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Chromium (Cr) is a heavy metal of commercial importance; thus, significant amounts are released in wastewaters. The mobility and distribution of metals in the environment is related not only to their concentration but also to their availability in the environment. Most chromium (Cr) exists in oxidation states ranging from 0 to VI in soils but the most stable and common forms are Cr(0), Cr(III), and Cr(VI) species. Cr can have positive and negative effects on health, according to the dose, exposure time, and its oxidation state. Its behavior in soil, its soil-plant transfer and accumulation in different plant parts vary with its chemical form, plant type and soil physicochemical properties. Soil microbial community plays a key role in governing Cr speciation and behavior in soil. A number of factors have been identified to influence Cr toxicity on activated sludge, such as, pH, biomass concentration, presence of organic substances or other heavy metals, acclimation process, exposure time, etc. Inside plants, Cr provokes numerous deleterious effects to several physiological, morphological, and biochemical processes. Cr induces phytotoxicity by interfering plant growth, nutrient uptake and photosynthesis, inducing enhanced generation of reactive oxygen species, causing lipid peroxidation and altering the antioxidant activities. The present review describes the consequences of Cr toxicity on plants, including morphological, physiological and ultrastructural changes. This review also provides the basic concepts of Cr translocation and interaction with other essential macro- and microelements. Moreover, based on the available literature and current research scenario, this review suggests some possible management and remediation strategies to alleviate Cr toxicity and contamination in soil. It also provides valuable knowledge for further studies towards enhancement of soil phytoremediation and crops improvement. Therefore, there is a dire need to monitor biogeochemical behavior of Cr in soil-plant system. [ABSTRACT FROM AUTHOR]

Nitrogen management is a major challenge in the environment due toNO3-leaching and volatilization. To address this problem, a lysimeter experiment was conducted for rice-wheat with two lower N rates (15 and 30%) and three higher rates (15, 30 and 45%) than recommended rate (N100%). Higher leaching of NO3 - was noted with N145% up to86.84 mg/leachate in rice while wheat crop showed maximum leaching 48.62 mg/leachate in same treatment. This revealed that during the rice-wheat rotation, NO3-leaching losses were the highest during rice growth than that of wheat. The uppermost rice-wheat grain yield was obtained with 15% higher N. The highest rice-wheat NUE was 31.26 g/g and 45.52 g/g with treatment N115%, respectively. It is concluded that treatment of N115%proved to be efficient than other treatments due to enhanced NUE and yield by reducing NO3-leaching losses. The findings of current study can be helpful to develop proper N fertilizer management strategies for rice-wheat rotation. [ABSTRACT FROM AUTHOR]

The impact of heavy metal, i.e., cadmium (Cd), on the growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, and antioxidants machinery (enzymatic and non-enzymatic antioxidants), ions uptake, organic acids exudation, and ultra-structure of membranous bounded organelles of two rice (Oryza sativa L.) genotypes (Shan 63 and Lu 9803) were investigated with and without the exogenous application of ferrous sulfate (FeSO4). Two O. sativa genotypes were grown under different levels of CdCl2 [0 (no Cd), 50 and 100 µM] and then treated with exogenously supplemented ferrous sulfate (FeSO4) [0 (no Fe), 50 and 100 µM] for 21 days. The results revealed that Cd stress significantly (p < 0.05) affected plant growth and biomass, photosynthetic pigments, gas exchange characteristics, affected antioxidant machinery, sugar contents, and ions uptake/accumulation, and destroy the ultra-structure of many membranous bounded organelles. The findings also showed that Cd toxicity induces oxidative stress biomarkers, i.e., malondialdehyde (MDA) contents, hydrogen peroxide (H2O2) initiation, and electrolyte leakage (%), which was also manifested by increasing the enzymatic antioxidants, i.e., superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidant compounds (phenolics, flavonoids, ascorbic acid, and anthocyanin) and organic acids exudation pattern in both O. sativa genotypes. At the same time, the results also elucidated that the O. sativa genotypes Lu 9803 are more tolerant to Cd stress than Shan 63. Although, results also illustrated that the exogenous application of ferrous sulfate (FeSO4) also decreased Cd toxicity in both O. sativa genotypes by increasing antioxidant capacity and thus improved the plant growth and biomass, photosynthetic pigments, gas exchange characteristics, and decrease oxidative stress in the roots and shoots of O. sativa genotypes. Here, we conclude that the exogenous supplementation of FeSO4 under short-term exposure of Cd stress significantly improved plant growth and biomass, photosynthetic pigments, gas exchange characteristics, regulate antioxidant defense system, and essential nutrients uptake and maintained the ultra-structure of membranous bounded organelles in O. sativa genotypes. [ABSTRACT FROM AUTHOR]