed. These results indicated that after crop cultivation and drip irrigation, soil physical environment and nutrients status were both improved. This was benefit for microorganism＇s activity and plant＇s growth.

Long-Term Fertilization Effect on Fertility of Salt-Affected Soils

The long-term effects of annual fertilizer applications on the fertility of salt-affected soils under the rotation system of wheat （Triticum aestivum L.） and maize （Zea mays L.） are not well documented. In 1984, research plots were established to test the effects of annual applications of different rates of nitrogen （N） and phosphorus （P） fertilizers on the fertility of a salt-affected soil （Typic Ustochrept） at the Quzhou Experimental Station, Quzhou County, Hebei Province, China. In October 2001, composite soil samples （0-20 and 20 40 cm） were collected from each plot and analyzed for soil fertility indices. Seventeen years of N and P fertilizer applications increased the soil organic matter （SOM） in the surface layer. With combined N, 270 （N1） and 540 （N2） kg N ha^-1 year^-1, and P, 67.5 （P1） and 135 （P2） kg P205 ha^-1 year^-1, fertilizer applications, total soil N mostly significantly decreased （P〈0.05）. Soil total P in the 0-20 cm layer of the P2 treatment significantly （P （0.05） increased as compared to those of the other treatments. Rapidly available P （RP） in the 0-20 cm layer of the N1P2 treatment was significantly higher than those in the other treatments except the P2 treatment; and RP in the 0-20 cm layer of the P2 treatment significantly increased as compared to those of the other treatments except the P1 and N1P2 treatments. RP in the subsurface soil layer （20-40 cm） of the P2 treatment （4.2 mg P kg^-1） was significantly （P〈0.05） higher than those in the other treatments. Nevertheless, long-term N fertilization did not significantly increase the alkali-hydrolyzable N in the soil. However, in the salt-affected surface soils the application of combined N and P fertilizers over 17 years significantly （P〈0.05） decreased rapidly available potassium （K）. The results suggested that while under long-term fertilizer applications some soil fertility parameters could be maintained or enhanced, careful monitoring of soil fertility was necessary as other nutrients such as K could become depleted.

Land Management Effects on Biogeochemical Functioning of Salt-Affected Paddy Soils

Most lowlands in Northeast Thailand(Isaan region)are cultivated with rice and large areas are affected by salinity, which drastically limits rice production.A field experiment was conducted during the 2003 rainy season to explore the interactions between salinity and land management in two fields representative of two farming practices:an intensively managed plot with organic inputs and efficient water management,and one without organic matter addition.Field measurements,including pH,Eh,electrical conductivity(EC),and soil solution chemistry,were performed at three depths, with a particular focus on Fe dynamics,inside and outside saline patches. High reducing conditions appeared after flooding particularly in plots receiving organic matter and reduction processes leading to oxide reduction and to the release of Fe and,to a lesser extend,Mn to the soil solution.Oxide reduction led to the consumption of H^+ and the more the Fe reduction was,the higher the pH was,up to 6.5.Formation of hydroxy-green rust were likely to be at the origin of the pH stabilization.In the absence of organic amendments,high salinity prevented the establishment of the reduction processes and pH value remained around 4.Even under high reduction conditions,the Fe concentrations in the soil solution were below commonly observed toxic values and the amended plot had better rice production yield.

Feasibility and Prospect about the Cultivation of Apocynum venetum L. in Coastal Salt-affected Soils

[Objective]The aim of this paper was to analyze the feasibility and prospect of Apocynum venetum L.cultivation in coastal salt-affected soils.[Method]The habitat and distribution of Apocynum venetum L.in coastal area of north China were studied.A method to integrate the charicteristics of Apocynum venetum L.（Luobuma） with the utilization of salt-affected soils in this region was proposed.[Result]The introduction,domestication and growth of plants on coastal salt-affected soils can realize the protection of endangered wild species,and achieve the purpose of improving soil.The characteristics of Apocynum venetum L.can produce optimum economic and ecological benefits.[Conclusion]The implementation will provide references for the protection and exploitation of wild plant,and it is of positive significance for the integration of soil and plant resources.

Salt-affected marginal lands:a solution for biochar production

The literature has shown that biochar can serve as potential amendment to achieve sustainable agriculture and environment.The accessibility and availability of cheap feedstock are considered as important constraint factors for the widespread application of biochar in agriculture.Marginal lands are widely distributed globally,several times larger than arable land,and hold little value for food production due to poor soil conditions.However,these lands are suitable for growing plants,which can be used as feedstock for biochar production.The salt-affected lands,as one of the main marginal lands,are particularly suitable for cultivating diverse varieties of halophytes that can be pyrolyzed into biochar,bio-gas,and bio-oil.The halophyte-derived biochar is useful to produce a desirable acid soil conditioner due to its high ash and rich bases,and improves soil characteristics under extreme saline conditions.Additionally,syngas and bio-oil hold potential benefits as fuels and industrial raw materials.This study introduces an innovative management technique for marginal lands such as salt-affected land,which can provide all-round benefits in food production,land management,vegetation coverage,carbon sequestration,and climate change mitigation.

Hydraulic properties of typical salt-affected soils in Jiangsu Province, China

Every year about 1,500 ha of land is reclaimed from the sea along the coastline of Jiangsu Province,China.It is important to characterize the hydraulic properties of this reclaimed land to be able to predict and manage salt and water movement for amelioration of these saline soils.In this paper,we report hydraulic properties of these salt-affected soils.The pressure-plate method,constant head method,the crust method and Klute’s method were used in this study.The satu-rated hydraulic conductivities of the soils ranged from 128.66 to 141.26 cm/day and decreased with increasing soil depth.The unsaturated hydraulic conductivities followed an expo-nential function of pressure head.The soil water retention curves were similar for three soil layers in the soil.The satu-rated water content,field capacity and wilting point decreased with increasing soil depth.Plant available water contents of the three layers in the soil profile were 0.21,0.20 and 0.19 cm3/cm3,respectively.The unsaturated soil water diffu-sivity of the studied soils ranged from 0.07 to 10.46 cm^(2)/min,and was related to the water content via an exponential relationship.

Study on Cultural Technologies and Salt-resistance of Nitraria sibirica in Coastal Areas with Serious Salt-affected Soil

In this research, five Nitraria sibirica provenances such as Dayilu were selected to do experiment of salt-resistance, combining fixed plots test with typical plot investigation, measuring survival rate and growth as main indicators. The experiments of main cultural technology were done on Nitraria sibirica in 4 types of site preparation, 3 types of planting, 3 designs for planting density. The Nitraria sibirica experiments for the effects of curbing salt and improving soil were done by testing soil nutrients, salt content, soil physical properties as focal points in typical site of 3-4 years woods. The experiment results showed that the Nitraria sibirica could survive well with soil salt content of 0.6%, and that survival rate declined distinctively as soil salt content exceeded 0.8%. However, high soil salt content did not influence growth in the year of planting. There were obvious differences in salt-tolerance among Nitraria sibirica provenances; Dayilu was the best on salt-tolerance, the other 4 provenances had no differences, and obviously inferior to Dayilu. The different types of site preparation clearly influenced planting survival rate, conserving rate and growth. The method of two-ploughing-two-harrowing was the best among all 4 types of site preparation. Seed forestation was largely limited, bared-rooted seedling forestation may be popularised when soil salt content was less than 1% and soil moisture content was better in spring. Forestation with container seedling was suited to coastal saline soil in rainy season. The optimum planting density of Nitraria sibirica was 2 505/ha in the Yellow River Delta area in view of coverage rate, yield of fruits and cost of planting. Generally speaking,Nitraria sibirica could effectively refrain soil from accumulation of salt in the surface soil, decrease salt content and increase soil nutrient, and heighten soil capillary pore rate.

Features of Salt－Affected Soils and Salinization Hazard in East Asia and Its Neighboring Regions

Asia is the largest distribution area of salt-affected soils in the world. Very few countries in Asia couldescape from hazard of salinization. This paper deals with various salt-affected soils spreading in East Asiaand its neighboring regions (including China, Japan, Kampuchea, Democratic People’s Republic of Korea,Republic of Korea, Laos, Mongolia, Burma, Thailand and Vietnam). Principles of occurrence of salinization,and features of salt-affected soils in these regions have been studied in the present paper. Based on studieson types, features and distribution patterns of salt-affected soils, a salt-affected soil map of East Asia andits neighboring regions has been complied. Mechanism and manifestation of the salinization hazard on theregional agriculture and ecological environment, measures of preventing salinization hazard and exploitingsalt-affected soils in these regions are also discussed.

地理图象系统与现代地理教学

地理图象系统与现代地理教学王磊（平顶山师专地理系）由于地理学科的特点，地理教学历来注重地图的应用．地图作为一种特殊的地理语言，成为传递地理知识的形象教材．地理图象系统是以具有直观形象特点的地图、照片、绘画等形式的储存和传递地理教学信息，并具有独立性的...

Saline-alkali land reclamation boosts topsoil carbon storage by preferentially accumulating plant-derived carbon

Saline–alkali land is an important cultivated land reserve resource for tackling global climate change and ensuring food security, partly because it can store large amounts of carbon(C). However, it is unclear how saline–alkali land reclamation(converting saline–alkali land into cultivated land) affects soil C storage.We collected 189 adjacent pairs of salt-affected and cultivated soil samples(0–30 cm deep) from the Songnen Plain, eastern coastal area, Hetao Plain, and northwestern arid area in China. Various soil properties, the soil inorganic C(SIC), organic C(SOC), particulate organic C(POC), and mineral-associated organic C(MAOC) densities, and plant-and microbial-derived C accumulation were determined.Saline–alkali land reclamation inconsistently affected the SIC density but significantly(P < 0.001)increased the SOC density. The SOC, POC, and MAOC densities were predicted well by the integrative soil amelioration index. Saline–alkali land reclamation significantly increased plant-derived C accumulation and the plant-derived C to microbial-derived C ratios in all saline–alkali areas, and less microbial transformation of plant-derived C(i.e., less lignin degradation or oxidation) occurred in cultivated soils than salt-affected soils. The results indicated that saline–alkali land reclamation leads to plant-derived C becoming the dominant contributor of SOC storage. POC storage and MAOC storage were strongly linked to plant-and microbial-derived C accumulation, respectively, caused by saline–alkali land reclamation.Our findings suggest that saline–alkali land reclamation increases C storage in topsoil by preferentially promoting plant-derived C accumulation.

Effect of organic materials on the chemical properties of saline soil in the Yellow River Delta of China

A 180-day incubation experiment was con- ducted to investigate the effect of different organic materials on the chemical properties of coastal soil with high salinity and relatively low pH. Four organic materials （three kinds of plant residues： straw, composted straw, and fresh reed; and one kind of poultry manure： chicken manure） were applied at a ratio of 15 g·kg^-1 to samples of costal saline soil from the Yellow River Delta of China. The results showed that the soil pH and exchangeable sodium percentage （ESP） decreased, whereas soil cation exchangeable capacity （CEC） and macronutrient concen- trations increased, regardless of the type of organic material used. All treatments showed a remarkable increase in soil soluble organic carbon （SOC） during the 180-day incubation. The peak values of SOC in descend- ing order were chicken manure, reed, composted straw, straw, and control soil. At the end of incubation, the highest level of SOC occurred in the straw-amended soil, followed by composted straw, reed, and chicken manure- amended soils. Soil respiration rate and available nitrogen were significantly influenced by the type of material used. Although reed-amended soil had a relatively high SOC and respiration rate, the ESP was reduced the least. Consider- ing the possible risk of heavy metals caused by chicken manure, it is proposed that straw and composted straw are the more efficient materials to use for reclaiming costal saline soil and improving the availability of macronu- trients.

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

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

Characteristics of Salt Affected Soil and Its Amelioration by Trees

Salt-affected soils extensively distribute on the earth.Although the causes are various,generally speaking salinization occurrence results from the accumulation of free salts to an extent that causes degradation of vegetation and soils.Besides,irrational human practices have increased soil salinity by allowing excess recharging of groundwater to change the natural balance of the water cycle in the landscape. This reduces the suitability to plant growth and increases the potential for other forms of land ...

Impact of Salinity on Respiration and Organic Matter Dynamics in Soils is More Closely Related to Osmotic Potential than to Electrical Conductivity

Osmotic potential （OP） of soil solution may be a more appropriate parameter than electrical conductivity （EC） to evaluate the effect of salts on plant growth and soil biomass. However, this has not been examined in detail with respect to microbial activity and dissolved organic matter in soils with different texture. This study evaluated the effect of salinity and sodicity on respiration and dissolved organic matter dynamics in salt-affected soils with different texture. Four non-saline and non-sodic soils differing in texture （S-4, S-13, S-24 and S-40 with 4%, 13%, 24~ and 40~~ clay, respectively） were leached using combinations of 1 mol L-1 NaC1 and 1 mol L-1 CaC12 stock solutions, resulting in EC （1：5 soil：water ratio） between 0.4 and 5.0 dS m-1 with two levels of sodicity （sodium absorption ratio （SAR） 〈 3 （non-sodic） and 20 （sodic）, 1：5 soil：water ratio）. Adjusting the water content to levels optimal for microbial activity~ which differed among the soils, resulted in four ranges of OP in all the soils： from -0.06 to -0.24 （controls, without salt added）, -0.55 to -0.92, -1.25 to -1.62 and -2.77 to -3.00 Mpa. Finely ground mature wheat straw （20 g kg-1） was added to stimulate microbial activity. At a given EC, cumulative soil respiration was lower in the lighter-textured soils （S-4 and S-13） than in the heavier-textured soils （S-24 and S-40）. Cumulative soil respiration decreased with decreasing OP to a similar extent in all the soils, with a greater decrease on Day 40 than on Day 10. Cumulative soil respiration was greater at SAR ---- 20 than at SAR 〈 3 only at the OP levels between -0.62 and -1.62 MPa on Day 40. In all the soils and at both sampling times, concentrations of dissolved organic C and N were higher at the lowest OP levels （from -2.74 to -3.0 MPa） than in the controls （from -0.06 to -0.24 MPa）. Thus, OP is a better parameter than EC to evaluate the effect of salinity on dissolved organic matter and microbial activity in different textured soils.