Salt-affected Regions Research Articles

Use of biochar to manage soil salts and water: Effects and mechanisms

Soil salinization is a widespread land degredation, especially in water-stressed regions, jeopardizing agriculture sustainability. Current desalinization methodology involves excessive water consumption. Biochar has the potential to mitigate soil salinization while increasing water holding capacity. As a saline and sodic material, however, how it works and whether it can be used to sustain the agriculture at reduced water resource remain to be studied. Here, by monitoring transport of water, salts and nutrients in the profile of irrigation-silt soil during watering and evaporation in both laboratory and field in Kashgar oasis, Xinjiang, China, we find biochar exacerbates salinization upon application. This is changed, however, after several cycles of irrigation-evaporation due to strengthened salt leaching in irrigation and salt removal out of the depth through intensified top accumulation by evaporation, both resulting from increased capillary effect and thereby the enhanced movement of salts despite the competing electrical adsorption to the cations. The resulted salt distribution facilitates desalinization by removing the top 2 cm soil. Biochar also promotes evaporation after irrigation due to inceased water content and capillary suction. This is reversed once the soil cracks, a common phemomenon in irrigated land. Biochar counteracts the cracking through alleviation of soil compaction, saving tillage while lowering water evaporation, e.g., by 43% at 10% biochar. Our findings indicate that application of biochar changes salt distribution, enabling desalinization with little water consumption. Together with the effect of anti-fracturing and enhanced salt leaching, it lowers water demand substantially, providing a novel solution for agricultural sustainability in salt-affected regions.

The quantity and stability of soil organic carbon following vegetation degradation in a salt-affected region of Northeastern China

Understanding the influence of vegetation conversion induced by land degradation on soil organic carbon (SOC) dynamics provides a basis for the sustainable use of grasslands. While labile carbon fractions often vary with the type of vegetation, little is known about whether and how vegetation degradation affects the recalcitrant carbon fraction that is highly resistant to oxidation. Here, we studied the influence of vegetation degradation on changes in SOC and four oxidizable fractions with different stabilities in Northeastern China. The soil was collected from a vegetation degradation sequence, including Leymus chinensis (LEY, native grassland), Puccinellia tenuiflora(PUC, light degradation), Chloris virgata (CHL, moderate degradation), and Suaeda heteroptera (SUA, severe degradation). Contents of total SOC and four oxidizable SOC fractions extracted under a gradient of oxidation (F1, very labile; F2, labile; F3, less labile; F4, oxidizable resistant) were measured using a modified Walkley-Black method. Results showed that the contents of total SOC and oxidizable SOC fractions were significantly different under different vegetation types and soil depths. Under PUC, CHL, and SUA, contents of total SOC (29.0%, 34.3%, and 55.4%, respectively), F1 (22.5%, 20.8%, and 40.8%, respectively), F2 (28.2%, 53.8%, and 72.1%, respectively), F3 (52.0%, 40.6%, and 66.2%, respectively), and F4 (15.0%, 21.9%, and 42.8%, respectively) were lower than those under LEY. Vegetation degradation had a significant effect on the F4 fraction as well as the F1, F2, and F3 fractions. Regression coefficients of the relationship between oxidizable SOC fractions as a function of total SOC showed that these fractions, as a proportion of total SOC, were 22% for F1 and F2, 26% for F3, and 31% for F4. There were no significant differences in the percentages of active carbon fractions (F1 + F2) in total SOC and the lability of total SOC among the four vegetation types. These findings suggest that the recalcitrant carbon fraction can be affected by land degradation as well as the labile carbon fraction, and that shifts in land use affect the contents of total SOC and its fractions, but have no effect on the stability of SOC in semi-arid areas.

If the combination of straw interlayer and irrigation water reduction maintained sunflower yield by boosting soil fertility and improving bacterial community in arid and saline areas

Limited water resources have severely restricted saline soil amelioration and utilization in the Hetao irrigated area, China. Burying straw interlayer is an effective management for salt-affected soil amelioration. However, little is known whether the straw interlayer could boost soil fertility and improve bacterial community, while reducing irrigation water consumption by 10% in the third and fourth years after application. Therefore, the legacy effect of the combination of straw interlayer and irrigation water reduction was investigated following the three treatments: (i) no straw interlayer plus 100% irrigation (CK); (ii) straw interlayer plus 100% irrigation (SI+W100), and (iii) straw interlayer plus 90% irrigation (SI+W90). SI+W90 significantly increased 0–40 cm soil organic carbon (SOC) content and soil SOC/TN (C/N) ratio than CK by 12% and 13%, respectively. In addition, SI+W90 significantly decreased 0–40 cm soil total nitrogen (TN) and SOC contents by 10% and 8% respectively, but significantly increased 0–40 cm soil C/N ratio by 9%, compared to SI+W100. Furthermore, SI+W100 and SI+W90 significantly increased the relative abundance of Proteobacteria, Bacteroidetes, and Nitrospirae than that of CK, while SI+W90 significantly decreased the relative abundance of Acidobacteria compared to SI+W100, and these bacterial phyla were significantly correlated with 0–40 cm SOC content. Notably, there was no significant correlation between crop yield and soil parameters in 2018 with the relatively low yield, while crop yield was significantly correlated with 0–20 cm SOC content and the relative abundance of Proteobacteria and Firmicutes in 2019 with relatively high yield. These results indicated that both soil fertility and certain bacterial phyla may contribute to yield variation. Therefore, SI+W90 maintained crop yield in the two years. In conclusion, the combination of straw interlayer and irrigation water reduction may be more recommended for agricultural sustainable development under the condition of limited irrigation water supply in the arid and salt-affected regions.

Abscisic acid signaling reduced transpiration flow, regulated Na+ ion homeostasis and antioxidant enzyme activities to induce salinity tolerance in wheat (Triticum aestivum L.) seedlings

Salinity, one of the catastrophic abiotic stresses that uces wheat production around the globe. Abscisic acid (ABA) is a stress phytohormone as a signaling molecule that led us to investigate its potential to improve morpho-physiological characteristics, antioxidant metabolism, and ion homeostasis in wheat ( Triticum aestivum L.) seedlings grown under salinity stress (0, 50, and 100 mM NaCl). The findings suggested that salt-induced toxicity significantly ( P < 0.05) damaged root morphological characteristics, plant growth, photosynthetic pigments, and water contents, while trigger the oxidative injury, Na + ion accumulation and uptake in wheat leaf and root tissues with the increasing NaCl concentration in the nutrient media. However, root-zone supply of ABA (0, 5, and 10 μ M) prominently alleviated salt induced phytotoxicity. The 10 μ M concentration of ABA promoted shoot (81.7%) and root (102.1%) dry weight, root length (38.2%), Chl. a (65.3%), Chl. b (149.0%), carotenoids (95.7%) and membrane damage (36.7%) when NaCl was added at 100 mM, relative to the corresponding treatment without ABA. Moreover, ABA (10 μ M) supply decreased Na + ion uptake (root to leaf) due to reduced transpiration rate (81.1%), and thereby ameliorated oxidative injury by ucing leaf malondialdehyde (MDA) and H 2 O 2 contents by 36.8% and 29.9%, respectively, at 100 mM NaCl stress, relative to the similar treatment without ABA. In addition, the activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) were upregulated by 143.9%, 20.2%, and 19.5% in leaves and by 144.9%, 23.4% and 41.1% in roots respectively, with 10 μ M ABA application under 100 mM salinity stress, compa to the 100 mM NaCl treatment without ABA. Conclusively, this study proposed that root-zone ABA application promoted salinity tolerance in wheat seedlings and could be a practical approach for wheat production in salt-affected regions to ensure food security. • Na + ion uptake was increased by wheat tissues under salinity stress. • Abscisic acid (ABA) alleviated salt injury by promoting growth and physiology. • ABA reduced Na+ uptake and accumulation by ucing transpirational flow. • ABA regulated antioxidant metabolism in wheat tissues exposed to salinity stress.

Anatomical characteristic, ionic contents and nutritional potential of Buffel grass (Cenchrus ciliaris L.) under high salinity

Cenchrus ciliaris is a potential forage grass that is widely distributed in saline desert condition across Africa, Australia and Asia. To examine anatomical characteristics relating to ionic and nutritional contents in response to salinity, Cenchrus ciliaris populations from the naturally salt-affected region of the Cholistan Desert, Pakistan were collected. The experiment was planned in a completely randomized design (CRD) with four replications and four treatment levels (0, 100, 200, and 300 mM NaCl) in a hydroponic system. After six months of growth in nutrient solution anatomical characteristics relating to ionic and nutritional traits were studied. It was hypothesized that C. ciliaris at higher salt stress must have developed some specific structural adaptations, which are responsible for better survival under high salt stress. At root level, C. ciliaris showed decreased root thickness with greater proportion of parenchyma cells in cortical region and increased sclerification in cortex and pith regions at high salinity levels, which are vital for water conservation under osmotic stress. At stem level increased stem area, cortical and vascular bundle cell area were recorded with increase in salinity level of external growth medium. Salt tolerance in C. ciliaris mainly associated with restricted uptake of toxic Na+ and Cl− ions at roots, accompanied by increased concentration of K+ and Ca++ in shoot. Under high salinities, C. ciliaris showed increased epidermis thickness, well developed bulliform cells, and increased trichome density at leaf level. All these structural modification in this species may contribute towards water conservations under physiological stress that is caused by high level of soil salinity. Various nutritional traits such as crude protein, ash content, relative feed value, and net energy of lactation slightly improved with salinity. Present study revealed nutritional potential, ionic contents and anatomical adaptations of C. ciliaris to cope with salinity. As such this species can be used to produce valuable fodder under saline desert environment.

Soil spatial variability characterization: Delineating index-based management zones in salt-affected agroecosystem of India

Farm level recommendation in salt-affected agricultural landscapes is practically difficult due to spatial variations in inherent soil salinity, diverse farming situations and associated land ownerships with small-scale production systems. This study presents spatial array analysis of 354 geo-referenced soil samples revealing widespread heterogeneity in soil sodicity and fertility status across salt-affected Ghaghar basin of Kaithal district in Haryana, India. Six principal components accounted for 73% of the total variability, and the most important contributors [electrical conductivity (ECe), sodium adsorption ratio (SAR), DTPA extractable copper (Cu) and boron (B), soil organic carbon (OC) and available phosphorus (AP)] as minimum data set were used to develop the soil quality index (SQI). Geostatistical analysis revealed Circular (ECe and AP), Exponential (SAR, OC and B) and Gaussian (Cu) as the best fit semivariogram ordinary kriging model with weak to moderate spatial dependence. Three soil management zones (SMZs) were delineated by grouping the entire area based on soil quality index (SQI). Fertilizer recommendations for rice-wheat cropping system in different SMZs were calculated using soil test crop response (STCR) equation to ensure balanced fertilization, resource saving and reducing environmental footprints. Gypsum requirement map was prepared for systematic allocation and distribution, and enabling farmers to precisely use the mineral gypsum in order to reclaim and reduce stresses led by sodic lands. The implications of this study showed zone-specific advocacy for gypsum application (as soil ameliorant) and balanced fertilization in sustainable restoration of sodic lands, improving nutrient use efficiency and stabilizing crop production in salt-affected regions of India and similar ecologies elsewhere.

Developing geographic weighted regression (GWR) technique for monitoring soil salinity using sentinel-2 multispectral imagery

Soil salinity is a widespread natural hazard that negatively influences soil fertility and crop productivity. Using the potential of earth observation data and remote sensing technologies provides an opportunity to address this environmental issue and makes it possible to identify salt-affected regions accurately. While most of the utilized methods and model development techniques for monitoring soil salinity to date have been globally considered and tried to detect salinity and create predictive maps with a single regression algorithm, fewer studies have investigated the potential of local models and weighted regression techniques for estimating soil salinity. Accordingly, this research deals with monitoring surface soil salinity by the potential of Sentinel-2 multispectral imagery using the geographic weighted regression (GWR) technique. The field study was conducted in an area that has suffered from salinization, and the salinity of several soil samples was measured to be used as a source of ground truth data. The most efficient satellite features, which accurately predict surface soil salinity by its higher spectral reflectance, were derived from the Sentinel-2 data to be used as explanatory variables in the analysis. The GWR algorithm was then implemented with a fixed Gaussian kernel, and the optimized bandwidth was calculated in a calibration process using the cross-validation score (CV score). The results of the analysis proved that the GWR method has a great capability to predict soil salinity with an accuracy of two decimal places. The visual interpretation of the local estimates of coefficients and local t-values for each predictor variable has also been provided, which highlights the local variations in the study site. Finally, the achieved results were compared with the outcomes obtained from implementing two global regression techniques, Support Vector Machines (SVM), and Multiple Linear Regression (MLR), which confirmed the higher performance of the GWR algorithm.

Haloengineering as a vital component of sustainable development in salt-affected ecosystems

Utilization of saline soil and water resources through saline agriculture systems, such as Haloculture, is necessary to provide the escalating demand for human food. However, despite acceptable research and commercial activities, saline agriculture systems still have not played a major role in expansion of sustainable agriculture in salt-affected regions of under-developed countries. This is mainly due to inadequate attention to the needs and potentials of human societies in salt-affected ecosystems. The objective of this paper is to introduce and describe Haloengineering as a practical solution for successful implementation of Haloculture in sustainable development of salt-affected ecosystems. Haloculture is sustainable use of the services and potentials of saline environments for manufacture of useful products. Haloculture conforms to the concepts and objectives of Water-Energy-Food Nexus, and takes into consideration the importance of providing water and energy along with promotion of food security. It is necessary to integrate the engineering tools and methods into Haloculture, referred to as Haloengineering. Haloengineering is the harmonic, interdisciplinary application of concepts, methods, and tools of all engineering fields, for improvement of living standards in salt-affected regions. By providing water and energy needs, Haloengineering would play a vital role in sustainable development of salt-affected ecosystems through Haloculture.

Rhizobacteria Isolated from Saline Soil Induce Systemic Tolerance in Wheat (Triticum aestivum L.) against Salinity Stress

Halo-tolerant plant growth-promoting rhizobacteria (PGPR) have the inherent potential to cope up with salinity. Thus, they can be used as an effective strategy in enhancing the productivity of saline agro-systems. In this study, a total of 50 isolates were screened from the rhizospheric soil of plants growing in the salt range of Pakistan. Out of these, four isolates were selected based on their salinity tolerance and plant growth promotion characters. These isolates (SR1. SR2, SR3, and SR4) were identified as Bacillus sp. (KF719179), Azospirillum brasilense (KJ194586), Azospirillum lipoferum (KJ434039), and Pseudomonas stutzeri (KJ685889) by 16S rDNA gene sequence analysis. In vitro, these strains, in alone and in a consortium, showed better production of compatible solute and phytohormones, including indole acetic acid (IAA), gibberellic acid (GA), cytokinin (CK), and abscisic acid (ABA), in culture conditions under salt stress. When tested for inoculation, the consortium of all four strains showed the best results in terms of improved plant biomass and relative water content. Consortium-inoculated wheat plants showed tolerance by reduced electrolyte leakage and increased production of chlorophyll a, b, and total chlorophyll, and osmolytes, including soluble sugar, proline, amino acids, and antioxidant enzymes (superoxide dismutase, catalase, peroxidase), upon exposure to salinity stress (150 mM NaCl). In conclusion, plant growth-promoting bacteria, isolated from salt-affected regions, have strong potential to mitigate the deleterious effects of salt stress in wheat crop, when inoculated. Therefore, this consortium can be used as potent inoculants for wheat crop under prevailing stress conditions.

Responses of soil specific enzyme activities to short-term land use conversions in a salt-affected region, northeastern China

Soil enzyme activity is a sensitive indicator of soil quality changes. The response of soil enzyme activity to different land uses is important in addressing the issues of agricultural sustainability. The objectives of this study were to investigate the effects of short-term land use conversions on soil specific enzyme activity (per unit microbial biomass carbon) of sodic soils and compare the responses of soil absolute (per unit soil mass) and specific enzyme activities in northeastern China. Four specific enzyme activities, including catalase, invertase, urease and alkaline phosphatase were assayed at 0 to 20 cm depth under five land uses, including cropland (CL), alfalfa perennial forage (AF), monoculture grassland (AG), monoculture grassland for hay once a year (AG + M) and successional regrowth grassland (RG). The specific activities of catalase, urease and alkaline phosphatase at 10 to 20 cm depth were 117.3%, 40.0% and 35.6% higher than that in 0 to 10 cm depth, irrespective to the land uses. Conversion of cropland to re-vegetation land increased the specific activities of catalase (2.8%), invertase (99.0%), urease (14.3%) and alkaline phosphatase (14.0%). Under land uses of AF, AG + M, AG and RG, the geometric mean (0.2%, 32.8%, 65.7% and 24.3%, respectively) and sum (2.6%, 38.0%, 82.8% and 29.6%, respectively) of specific enzyme activities at 0 to 20 cm depth were higher than that under CL treatment. The soil specific enzyme activities showed the better discrimination to different land uses than the soil absolute enzyme activities. In conclusion, re-vegetation has a positive effect on the improvement of soil enzyme activity in northeastern China, and the responses of soil specific enzyme activities to short-term land-use conversions are more obvious than the absolute enzyme activities, which could be used as s suitable and sensitive indicator of land use change in semiarid agroecosystems.

Expression of the high-affinity K+ transporter 1 (PpHKT1) gene from almond rootstock 'Nemaguard' improved salt tolerance of transgenic Arabidopsis.

Soil salinity affects plant growth and development, which directly impact yield. Plants deploy many mechanisms to cope with, or mitigate, salt stress. One of such mechanism is to control movement of ions from root to shoot by regulating the loading of Na+ in the transpiration stream. The high-affinity K+ transporter 1 (HKT1) is known to play a role in the removal of Na+ from the xylem and bring it back to the root. As almond is a salt-sensitive crop, the rootstock plays an important role in successful almond cultivation in salt-affected regions. We currently lack knowledge on the molecular mechanisms involved in salt tolerance of almond rootstocks. In this study, we complemented the Arabidopsis athkt1 knockout mutant with HKT1 ortholog (PpHKT1) from the almond rootstock ‘Nemaguard’. Arabidopsis transgenic lines that were generated in athkt1 background with the constitutive promoter (PpHKT1OE2.2) and the native promoter (PpHKT1NP6) were subjected to different salt treatments. Both transgenic lines survived salt concentrations up to 120 mM NaCl, however, the mutant athkt1 died after 18 days under 120 mM NaCl. At 90 mM NaCl, the dry weight of athkt1 decreased significantly compared to the transgenic lines. Both transgenic lines showed significantly longer lateral roots compared to the athkt1 mutant at 80 mM NaCl treatment. The transgenic lines, PpHKT1OE2.2 and PpHKTNP6 had lower electrolyte leakage and higher relative water content compared to athkt1, suggesting that transgenic plants coped well with increased salt concentration by maintaining the integrity of the membranes. The expression analyses showed that PpHKT1 was induced in PpHKT1OE2.2 and PpHKTNP6 lines under salt treatment, which confirmed that both over-expression and native expression of PpHKT1 in the Arabidopsis mutant can complement salt tolerance function.

Response of soil nutrients and stoichiometric ratios to short-term land use conversions in a salt-affected region, northeastern China

Soil organic carbon (SOC), nitrogen (N), phosphorus (P) and potassium (K) are essential soil nutrients needed for plant growth and their stoichiometric ratios are important indicators of the elemental balance in soil ecosystem. However, changes in contents and stoichiometric ratios of SOC, N, P and K under different land uses in salt-affected region remain poorly understand. Soils from five land use treatments, including corn cropland (CL), alfalfa perennial forage (AF), monoculture Lyemus chinensis grassland (AG), monoculture Lyemus chinensis grassland for hay (AG + M) and successional regrowth grassland (RG) were used to assess the influences of land use conversion on the contents and stoichiometric ratios of SOC, N, P and K in a salt-affected region, northeastern China. Results showed that conversion of cropland to forage and grasslands increased by 40.42%, 17.66%, 15.71% and 11.5% for SOC, total N, total P and total K contents in 0–20 cm depth, while the effects of land use conversion on these soil nutrients in 20–50 cm depth were very limiting. Similar with these soil nutrients, the influences of land use conversion on soil stoichiometric ratios were higher in topsoil (0–20 cm) than that in the subsoil (20–50 cm), and re-vegetation increased most of the soil stoichiometric ratios due to the increase of soil nutrient contents. The average C:N, C:P and N:P ratios in the study site were 7.4, 21.3 and 3.0, respectively, in 0–20 cm depth, which were relatively lower than the average values in China and global. The C:K, N:K and P:K ratios were relatively consistent in Songnen grassland, which were 2.0, 0.3 and 0.1, respectively. These findings suggested that land-use type is a major factor that affect the contents and stoichiometric ratios of soil nutrients, and re-vegetation on the cropland improves the soil nutrients in northeastern China.

Soybean PI 675847 A as a new source of salt tolerance

AbstractSoil salinity is a major limitation to legume production in many areas of the world. Identification of the genetic source of salt tolerance is critical in soybean breeding for improving soybean production in salt-affected regions. Vietnam has unique sources of soybean germplasm and varieties are grown in the area where exposure to salinity is frequent. However, there is little research on the identification of salt tolerant sources in the Vietnamese gene pool. The present study compared 18 Vietnamese soybean cultivars for their differences in salt tolerance. Under a range of NaCl stress from 0 to 200 mM NaCl, there was a large variation in salt tolerance among the 18 soybean lines evaluated. The soybean accession PI 675847 A (Vietnamese variety DT2008), was identified as a useful source of salt tolerance. During vegetative growth, PI 675847 A had lower leaf scorch scores, higher cell membrane stability, better photosynthesis and biomass accumulation under NaCl stress than the other 17 strains evaluated. In addition, PI 675847 A maintained better growth and seed yield in salt-affected soils compared with the sensitive lines. Analyses of ion contents in plant leaves under saline conditions showed that PI 675847 A was able to limit uptake and transport of Na+ and Cl−. Because of its higher productivity under saline conditions, PI 675847 A will be a useful germplasm source in soybean improvement programs for salt tolerance.

Slow Pyrolysis as a Promising Approach for Producing Biochar from Sunflower Straw

Slow pyrolysis opened new channels for the highly efficient utilization of sunflower straw in salt-affected regions and obtained not only 28% to 40% biochar, but also 29% to 44% syngas and 29% to 31% bio-oil. Biochar yield decreased with increasing temperature, whereas syngas increased and bio-oil changed minimally. Both syngas and bio-oil had potential value as fuel. The biochar produced at 700 °C had the highest pH, ash content, and water-soluble K+ of 11.9, 212 g/kg, and 23.9 g/kg, respectively, and the lowest atomic ratios for H/C and O/C of 0.19 and 0.10, respectively. However, C, other minerals, surface area, and cation exchange capacity (CEC) of biochar reached a stable level at 500 °C. Therefore, the differential characteristics of the biochar derived from sunflower straw might show potential value in removing pollutants and improving soil fertility at 500 °C.

Assessment of soil quality indices for salt-affected agricultural land in Kurdistan Province, Iran

Soil quality indices (SQIs) were an important tool for evaluating agro-ecosystems. Salinization and alkalization are major environmental problems that have threatened agricultural productivity since ancient times. The aim of this study is to assess soil quality in salt-affected agricultural land in Kurdistan Province, Iran, using three indices; the Additive Soil Quality Index (SQIa), the Weighted Additive Soil Quality Index (SQIw), and the Nemoro Soil Quality Index (SQIn). Each of the soil quality indices were calculated using a Total Data Set (TDS) and a Minimum Data Set (MDS) approach. The TDS consisted of nine soil quality parameters measured on 150 samples (0–30 cm depth): pH, Electrical Conductivity (EC), Organic Carbon (OC), Cation Exchange Capacity (CEC), Carbonate Calcium Equivalent (CCE), Exchangeable Sodium Percentage (ESP), Sodium Adsorption Ratio (SAR), Mean Weight Diameter (MWD), and Bulk Density (BD). Principal components analysis (PCA) was used to determine which indicators were to be included in the MDS. Indicator Kriging (IK) highlighted areas with a high risk of exceeding critical threshold values of EC, ESP, and SAR and having low soil quality. In non-salt-affected areas soil quality and the risk of exceeding critical threshold values and having low soil quality were lower and higher, respectively, compared to salt-affected regions. The MDS method showed a decrease in the area and proportion of grades with high and very high quality (I and II) and an increase in grades with low and very low quality (IV and V) compared to the TDS. The results of linear correlation, match, and kappa statistic analysis showed that soil quality was better estimated using the SQIw compared to the SQIa and the SQIn. In addition there were higher values of agreement (match and kappa statistic) for the TSD than MSD. However, using the SQIw index and MDS method can adequately represent the TDS (R2 = 0.82) and thus reduce the time and cost involved in evaluating soil quality.

Effects of Rice-Wheat Rotation and Afforestation on Microbial Biomass Carbon in Coastal Salt-Affected Soils of Eastern China

AbstractRice-wheat rotation and poplar afforestation are two typical land use types in the coastal reclaimed flatlands of eastern China. This study investigated two rice-wheat rotation lands (one reclaimed from 1995 to 2004 and cultivated since 2005, RW1, and the other reclaimed from 1975 to 1995 and cultivated since 1996, RW2) and a poplar woodland (reclaimed from 1995 to 2004 and planted in 2004, PW1) to determine the effects of land use types and years of cultivation on soil microbial biomass and mineralizable carbon (C) in this coastal salt-affected region. The results showed that the soil in PW1 remained highly salinized, whereas desalinization was observed in RW1. The total organic C (TOC) in the top soil of PW1 and RW1 did not show significant differences, whereas at a soil depth of 20–30 cm, the TOC of RW1 was approximately 40%–67% higher than that of PW1. The TOC of 0–30-cm soil in RW2 was approximately 37% higher than that in RW1. Microbial biomass C (MBC) and mineralizable C (MNC) exhibited the trend of RW2 > RW1 > PW1. Sufficient nutrition with more abundant C substrates resulted in higher MBC and MNC, and soil respiration rates were negatively correlated with C/N in RW1 and RW2. Nutrient deficiency and high salinity played key roles in limiting MBC in PW1. These suggested that rice-wheat rotation was more beneficial than poplar afforestation for C accumulation and microbial biomass growth in the coastal salt-affected soils.

Determination of Growth Stage-Specific Crop Coefficients (Kc) of Sunflowers (Helianthus annuus L.) under Salt Stress

Crop coefficients (Kc) are important for the development of irrigation schedules, but few studies on Kc focus on saline soils. To propose the growth-stage-specific Kc values for sunflowers in saline soils, a two-year micro-plot experiment was conducted in Yichang Experimental Station, Hetao Irrigation District. Four salinity levels including non-salinized (ECe = 3.4–4.1 dS·m–1), low (ECe = 5.5–8.2 dS·m–1), moderate (ECe = 12.1–14.5 dS·m–1), and high (ECe = 18.3–18.5 dS·m–1) levels were arranged in 12 micro-plots. Based on the soil moisture observations, Vensim software was used to establish and develop a physically-based water flow in the soil-plant system (WFSP) model. Observations in 2012 were used to calibrate the WFSP model and acceptable accuracy was obtained, especially for soil moisture simulation below 5 cm (R2 &gt; 0.6). The locally-based Kc values (LKc) of sunflowers in saline soils were presented according to the WFSP calibration results. To be specific, LKc for initial stages (Kc1) could be expressed as a function of soil salinity (R2 = 0.86), while R2 of LKc for rapid growth (Kc2), middle (Kc3), and mature (Kc4) stages were 0.659, 1.156, and 0.324, respectively. The proposed LKc values were also evaluated by observations in 2013 and the R2 for initial, rapid growth, middle, and mature stages were 0.66, 0.68, 0.56 and 0.58, respectively. It is expected that the LKc would be of great value in irrigation management and provide precise water application values for salt-affected regions.

Effects of concentrations of sodium chloride on photosynthesis, antioxidative enzymes, growth and fiber yield of hybrid ramie

Ramie (Boehmeria nivea L.) is one of the oldest and most important fiber crops in China due to the comfortable textile of its fine fiber. Increased ramie fiber demand brings ramie cultivation to salt-affected regions. The aim of this research was to determine morphological, physiological and biochemical responses of ramie by subjecting plants to varying concentrations of NaCl (0, 2, 4, 6 and 8 g NaCl/kg dry soil) at vigorous growth stage for 10 and 20 days. Results indicated that salinity stress substantially inhibited the growth of hybrid ramie plants and led to remarkable decline in fiber yield. However, when grown at 2 g NaCl/kg growth and fiber yield were similar to non-saline control. In addition, chlorophyll fluorescence and gas exchange parameters were correlated with growth and yield response. Salt treatments promoted a subsequent decrease in maximum quantum efficiency of PSII photochemistry (Fv/Fm), quantum efficiency of open PSII reaction centers (Fvʹ/Fmʹ) and quantum yield of PSII (φPSII) while non-photochemical quenching (NPQ) changed conversely. Photochemical quenching (qP) and electron transport rate of PSII (ETR) increased at 2 and 4 g NaCl/kg then decreased at 6 and 8 g NaCl/kg. Substantial decline in the PSII activity at high salinity was associated with the loss of chlorophyll contents. Moreover, marked decrease in net photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs) was also recorded. Nonetheless, intercellular CO2 (Ci) decreased at low salt stress, subsequently increased at high salt stress while water use efficiency (WUE) and instantaneous water use efficiency (WUEi) altered in opposite direction. Substantial decrease of photosynthesis at high salinity was due to non-stomatal factors. Furthermore, salinity stress led to decrease of proteins and accumulation of proline and malondialdehyde (MDA), as well as enhanced activities of superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POD, EC 1.11.1.6), whereas, catalase (CAT, EC 1.11.1.7) enhanced at low salinity, decreased at high salinity. Nonetheless, these changes were closely related with the severity and duration of the salinity stress and their interaction. The results suggested a certain tolerance to salinity stress for hybrid ramie. This meets the essential condition for utilization in salinity-prone environments.

English

Salicornia bigelovii is a promising resource to cultivate under extreme climatic conditions of arid-desert regions. However, the production of Salicornia depends on the appropriate supplementation of nitrogen rich synthetic fertilizers. Application of specific halotolerant nitrogen-fixing bacteria associated with S. bigelovii could be an important practice for crop production in salt-affected regions. Seedlings of S. bigelovii were inoculated and developed with plant growth promoting rhizobacteria (Klebsiella pnseumoniae) at different salinities (0 and 0.25 M NaCl) grown under in vitro conditions. The inoculation increased growth and physiological activity at a high salinity. The major benefits of inoculation were observed on total seedlings biomass (320 and 175 g at 0 and 0.25 M NaCl, respectively) and adjacent branches of stem biomass (150 and 85 g at 0 and 0.25 M NaCl, respectively). The inoculation with Klebsiella pneumoniae also significantly improved seedlings salinity tolerance compared to the noninoculated controls. In non-salinity conditions, the inoculated seedlings enhanced the CO 2 fixation and O 2 evolution. The non-inoculated controls were more sensitive to salinity than inoculated seedlings exposed to salinity, as indicated by several measured parameters. Moreover, inoculated seedlings had significantly increase on proline, phenolics content, but not significant in starch compared to noninoculated controls. In conclusion, K. pneumoniae inoculation mitigates the salinity effects and promotes the Salicornia growth. Keywords: Salicornia bigelovii, Klebsiella pneumoniae , halophyte, ecotype, stress salinity. African Journal of Biotechnology Vol. 12(34), pp. 5278-5284

Assessment of Underground Tube Well Water Quality in Different Agro-climatic Regions of the Punjab State, India

During the past five decades, Punjab has witnessed a tremendous progress in agricultural production. Improved irrigational facilities, especially, the increased utilization of underground water resources among others, have played a major role in giving a boost to agriculture sector. Due to increased dependence on these, underground water quality in certain areas has deteriorated posing a serious health concern for the environment. Assessment of the ground water quality may provide useful information to ensure sustainable use of the natural resources for various purposes. The present study was conducted in June–July 2012 with the objectives of investigating the quality and suitability of irrigation water in the three agro-climatic regions, namely, sub-mountaneous, central and south western of Punjab. Various water parameters viz., pH, Electrical Conductivity (EC), cations (Ca2+ and Mg2+) and anions (CO32-, HCO3− and Cl−) were analysed using standard procedures. Based on the residual sodium carbonate values, all the samples in the sub-mountaneous region were found to be fully fit for irrigation, while in the central and south western regions only around 40% and 41% of the tube well water samples were found to be fully fit for irrigation. In certain areas, higher values of residual sodium content in the tube well water samples were observed, possibly, due to lower concentration of Ca + Mg ions. Poorly drained or fine textured soils if irrigated with these waters, could witness the development of black kallar. Around 2% samples in the south-western region were found to be unfit for irrigation on the basis of EC values. This indicates towards higher accumulation of soluble salts in underground water aquifers of the region. Efficient water resource management along with the judicious use of these resources with proper amendments is necessary to avoid any impeding health hazards in these salt-affected regions of Punjab.