Agriculture is a multifarious interface between plants and associated microorganisms. In contemporary agriculture, emphasis is being given to environmentally friendly approaches, particularly in developing countries, to enhance sustainability of the system with the least negative effects on produce quality and quantity. Modern agricultural practices such as extensive tillage, the use of harmful agrochemicals, mono-cropping, etc. have been found to influence soil microbial community structure and soil sustainability. On the other hand, the question of feeding the ever-growing global population while ensuring system sustainability largely remains unanswered. Agriculturally important microorganisms are envisaged to play important roles in various measures to raise a healthy and remunerative crop, including integrated nutrient management, as well as disease and pest management to cut down agrochemicals without compromising the agricultural production. These beneficial microorganisms seem to have every potential to provide an alternative opportunity to overcome the ill effects of various components of traditional agriculture being practiced by and large. Despite an increased awareness of the importance of organically produced food, farmers in developing countries still tend to apply inorganic chemical fertilizers and toxic chemical pesticides beyond the recommended doses. Nutrient uptake enhancement, biocontrol of pests and diseases using microbial inoculants may replace/reduce agrochemicals in agricultural production system. The present review aims to examine and discuss the shift in microbial population structure due to current agricultural practices and focuses on the development of a sustainable agricultural system employing the tremendous untapped potential of the microbial world.

A wide range of root-associated mutualistic microorganisms have been successfully applied and documented in the past for growth promotion, biofertilization, biofortification and biotic and abiotic stress amelioration in major crops. These microorganisms include nitrogen fixers, nutrient mobilizers, bio-remediators and bio-control agents. The present study aimed to demonstrate the impact of salt-tolerant compatible microbial inoculants on plant growth; Zn biofortification and yield of wheat (Triticum aestivum L.) crops grown in saline-sodic soil and insight of the mechanisms involved therein are being shared through this paper. Field experiments were conducted to evaluate the effects of Trichoderma harzianum UBSTH-501 and Bacillus amyloliquefaciens B-16 on wheat grown in saline-sodic soil at Research Farm, ICAR-Indian Institute of Seed Sciences, Kushmaur, India. The population of rhizosphere-associated microorganisms changed dramatically upon inoculation of the test microbes in the wheat rhizosphere. The co-inoculation induced a significant accumulation of proline and total soluble sugar in wheat at 30, 60, 90 and 120 days after sowing as compared to the uninoculated control. Upon quantitative estimation of organic solutes and antioxidant enzymes, these were found to have increased significantly in co-inoculated plants under salt-stressed conditions. The application of microbial inoculants enhanced the salt tolerance level significantly in wheat plants grown in saline-sodic soil. A significant increase in the uptake and translocation of potassium (K⁺) and calcium (Ca²⁺) was observed in wheat co-inoculated with the microbial inoculants, while a significant reduction in sodium (Na⁺) content was recorded in plants treated with both the bio-agents when compared with the respective uninoculated control plants. Results clearly indicated that significantly higher expression of TaHKT-1 and TaNHX1 in the roots enhances salt tolerance effectively by maintaining the Na⁺/K⁺ balance in the plant tissue. It was also observed that co-inoculation of the test inoculants increased the expression of ZIP transporters (2–3.5-folds) which ultimately led to increased biofortification of Zn in wheat grown in saline-sodic soil. Results suggested that co-inoculation of T. harzianum UBSTH-501 and B. amyloliquefaciens B-16 not only increased plant growth but also improved total grain yield along with a reduction in seedling mortality in the early stages of crop growth. In general, the present investigation demonstrated the feasibility of using salt-tolerant rhizosphere microbes for plant growth promotion and provides insights into plant-microbe interactions to ameliorate salt stress and increase Zn bio-fortification in wheat.

Yield stability and carbon sequestration of agricultural systems are impacted by nutrient management strategies. Major objectives of this study were to understand the effects of long‐term (43 years) manure application on a) environmental parameters such as soil organic carbon (SOC) sequestration, enzyme activities in surface and subsurface layers, and b) yield, and yield stability under a soybean–wheat cropping system in a Vertisol. For this, 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), NPK + farmyard manure (NPKM) was compared with an unfertilized control (UC) and a fallow land. After 43 years, NPKM and NPK plots had ∼63 and 30% higher total SOC stock than UC, and 45 and 17% higher total SOC stock than fallow plots, respectively in the 0–30 cm layer. Acid hydrolysable C was ~ 42 and 57% higher for NPKM plots in those layers respectively than fallow land. The proportion of macroaggregates was less than 30% in both soil layers of cultivated plots. NPKM had 44 and 28% greater humic and fulvic acid‐associated C than fallow land in top layer. Enzyme activities improved in NPKM by ~ 60 and 61% as compared with fallow land. A steady decline in soybean productivity over the years might be due to residue effect. However, wheat yield increased steadily with manuring. Higher SOC accumulation ( p < .001), greater enzyme activities ( p < .05), improved structure ( p < .05) could enhance wheat yield under NPKM. Thus, manure application could lead to yield stability and enhance SOC sequestration in subtropical region simultaneously.

The crop productivity in calcareous soils is low due to their low organic matter content, high pH levels and improper nutrient management without considering the indigenous nutrient supplying capacity and crop yield potential; therefore, this study was conducted for a quantitative assessment of the nutrient supplying capacity of a calcareous soil on the productivity of hybrid and conventional rice and maize crops using an omission plot technique. The treatments included the ample application of Nitrogen (N), Phosphorus (P), Potassium (K), Sulphur (S) and Zinc (Zn), and an unfertilized check and omissions of N, P, K, S and Zn in rice and maize for six cropping seasons. The impact of the nutrient omission towards crop productivity was highest for nitrogen followed by phosphorous, potassium, zinc and sulphur. The total grain yield (3 yr average) in the hybrid rice–maize system was highest (16.32 t ha⁻¹) for the optimum fertilized plot and lowest (6.34 t ha⁻¹) for the unfertilized check. The sustainable yield index indicated that hybrid and conventional rice-maize cropping systems were more sustainable in the amply fertilized plot than in the nutrient-limited and unfertilized treatment plots. The average percent contributions of nitrogen, phosphorous, and potassium from the soil towards total nutrient removal were 36, 80 and 137 kg ha⁻¹, in the hybrid system and 24, 54 and 104 kg ha⁻¹ in the conventional system, respectively. The return on investment (ROI) of the N, P, K, S and Zn for the hybrid rice was 21.2, 7.1, 6.7, 4.1, and 0.3 USD, respectively, while for the maize it was 28.8, 7.6, 4.9, 6.5, and 0.7 USD, respectively. The results suggest that there is a direct link between the soil nutrient supplying capacity and the nutrient requirements by different types of crops in calcareous soil; therefore, the omission plot technique used for the assessment of the indigenous nutrient supplying capacity could be used in the larger domain for improved nutrient management, through synchronization with a targeted crop yield for improved productivity, soil fertility, nutrient use efficiency and farm income.