In order to establish the natural processes and geochemical factors responsible for enrichment of trace metal ions (Cu, Co, Ni, Zn and Cr) with respect to textural parameters (sand, silt and clay weight percentages) along with depth, multivariate statistical approach has been carried out for sediments in different water zones of Chilika lake, the largest brackish water lagoon in Asia. The rotated varimax factor results reveal that Cobalt enrichment is controlled by both textural parameters as well as adsorption mechanism. In fresh and saline water region, textural parameters and in mixed water, adsorption phenomenon predominates. Zn in fresh water is related to clay, whereas it is in adsorbed state in mixed water. Cu in fresh water sediments is in absorbed state and in mixed water it is related to depth and Co concentration. Cr does not show any specific association in fresh water, but in both mixed and saline water it is associated with clay minerals. Although both textural parameters and adsorption mechanism play an important role for the enrichment of trace metal ions in these lagoonal sediments, their relative importance varies with specific metal ions as well as the water quality. Sequential extraction technique was used to characterize the various forms of metals in the < 63 micro size sediments of Chilika lake. The concentrations determined indicated selective accumulation of the various metals in the different phases with spatial variability in different water zones. Slightly higher availability of Co and Zn near Balugaon township in exchangeable phase may be related to anthropogenic activities. Among the non-lithogenous (NL) phases, reducible phase associated with higher concentration of Ni, Cu and Cr. Organic bound Zn and Co contributed highest percentages among NL fractions. Residual fraction contributed more than 50% in most of the cases, reflected the predominance of physical weathering, high erosion rate along the drainage basin.

Although silicon (Si) is ubiquitous in the earth's crust, its essentiality for growth of higher plants is still under discussion. By recognising the overwhelming potential of Si in alleviating a wide range of biotic and abiotic stresses, the Association of American Plant Food Control Officials and the International Plant Nutrition Institute, Georgia, USA, have designated Si as a plant 'beneficial substance' in 2014 and 2015, respectively. Sugarcane is a Si-accumulating crop which strongly responds to Si fertilisation especially in Si-deficient soil. Due to intensive weathering prevailing in humid and sub-humid regions, most of the soil-available Si, taken up by plants in the form of monosilicic acid (H 4 SiO 4), is lost through leaching. If the concentration of monosilicic acid is being maintained at a fixed level by soil reserves, the highly weathered soils of humid and sub-humid regions tend to become depleted in Si if continuously cultivated with sugarcane. Hence, leaching of Si from the soil coupled with plant uptake is an important factor in determining Si concentrations in soil. Consequently, it can be said that the intensive cultivation of sugarcane depletes the existing low available Si content in soil, resulting in necessity for Si fertilisation. Moreover, the uptake of Si by sugarcane (500-700 kg Si ha −1) sometimes surpasses those of the macronutrients (especially N, P and K). At the same time, due to change in global climate and monoculture system followed in sugarcane, it is affected by a wide range of biotic and abiotic stresses in field condition which calls for external Si supplementation to achieve sustainable growth and yield of sugarcane. The beneficial effects of Si in sugarcane include improvement of photosynthesis and lodging, enhancement of growth and development, regulation of reactive oxygen species, protection from soil salinity, reduction in metal toxicity, alleviation of freeze damage, mitigation of water stress and suppression of diseases and pests. In this review, we made an effort to compile the existing literature describing the potential of Si in promoting defence against various biotic and abiotic stresses in sugarcane and suggested possible future research perspectives.

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In many countries, blanket fertilizer recommendations for different crops have caused poor nutrient supply, low nutrient use efficiency and limited crop response. In contrast, soil and area specific, customized fertilizers may help to sustain soil health by ensuring appropriate fertilization. Hence, specific customized fertilizers should be promoted to counteract the problem of expanding multi-nutrient deficiencies in Indian soils. This article discusses the manufacturing methodologies, eligibility criteria, success in Indian fertilizer industry, adoption of fertilizer recommendations and problems in marketing of customized fertilizer.