Rhizosphere Engineering and Soil Sustainability

The intensive application of chemical fertilizers to meet the growing demand of food for burgeoning population has led to an unprecedented perturbation of the soil environment. Environment degradation has had serious impacts on the nutrient use efficiency by the soil crop plants owing to irrational use of chemical fertilizers, thus warranting prioritization of the beneficial soil microorganisms for improving the soil health. Rhizosphere supports huge diversity of microbial community including beneficial plant growth promoting rhizobacteria (PGPR) as primary determinants of plant health and soil fertility. PGPR colonize roots of dicots and monocots and improve plant growth either by assisting nutrient acquisition (N, P, and essential nutrients) or modulating root system architecture by releasing phytohormones (direct effect) or reducing detrimental effects of various biotic and abiotic stress (indirect effect). The abilities of PGPR are of immense importance in sustainable agriculture in terms of improving crop production and soil health, therefore declining the negative effect of inorganic fertilizers on the environment. This chapter is an effort to illuminate the prevailing scenario on underlying mechanisms of nutrient management by PGPR. It is vital that soil microbiologists and agronomists pay due attention to strategies for nutrient management for enhancing crop production in a sustainable manner.

Soil microbial dynamics are the backbone of sustainable agriculture, fostering soil health, fertility, and ecosystem resilience. These practices cultivate a thriving soil microbial community, boosting agricultural productivity and soil fertility. Promoting diverse microbial interactions is vital for maintaining a healthy soil ecosystem, supporting nutrient cycling, disease suppression, and overall soil fertility. Microbial by-products play a crucial role in soil aggregation, influencing soil structure, water dynamics, and aeration, impacting plant growth and nutrient cycling. Nitrogen fixation, a vital biological process, transforms atmospheric nitrogen into a plant-usable form, enriching soil fertility and quality. Mycorrhizal symbiosis, a remarkable mutualistic interaction between fungi and plants, promotes nutrient uptake, soil development, and sustainable agricultural practices. Soil health improvement is a comprehensive approach that addresses various aspects of soil management, promoting sustainable agriculture, ecosystem resilience, and long-term soil health. Organic matter addition, crop rotation, and diversity are integral components of sustainable agriculture, fostering a healthy and dynamic soil ecosystem. Reduced tillage, cover cropping, and effective nutrient management optimize soil health, while water management and erosion control ensure sustainable agricultural practices. Community involvement and precision agriculture are crucial for advancing sustainable soil management, with carbon sequestration being a vital strategy for addressing climate change and enhancing soil health.

In recent times, numerous concrete efforts have been made by global scientific community for maintenance and judicious utilization of certain non-renewable natural resources like metal ores, fossil fuels and to an extent groundwater. However, soil, an important non-renewable asset, has received little attention and demands more awareness and exploration by researchers worldwide. Soil regeneration through chemical and biological processes of rock weathering takes several thousand years; thus, soil is classified as a vital, finite and non-renewable source. Soil health, thus, becomes a critical factor for humans, animals, plants and all natural ecosystems. Soil health deterioration, increased by industrialization and indiscriminate use of chemical fertilizers, has become a major environmental concern with high precedence. Public awareness to these problems has shifted approach to alternative strategies like using plant growth-promoting rhizobacteria (PGPR), also popular as bio-fertilizers, for achieving cleaner, safer and cost-effective increase in agricultural productivity. Amongst several bacteria reported as PGPR, actinomycete is one of the most promising options due to properties like nutrient cycling, antibiosis, rhizosphere competence and beneficial plant growth-promoting (PGP) traits. In this chapter, we intend to discuss about how actinomycetes are crucial as PGPR in maintaining soil health, fertility and agricultural productivity and investigate underlying PGPR mechanisms. We shall also briefly enlist few successful PGP actinomycetes, challenges associated and future implications to increase soil fertility.

Under green revolution practices, the imbalanced use of chemical fertilizers and pesticides causes a negative impact on soil health due to the loss of soil microbial flora and fauna. To overcome this negative impact of the green revolution and to increase sustainable agricultural production without damaging further agricultural lands, the only alternative and effective means is to reduce the use of chemicals in agriculture specifically for plant nutrition and plant protection. Under sustainable agricultural practices, plant growth-promoting rhizobacteria (PGPR) can be effective tools to increase productivity while ensuring sustainability in agriculture. PGPR colonize the rhizosphere zone and help in promoting plant growth and development by regulating nutrient acquisition, modulation of plant hormones, and ameliorating various negative effects of various pathogens. PGPR also help sustain the plant growth productivity and significantly increase soil fertility and health under different biotic and abiotic stresses. As per the literature, many studies prove to increase agriculture productivity due to the use of PGPR as eco-friendly microbial inoculants for promoting plant growth attaributes through various direct and indirect mechanisms. The mechanisms of PGPR include biological nitrogen fixation, phytohormones production, Phosphate, potassium, and zinc solubilization, siderophores production, and secretion of other secondary metabolites (phenolic compounds (phenylpropanoids and flavonoids)) that enhance crop productivity and control phytopathogens. Therefore, this chapter focuses on a detailed description of PGPR keeping in view their functional mechanisms as eco-friendly approaches to increase productivity and enhance soil fertility. PGPR can be used as an eco-friendly, socially acceptable, and cost-effective technology for challenges in the future.KeywordsPGPRProductivitySoil fertility and healthRhizosphereSustainable agriculture

Plant growth-promoting rhizobacteria (PGPR) are the bacterial strains that are associated with the rhizospheric part of plants and are known to positively influence plant growth. These microorganisms induce plant growth promotion directly through production of phytohormones, solubilization of phosphates, biological fixation of nitrogen, inhibition of ethylene biosynthesis, and indirectly by imparting resistance to combat pathogenic attacks by the production of secondary metabolites such as antibiotics, siderophores, and many enzymes, and also by inducing tolerance to abiotic stress conditions. PGPR are especially used as bioinoculants due to their role in increasing crop production. PGPR are influenced, inter alia, by plant genotype, environmental conditions (both biotic and abiotic), and various biotic interactions (plant-microbe interactions and microbe-microbe interactions) taking place in the rhizosphere. Besides, agricultural activities, including use of chemical fertilizers, pesticides, and soil tillage, also have substantial influence not only on the PGPR population but also on physical, chemical, and biological characteristics of soil. In view of their profound growth-promoting characteristics and ever-increasing demand for adoption of ecologically compatible and eco-friendly practices in agriculture, PGPR could be an important tool in sustainable agriculture and can be safely relied upon for increasing productivity. It is in this backdrop, an attempt has been made in the present chapter to emphasize the importance of rhizobacteriain the promotion of plant development and sustainable agriculture.

Symbiotic (Rhizobia, Frankia, and VAM) or free-living (Azotobacter, and Clostridium) association of plant growth-promoting rhizobacteria (PGPR) and fungi (PGPF) is essential for plant and soil health. Nitrogen (N), phosphorus (P) and potassium (K) as major and iron (Fe) and zinc (Zn) as the minor elements are key to plant health. They are important constituents of plant genetic material (N, P) and chlorophyll content (N, Fe) and important for enzymatic activities (Fe, Zn) and are involved in many biochemical and physiological activities. The ‘microbiome’ around the rhizosphere is specific to plant type and involved in nutrient cycling through various processes such as fixation (N), solubilization, mineralization (P, K) and uptake, with the help of various organic acids (gluconic acid, oxalic acid, and tartaric acid), siderophore activity (Fe uptake) and enzymatic actions (nitrogenase, phytases, and acid phosphatases). Phytohormones essential to plant growth and development are produced by microbes themselves or induce their production via other hormones or communication chemicals, viz., volatile organic compounds (VOCs) like 2-pentylfuran, 2,3-butanediol and acetonin. PGPR (Pseudomonas, Trichoderma and Streptomyces) helps the host plant to fight against various abiotic and biotic stresses by the release of bactericidal and fungicidal enzymes, metabolite accumulation and induced systemic resistance (ISR), systemic acquired resistance (SAR) by phytohormones (jasmonic acid, salicylic acid, and ethylene) and VOCs. Attributing to so many benefits, microbes are increasingly becoming part of sustainable agriculture where PGPR (Rhizobium and Pseudomonas) and fungi (Aspergillus, Trichoderma and VAM) are being used as biofertilizers either single strained or in consortia approach, where the latter is found to be more beneficial for plant and soil health.

Role of humic acid for climate change adaptation measures to boost up sustainable agriculture and soil health: A potential review.

This review provides an in-depth examination of the principles, practices, and challenges associated with sustainable and climate-smart agriculture. Sustainable agriculture, with its focus on soil health, biodiversity, water management, and reduced chemical inputs, is crucial for meeting current food production needs while preserving resources for future generations. Climate Smart Agriculture builds upon sustainability by emphasizing climate adaptation and mitigation strategies, including climate-resilient crop selection, greenhouse gas reduction, and technology integration. However, several challenges hinder the widespread adoption of these practices. Indian Farmers often lack knowledge and resources, while financial constraints and policy barriers pose significant hurdles. Additionally, climate variability and market access issues further complicate the transition to sustainable and climate-smart agriculture. Efforts to address these challenges require comprehensive education and training programs, supportive policies, financial incentives, and increased collaboration among governments, NGOs, and the private sector. Achieving sustainable and Climate Smart Agriculture is crucial for ensuring food security and resilience in the face of climate change.

Biofertilizers: A Nexus between soil fertility and crop productivity under abiotic stress

Sustainable farming practices aim to produce agricultural products at a low environmental cost, ensuring food availability for future generations. These approaches combine the production of agricultural crops and livestock for site-specific uses, with an emphasis on long-term objectives including satisfying the food supply worldwide, improving the environment, making the most efficient use of resources and boosting the welfare of farmers and society as a whole. Sustainability in farming is mostly dependent on soil health, which is the soil’s capacity to function within ecological and land-use boundaries. It enhances general wellness, maintains the purity of the air and water, and supports biological productivity. The depletion of soil functions brought about by modern agricultural intensification has an impact on ecosystem services and long-term productivity. The goal of sustainable farming is to raise fertility and organic matter in the soil. Key practices include carbon farming, conservation agriculture, integrated pest management (IPM), and precision farming. In order to support sustainable crop production, these techniques improve soil fertility, structure, and biodiversity. Going forward, research should concentrate on developing novel approaches to tackle the issues of climate change and global food security.

Background: Climate change poses significant threats to global agriculture, intensifying the effects of biotic and abiotic stresses that reduce crop production and imperil food security. Bioinoculants, specifically arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), and other beneficial microbial consortia, offer potential, eco-friendly alternatives to traditional agrochemical fertilizers within the structure of climate-smart agriculture. Methods: This review explores the mechanisms through which bioinoculants promote plant adaptation and mitigate stress, including their roles in nutrient acquisition, antioxidant synthesis, modulation of phytohormones, and improvement of soil structure and health. Results: Diverse applications of bioinoculants are discussed, with emphasis on enhancing crop yield and resilience under various harsh climate conditions, including salinity, drought, and extreme temperatures. The review critically peruses the challenges and limitations of bioinoculant use, such as their interaction with the native soil microbial community, variable efficacy, formulation stability, and scalability. Conclusions: By synthesizing current advances and identifying knowledge gaps, this review provides a comprehensive evaluation of the potential and limitations of bioinoculants in advancing climate-smart agriculture and offers strategic insights for researchers, policy makers, and practitioners dedicated to the development of agricultural sustainability.

Soil health is fundamental to sustainable agriculture, underpinning crop yield, environmental resilience, and long-term ecosystem stability. Modern agricultural practices, marked by excessive use of pesticides and fertilizers, monoculture, and high ploughing, have led to significant soil deterioration, necessitating innovative approaches to restore and maintain soil health. This study analyzed sustainable approaches to augment soil health and boost crop quality in contemporary agricultural systems. Maintaining the physical, chemical, and biological properties of soil is crucial for its health, attainable via several agronomic methods. Methods including crop rotation, cover cropping, no-till farming, carbon farming, conservation agriculture (CA), and the use of organic amendments were examined for their efficacy in restoring soil structure, enhancing organic matter, and fostering biodiversity. These projects aim to conserve and improve soil ecosystems by integrating agricultural techniques with ecological principles, so assuring long-term production and environmental stability. Improving soil health will enhance soil functions, reinforcing the notion that augmenting soil organic carbon (SOC) is essential. This research established that conservation tillage is superior to conventional tillage regarding soil health, a subject that remains contentious among scientists and farmers, and that different tillage methods demonstrate unique interactions. These solutions would improve soil health by integrating the management of plant, soil, microbial, and human interactions.

Background: Grain legumes are considered as an important group of food crops that can play a vital role to address national food and nutritional security and also tackle environmental challenges. They are known as the basis for an ecologically-sound, farmer-focused agricultural development effort and an important component of sustainable farming systems. Biofertilizers, being a cheap and environment friendly source of plant nutrients assume a special significance in supplying the plant nutrients under the present context of indiscriminate use and high costs of chemical fertilizers. Biofertilizers could be a good alternative to supplement the chemical fertilizers. Methods: A field experiment was carried out at Pantnagar in Mollisols during 2017-18 and 2018-19 to study the performance of Rhizobium sp. and plant growth promoting rhizobacteria (PGPR) inoculation in mungbean on productivity, soil health and economics. Result: A pronounced effect of biofertilizers application in mungbean was observed on the root nodulation, yields, nutrient uptake and soil health. Co-inoculation of Rhizobium and PGPR significantly increased the nodule number, nodule dry weight, plant dry weight, grain yield, straw yield, N and P uptake in mungbean and improved soil health over the no inoculation. The study suggested that combined application of PGPR and Rhizobium sp. in mungbean is better than Rhizobium sp. alone in increasing crop yields, soil health and farmer’s profit.

<p>This study aimed to explain the crop yield prediction system as a way to address the challenges posed by global warming and climate change in Saudi Arabia, while also taking into account socio-economic factors. Machine learning models were trained using crop yield prediction data to provide recommendations for future crop production. Climate change poses significant challenges, with rising temperatures and extreme weather events being increasingly evident. Agriculture, contributing 14% of greenhouse gas emissions, plays a crucial role in exacerbating this issue. This study introduced a crop yield prediction system leveraging machine learning models trained on comprehensive datasets. Recommendations derived from these models offer insights into optimal crop rotation strategies, particularly relevant for regions like the Kingdom of Saudi Arabia. Collaboration between farmers and governments, informed by data-driven approaches, is crucial in this endeavor. Utilizing a customized dataset, this study analyzed a machine learning model performance and identified optimal hyperparameters. XGBoost ensemble emerged as the top performer with an R<sup>2</sup> score of 0.9745, showcasing its potential to advance crop yield prediction capabilities. By integrating machine learning into agricultural decision-making processes, stakeholders aim to enhance crop production and soil health and contribute to climate change mitigation efforts. This collaborative effort represents a significant step toward sustainable agriculture and climate resilience in Saudi Arabia.</p>

Soil health underpins ecosystem services like food security and therefore underpins human health. Poor soil health is a global problem which is hindering attempts to deliver the UN’s Sustainable Development Goals. We focus on goals 3 (human health), 13 (climate change) which are intimately linked to goal 15 (soil health). Soil health is arguably most fragile in regions such as sub-Saharan Africa (SSA) where aged soils are characterised by poor nutrient and water holding capacity, and are largely deficient in micronutrients such as Zinc. Poor soil health coupled with the largely cereal-based diets can mean that micronutrient malnutrition is high in the region. In sub-Saharan Africa, where much of the population is too poor to purchase mineral supplements, poor soil health (SDG15) can therefore negatively impact on human health (SDG3). We surveyed 3661 school children aged 13–15 in three African countries, Ghana, South Africa and Zimbabwe, for their ‘Attitudes, Behaviours and Competencies’ of soil, which we termed ‘ABC’. The ‘ABC’ survey results showed significant soil illiteracy. The survey showed that although students were generally equipped with a good attitude to (overall 52% positive) and behaviour towards soil (overall 60% engagement), they had little competency as to how to improve soil health (overall 23% knowledge). For example, less than 35% of respondents across all countries know that soil is living. Less than 13% of students are aware of the important role of soil in climate change mitigation. We believe that these two knowledge gaps must be addressed for Generation Z to understand the important linkages between climate change, soil and human health. We propose a hands-on ‘ethics of care’ approach to engage society with soil, piggybacking on existing climate change educational resources by building terrariums with living soil can empower children to learn about soil, plant, human and planetary health. The future of food security depends on Generation Z having soil literacy. Our survey clearly shows that students who think farming is a good way to make money have significantly higher levels of overall soil literacy. We propose that the future of human health depends on soil literacy.