1. Introduction

2. Materials and methods

3. Results and discussion

4. Conclusions

Acknowledgements

Appendix A. Supplementary data

References

Abstract

Soil organic matter (SOM) or humus is essential for the agricultural and environmental functionality of soils. Humus comprises small-size heterogeneous organic molecules arranged in complex meta-stable suprastructures, whose composition can be greatly affected by land management. Here, we report the molecular dynamics of the fractions extracted from an agricultural soil cropped with wheat after one and three years of tillage. The total molecular components, named Humeome, of soil under wheat found in both hydrosoluble and organosoluble fractions isolated by the Humeomic procedure, as determined by GC–MS and high-resolution Orbitrap LC–MS, were compared to the Humeome characterized in the same soil when cropped with maize. While the three-years tillage did not vary the total soil organic carbon under both wheat and maize, the carbon recovered for the sum of Humeomic fractions isolated from soil was significantly larger for maize than for wheat, thus suggesting a general destabilization of SOM under wheat cropping. Moreover, the soil Humeome under wheat resulted more hydrophilic than under maize. While fatty acids and carbohydrates were periodically replenished by crop residues, nitrogen-containing molecules, such as amides and heterocyclic nitrogen, and iron-bound molecular systems were the SOM components mostly reduced under wheat. The losses of these compound classes from the soil Humeome was possibly attributed to the exudation differences between wheat and maize cropping. These results reveal that the molecular dynamics and stability of SOM molecular components can be controlled by crops even in a short term.

Introduction

World soils contain the greatest reservoir of organic carbon (OC) in the biosphere (Batjes, 2014), and innovative measures to reduce OC losses from soils are required to limit global changes (Minasny et al., 2017; Piccolo et al., 2018). Nevertheless, agriculture intensification to produce food for an increased population will inevitably put soil at risk of SOM degradation and fertility losses (Lal, 2009), thus menacing human sustainability on the planet. Due to the still large uncertainty in strategies to sequester OC in soil (Baveye et al., 2018), there is an urgent need to enlarge knowledge on SOM dynamics, in order to control soil OC and prevent degradation of soil fertility.

Humus represents the metabolic substrate for soil microbial activity that, in turn, continues to transform the bioavailable humic pools until a new equilibrium is established between microbial communities, humic matter and plant species (Basler et al., 2015). While the concept of ecological succession was introduced as a theory (Putnam, 1994), few reports were so far published on the molecular changes of humus due to plant species, even though plant rhizodeposition is reckoned to play an important role in OC turnover in soil (Hütsch et al., 2002; Wang et al., 2006). Larger microbial and CO2-C exudates were reported in wheat than in maize (Marx et al., 2007), while wheat residues were found to rapidly and persistently stimulate a microbial degradation of fresh organic matter (Bernard et al., 2007), thereby enhancing mineralization of rhizospheric SOM (Schenck zu Schweinsberg-Mickan et al., 2012).

1- Introduction

2- Material and methods

3- Results

4- Discussion

5- Conclusion

References

Abstract

Soil microbes play vital roles in energy flow and nutrient cycling and, thus, are important for agricultural production. A better understanding of the complex responses of microbial communities to various organic and inorganic fertilization regimes is critical for sustainable development of agroecosystems. Changes in bacterial and fungal abundance and diversity in fluvo-aquic soil in Northern China were studied under 38-year long-term fertilization strategies: four chemical-fertilization strategies (i.e., no fertilizer, N, NP, or NPK), with or without manure amendment, were investigated by high-throughput sequencing and quantitative polymerase chain reaction-based amplification of bacterial 16S rRNA and fungal internal transcribed spacer (ITS) rRNA genes. Chemical fertilizer plus manure addition clearly increased the soil fertility and was recommended for further optimization of fertilization patterns. Both principal component analysis and partial least-square discriminant analysis showed greater impacts of manure addition than chemical fertilizer on bacterial community distributions, whereas fungal communities were more sensitive to inorganic fertilizer. The linear discriminant analysis effect size method revealed that the number of responding microbes (microbes significantly affected by various fertilizations) in bacterial communities in manure-treated soils was markedly higher than that in chemical fertilizer-treated soils, whereas those of fungal communities showed the opposite trend. In addition, redundancy analysis further illustrated the primary importance of organic matter in shaping community distributions of bacteria, rather than in driving fungal community patterns. These results suggested that organic and inorganic fertilizers, respectively, dominated in shaping bacterial and fungal community distributions in fluvo-aquic soils.

Introduction

Soil microorganisms play vital roles in the maintenance of soil health, productivity, and sustainability, and thus crop production, because of their contributions to soil nutrient transformation, formation and decomposition of organic matter, and stabilization of soil aggregates (Van Der Heijden et al., 2008; Zhao et al., 2014; Singh, 2016; Pan et al., 2018a). Therefore, a profound understanding of soil microbial ecology has become increasingly recognized and emphasized because of the ecological and economic importance of microorganisms (Mele and Crowley, 2008). Due to the increasing concerns regarding food demands and the scarcity of land available for agriculture, high amount of fertilizer is implemented to increase crop productivity (Inselsbacher et al., 2010). The application of organic and inorganic fertilizers can cause detectable changes in nutrient availability to plants, as well as in the diversity and function of microorganisms (Marschner et al., 2003). For example, long-term field experiments involving polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) demonstrated the importance of balanced fertilization in promoting the activities of bacterial communities (Chu et al., 2007a,b; Luo et al., 2015). Nitrogen (N) is regarded as a key limiting factor for soil microbes, and N amendment can alter the activity and diversity of soil organisms (Sarathchandra et al., 2001; Xu et al., 2017; Liu et al., 2019). Organic fertilization exerted no effects on the fungal biomass, while increasing the bacterial biomass by increasing soil organic carbon (Corg) and C/N ratio (Crecchio et al., 2001; Marschner et al., 2003). In addition, manure application promoted soil bacterial communities by enhancing root exudates and also improved plant growth (Bittman et al., 2005). Suzuki et al.

Occurrence and Functions of Mucilage

A Model of a Mucilage-Supported Diazotrophic Microbiota

Disassembly of the Complex Mucilage Polysaccharide

Sugar Utilization to Support Nitrogenase Activity

Reduction of Oxygen Levels in the Mucilage Environment

Maintaining Low Nitrogen Levels in the Mucilage Environment

Concluding Remarks

Acknowledgement

References

Role for Nitrogen Fixation in Cereal Crops

Nitrogen-fixing microbial associations with nonlegumes, especially cereals, have been a topic of intense interest for more than a century, since such associations could reduce the requirement for nitrogen fertilizers [1–4]. For instance, sugarcane associates with diazotrophic endophytes that contribute to its nitrogen nutrition in some environments [5–7] and a study based on 15N dilution experiments in Miscanthus × giganteus concluded that this bioenergy feedstock could acquire about 16% of its nitrogen from the air [8]. These examples indicate that some monocots have the potential to associate with diazotrophs and acquire small, but significant, amounts of fixed nitrogen from the atmosphere. It has been shown that the model C4 grass Setaria viridis can obtain most of its fixed N from associative nitrogen fixation following inoculation with diazotrophs [9]. The possibility that cereal crops obtain a significant proportion of total N by associative nitrogen fixation has also been suggested by a 50-year assessment of global nitrogen budgets in maize (Zea mays), rice (Oryza sastiva), and wheat (Triticum aestivum), which concluded that up to 24% of the total nitrogen in these crops was derived from nonlegume symbiotic nitrogen fixation [10]. Interestingly, mucilage on aerial roots of sorghum (Sorghum bicolor) with an inset micrograph of Azospirillum brasilense was highlighted on the cover page of the proceedings of a conference on cereal nitrogen fixation held in India in 1984 [11], suggesting that it was suspected more than 35 years ago that sorghum mucilage harbors a diazotrophic microbiota. However, no report on nitrogen fixation in sorghum mucilage was published in the 1984 proceedings volume or elsewhere.

Occurrence and Functions of Mucilage

A key feature of the Sierra Mixe maize landrace mucilage is the abundance of sugars that potentially serve as a source of energy for the diazotrophs. The monosaccharide composition indicated that the mucilage primarily comprises fucose (41%), galactose (36%), arabinose (14%), xylose (3%), glucuronic acid (3%), and mannose (3%) [12]. This composition is similar to the mucilage reported for maize underground roots [15,16]. Osborne et al. found that underground root mucilage contained fucose (61.0%) and glucose (31.4%), while Chaboud found the mucilage to contain galactose (30.7%), fucose (19.3%), glucose (18.5%), xylose (15.2%), and arabinose (13.4%). Both of these previous studies showed high amounts of fucose, xylose, arabinose, and galactose, which agrees qualitatively with the analysis of the Sierra Mixe aerial root mucilage. This monosaccharide composition is not commonly found in plant cell wall polysaccharides and may play a role in signaling associative diazotrophic bacteria that can degrade the mucilage complex polysaccharide and use the released monosaccharides to support growth and nitrogen fixation.

1- Introduction

2- Sources and characterization of agricultural wastewater

3- Struvite and its recovery performance from agricultural wastewaters

4- Commercial development of struvite products

5- Hindrances to struvite recovery from agricultural wastes

6- Strategies for performance intensification and operational cost reductions

7- Use of struvite as an alternative fertilizer in the soil

8- Economic evaluation

9- Conclusions

References

Abstract

To meet the needs of a fast growing global population, agriculture and livestock production have been intensified, resulting in environmental pollution, climate change, and soil health declining. Closing the nutrient circular loop is one of the most important sustainability factors that affect these issues. Apart from being a serious environmental issue, the discharge of N and P via agricultural wastewater is also a major factor that disturbs nutrient cycling in agriculture. In this study, the performance, in terms of recovery, of N and P (individually, as well as simultaneously) from agricultural wastewaters via struvite has been comparatively summarized. Details on the hindrances to nutrient recovery through struvite formation from agricultural effluents, along with strategies to overcome these hindrances, are provided. In addition, various strategies for recovery performance intensification and operational cost reduction are comprehensively discussed. This work will provide scientists and engineers with a better idea on how to solve the bottlenecks of this technique and integrate it successfully into their treatment systems, which will ultimately help close the nutrient loop in agriculture.

Introduction

The manifestations of rapid population growth, urbanization, improved standards of living, and concurrent intensification of socioeconomic activities on overall environmental health are well recognized and acknowledged (Cordell et al., 2009; Clarke, 2013). Global cereal production has doubled in the past 40 years, mainly from the increased yields resulting from greater inputs of fertilizer, water, pesticides, and so on. This has increased the global per capita food supply and alleviate hunger in poverty-stricken areas (Alexandratos and Bruinsma, 2012). During this process, however, the increase in nitrogenous fertilizer application and exhaustion of the limited reserves of rock phosphate have been quite considerable. At present, the annual fertilizer consumption of rock phosphate is reported to be over one million tons, while the use of N fertilizer could be three times as much (Rahman et al., 2011). Moreover, it is estimated that within 100 years, mined P rocks will be completely exhausted (Cordell and White, 2014”). Global cycling of these nutrients has been altered, owing to their widespread use in intensive agriculture, in ways that can contribute to severe environmental issues. Predominantly, nutrients can escape from farm fields to the surrounding soils, air, and waterways, when applied in excess of the plants’ needs (Deng et al., 2006). Hence, the notion of a closed-loop nutrient cycle provides a simple, persuasive, and elegant approach for realizing efficient natural resource management-improved human well-being, and long-term food security (Maurer et al., 2006). The closing of the nutrient loop includes a wide range of ongoing efforts to make sure that nutrients are applied at times and places that align with the requirements of the plants. It also includes efforts to recover nutrients in usable forms from waste effluents and recycle them into cropping systems (Yorgey, 2014). The logic is that by recovering nutrients from waste effluents, a more “closed” system for sustainable agricultural development can be created.

1- Introduction

2- Material and methods

3- Results and discussion

4- Conclusions

References

Abstract

Soil erosion controlled by the wind effect on the surface, has been largely studied by field in-situ measurements as well as laboratory or numerical simulations. Nevertheless, more in-situ measurements and observations are needed to document this phenomenon for various desert areas. In the present study, we focus on the documentation of different properties of a wide range of semi-arid and arid soils of the Fars province, and how they control the soil erosion by wind. By improving our knowledge on soil properties which lead to the limitation of soil erosion by wind, it will be possible to better prevent wind erosion in the Fars province. Extensive wind tunnel experiments were conducted in 20 different arid and semi-arid regions. For each region, three wind tunnel experiments were done to encounter local soil variability. We determined threshold wind speeds for which soil erosion was observed. Other experiments were conducted at the same high wind speed, and duration conditions, allowing discussing soil erosion rates by wind regarding soil properties. As already documented in the literature, our results pointed out a significant negative power relationship between wind erosion rate and different soil physical properties, including soil surface gravel cover, the mean weight diameter (MWD) of soil particles, and soil clay and moisture contents. Moreover, a nonlinear relationship as a power function was found between the increase of soil organic carbon and the decrease of soil losses by wind in the studied semi-arid and arid soils. We determined critical values of these soil properties for which wind erosion in Fars province is limited under high wind speed conditions. Additionally, the effects of the electrical conductivity (EC), sodium adsorption ratio (SAR), and calcium carbonate equivalent (CCE) on wind erodibility were discussed at low and high concentrations and for different soil textures.

Introduction

Soil erosion by wind is a serious environmental problem in many arid and semi-arid regions; it is considered as a soil-degrading process (Webb et al., 2017) that affects over 500 million ha of land worldwide (Grini et al., 2005). In fact, wind erosion degrades soil by removing and emitting in the atmosphere fine soil particles that contain most of the soil organic carbon and nutrients (Van Pelt and Zobeck, 2007). The appraisal of this process at the soil-atmosphere interface is central to estimate of soil loss for soil conservation planning (Black and Chanasyk, 1989). The emission of top soil particles from land surfaces into the atmosphere impacts the soil productivity, and should also be considered for air quality and health issues (Webb et al., 2017; Pi and Sharratt, 2017; Pi et al., 2017). Soil erosion by wind is a function of the soil erodibility and the wind erosivity (Chepil and Woodruff, 1963). It is a threshold phenomenon controlled by surface winds and soil properties. There is a minimum wind stress that corresponds to a threshold velocity needed to initiate wind erosion on semi-arid and arid surfaces (Chepil, 1951; Gillette et al., 1982). Non-erodible elements such as vegetation and gravels on an erodible surface not only increase the apparent threshold wind velocity but also reduce the mass erosion rate. Even if the erosive action of the wind depends on its speed, several factors like the size and stability of the soil aggregates, clay content, and near-surface soil moisture affect the threshold velocity (Ravi et al., 2006). The size and stability of soil aggregates are significant factors that affect the soil susceptibility to wind erosion (Colazo and Buschiazzo, 2010; Négyesi et al., 2016). In general, soil aggregates are formed through the combination of mineral particles with organic and inorganic substances (Bronick and Lal, 2005; Mahmoodabadi and Ahmadbeigi, 2013). The binding of soil particles into stable aggregates is essential for the production of optimum soil tilth (Harris et al., 1966). Inter particle cohesion is a combined effect of the van der Waals force, liquid and chemical force, and electrostatic force. These effects are sensitive to soil properties, such as the particle shape and texture, the soil mineralogy, the packing arrangement, and the presence or absence of bonding agents such as soil moisture and soluble salts (Shao and Lu, 2000).

Appropriate tillage practices reduce a crop’s carbon footprint (CF) and mitigate climate change. However, little is known about the CF of winter wheat and spring maize production under different tillage practices in the Loess Plateau of China. To quantify the tillage differences and crop type differences in CF, a field experiment was established in 2007 in which the following six tillage practices were evaluated: plow tillage (PT), no-tillage (NT), subsoil tillage (ST), PT/NT rotation, NT/ST rotation and ST/PT rotation. The results showed PT had the positive CF value (488 kg CO2-eq ha
1 ), indicating a carbon source. However, NT, ST, ST/PT, PT/NT and NT/ST significantly decreased the CF (
628,
1382,
2328,
3038 and
3545 kg CO2-eq ha
1 ), demonstrating these tillage practices served as carbon sinks. The functional unit-scaled CFs (yield-scaled CF, cost-scaled CF, production value-scaled CF and net income-scaled CF) were similar to the trend of CF, which exhibited the following order: NT/ST > PT/NT > ST/PT > ST > NT > PT. The CF and functional unit-scaled CFs of winter wheat production were significantly higher than those of spring maize production. The CF and functional unit-scaled CFs decreased as planting year increased. In addition, increasing SOC storage and grain yield were benefit for decreasing CF. The results of this study showed NT/ST rotation produced the highest grain yield and SOC storage with the lowest CF and functional unit-scaled CFs and was thus determined to be the best tillage practice for balancing sustainable production with the environment in the Loess Plateau.

Introduction

Climate change is a global issue. Greenhouse gases (GHGs) from human activities are continuously emitted into the atmosphere from industrialization, energy and agricultural activities (Linquist et al., 2012). Globally, agricultural activity-produced total non-CO2 GHG emissions comprised 10e12% of the anthropogenic emissions recorded in 2010 (Edenhofer et al., 2014). In China, GHG emissions from agricultural activities were 0.94 Gt CO2-eq$yr
1 in 2012 (NDRC, 2016). Therefore, promoting cleaner production technology with less GHG emissions is necessary to mitigate global climate change and realize sustainable agricultural development. Carbon footprint (CF) is used to effectively evaluate the GHG emissions of a product (BSI, 2011) and have been used recently as a robust research approach to study climate change phenomena. Pishgar-Komleh et al. (2017) quantified the CF variability of tomato production in two farms in Iran. Ali et al. (2017) estimated the effect of 12 management practices on CF in Italy. Yang et al. (2014) compared the CF of five cropping systems in the North China Plain. These studies aimed to attain proper measures for reducing GHG emissions in the local crop production by comparing CF. In addition, different CF have been observed in major grain crops production. Previous studies have reported the CF of wheat production was higher than that of maize production (Huang et al., 2017; Yan et al., 2015).

Abstract

The root growth of most crop plants is inhibited by soil salinity. Roots respond by modulating metabolism, gene expression and protein activity, which results in changes in cell wall composition, transport processes, cell size and shape, and root architecture. Here, we focus on the effects of salt stress on cell wall modifying enzymes, cellulose microfibril orientation and non-cellulosic polysaccharide deposition in root elongation zones, as important determinants of inhibition of root elongation, and highlight cell wall changes linked to tolerance to salt stressed and water limited roots. Salt stress induces changes in the wall composition of specific root cell types, including the increased deposition of lignin and suberin in endodermal and exodermal cells. These changes can benefit the plant by preventing water loss and altering ion transport pathways. We suggest that binding of Na+ ions to cell wall components might influence the passage of Na+ and that Na+ can influence the binding of other ions and hinder the function of pectin during cell growth. Naturally occurring differences in cell wall structure may provide new resources for breeding crops that are more salt tolerant.

Introduction

Plant evolution has resulted in a large array of mechanisms to tolerate the stresses associated with increased soil salinity. However, for most cereal crops the growth of roots is disrupted when soil salinity exceeds 4 dS/m, equivalent to about 40 mM NaCl. Increased soil salinity exposes plants to ionic sodium (Na+) and chloride (Cl−), which leads to a cascade of responses in the plant due to the ionic and osmotic components of salt stress [1,2].

Salt stress can indirectly affect cell wall properties by causing changes in gene expression, but Na+ can also physically interact with the cell wall components directly, and change their chemical properties [3]. An increase in soil salinity results in accumulation of Na+ in the apoplast, which can lead to an increase in interactions between Na+ and negatively charged sites within cell wall polymers, and also influence apoplastic pH. Salinity causes transient alkalinisation of the apoplast, and this could limit growth in the context of the acid growth theory [4,5]: Auxin activates plasma membrane H+-ATPases and protons are extruded into the apoplast, apoplastic acidification induces cell wall loosening by activating expansins and other remodelling enzymes resulting in loosening of the cell wall. Hence, growth could be limited by a decrease in free apoplastic protons causing a shift in the apoplastic pH away from the range that favors cell-wall loosening [4], although in maize the inhibition of growth as a result of salinity was not associated with the capacity of the epidermal cells to acidify their walls [6].

Microorganisms are the key players in every agro-ecosystem. They are the natural inhabitants of all the soil and plant systems, in which they represent dominant presence in terms of their vast diversity and multipronged functional capabilities. Multifarious physical, chemical and biological factors usually represent good soil fertility status as a guaranty of sustainable agro-ecology, plant health and crop productivity. Since healthy soils are largely characterized by their profound biological and chemical behavior, microbial functionalities related to nutrient fixation, recycling, acquisition, sequestration, solubilization, mobilization, decomposition, degradation and remediation may act as definitive indicators. Functional capabilities of microbial communities associated with soils and plant parts have been critically identified and characterized in the past few decades. Application of individual microbes or their consortia in many crops established their role in finding out a supplement and/or substitute in the existing agricultural practices which are largely dependent on synthetic chemical inputs in present time. We are presenting here a detailed account of microbial community functions, their relation with the soil and plant health and the potential indicative roles they play to establish a sustainable soil ecological environment for supporting crop growth, development and yield in long term.

Introduction

At the time when we are looking for advances in producing more and more crops to feed the ever-increasing population and harvesting benefits from agricultural economy (Zhang et al., 2010), the adversities of the agro-ecosystem and socio-economic challenges are becoming severe. Farmers are facing issues of unpredictable climate, shrinking agricultural lands, depleting natural resources, balanced nutrition in soil and diminishing crop responses to agrochemicals. Therefore, the concerns for sustainable soil and plant health improvement are rising. Soil is the ultimate nutrient hub and bioresource reservoir for agricultural crops. Among the all biological entities, soil harbors huge diversity of microbial life forms. The microorganisms serve as active agents for nutrient sequestration, recycling and supply to plants. Wide array of benefits are extended to the plants by the rhizosphere microorganisms that fix dinitrogen (Brahmaprakash and Sahu, 2012; Gothandapani et al., 2017), improve phosphorus uptake (Ahilandeswari and Maheswari, 2016), degrade xenobiotics and sequester heavy metals (Ahemad and Malik, 2011; Pant et al., 2016), suppress phytopathogens and pests (Feng et al., 2013; Cheng et al., 2016), improve soil aggregation (Van Veen et al., 1997; Yilmaz and Sonmez, 2017), help plants tolerate abiotic stresses (Meena et al., 2017), remediate problematic soils (Yao et al., 2010; Tiwari et al., 2011) and chelate minerals like Fe, B and Zn (Ghosh et al., 2015). The microenvironment of plant rhizosphere is a major hub for microbial diversity and functionalities that contribute enormously to the plant and soil health. As microorganisms play crucial roles in the soil processes, any physical, chemical or biological changes happening in the soils clearly affect the microbiota. Microbes respond quickly to any changes happening in the soil ecosystem and act as true indicators for specific functions in the soil environment. Having seen the prospects and perspectives of microorganisms as critical biological players that can even play role of indicators, we elaborately described their potential functions as prominent soil and plant health indices in the agroecosystem.

This study describes the history and outcomes of the Iranian Soil Science Congress (ISSC). From 1972, the Soil Science Society of Iran (SSSI) has organized 15 ISSCs. The ISSC has been organized at six disciplines including (I) soil chemistry, (II) soil physics, (III) soil genesis and classification, (IV) soil biology, (V) soil erosion and conservation, (VI) soil fertility and plant nutrition, this structure still has remained. In the past 25 years, 7864 papers have been presented at ISSC and the soil fertility and plant nutrition discipline has the highest number of papers. The number of papers published in the ISSC has sextupled in the 10 years from 2001 to 2011, followed by a sharp decline (i.e., 43%) in 2015. Despite the large number of papers presented in the ISSCs, knowledge about how soils should be governed is little. It is expected that studies on climate change will have a special place among Iranian soil scientists in the future. To increase trends in environmental challenges and policy issues, interdisciplinary approaches are required. Therefore, Iranian soil scientists require national and international collaboration and communication with scientists in other disciplines to successfully manage the soils. Unfortunately, there are several pessimism and concerns on the future of soil science in Iran. To get out of this situation, modeling from the successful countries in this field seems necessary.

Introduction

Soil is essential for life and identified as being central to many of the challenges facing society, including food, water, energy security and supporting biodiversity, all of which contribute to human health (Bouma, 2014; McBratney et al., 2014; Arrouays et al., 2017). The soil is a critical component in understanding global issues and these require research that leads to understanding and solutions at national and regional levels (Hartemink, 2014). Soil science is special and maturing science that became a scientific discipline in the 19th century when agricultural chemists and agrogeologists combined their efforts and soils were seen as natural bodies that ought to be studied independently (Hartemink et al., 2014). The content of soil science is uneasily placed between natural science on the one hand, and the world of professional practice on the other (Philip, 1991). In the first half of the 20th century, soil science grew rapidly and established some sub-disciplines such as pedology, soil chemistry, soil biology, soil fertility and soil physics (Brevik and Hartemink, 2010). Although, the soil science developments have been different in various parts of the world, one of the main pillars in the development of the soil science discipline has been the formation of an international learned society. The International Society of Soil Science (ISSS) or its successor the International Union of Soil Sciences (IUSS) has played a major role in the development and promotion of soil science as a discipline. Since the ISSS had paid little attention to historical developments, a working group was formed to deal with the history and sociology of soil science at the 12th congress of ISSS, held in New Delhi in 1982 (Boulaine, 1989). The IUSS provides opportunities to: (i) ensure the advancement of soil science and its application, (ii) to handle the business of the society, (iii) working groups through the World Congress of Soil Science (WCSS). The Soil Science Society of Iran (SSSI) as a member of IUSS was formed 45 years ago with the aim of exchanging the latest research results and international sharing the advanced research methods in soil and environmental issues. The SSSI started with 5 members and presently has nearly 1223 members. Number of SSSI members increased dramatically (i.e., 5 versus 1223) over time from 1992 to 2017. From 1992 to 2000, the number of members grew steadily but between 2000 and 2017 the growth occurred with a higher rate (Fig. 1). This paper aims to investigate the history and outcomes of the ISSC from 1972 to 2017.

In tea (Camellia sinensis) plantation areas, soil acidification mainly results from excessive nitrogen fertilization. However, the proposed theoretical explanations for soil acidification due to nitrogen fertilization are still lacking empirical validation because most studies have used short-term incubation periods or pot experiments. Here, both soil and soil solution samples were taken from a tea plantation field (Ultisol in USDA taxonomy system, or Alisol in WRB taxonomy system) treated using different nitrogen application rates: 0 (N0), 119 (N119), 285 (N285), and 569 (N569) kg N ha−1 yr−1 for 8 years (2006–2013). Soil pH and the concentrations of the relevant cations and anions were also determined. With no nitrogen fertilization (N0), the surface soil pH decreased from 4.16 to 3.32 after 8 years in the tea plantation. Compared with no nitrogen fertilization (N0), high nitrogen fertilization (N569) significantly decreased the soil pH from 3.32 to 3.15 and 3.67 to 3.35 in the soil at depths of 0–40 cm and 40–90 cm, respectively. However, the low (N119) and moderate (N285) nitrogen treatments showed non-significant effects upon soil pH. Our results confirm the previous findings that a high nitrogen application rate can accelerate soil acidification in a tea plantation, and that the subsoil is particularly susceptible to acidification after heavy nitrogen fertilization. Soil acidification also significantly decreased the nutrient base cations Ca2+, Mg2+, and K+ in the soil. Our results suggest that heavy synthetic nitrogen fertilization should be partly replaced with compound or organic fertilizers to mitigate soil acidification and nutrient cation deficiency in tea plantation fields.

Introduction

The tea plant (Camellia sinensis) is an important cash crop cultivated in many tropical and subtropical countries. Unlike many other crops, tea is a perennial leaf-harvested crop that grows best in acidic soil with an optimum pH between 4.0 and 5.5 (Ruan et al., 2007; Fung et al., 2008). Nevertheless, soil acidification can lead to the accumulation of aluminum (Al) and deficiencies in phosphorus (P), potassium (K), and magnesium (Mg) nutrients in tea field soil (Tachibana et al., 1995; Wang et al., 1997; Ruan et al., 2012). Concerning the quality of tea, soil acidification can increase the content of heavy metals (e.g., lead, Pb) and fluorine (F) in the harvested leaves, which may entail a risk to human health (Ruan et al., 2003; Jin et al., 2005; Zhang and Fang, 2007). Generally, N fertilization or deposition is considered the major driver of soil acidification in croplands (Debreczeni and Kismanyoky, 2005; Schroder et al., 2011; Cai et al., 2015), grasslands (Martins et al., 2014; Chen et al., 2015), and forest ecosystems (Hogberg et al., 2006; Zhu et al., 2016). Specifically, it is thought that the accelerated soil acidification from N fertilization is directly caused by the production of protons via the nitrification process after ammonium nitrogen fertilization occurs (Barak et al., 1997; Zhou et al., 2014). The generated hydrogen ions (H+) are buffered by a suite of factors, including carbonate, silicate, exchangeable base cations, and the Al and/or iron (Fe) content, which depend on the soil pH (Bowman et al., 2008). Since base cations enter the soil solution as accompanying ions with the leaching NO3 −, the buffering capacity of soil is consequently decreased under increasingly acidic conditions (Lucas et al., 2011). How much N fertilization contributes to soil acidification remains unclear since the latter could happen naturally in tea plantation settings. Ding and Huang (1991) proposed that this might arise when the accumulated Al in the tea plant residue returns to the soil via litter fall and regular pruning. Recent studies have revealed that the root uptake of NH4 + and Al3+, and the subsequent release of protons, could also cause soil acidification in tea plantations (Ruan et al., 2004; Wan et al., 2012). However, several processes may also weaken the rate of soil acidification in tea plantation soil. The contribution of nitrification to soil acidification could be diminished by reductions in the availability of substrate, as tea plants preferentially assimilate NH4 + (Ruan et al., 2007). Additionally, the soil acidification rate may be reduced by less nitrate leaching, since the nitrification rate is typically inhibited by a low soil pH (Kemmitt et al., 2005).

Introduction

Farming, for the most part being a mantle passed down from generation to generation, farmers feel obliged to stick to age old patterns of farming right from the seasons of working the ground to ritualistic harvest practices. Only recently in the past decade have farmers started adopting informed crop cycle patterns (Soleri and Cleveland (2004). In general, farmers have an opinion that more fertilizer equals more yields yet it cannot be farther from the truth. The role of chemical fertilizers is very important and acceptable, because it plays an important role in increasing soil fertility and increasing crop production (Jallah et al., 1991; Simonne et al., 2017). However, long term usage of inappropriate chemical fertilizers will decrease the quality of soil and increase the soil degradation and effects ecological pollution (Ayoub, 1999; Patnaik, 2010). Sometimes the fertility and quality of the soil is heavily affected due to the knowledge void of the farming community. The impact of the chemicals is the most severe among the various others. Savci (2012) and Ning et al. (2016) have mentioned the vulnerabilities of chemical fertilizers and the contamination of various types of environmental pollutions. Aziz et al. (2015) have reported in detail about the need of fertilizers and their impacts on environment. On this basis, we have come to know the effects of chemical agriculture and the adverse effects it has on our agricultural lands. So every attempt at remediating the damage done is being attempted by mindful and discerning farmers/agricultural engineers. But the efforts to shift from modern agricultural practices to primitive yet more effective methods of cultivation presents its own set of complications, as our lands have lost the bounce back ability to cope up with organic and natural cultivation methods to produce a similar quantum of agricultural produce upon termination of chemical inputs. Fertilizer usage and crop production are heavily interlinked processes, especially in horticultural crops (Fageria, 2001). Soil and Water quality, fertilizer quality and quantity, micro nutrients, and climatic factors, are all equally important, and if even one of them is not optimum, then the production is affected (Lal and Moldenhauer, 1987). Several models have been proposed by many researchers for the issue of fertilizer consumption considered through various points of view. Zhang et al. (2016) using the platform of Network of Science and Technology Backyards (STB), have examined fertilizer consumptions during the span of crop cultivation. As per their findings, the yield of wheat increased by 11% with addition of 1.5% Nitrogen alone. Nájera et al. (2015) evaluated soil fertility from soil samples of 31 maize cultivating farmers by testing micronutrient and macronutrients. They found that the Maize does fairly well in neutral- alkaline soils along with high inputs of NPK and Zn. Delzeit et al. (2017) presented a concept of trade-off between crop production and crop diversity, along with crop land expansion for improving food security, in the context of possible food shortage scenario in the decades to come (Natarajan et al., 2016) have analysed sugarcane yields in Coimbatore, Tamil Nadu and have suggested optimum parameters for both soil nutrients as well as environmental factors for cultivating sugarcane. Toyonaga et al. (2005) addressed the problem of crops chosen seasonally in Japan. Apart from their formulated problem, they also introduced the concept of fuzzy based profit coefficients for a more efficient and effective farming model. Fan et al. (2011) concentrates on the use of minimum amount of fertilizer to get efficient outcome with respect to environmental pollution in China. Papadopoulos et al. (2011) analysed the nitrogen fertilization requirement for cotton through a fuzzy based decision support system, which analysed 30 years of rainfall data and 8 years of temperature data.

Abstract

Accurate modeling of soil deformation depends on the consideration of both frost heave deformation in the frozen zone and consolidation deformation in the unfrozen zone. Pore water pressure investigations are important for revealing these two deformation behaviors. Herein, we aim to reveal the consolidation process by measuring and analyzing changes in pore water pressure in the unfrozen zone. Using a custom-made pore water pressure gauge, we performed a series of real-time pore water pressure measurements in the unfrozen zone of silty clay and sandy soil samples that were exposed to closed and open freezing systems. The results show that the pore water pressure in the unfrozen zone generally increases at first and then decreases. The temperature changes in the unfrozen zone have no significant influence on the changes in pore water pressure, and the variations of the pore water pressure are mainly controlled by the stress and hydraulic boundary (changes in pore water pressure) conditions at the freezing front. Furthermore, changes in the pore water pressure are affected by several parameters, including soil type, water supply condition, initial moisture content, measured soil layer depth, and hydraulic conductivity. Soil consolidation is mainly caused by change in effective stress, which results from increase in total stress or decrease in pore pressure. Based on the observed pore water pressure variations and its numerical simulations, we propose that consolidation in the unfrozen zone during soil freezing includes compression-induced consolidation, which results from an increase in frost heaving stress, and vacuum-induced consolidation, which results from a decrease in pore water pressure. Each consolidation pattern plays an important role in the different stages of soil freezing. Compression-induced consolidation primarily occurs during the early stage of soil freezing, while vacuum-induced consolidation mainly occurs during the later stage of soil freezing.