Abstract: Nickel (Ni) is a required element but may become toxic to plants, animals and humans if normal levels are exceeded. At very high levels of exposure, Ni salts are known to be carcinogenic. To assess the health and environmental effects of Ni, the bioavailable, not total, concentration of Ni in soil must be accurately measured. Urease has an absolute requirement for Ni to function, and this was used to develop a method to assess Ni bioavailability in soil. Bacteria with Ni-deficient urease were enriched from Spinks sandy soil by growing the cells in Luria Broth (LB) medium. This created a culture with high amount of potential urease activity but with low actual activity because of Ni limitations. Culture cells were equilibrated with different concentrations of Ni salt for four hours and the urease response to the added Ni was measured using steam distillation. When Ni concentration increased from 0 to 1.0 mM, urease activity also increased, proving that urease activity was positively correlated to bioavailability of Ni. To test bioavailability of Ni, not from added Ni salts but in soil, the bacterial culture was inoculated into a test soil that was composed of acid-washed Spinks sandy soil as a carrier soil and the soil with unknown Ni bioavailability. Nickel bioavailability was then measured using the urease bioassay optimized for conditions in terms of amount of culture, urea concentration, incubation time and THAM buffer pH. The following equation could be used to calculate Ni bioavailability from urease activity response when Ni bioavailability is in the range from 0 to 0.06 mM: Ni Bioavailability = Urease Activity/k/f where Ni Bioavailability has a unit of mM, Urease Activity has a unit of ug 30 mL−1 culture 2 h−1, k is equal to 15646 ug 30 mL1−1 culture 2 h−1 mM−1 , and f is the percentage of unknown soil in the test soil. The urease bioassay was able to detect as little as 1.99 mg kg−1 of bioavailable Ni in soil or 0.282 uM of bioavailable Ni in culture. The coefficient of variation for the urease bioassay was approximately 10%, indicating good precision. A significant correlation (r=0.9957**) was observed between Ni bioavailability measured using urease bioassay and Mehlich III extractable Ni. This indicates the bioassay method provided a relatively good indication of the bioavailable Ni content in the soil samples compared to chemical extraction. The urease bioassay was applied to measure the Ni bioavailability in soils with different properties and to evaluate the effects of soil pH and soil organic matter content on Ni bioavailability. Twenty soil samples that varied in soil pH and total C content were studied. The Ni bioavailability measured by urease bioassay in these twenty soils ranged from 19.9 to 68.3 mg kg−1 . Significant correlations were observed between bioavailable Ni measured by urease bioassay, Ca(N03)2 extractable Ni and Mehlich III extractable Ni. Nickel bioavailability decreased with the increase in total C content. When 1000 mg kg−1 Ni was added to soils with total C content ranging from 0.009% to 12.7%, Ni bioavailability decreased about 50%. Nickel bioavailability also decreased with increase in soil pH, and a change in soil pH from 4.15 to 9.94 decreased Ni bioavailability by 70%. Urease bioassay is recommended over chemical extraction methods to measure Ni bioavailability in soil because it is accurate, simple, sensitive, and directly measures biological response. Urease bioassay can be applied to soils with different properties, and can be used in most laboratories.

Soils with high Ni contents occur in several parts of the world, especially in areas with ultramafic rocks which cause serious environmental impacts. This book aims to extend the knowledge on the risks and problems caused by elevated Ni contents and to cover the existing gaps on issues related to various aspects and consequences of high Ni contents in soils and plants. Nickel in Soils and Plants brings together discussions on Ni as a trace element and as a micronutrient essential for plant growth and its role in plant physiology. It analyzes the biogeochemistry of Ni at the soil plant interface, and explains its behavior in the rhizosphere resulting in Ni deficiency or toxicity, or Ni tolerance of various Ni hyperaccumulators. Included are Ni resources and sources, the origin of soil Ni, its geochemical forms in soils and their availability to plants, a special reference on soils enriched with geogenic Ni, such as serpentine soils, and the special characteristics of those ecosystems. Recent advancements in methods of Ni speciation, including the macroscale and X- ray absorption spectroscopy studies as well as serious views on Ni kinetics, are also covered. Written by a team of internationally recognized researchers and expert contributors, this comprehensive work addresses the practical aspects of managing Ni in soils and plants for agricultural production, and managing soils with high Ni levels by using organic and inorganic amendments. The text also addresses practical measures related to Ni toxicity in plants, the removal and recovery of Ni from high Ni wastes, and offers environmentally friendly innovative processes for mining Ni from soils containing high Ni levels.

In Soil Fertility Management in Agroecosystems, Editors Amitava Chatterjee and David Clay provide a thoughtful survey of important concepts in soil fertility management. For the requirements of our future workforce, it is imperative that we evolve our understanding of soil fertility. Agronomists and soil scientists are increasingly challenged by extreme climatic conditions. Farmers are experimenting with integrating cover crops into rotations and reducing the use of chemical fertilizers. In other words, there is no such a thing as a simple fertilizer recommendation in today's agriculture. Topics covered include crop-specific nutrient management, program assessment, crop models for decision making, optimization of fertilizer use, cover crops, reducing nitrous oxide emissions, natural abundance techniques, tile-drained conditions, and soil biological fertility.

There is significant concern about the accumulation of potentially toxic elements (PTEs) in soils because of both direct and indirect impacts on human and ecosystem health. Knowledge of the fate and distribution of such contamination can lead to an effective assessment of the hazards to soil biota and the need for protective or mitigation activities. This is a particular challenge due to the heterogeneity of the soil matrix and complexity of the processes that determine PTE availability to soil biota. While whole-cell bacterial biosensors have been proposed as tools in enabling greater confidence in addressing such biological and chemical interfaces their genuine value remains to be realised. The underpinning objective of this work was to link the response of microbial biosensors to detailed chemical analysis and to relate the dose response sensitivity to other biological measurements. To better understand the phenomena of PTE bioavailability, the study considered changes in toxicity within the context of ion competition in both freshly amended and historically impacted soils. The interaction of test bacteria with both free (soil pore water) and sorbed (solid phase) fractions of the target analytes (copper, nickel and zinc) has enabled a better estimation of bioavailability/toxicity of PTEs in soils. In comparison to other assays, the responses of the microbial sensor to Cu, Ni and Zn highlighted its relative sensitivity to PTE contamination. The use of luminescence marked microbial sensors complements the performance of rigorous analytical soil chemistry approaches. Their value in soil pollution should be considered a technique that should be interpreted alongside chemical analysis rather than an alternative as their performance in complex environmental matrixes is yet to be validated.

In this timely monograph, the author summarizes the rapidly growing body of knowledge regarding nickel by providing a balanced discussion of its harmful and beneficial effects. Coverage includes a history of nickel; the chemistry of nickel, descriptions of the four known enzymes which contain nickel; and nickel metabolism in microbes, plants, and animals. Taken as a whole, Dr. Hausinger's work will highlight key features of this important element and help define future research.

SOIL BIOREMEDIATION A practical guide to the environmentally sustainable bioremediation of soil Soil Bioremediation: An Approach Towards Sustainable Technology provides the first comprehensive discussion of sustainable and effective techniques for soil bioremediation involving microbes. Presenting established and updated research on emerging trends in bioremediation, this book provides contributions from both experimental and numerical researchers who provide reports on significant field trials. Soil Bioremediation instructs the reader on several different environmentally friendly bioremediation techniques, including: Bio-sorption Bio-augmentation Bio-stimulation Emphasizing molecular approaches and biosynthetic pathways of microbes, this one-of-a-kind reference focuses heavily on the role of microbes in the degradation and removal of xenobiotic substances from the environment and presents a unique management and conservation perspective in the field of environmental microbiology. Soil Bioremediation is perfect for undergraduate students in the fields of environmental science, microbiology, limnology, freshwater ecology and microbial biotechnology. It is also invaluable for researchers and scientists working in the areas of environmental science, environmental microbiology, and waste management.