Soil microorganisms interact with plants in diversified manner ranging from mobilising nutrients and enhancing their growth, to inducing diseases. They also produce allelochemicals directly or indirectly through conversion from other compounds. In order to hamper plant growth, allelochemicals must accumulate and persist at phytotoxic levels in the rhizosphere soil. However, after their entry into environment, persistence, availability and biological activities of allelochemicals are influenced by microorganisms. Transformation of allelochemicals by soil microbes may result into the compounds with modified biological properties. Such bio-transformations affect the overall allelopathic capability of the producer plant in a direct manner. Several reports describe the allelopathic significance of microbial metabolism products. For instance, a bacterium Actinetobacter calcoaceticus, can convert 2(3H)-benzoxazolinone (BOA) to 2,2´-oxo-l,l´-azobenzene (AZOB) which is more inhibitory to some plants. On the contrary, bacterium Pseudomonas putida catabolises juglone in soils beneath walnut trees; otherwise, juglone accumulates at phytotoxic levels. This review article describes the nature of microbially produced allelochemicals, and the ways to mediate microbial degradation of putative allelochemicals. The given information develops an understanding of persistence, fate and phytotoxicity of allelochemicals in the natural environment, and also points out the possible solution of the problems due to microbial interventions in the soil.

Article Info Received : 24.01.2017 Accepted : 07.04.2017 Our daily diet is largely contributed by cereals, which have low genetic abilities to amass higher concentrations of micronutrients in their grains. Hence, wide spread deficiencies iron, zinc and other essential nutrients have prevailed. Present study focuses the biofortification of Zn in wheat grains, taking advantage of nutrient-nutrient synergy between Zn and N. Three wheat genotypes (NIA-Amber, BWQ-4 and SD-998) were tested in a field experiment following randomized complete block factorial design with three replicates. Urea fertilizer was applied at the rates of 120 (recommended), 150 and 180 kg N ha -1 in combination with three levels of Zn (0, 5 & 10 kg ha -1 ). Outcomes of the experiment revealed that NIA-Amber had the highest grain yield of 6.03 tons/ha against 150 kg N ha -1 and 10 kg Zn ha -1 . Maximum Zn contents of 447.86, 429.56 and 395.56 g ha -1 were observed in BWQ-4, SD-998 and NIA-Amber at 180 kg N ha -1 in combination with 10 kg Zn ha -1 . Maximum enhancement in protein contents was observed in BWQ-4 (743 kg ha -1 ) at 180 kg N ha -1 and combined with 5 kg Zn ha -1 . For NIA-Amber, 180 kg N ha -1 in combination of 10 kg Zn ha -1 proved the most suitable in terms of Zn concentration and other quality attributes. Nitrogen @ 180 kg N ha -1 with 5 kg Zn ha -1 depicted appreciable zinc and protein contents in grains of BWQ-4 and SD-998.

Zinc (Zn) deficiency causes low crop production and malnutrition in human. Agronomic biofortification of food crops can resolve the issues of global food security and human nutrition on sustainable basis. Field experiments were conducted to improve Zn bioavailability, growth and yield of wheat in response to varying Zn application rates for two consecutive years (2016-17 & 2017-18). Significant increase in grain yield was recorded with the application of Zn. Highest grain yield (5.41 t ha-1) was recorded with the application of 5.00 kg Zn ha-1. Human available Zn fraction was also improved in response to Zn application. Zn application resulted in lowering phytate/Zn molar ration in wheat grains. Higher Zn accumulation (338.72 g ha-1) was observed by applying 7.5 kg Zn ha-1. Zinc application was found critical to meet internal (36.53 µg g-1) and external (4.48 kg Zn ha-1) Zn requirements to achieve near maximum yield of wheat. The results reinforced the concept of Zn fertilization to achieve better productivity and quality.

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Depleting soil fertility and low fertilizer efficiency in alkaline calcareous soils are serious issues worldwide creating an immediate threat to environment and food security. Integrated nutrient management (INM) can be a promising eco-friendly strategy for improving crop performance and resource efficiency to resolve these concerns. A field study was conducted to investigate the integrated effect of organic sources [farm yard manure (FYM) @ 10 tons ha-1 and press mud (PM) @ 5 tons ha-1] along with various NPK rates [100, 75, 50% recommended dose of fertilizer (RDF)] on root system, nutrient efficiency, and yield of wheat cultivar Kiran-95. Longest roots were measured in FYM + RDF50 while highest surface area and number of root tips were recorded in PM + RDF50 than RDF alone. However, maximum root volume and average root diameter was observed in PM + RDF100 and PM + RDF75, respectively compared with RDF only. PM + RDF100 considerably enhanced grain yield and related traits i.e., spike length, tillers count m-2 and 100-grain weight as compared to RDF only. Integration of PM and 100% RDF showed higher NPK uptake, than RDF alone. Recovery efficiency (RE) of NPK was calculated higher at lower fertilizer rates and vice versa. The sole application of RDF100 showed least RE of NPK whilst PM + RDF50 revealed higher RE of NPK. The results suggested that INM could be a sustainable approach to enhance wheat productivity and nutrient efficiency in alkaline calcareous soils. In addition, PM along with RDF100 NPK fertilizers proved superior in improving root traits and nutrient accumulation thereby increasing wheat grain yield.