Humic products in agriculture: potential benefits and research challenges—a review

Journal of Soils and Sediments - Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of...     

Depletion of plant‐available silicon in soils: A possible cause of declining rice yields

Abstract

The phenomenon of yield decline in different rice ecosystems from many parts of the world has been reported to be associated with decreases in the effective nitrogen (N) supply from soil. However, many reports in the literature suggest that silicon (Si) is an agronomically essential element for sustainable rice production. Depletion of plant‐available Si in soils where rice is grown could be a possible limiting factor contributing to declining yields. In order to address this problem of yield decline or stagnation, it seems necessary to survey Si status of soils and rice grown in different ecosystems throughout the world and develop region‐specific integrated nutrient management systems that include the element Si.     

Encapsulation of plant growth promoting Rhizobacteria—prospects and potential in agricultural sector: a review

Plant growth promoting rhizobacteria (PGPR) are a group of bacteria that can enhance plant growth. In fact, PGPR are biologically unstable and the bacteria activity degrades over time due to environmental factors, survival rate in soils, the compatibility with the crop and the interaction ability with the indigenous microflora in soil. Therefore, the utilization of PGPR as plant growth promoter agent is a major challenge in the agricultural sectors because of their bioactivity degradation needs to be inhibited to maximize its function as a plant growth promoter. The application of delivery system based on encapsulation technology shows a promising technique to store and deliver PGPR. However, the task to find the appropriate PGPR encapsulation method is the most challenging for agricultural industry. In addition, the lack of knowledge on the action mechanism of encapsulated PGPR, physico-chemical properties and their survival in the environment are the many challenges need to be addressed. In the present review, the encapsulation technology of PGPR and its properties have been reviewed in detail. Moreover, the remaining technical challenges of encapsulation systems including insignificant stabilization of PGPR, instability of the environmental and difficulty of their preparation are also extensively discussed here.     

Lectures: Impact of genomics on the study of plant nutrition. 6. Advance in recent QTL studies—basic research toward application for agriculture

(Jpn. J. Soil Sci.Plant Nutr., 77, 337–342, 2006)     

Is sustainable development based on agriculture attainable in Kenya? A multidisciplinary case study of Murang'a district

Kenya's development seems trapped in a vicious circle caused by soil erosion, declining soil fertility, land fragmentation, fluctuating agricultural production, widespread poverty, corruption, ethnic tension, rapid population, urban growth and a declining economy. The development challenge is to reverse the negative effects of these processes and promote sustainable development. This paper, based on multidisciplinary work discusses whether sustainable development based on agriculture is attainable in Murang'a district in Kenya's Central Highlands. Firstly, it investigates some biophysical aspects of sustainable agriculture such as land use across time, soil nutrient status and yield, cultivated crops and soil productivity by analysing aerial photographs and soil samples and conducting interviews. It suggests that the area has gone through major biophysical changes. Second, it relates the farmers' attitude to promotion of sustainable development as carried out by the National Soil and Water Conservation Programme. It suggests that farmers carry ideas of corruption, often following ethnic lines that hampers efficient implementation of the extension advise. Finally, it identifies links behind rural‐urban migration by estimating households' probability of generating incomes outside the farm, typically in urban areas. Opportunistic farming, manifested by temporary reduction of farming on own land to satisfy immediate income needs, is very common among farmers. More needs to be done to promote agro‐based, small‐scale rural industries, improve agricultural management practices, facilitate appropriate credits, enhance marketing opportunities, ensure timely crop payments, and increase participation in decision making. It is important to realize that for farmers to embrace policies which promote agriculturely‐based sustainable development the policies ought to biophysically possible, socio‐politically acceptable and economically feasible. Copyright © 2001 John Wiley & Sons, Ltd.     

Recent advances in the chemistry of nitrogen,phosphorus and potassium as fertilizers in soil: A review

The advent of civilization has made humans dependent on plants for food and medicine, leading to the intensification of agricultural production. The intense cultivation of crops has resulted in the depletion of available nutrients from soil, thereby demanding the application of excess nutrients to soil to improve yield. Thus, mineral fertilizer discovery and application have, in many ways, contributed greatly to meeting global food demands. However, aside from the positive effects of mineral fer...     

Potential effect of conservation tillage on sustainable land use: A review of global long-term studies

Although understood differently in different parts of the world, conservation tillage usually includes leaving crop residues on the soil surface to reduce tillage. Through a global review of long-term conservation tillage research, this paper discusses the long-term effect of conservation tillage on sustainable land use, nutrient availability and crop yield response. Research has shown several potential benefits associated with conservation tillage, such as potential carbon sequestration, nutrient availability, and yield response. This research would provide a better perspective of the role of soil conservation tillage and hold promise in promoting application of practical technologies for dryland farming systems in China.     

Making knowledge and meaning in communities of practice: What role may science play? The case of sustainable soil management in England

Social learning is gaining popularity as a tool for understanding and designing interactions between experts and farming communities to enhance the uptake of sustainable and innovative farming practices. To date, the literature has mainly focused on the technical role scientists and researchers play in social learning, as sources of or co‐producers of knowledge. Social learning, however, implies a dynamic between the creation of knowledge (what can be done) and the creation of meaning (what is considered worth doing). This paper addresses this research gap by exploring the roles that “expert” actors and their narratives perform in meaning‐creation. I argue that a sustainable soil management community of practice is emerging in England and discuss the dynamics of farmer participation in this community. I further argue that members of this community use scientific “experts” and narratives to inspire, justify and legitimise sustainable soil management as a valid way of being a “good farmer.” This paper thus stresses the role that scientific or “expert” actors and narratives play in communities of practice as contributors to meaning‐creation inherent to social learning. How soil degradation will be addressed is as much a technical question, a question of what can be done, as a question of meaning, a question of what land managers consider worthwhile doing. The scientific community thus needs to work with the farming community not only to co‐produce technical solutions, but also to co‐produce shared visions of agrarian futures which put soils at their heart.     

Assessment of plant nutrients’ dynamics in organically and conventionally managed soils by means of different extraction methods

The aim of this study was to investigate what kind changes in the soil fertility parameters occur depending on different farming methods. The field experiment was performed on sandy loam Luvisol during 2008–2014. The following treatments were carried out: organic (ORG), organic with farmyard cattle manure (ORGFYM) and conventional with farmyard cattle manure and mineral fertilizers (CONFYM). Soil samples were collected yearly in September and analyzed for P, K, Mg and Ca by the Mehlich III method. In parallel, ammonium lactate extractable P and K (AL method), and ammonium acetate extractable Mg and Ca (NH₄OAc-method) were determined. The Pearson correlation coefficients between the analysis results achieved by the Mehlich III method and alternative methods were calculated. In all the treatments, no significant changes in soil Corg content were established over seven years. A significant (p?AL in the soil but considerable decrease in the soil K_AL content was revealed. The application of cattle manure (60?t?ha^?1 for the 5-year crop rotation) in both organic and conventional treatments sustained the status of available nutrients in the soil. The Pearson correlation coefficients between Mehlich III and AL methods for P (r?=?0.770, p?r?=?0.922, p?4OAc-methods was found in the case of Mg (r?=?0.951, p?r?=?0.841, p?Mehlich III/P_AL quotient was inversely proportional with the Ca_{Mehlich III} values.     

Studies on soil fumigation—I: Effects on ammonium,nitrate and phosphate in soil and on the growth,nutrition and yield of wheat

Fumigation of field soil with chloropicrin alone or followed by methyl bromide, each at 220Kg·ha^?1, released 20–30 parts/10⁶ NH⁺₄-N which persisted for 75 days; such fumigation also doubled the amount of bicarbonate-extractable phosphate 28 days after fumigation. Soil fumigation increased both the vegetative and grain yields as well as increasing the content of N in the grain and the content of K and Cl in the tops at ear emergence. Root growth and the phosphate uptake activity of the roots were increased by soil fumigation.     

The role of stromatolites in explaining patterns of carbon, nitrogen, phosphorus, and silicon in the Se?ovlje saltern evaporation ponds (northern Adriatic Sea)

Purpose

In summer 2007, biweekly benthic fluxes of the biogenic elements carbon (C), nitrogen (N), silicon (Si), and phosphorus (P) were studied in the Se?ovlje saltern (salt-making facility) in the northern Adriatic Sea, Slovenia in order to determine the impact of stromatolite (??petola??) on the geochemical properties of saltern sediments.

Materials and methods

The brine and pore waters were analyzed for salinity, NH ₄ ⁺ , NO ₃ ^? , PO ₄ ^3? , SiO ₄ ^4? , total dissolved nitrogen, total dissolved phosphorus, and fluorescent dissolved organic matter. The sediment was analyzed for organic carbon (OC), total nitrogen (TN), total and organic phosphorus (OP), and biogenic Si concentrations, as well as values of ?? ¹³C_OC and ?? ¹⁵N_TN.

Results and discussion

Nutrient concentrations in brine water increased along the salinity gradient due to different processes, such as the evaporative concentrations of seawater, bacterial activity, more pronounced transformation and degradation of organic matter, and regeneration of nutrients. The petola from the Se?ovlje saltern, which is predominately composed of cyanobacterial and diatom communities, develops during the early evaporation stage and survives during high salinity and halite crystallization. Nitrogen fixation and P removal were the principal biogeochemical processes controlling dissolved inorganic N and P concentrations. At higher salinities, N limitation was more important. Microbes decomposed at higher salinities, and the remineralized N and P nutrients were released from surface pore waters to the brine. OP remineralization was also an important process influencing the distribution of PO ₄ ^3? concentrations in pore waters deeper in the sediments. The increasing SiO ₄ ^4? concentrations with increasing salinity in the brine waters were due to dissolution of diatom frustules, while the decrease in pore water SiO ₄ ^4? was probably the consequence of microbial uptake.

Conclusions

This study provides a better understanding of nutrient cycling and the geochemical processes in the Se?ovlje saltern.     

Who is sowing our seeds? A systematic review of the use of plant genetic resources in research

Collections of plant genetic resources managed by genebanks function to conserve the range of genetic diversity present in crop genepools. They can facilitate access to valuable allelic variation for both plant breeders and researchers who are able to request germplasm for use in crop improvement and both basic and applied scientific research. The direct impact of genebank collections is often unclear as downstream uses of germplasm samples may not be reported back to the genebank of origin. This study aims to systematically review scientific use of germplasm using the UK Vegetable Genebank (UKVGB) as a model. Between the years of 1980–2016, a total of 271 publications were identified as using UKVGB material. The frequency of publications and the international nature of use increased significantly over the time period studied. Accessions directly sourced from the UKVGB made up the majority of material used by researchers, but material from research-derived resources such as differential sets and core collections or diversity sets have also been used. Resistance to pests and diseases and genetic diversity were the main topics of study although germplasm was used to address a wide range of other research questions. Genebanks such as UKVGB provide an essential resource of allelic diversity in crop genepools which supports a diverse range of research projects. The utilisation of these plant genetic resources has increased over time, contributing to a substantial number of publications. Developments in sequencing technologies have no doubt played a part as larger numbers of accessions can be utilized in a single experiment, but the increase also no doubt reflects a greater interest in the use of allelic diversity to overcome challenges in crop improvement and research.     

The versatile,changing, and advancing roles of fish in sediment toxicity assessment—a review

Purpose  

Sediments serve as integral and dynamic parts of our aquatic systems. Within the last 15 to 20 years, however, the scientific community has begun noticing deterioration of sediment quality at an alarming rate worldwide. Sediments are now harboring hazardous pollutants that can directly influence water quality, thereby creating very stressful conditions for aquatic life. As a consequence, global efforts were initiated in the early 1970s, to find ways to assess sediment quality. Because of their obvious ecological and economic significance, fish have remained a major taxonomic group for appraising the general quality of aquatic systems. However, for sediment risk assessment, fish have lagged behind invertebrates due to their mobility and generally, pelagic lifestyle. To our knowledge, this is the first paper that comprehensively presents and reviews the versatile role of fish in assessing the state of health of aquatic sediments.     

Nitrate versus chloride nutrition effects in a soil‐plant system on the growth,nitrate accumulation,and nitrogen,potassium, sodium,calcium, and chloride content of carrot

The experiment was conducted to evaluate the effects of various nitrate/ chloride (NO₃/Cl) ratios on growth, nitrate accumulation, and mineral absorption in carrot, Daucus carota L., plants in a controlled environment. The experiment included two Cl sources [potassium chloride (KC1) and calcium chloride (CaCl₂)] and five NO/Clratios at 100/0, 90/10, 80/20, 70/30, and 60/40 with total‐nitrogen (N) concentration of 400 mg NO₃ kg^‐1 soil in 100/0 treatment. Fresh and dry weights of shoots and storage roots, and length and diameter of storage roots increased significantly with mixed NO₃/C1 treatments with both Cl sources as compared to single NO₃ (100/0) treatment. Growth was enhanced up to the 80/20 NO₃/C1 treatments. With Cl present in the treatments, the concentration of total‐N unchanged and NO₃ decreased in plants, and Cl and potassium (K) increased with the Cl sources. In KC1 treatments, Na absorption decreased. Calcium (Ca) content of the plants significantly differed by the treatments. It was concluded that N fertilization provided with combined Cl forms and NO₃/Cl rates can enhance production of better quality carrot and at the same time decrease of the N fertilizer input.     

Diurnal variations in uptake,transport and assimilation of NO3 ‐and efflux of OH‐ in maize plants

Maize plants, grown for 7 and 21 days on a nutrient solution with NO₃ ^‐ as the sole nitrogen source showed a clear diurnal pattern with respect to the in vivo NRA. Especially in roots dark/light fluctuations of the enzyme activity were high. Also in NO₃ ^‐ uptake, OH^‐ efflux and endogenous content of water soluble carbohydrates a diurnal variation was found. The plant age did not significantly affect the daily rhythm.

Because day/night changes of the in vivo root NRA and nitrate uptake were proportional, the relative content of reduced N in the xylem sap of the plants was constant during a day/night interval. At both day 7 and day 21 about 40–50% of the N was transported via the xylem as amino N. As a result of non‐synchronous variation of the specific root and shoot NRA, root reduction capacity showed a great within‐day variation. It varied between 20 and 40% of the whole plant reduction capacity. Since the ratio N‐organic to N‐total in the xylem sap was about 0.5, cycling of organic nitrogen was very likely in these maize plants.     

Aluminum tolerance,mineral nutrition,and growth of ‘Helleri’ holly in solution culture

‘Helleri’ holly (Ilex crenata Thunb. ‘Helleri') plants were grown in solution culture at aluminum (Al) concentrations of 0, 6, 12, 24, and 48 mg.L^‐1 for 116 days. Aluminum did not affect root or crown index, stem length growth, plant dry weight, or leaf area. Aluminum treatments significantly increased Al uptake and reduced nutrient uptake of magnesium (Mg), calcium (Ca), zinc (Zn), and copper (Cu) on some sampling dates. Iron (Fe) and manganese (Mn) uptake decreased on most sampling dates but increased on some with Al treatments. Potassium (K), phosphorus (P), and boron (B) uptake were significantly affected by Al, decreasing and increasing at different sampling dates. Although plants preferentially took up ammonium‐nitrogen (NH₄ ⁺‐N) in all treatments (including 0 Al controls), neither NH₄ ⁺‐N nor nitrate‐nitrogen (NO₃ ‐N) uptake were affected by Al. Tissue concentrations of P, K, B, Zn, and Al increased with Al treatment; whereas tissue Ca, Mg, and Cu concentrations decreased with increasing Al. Iron and Mn tissue concentrations exhibited increases and decreases in different tissues. Results indicated that ‘Helleri’ holly was tolerant of high concentrations of Al.     

Limitless decomposition in leaf litter of Common beech: Patterns,nutrients’ and heavy metal's dynamics

Long-term studies of Common beech litter decomposition are scarce and the relationship of its limit values to nutrients/heavy metals dynamics has not been sufficiently studied. The present study is a rare case in which beech litter decomposes almost entirely and enables analyses of the impacts of nutrients and heavy metals on litter decomposition. The aim of the present paper is to (i) determine a decomposition pattern of leaf litter and estimate the limit values and to (ii) determine the dynamics of the main nutrients and heavy metals (concentration and net amounts, based on ash-free litter) in an unpolluted stand of Common beech.Common beech (Fagus sylvatica L.) leaf litter was incubated in polyester litterbags (1.5 mm mesh size) and 41 samplings were made over a period of 6.5 years until a mass loss of 88.9% was achieved. Carbon (C) plus 12 more nutrients and heavy metals were analyzed.Mass losses of both whole litter and of C were used in order to estimate the limit values as well as to determine significant differences between the two approaches. An asymptotic function gave significant limit values that were close to 100% (p < 0.0001). These results were also supported by a single exponential function (p < 0.0001). The initial increase in concentrations of nutrients was followed by a decrease of N, P, K, Ca, Na and Mn. A similar pattern was observed for some of the heavy metals (Cu, Cd and Fe) while Zn concentrations decreased continuously. A net release (e.g. a decrease in the net amounts) was observed for all nutrients and heavy metals except for Cd. The litter fraction did not leave any stable residues (i.e. limit values were close to 100%), which was at least partly due to the low initial N and very high Mn concentration (20 times higher than in other studies).     

Growth,physiology, and biochemical activities of plant responses with foliar potassium application under drought stress – a review

Drought stress affects plant growth and ultimately yield is reduced. Potassium (K) is an essential macronutrient that is required to increase the growth and yield under drought. K plays an important role in osmotic adjustment, opening and closing of stomata, and enzymes activation. K is the component of plant structure that optimizes many physiological as well biochemical processes and ultimately improves the plant growth and yield. This review mainly covers the following topics: impact of drought on plant growth, physiological and biochemical characteristics, the role of K in plant growth, and physiology under drought stress. K is also responsible for enhancing the growth as well as yield attributes of crops under drought stress conditions by altering the physiological and biochemical process.