Soil testing for heavy metals
Soil testing for metal contaminants is a continually evolving process aimed at improving the assessment of environmental and human health hazards associated with heavy metals in soils and plants. A number of challenges present themselves before accurate, reliable and precise contaminant hazard assessment criteria for soils and plants can be made. These include: sampling, extraction and analytical obstacles associated with the determination of trace levels of metals in environmental media; quality assurance and quality control issues associated with both extraction and analytical procedures (especially for metals where non‐compliance with regulatory standards may be penalised); and confounding environmental effects (e.g. rooting depth, soil salinity, Eh, pH, plant species, metal species) which limit the usefulness of the relationship between the current tests and actual hazards. These difficulties have combined to produce soil tests for heavy metals often poorly correlated with hazardwhether this be crop uptake of a contaminant (e.g. Cd), or the adverse effects of metals or metalloids on human or environmental health (e.g. As, Cr, Cu, Hg, Ni, Se, Pb, Zn). Assessment of an “available” fraction of a particular soil nutrient is the accepted norm of soil testing for crop nutrition. In many countries, assessment of metal hazard is still inappropriately based on the total soil metal concentration, despite increasing recognition that the concept of elemental availability is just as relevant for environmental hazard as for crop nutrition. Tests that aim to assess metal “bioavailability” are now gaining widespread acceptance by regulators as a means to characterise hazards from contaminants in soil.
 Soil Testing
Most agricultural soils in the virgin state contained some accumulation of nitrogen (N) from tree or grass residues. They were generally low in phosphorus (P) because the parent materials from which they were formed were low in this nutrient. Therefore, P is most frequently the first limiting nutrient when soils are first put into production. Use of chemical fertilizers began with use of P from organic and mineral sources in Europe and the USA. Phosphorus was used to increase production of food and fiber crops and also of legumes used in rotations to supply N. As yields increased from use of P fertilizers, legumes, and later N fertilizers, soils were depleted of other nutrients and a need for potassium (K) and some of the macro- and micronutrients was discovered. Economical production of most crops in developed countries is now dependent on use of fertilizers. Choice of the most profitable rates of the nutrients that may limit yields cannot be made by farmers without a research base that has been developed by agricultural experiment stations.
 Soil Testing to Predict Phosphorus Leaching
Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that had a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water‐soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2–P), iron‐strip phosphorus (FeO‐P), and Mehlich‐1 and Mehlich‐3 extractable P, Al, and Fe. The Mehlich‐3 P saturation ratio (M3‐PSR) was calculated as the molar ratio of Mehlich‐3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2–P, and FeO‐P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich‐1 P, Mehlich‐3 P, and the M3‐PSR), although the M3‐PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich‐3 P and M3‐PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.
 Bacillus thuringiensis Strains Isolated from Agricultural Soils in Mali Tested for Their Potentiality on Plant Growth Promoting Traits
Aims: To screen of the multiple plant growth promoting activities of some Bacillus thuringiensis strains isolated from Malian Agricultural soils and evaluate their ability to improve maize seed germination and seedling vigor in vitro.
Study Design: Strains of Bacillus thuringiensis (Bt) used in this study belong to collection of the Laboratory of Research in Microbiology and Microbial Biotechnology (LaboREM-Biotech) isolated from different agricultural soils of Mali.
Methodology: Different tests, namely: Phosphate solubilization, Siderophore production, Indol acetic acid cellulase and chitinase production tests were performed to confirm the PGP characteristic of the insecticidal B. thuringiensis strains screened. In vitro test was performed in the laboratory to confirm the capacity of these bacteria to enhance maize germination and seedling vigor.
Results: All tested Bacillus strains solubilize efficiently insoluble phosphate, but BtI4″ showed the highest clearance zone around its colony. In this study, except in BtI4’, the siderophore production was significantly elevated in the other Bt strains tested. Only BtD5 was able to produce Indol acetic acid. Contrary, except BtD5, all the isolates produce chitinase and cellulase. Exept IAA, the isolate BtI4″ produce all the tested compounds and showed the highest % seed germination and seedling vigor.
Conclusion: In the current study, plant growth promotion analysis of three B. thuringiensis strains from Malian agricultural soils were assessed in relation with maize seed germination and seedling vigor. These tested Bt strains showed several plant growth-promoting characteristics. These activities may allow the use of these isolates for plant growth promotion. Future work will address the applications of the selected bacteria in biocontrol and plant growth promotion. Insect pest biocontrol, enhancement of plant nutrition and production of phytohormon are the mechanisms involved.
 Prediction of Unsaturated Hydraulic Conductivity of Agricultural Soils Using Artificial Neural Network and c#
Aims: The objective of this study was to develop an artificial neural network model and interactive application using C# application to predict unsaturated hydraulic conductivity of soil.
Study Design: The actual measurements of unsaturated hydraulic conductivity of soil were obtained using the Mini Disk Infiltrometer (Decagon Devices, Inc.).
Place and Duration of Study: The study was conducted in laboratory located in Community College, Huraimla, Shaqra University, Saudi Arabia during March-April 2015.
Methodology: The experiments were conducted using water having electric conductivity of 2.26 dS/m and sodium adsorption ratio of 4.8. Unsaturated hydraulic conductivity of different soil textures (sand, sandy loam, loam and loamy sand) was determined at suction of -6 cm using Mini Disk Infiltrometer. The soil samples were taken from depth of 0-20 cm and repacked in a plastic 1000 cm3 container.
Results: The predicted unsaturated hydraulic conductivity of soils compared favorably with the actual measurements in testing stage, however, mean relative error was 4.184% and coefficient of determination (R2) was 0.9979. In general, artificial neural network model gave considerable results but more data is still necessary. The main equations for C# application were obtained from the trained artificial neural network model.
Conclusion: It could be concluded that the developed interactive application is recommended for estimating unsaturated hydraulic conductivity of agricultural soils within the range of the studied variables to provide data for water management in Saudi Arabia.
 McLaughlin, M.J., Zarcinas, B.A., Stevens, D.P. and Cook, N., 2000. Soil testing for heavy metals. Communications in Soil Science and Plant Analysis, 31(11-14), pp.1661-1700.
 Cope, J.T. and Evans, C.E., 1958. Soil testing. In Advances in soil science (pp. 201-228). Springer, New York, NY.
 Maguire, R.O. and Sims, J.T., 2002. Soil testing to predict phosphorus leaching. Journal of environmental quality, 31(5), pp.1601-1609.
 Kassogué, A., Dicko, A.H., Traoré, D., Fané, R., Valicente, F.H. and Babana, A.H., 2016. Bacillus thuringiensis Strains Isolated from Agricultural Soils in Mali Tested for Their Potentiality on Plant Growth Promoting Traits. Microbiology Research Journal International, pp.1-7.
 Al-Sulaiman, M.A. and Aboukarima, A.M., 2016. Prediction of unsaturated hydraulic conductivity of agricultural soils using artificial neural network and c. Journal of Agriculture and Ecology Research International, pp.1-15.