Hafiz Mohkum Hammad

Arsenic uptake, accumulation and toxicity in rice plants: Possible remedies for its detoxification: A review

Arsenic (As) is a toxic metalloid. Serious concerns have been raised in literature owing to its potential toxicity towards living beings. The metalloid causes various water- and food-borne diseases. Among food crops, rice contains the highest concentrations of As. Consuming As-contaminated rice results in serious health issues. Arsenic concentration in rice is governed by various factors in the rhizosphere such as availability and concentration of various mineral nutrients (iron, phosphate, sulfur and silicon) in soil solution, soil oxidation/reduction status, inter-conversion between organic and inorganic As compounds. Agronomic and civil engineering methods can be adopted to decrease As accumulation in rice. Agronomic methods such as improving soil porosity/aeration by irrigation management or creating the conditions favorable for As-precipitate formation, and decreasing As uptake and translocation by adding a inorganic nutrients that compete with As are easy and cost effective techniques at field scale. This review focuses on the factors regulating and competing As in soil-plant system and As accumulation in rice grains. Therefore, it is suggested that judicious use of water, management of soil, antagonistic effects of various inorganic plant-nutrients to As should be considered in rice cultivated areas to mitigate the building up of As in human food chain and with minimum negative impact to the environment.

Application of CSM-CERES-Maize model in optimizing irrigated conditions:

Maize is one of the main cereal crops in Pakistan with sensitivity to drought at various developmental stages known to influence the yield. The impact of variable weather conditions on maize yield can be analyzed with crop simulation models. The CSM-CERES-Maize model has been widely used to assess irrigation strategies for maize. This research was conducted to test the CSM-CERES-Maize model for its ability to accurately predict maize biomass and grain yield under water limiting and non-limiting conditions in semiarid conditions. Four growth stage-based irrigation treatments and two potential soil moisture deficit-based treatments were defined. During model calibration, the simulated maximum leaf area index (LAI), total dry matter (TDM), and grain yield were all within 10% of observed values. During model evaluation, there was generally satisfactory agreement between observed and simulated values for two hybrids (Monsanto-919 and Pioneer-30Y87) with the model showing variability of −17.9–20.0%, −9.2–14.3%, and −19.6–19.9% for maximum LAI, TDM, and grain yield, respectively, for the two hybrids among various treatments. The CERES-Maize model was useful in providing information to decision-making regarding diverse irrigation regimes at the farm level in a semiarid environment.

Agroforestry: a sustainable environmental practice for carbon sequestration under the climate change scenarios—a review

Agroforestry is a sustainable land use system with a promising potential to sequester atmospheric carbon into soil. This system of land use distinguishes itself from the other systems, such as sole crop cultivation and afforestation on croplands only through its potential to sequester higher amounts of carbon (in the above- and belowground tree biomass) than the aforementioned two systems. According to Kyoto protocol, agroforestry is recognized as an afforestation activity that, in addition to sequestering carbon dioxide (CO2) to soil, conserves biodiversity, protects cropland, works as a windbreak, and provides food and feed to human and livestock, pollen for honey bees, wood for fuel, and timber for shelters construction. Agroforestry is more attractive as a land use practice for the farming community worldwide instead of cropland and forestland management systems. This practice is a win–win situation for the farming community and for the environmental sustainability. This review presents agroforestry potential to counter the increasing concentration of atmospheric CO2 by sequestering it in above- and belowground biomass. The role of agroforestry in climate change mitigation worldwide might be recognized to its full potential by overcoming various financial, technical, and institutional barriers. Carbon sequestration in soil by various agricultural systems can be simulated by various models but literature lacks reports on validated models to quantify the agroforestry potential for carbon sequestration.

Phosphate-Solubilizing Bacteria Nullify the Antagonistic Effect of Soil Calcification on Bioavailability of Phosphorus in Alkaline Soils

Phosphate-solubilizing bacteria (PSB) reduce the negative effects of soil calcification on soil phosphorus (P) nutrition. In this incubation study, we explored the ability of PSB (control and inoculated) to release P from different P sources [single super phosphate (SSP), rock phosphate (RP), poultry manure (PM) and farm yard manure (FYM)] with various soil lime contents (4.78, 10, 15 and 20%) in alkaline soil. PSB inoculation progressively enriched Olsen extractable P from all sources compared to the control over the course of 56 days; however, this increase was greater from organic sources (PM and FYM) than from mineral P sources (SSP and RP). Lime addition to the soil decreased bioavailable P, but this effect was largely neutralized by PSB inoculation. PSB were the most viable in soil inoculated with PSB and amended with organic sources, while lime addition decreased PSB survival. Our findings imply that PSB inoculation can counteract the antagonistic effect of soil calcification on bioavailable P when it is applied using both mineral and organic sources, although organic sources support this process more efficiently than do mineral P sources. Therefore, PSB inoculation combined with organic manure application is one of the best options for improving soil P nutrition.

Effects of Nitrogen Supply on Water Stress and Recovery Mechanisms in Kentucky Bluegrass Plants

Non-irrigated crops in temperate and irrigated crops in arid regions are exposed to an incessant series of drought stress and re-watering. Hence, quick and efficient recuperation from drought stress may be amongst the key determinants of plant drought adjustment. Efficient nitrogen (N) nutrition has the capability to assuage water stress in crops by sustaining metabolic activities even at reduced tissue water potential. This study was designed to understand the potential of proper nutrition management by studying the morphological and physiological attributes, and assimilation of nitrogen in Kentucky bluegrass under drought stress. In present study, one heterogeneous habitat and four treatments homogenous habitats each with four replications were examined during field trial. Drought stress resulted in a significant reduction in the nitrogen content of both mother and first ramets, maximum radius, above and below ground mass, number of ramets per plot, leaf water contents and water potential and increased the carbon content and the C:N ratio in both homogenous and heterogeneous plots compared to well-watered and nutritional conditions. Observation using electron microscopy showed that drought stress shrunk the vessel diameter, circumference and xylem area, but increased the sieve diameter, and phloem area in the leaf crosscutting structure of Kentucky bluegrass, first, second, and third ramet leaf. Thus, it can be concluded that water stress markedly reduced all the important traits of Kentucky bluegrass, however, proper nutritional management treatment resulted in the best compensatory performance under drought assuaging its adversity up to some extent and may be considered in formulating good feasible and cost-effective practices for the environmental circumstances related to those of this study.

Effect of water management and silicon on germination, growth, phosphorus and arsenic uptake in rice

Silicon (Si) is the 2nd most abundant element in soil which is known to enhance stress tolerance in wide variety of crops. Arsenic (As), a toxic metalloid enters into the human food chain through contaminated water and food or feed. To alleviate the deleterious effect of As on human health, it is a need of time to find out an effective strategy to reduce the As accumulation in the food chain. The experiments were conducted during September-December 2014, and 2016 to optimize Si concentration for rice (Oryza sativa L.) exposed to As stress. Further experiment were carried out to evaluate the effect of optimum Si on rice seed germination, seedling growth, phosphorus and As uptake in rice plant. During laboratory experiment, rice seeds were exposed to 150 and 300µM As with and without 3mM Si supplementation. Results revealed that As application, decreased the germination up to 40-50% as compared to control treatment. Arsenic stress also significantly (P < 0.05) reduced the seedling length but Si supplementation enhanced the seedlings length. Maximum seedling length (4.94cm) was recorded for 3mM Si treatment while, minimum seedling length (0.60cm) was observed at day7 by the application of 300µM As. Silicon application resulted in 10% higher seedling length than the control treatment. In soil culture experiment, plants were exposed to same concentrations of As and Si under aerobic and anaerobic conditions. Irrigation water management, significantly (P˂0.05) affected the plant growth, Si and As concentrations in the plant. Arsenic uptake was relatively less under aerobic conditions. The maximum As concentration (9.34 and 27.70mgkg DW-1 in shoot and root, respectively) was found in plant treated with 300µM As in absence of Si under anaerobic condition. Similarly, anaerobic condition resulted in higher As uptake in the plants. The study demonstrated that aerobic cultivation is suitable to decrease the As uptake and in rice exogenous Si supply is beneficial to decrease As uptake under both anaerobic and aerobic conditions.

Patterns of Climate Extremes in the Coastal and Highland Regions of Balochistan, Pakistan

AbstractClimatic extremes have direct and indirect effects on an ecosystem, whereby thermal variations bring warm and cold weather, and hydrological anomalies cause droughts and floods. Changing pa...

Fate of Antibiotics in Soil

An extensive amount of antibiotics is being used worldwide to enhance the health status, growth rate, milk, and meat production in dairy farms. In many aspects, the use of these veterinary antibiotics is crucial for the animals. But point of concern is that, animals don’t have enough ability to utilize these applied antibiotics, and it depends on the animal species and chemical composition of veterinary antibiotics. About 90% is obtained from the natural compounds like bacteria, fungi, and semisynthetic modifications and taken as “natural products,” and some are totally synthetic. Approximately 10–90% of the applied antibiotics are released in the form of urine and feces. The animal waste is used as fertilizer and exposed to the soil. Antibiotics present in manure are organic in nature and have the capability to bind with soil particles. These are many features that are affecting the fate of antibiotics in soil like the absorption and fixation rate of different antibiotics on the soil particles surfaces mainly depends on the soil pH, physico-chemical characteristics, climatic conditions, soil type, composition and quality of organic matter, soil texture, CEC, and iron oxide content and many other environmental factors. There are several procedures that are involved, including chemical nature, transport, leaching and runoff, sorption, plant uptake, and biodegradation that determines the fate of antibiotics in soil. The chemical nature determines the persistence of the antibiotic in soil and as a result of biodegradation or transformation different metabolites are produced that have different chemical composition and less risk will be associated with these metabolites than the actual antibiotic. Surface transport of antibiotics via runoff was attributed to delayed infiltration of water into the soil because of surface sealing through manure and particle bound transport. Surface runoff of antibiotics from animal waste spread the chemicals to the general water environment. Different plant organ and tissues have the ability to uptake and store the antibiotics, mostly in roots, cotyledons, and cotyledon petioles parts. Phytoremediation is potential of plants against the different antibiotics. In general, plants are used for the phytoremediation of toxic materials from soil in the past. But nowadays, phytoremediation (phytostabilization, phytotoextraction, phytovolatilization, and phytoaccumulation) emerging as a new technique was considered to be effective in elimination of antibiotic from planted soil. All these features help to determine the fate of antibiotic in soil.

Author Correction: Phosphate-Solubilizing Bacteria Nullify the Antagonistic Effect of Soil Calcification on Bioavailability of Phosphorus in Alkaline Soils

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Fate of Organic and Inorganic Pollutants in Paddy Soils

Paddy soils have a heterogenous nature, with complex physico-chemical interactions and varying soil characteristics. Paddy soils remain flooded and are considered as rich sources of nutrients for plant growth. The nutrient levels mostly depend on different management practices, such as fertilizer application, irrigation, and tillage, and the movement of nutrients in the soils. These paddy soils normally show less movement of applied nutrients out of the medium than other soils, because of stagnant water that reduces the mobility rate. Paddy soils can become polluted by anthropogenic practices such as the use of sewage wastewater; industrial wastewater containing heavy metals; fertilizers; and pesticides, and the leakage of petrochemicals. Some natural pollutants can be oxidized by microbial activity, but most pollutants do not undergo biotic and chemical degradation. Inorganic (heavy metals) and organic pollutants (polychlorinated biphenyls, polychlorinated dibenzodioxins, and polychlorinated dibenzofurans) are the major types of pollutants in paddy soils. The numerous organic and inorganic pollutants resulting from anthropogenic activities can remain for long periods in nature and can be transported over long distances. In particular, organic pollutants can be bioaccumulated and biomagnified, thus reaching high levels that can be dangerous for human wellbeing and biological communities. Inorganic pollutants such as the heavy metals Pb, Cr, As, Zn, Cd, Cu, Hg, and Ni cause hazards for human health, for plants, for animals, and for the fertility status of the soil. These heavy metals are common pollutants in paddy soil and they bioaccumulate; in this way the concentrations of these pollutants increase in living systems, owing to their retention rates being higher than their discharge rates in these systems. The fate of these pollutants depends on their bioavailability, degradation by microorganisms, adsorption, desorption, leaching, and runoff. The transport and degradation of these pollutants in paddy soils and groundwater results in contamination. The physico-chemical characteristics of the paddy soil framework; for example, the water content, soil organic matter, presence of clay, and pH, influence the sorption or desorption and degradation of pollutants and also influence leaching to the groundwater and runoff to surface waters. The translocation of natural pesticides in paddy soils depends upon the ionic or neutral behavior of the soil constituents, on the pesticides’ solubility in water, extremity on the substance, and the colloidal nature of the paddy soils.