The Effect of Growth Activators and Plant Growth-Promoting Rhizobacteria (PGPR) on the Soil Properties, Root Yield, and Technological Quality of Sugar Beet

Plant-Growth-Promoting Rhizobacteria Emerging as an Effective Bioinoculant to Improve the Growth, Production, and Stress Tolerance of Vegetable Crops

Vegetable cultivation is a promising economic activity, and vegetable consumption is important for human health due to the high nutritional content of vegetables. Vegetables are rich in vitamins, minerals, dietary fiber, and several phytochemical compounds. However, the production of vegetables is insufficient to meet the demand of the ever-increasing population. Plant-growth-promoting rhizobacteria (PGPR) facilitate the growth and production of vegetable crops by acquiring nutrients, producing phytohormones, and protecting them from various detrimental effects. In this review, we highlight well-developed and cutting-edge findings focusing on the role of a PGPR-based bioinoculant formulation in enhancing vegetable crop production. We also discuss the role of PGPR in promoting vegetable crop growth and resisting the adverse effects arising from various abiotic (drought, salinity, heat, heavy metals) and biotic (fungi, bacteria, nematodes, and insect pests) stresses.

Rhizosphere Bacteria in Plant Growth Promotion, Biocontrol, and Bioremediation of Contaminated Sites: A Comprehensive Review of Effects and Mechanisms

Agriculture in the 21st century is facing multiple challenges, such as those related to soil fertility, climatic fluctuations, environmental degradation, urbanization, and the increase in food demand for the increasing world population. In the meanwhile, the scientific community is facing key challenges in increasing crop production from the existing land base. In this regard, traditional farming has witnessed enhanced per acre crop yields due to irregular and injudicious use of agrochemicals, including pesticides and synthetic fertilizers, but at a substantial environmental cost. Another major concern in modern agriculture is that crop pests are developing pesticide resistance. Therefore, the future of sustainable crop production requires the use of alternative strategies that can enhance crop yields in an environmentally sound manner. The application of rhizobacteria, specifically, plant growth-promoting rhizobacteria (PGPR), as an alternative to chemical pesticides has gained much attention from the scientific community. These rhizobacteria harbor a number of mechanisms through which they promote plant growth, control plant pests, and induce resistance to various abiotic stresses. This review presents a comprehensive overview of the mechanisms of rhizobacteria involved in plant growth promotion, biocontrol of pests, and bioremediation of contaminated soils. It also focuses on the effects of PGPR inoculation on plant growth survival under environmental stress. Furthermore, the pros and cons of rhizobacterial application along with future directions for the sustainable use of rhizobacteria in agriculture are discussed in depth.

Integrated Application of Composted Agricultural Wastes, Chemical Fertilizers and Biofertilizers as an Avenue to Promote Growth, Yield and Quality of Maize in an Arid Agro-Ecosystem

Formulating new integrated plant nutrient management (IPNM) strategies in order to sustain crop production and protect the environment has become an important issue in the present agricultural system. Therefore, a field study was carried out in the two seasons 2016 and 2017 to formulate the best IPNM strategies for improving the growth, yield, and quality of maize grown in an arid agro-ecosystem. The IPNM comprised full-dose NPK (T1); composted agricultural wastes based on cow manure (T2), poultry manure (T3), and a mixture of sheep and camel manure (T4) as activators at the rate of 5 t ha−1 for each; half-dose NPK was combined with the mixture of the three types of composted agricultural wastes at the rate of 5 t ha−1 (T5) or 10 t ha−1 (T6), and a mixture of the three types of composted agricultural wastes at the rate of 10 t ha−1 (T7), 15 t ha−1 (T8), or 20 t ha−1 (T9), either with or without biofertilizers. The results showed that, as compared to T1, T6 or T9 significantly increased different growth, yield, and quality parameters of maize by 11.4–27.3%, 0.8–31.8%, and 4.6–17.2%, while T2 significantly decreased these parameters by 2.2–17.8%, 3.5–16.7%, and 4.5–9.4%, respectively. Seed inoculation with biofertilizers significantly increased different parameters of maize by 1.8–12.9%, compared to that of the non-inoculation seed treatment. Principal component analysis showed a strong relationship between different parameters of maize and treatments T5, T6, T8, and T9 with seed inoculation. Further, a significant and linear relationship was observed between different parameters of maize and the amount of N (R2 = 0.65–0.77), P (R2 = 0.58–0.71), and K (R2 = 0.63–0.73). These results indicated that any IPNM strategies that manage the NPK status and dynamics in the soil are a promising avenue for improving the growth and productivity of maize grown in the arid agro-ecosystem.

Bokashi, Boiled Manure and Penergetic Applications Increased Agronomic Production Variables and May Enhance Powdery Mildew Severity of Organic Tomato Plants

Research on organic fertilizers are of crucial importance for sustainable production systems with high efficiency of natural resource use. The objective of this study was to evaluate organic sources of fertilization (boiled manure (BM), effective microorganism (EM) Bokashi, and Penergetic) for their effects on agronomic variables (fruit size and yield, total soluble solids) and on foliar powdery mildew severity of tomato (Solanum lycopersicum L.). The crops were grown during two cropping cycles in protected cultivation. The treatments were: Control (water only); 50 g per plant of EM Bokashi compost in two applications; Penergetic at 1.5 g L−1 applied to the substrate before planting or sprayed on the plants 14 days after transplanting; and BM at 2.5%, 5.0%, 7.5%, and 10% concentrations (vol/vol) in water, via fertigation. Fruit production and quality were assessed. The effects of treatments on powdery mildew (Leveillula taurica Lév. G. Arnaud) were analyzed by using a diagrammatic scale. Bokashi, 10% BM, and Penergetic increased fruit production of the first three fruit trusses. Bokashi treatment increased tomato fruit diameter. The effects on fruit length and total soluble solids varied with each crop cycle. Powdery mildew severity increased with 10% BM, compared to the control. Both 10% BM and Penergetic presented similar fruit production to Bokashi and are good candidates as substitutes for Bokashi as organic fertilizers/amendments while maintaining tomato yield.

Plant Growth Promoting Rhizobacteria (PGPR) as Green Bioinoculants: Recent Developments, Constraints, and Prospects

The quest for enhancing agricultural yields due to increased pressure on food production has inevitably led to the indiscriminate use of chemical fertilizers and other agrochemicals. Biofertilizers are emerging as a suitable alternative to counteract the adverse environmental impacts exerted by synthetic agrochemicals. Biofertilizers facilitate the overall growth and yield of crops in an eco-friendly manner. They contain living or dormant microbes, which are applied to the soil or used for treating crop seeds. One of the foremost candidates in this respect is rhizobacteria. Plant growth promoting rhizobacteria (PGPR) are an important cluster of beneficial, root-colonizing bacteria thriving in the plant rhizosphere and bulk soil. They exhibit synergistic and antagonistic interactions with the soil microbiota and engage in an array of activities of ecological significance. They promote plant growth by facilitating biotic and abiotic stress tolerance and support the nutrition of host plants. Due to their active growth endorsing activities, PGPRs are considered an eco-friendly alternative to hazardous chemical fertilizers. The use of PGPRs as biofertilizers is a biological approach toward the sustainable intensification of agriculture. However, their application for increasing agricultural yields has several pros and cons. Application of potential biofertilizers that perform well in the laboratory and greenhouse conditions often fails to deliver the expected effects on plant development in field settings. Here we review the different types of PGPR-based biofertilizers, discuss the challenges faced in the widespread adoption of biofertilizers, and deliberate the prospects of using biofertilizers to promote sustainable agriculture.

Analysis of Changes in Soil Organic Carbon, Energy Consumption and Environmental Impact Using Bio-Products in the Production of Winter Wheat and Oilseed Rape

Agricultural management, environmentally friendly technologies, chemical, organic and bio-based substances used, as well as meteorological factors, have a significant impact on the fluctuations of soil organic carbon (SOC). The aim of this research was to analyze the effect of different biopreparations on the changes of SOC content and the winter wheat and winter oilseed rape yields by assessing the energy consumption efficiency and the environmental impacts. The experimental research was conducted from 2017 to 2019 in three different treatments, in two of which were used either a molasses and magnesium sulphate based-biopreparation (T1) or a bacteria-based biopreparation (T2), while treatment T3 was applied as a control where no biopreparations were used. The dynamics of SOC content were analyzed at two depths: 0–10 and 10–20 cm. For the analysis of energy efficiency indicators and environmental impacts, the greenhouse gas (GHG) and energy consumption conversion equivalents were used. A summary of the results showed that both types of biopreparations had a positive effect on the changes of SOC content, which was especially evident in the deeper layers at 10–20 cm depth, where, irrespective of the crop type, a more significant increase of the SOC content was observed every year of the experiment compared to the control treatment. Biopreparations had a significant effect in increasing the winter wheat and winter oilseed rape yield. The best energy efficiency ratio was observed in winter wheat (4.84) and winter oilseed rape (5.11) in treatment T1. The results of the environmental impact assessment showed that the lowest GHG emissions were recorded in the winter wheat production in treatment T1 at 108.7–149.1 kg CO2eq Mg−1, while the highest were observed in oilseed rape production in the control treatment T3 at 343.4 kg CO2eq Mg−1.