Soil Chemical Analysis

A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Current soil management strategies are mainly dependent on inorganic chemical-based fertilizers, which caused a serious threat to human health and environment. The exploitation of beneficial microbes as a biofertilizer has become paramount importance in agriculture sector for their potential role in food safety and sustainable crop production. The eco-friendly approaches inspire a wide range of application of plant growth promoting rhizobacteria (PGPRs), endo- and ectomycorrhizal fungi, cyanobacteria and many other useful microscopic organisms led to improved nutrient uptake, plant growth and plant tolerance to abiotic and biotic stress. The present review highlighted biofertilizers mediated crops functional traits such as plant growth and productivity, nutrient profile, plant defense and protection with special emphasis to its function to trigger various growth- and defense-related genes in signaling network of cellular pathways to cause cellular response and thereby crop improvement. The knowledge gained from the literature appraised herein will help us to understand the physiological bases of biofertlizers towards sustainable agriculture in reducing problems associated with the use of chemicals fertilizers.

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Biofertilizers function as key player in sustainable agriculture by improving soil fertility, plant tolerance and crop productivity

Unprecedented bioaccumulation and biomagnification of heavy metals (HMs) in the environment have become a dilemma for all living organisms including plants. HMs at toxic levels have the capability to interact with several vital cellular biomolecules such as nuclear proteins and DNA, leading to excessive augmentation of reactive oxygen species (ROS). This would inflict serious morphological, metabolic, and physiological anomalies in plants ranging from chlorosis of shoot to lipid peroxidation and protein degradation. In response, plants are equipped with a repertoire of mechanisms to counteract heavy metal (HM) toxicity. The key elements of these are chelating metals by forming phytochelatins (PCs) or metallothioneins (MTs) metal complex at the intra- and intercellular level, which is followed by the removal of HM ions from sensitive sites or vacuolar sequestration of ligand-metal complex. Nonenzymatically synthesized compounds such as proline (Pro) are able to strengthen metal-detoxification capacity of intracellular antioxidant enzymes. Another important additive component of plant defense system is symbiotic association with arbuscular mycorrhizal (AM) fungi. AM can effectively immobilize HMs and reduce their uptake by host plants via binding metal ions to hyphal cell wall and excreting several extracellular biomolecules. Additionally, AM fungi can enhance activities of antioxidant defense machinery of plants.

/pdf/heavy-metal-stress-and-some-mechanisms-of-plant-defense-3b8zkhmwzb.pdf

Heavy Metal Stress and Some Mechanisms of Plant Defense Response

Over-production of reactive oxygen species (ROS) in plants under stress conditions is a common phenomenon. Plants tend to counter this problem through their ability to synthesize ROS neutralizing substances including non-enzymatic and enzymatic antioxidants. In this context, ascorbic acid (AsA) is one of the universal non-enzymatic antioxidants having substantial potential of not only scavenging ROS, but also modulating a number of fundamental functions in plants both under stress and non-stress conditions. In the present review, the role of AsA, its biosynthesis, and cross-talk with different hormones have been discussed comprehensively. Furthermore, the possible involvement of AsA-hormone crosstalk in the regulation of several key physiological and biochemical processes like seed germination, photosynthesis, floral induction, fruit expansion, ROS regulation and senescence has also been described. A simplified and schematic AsA biosynthetic pathway has been drawn, which reflects key intermediates involved therein. This could pave the way for future research to elucidate the modulation of plant AsA biosynthesis and subsequent responses to environmental stresses. Apart from discussing the role of different ascorbate peroxidase isoforms, the comparative role of two key enzymes, ascorbate peroxidase (APX) and ascorbate oxidase (AO) involved in AsA metabolism in plant cell apoplast is also discussed particularly focusing on oxidative stress perception and amplification. Limited progress has been made so far in terms of developing transgenics which could over-produce AsA. The prospects of generation of transgenics overexpressing AsA related genes and exogenous application of AsA have been discussed at length in the review.

/pdf/ascorbic-acid-a-potential-oxidant-scavenger-and-its-role-in-4ztbj5r0jh.pdf

Ascorbic Acid-A Potential Oxidant Scavenger and Its Role in Plant Development and Abiotic Stress Tolerance.

Bacterial biofertilizers for sustainable crop production: a review.

Although relationships among plant, biological N2 fixation, and response to soil and environmental conditions have received considerable coverage in the scientific literature, a comprehensive summary and interpretation of these interactions with specific emphasis are lacking. Fluctuations in pH, nutrient availability, temperature, and water status, among other factors, greatly influence the growth, survival, and metabolic activity of nitrogen fixation bacteria. The subsequent inhibition of nitrogenase would result in O2 accumulation in the infected zones, inducing the decrease in nodule permeability. Poor nodulation of legumes in arid soils is likely due to decreases in population levels of rhizobia during the dry season. Fixation, therefore, also tends to decrease with legume age, mainly because of the concomitant increase in soil N. Calcium deficiency, with or without the confounding influence of low pH also affects attachment of rhizobia to root hairs. Rhizobia may have different tolerances to soil acidity factors than the host plant. Relatively, high-root temperature has also been shown to influence infection, N2- fixation ability, and legume growth. Also, root nodulation by the bacteria can be dependent on the formation of mycorrhiza.

	                   

	Key words: Legume, nitrogen fixation, rhizobia, root, stress.

https://africaneditors.org/journal/AJAR/full-text-pdf/56965-116404

Effective factors on biological nitrogen fixation

The two main types of mycorrhizas are ecto and endomycorrhizas, which differ in their structure and physiological relationships with host plant. Mycorrhizal fungi frequently stimulate plants to reduce root biomass while simultaneously expanding nutrient uptake capacity by extending far beyond root surfaces and proliferating in soil pores that are too small for root hairs to enter. Legume roots are invaded and colonized by rhizobia and also with mycorrhizal fungi. For legumes, arbuscular mycorrhizal (AM) fungi have fundamental effects on the eco-physiology, on the biota of the surrounding soil and on associated non-legumes. AM-fungi are known to be effective in increasing nutrient uptake, particularly phosphorus and biomass accumulation of many crops in low phosphorus soil. AM-fungi have an important role in promotion of biological and chemical properties of plants under stressed environment. Most reports note a positive effect of mycorrhizal inoculation on growth of plants in metal-contaminated soils.

http://textroad.com/pdf/JAEBS/J.%20Appl.%20Environ.%20Biol.%20Sci.,%201(9)310-319,%202011.pdf

A Review: Beneficial Effects of the Mycorrhizal Fungi for Plant Growth

In order to investigate the effects of Glomus species on some physiological characteristics of two chickpea types (Pirouz cultivar of Desi type and ILC-482 of Kabuli type) under non-stress (NS) and drought stress, an experiment was conducted using a factorial arrangement based on completely randomized design with three replications Drought stress decreased shoot and total dry weight in plants However inoculation of plants with mycorrhiza improved these traits Leaf chlorophyll content was decreased, but leaf proline content and guaiacol peroxidases (EC 11117) (POD), catalase (EC 11116) (CAT), and ascorbate peroxidase (EC 111111) (APX) activities were increased as a result of drought stress Drought stress had no significant effect on soluble protein content and polyphenol oxidase (EC 11031) (PPO) enzymatic activity in chickpea plants In general, drought stress and especially severe drought stress increased membrane lipid peroxidation (MDA) in chickpea plants, which was more evident in non-inoculated than in inoculated plants Inoculation of chickpea by AM significantly increased POD and PPO activities compared with non-inoculated chickpea, but had no effect on CAT activity and proline content of leaves The reaction of chickpea cultivars to inoculation by AM species and irrigation levels were different ILC-482 showed that antioxidant enzymes activities were more and thus less MDA compared with Pirouz cultivar In general, the most POD and PPO activities were recorded for inoculated plants with G etunicatum and G versiform species, and the most APX activity was observed in plants inoculated with G intraradices

Changes of antioxidative enzymes, lipid peroxidation and chlorophyll content in chickpea types colonized by different Glomus species under drought stress

Plants obtain nutrients from two natural sources: organic matter and minerals. Organic matter includes any plant or animal material that returns to the soil and goes through the decomposition process. Different soil organisms feed on different organic substrates. Their biological activity depends on the organic matter supply. In addition to providing nutrients and habitat to organisms living in the soil, organic matter also binds soil particles into aggregates and improves the water holding capacity of soil. Most soils contain 2 to 10% organic matter. However, even in small amounts, organic matter is very important. Tillage is one of the major practices that reduce the organic matter level in the soil. Each time the soil is tilled, it is aerated. Soil enzymes act as biological catalysts of specific reactions that depend on a variety of factors, such as the presence or absence of inhibitors, tillage and fertilization, and can be considered as early indicators of biological changes. The incorporation of organic amendments to soil influences soil enzymatic activities because the added material may contain intra- and extracellular enzymes and may also stimulate microbial activity in the soil. Integrated animal and crop production enterprises that use manure as the primary nutrient source for crop production are not without problems. Nutrient loading on a farm with an animal enterprise may exceed crop nutrient needs.

	 

	Key words: Fertilization, microbial activity, soil management, sustainable agriculture, tillage

https://www.academicjournals.org/article/article1380893821_Mohammadi et al.pdf

Khosro Mohammadi

Papers

Bacterial biofertilizers for sustainable crop production: a review.

Effective factors on biological nitrogen fixation

A Review: Beneficial Effects of the Mycorrhizal Fungi for Plant Growth

Changes of antioxidative enzymes, lipid peroxidation and chlorophyll content in chickpea types colonized by different Glomus species under drought stress

Soil management, microorganisms and organic matter interactions: A review