Asian Journal of Soil Science and Plant Nutrition

Heavy metals and phytochemicals were investigated in some selected vegetables grown at Kalambaina area of Sokoto. The levels of heavy metals and phytochemicals were analyzed using Atomic Absorption Spectrometric (AAS) and standard analytical procedures respectively. The concentration of heavy metals were found to be higher in Amarantus specie. Pb; (1.330 ± 0.0014 mg/kg),   Ni; (0.280 ± 0.0011 mg/kg), Cr; (0.110 ± 0.0012 mg/kg), Cd; (0.003 ± 0.0001 mg/kg) and spinacea oleracea Pb; (0.220 ± 0.0011 mg/kg), Ni; (0.020 ± 0.0002 mg/kg), Cr; (0.100 ± 0.0011 mg/kg) Cd; (0.010 ± 0.0001 mg/kg), however, low concentrations were observed in Allium cepa Pb; (0.080 ± 0.0011 mg/kg), Ni; (0.003 ± 0.0001 mg/kg), Cr; (0.130 ± 0.0020 mg/kg), Cd; (0.005 ± 0.0002 mg/kg). The results of the study for the three (3) vegetables revealed the concentrations of the heavy metals are  within the World Health Organization (WHO) and Standard Organization of Nigeria (SON) safe limits guidelines with the exception of Cr and Pb. Phytochemical screening of methanolic extracts of the vegetables showed the presence of alkaloids, saponins, tannins, flavonoids, phenolics and terpenoids. Therefore, this study revealed that the vegetables can be use as efficient source of secondary metabolites.

Due to good water shortage, accumulation of heavy metals in soil under irrigation with wastewater can cause serious hygienic and environmental problems. However, the availability of metal ions in contaminated soils can be reduced by addition of organic and inorganic amendments. In this study, columns experiment was conducted during the winter season of 2016/2017 to evaluate the effect of applying some organic amendments such as humic acid, rabbit manure and biochar on the availability and forms of some heavy metals (i.e. Zn, Cu, Pb and Ni) in contaminated soil of Abo Rawash area irrigated with wastewater and their impact on growing wheat plants as a strategic crop. The forms of the concerned heavy metals in soil were determined by the sequential extraction method. Results showed that treating the soil with such amendments decreased heavy metals concentrations in soil. The amount of the studied heavy metals was distributed among the different soil fractions following the descending order: organically bound> residual fraction> Fe-Mn oxides bound> carbonate associated> exchangeable.

The dry weight of whole plant, weight of 1000 grains and NPK concentrations in wheat plants were significantly increased due to application of these amendments especially humic acid compared to the control. In addition, heavy metals concentrations were significantly decreased in wheat plants under irrigation with wastewater, with the highest effect for humic acid treatment. These results went hand by hand with the effect of humic acid on increasing heavy metals solubility and leachability in soil, and increasing heavy metals concentrations values in the collected drainage water from soil columns under investigation.

This study determined the heavy metal concentrations of contaminated stream water and assessed the heavy metal contents of pre- and post-cropped sterilized soil. It also determined the the heavy metal uptake of the S. lycopersicum plant. This was with a view to assessing the potential of Pseudomonas aeruginosa and Trichoderma harzianum for transforming heavy metals in heavy metal contaminated stream water. Experimental pots containing 3000 g of sterilized soil was used for this experiment whereby 60 sample pots were used with various treatments in this study. Solanum lycopersicum seeds were raised in the nursery for a period of 3 weeks and treatments applied just before transplanting into the experimental pots. The plants were left for a week so as to be established properly and overcome transplanting shock before watering with the contaminated stream water. Heavy metal analysis using Atomic Absorption Spectroscopy (AAS) method was carried out on the contaminated stream water to determine the amount of heavy metal in the stream water before the commencement of the experiment. The contaminated stream water was applied to the pots in measured quantities; 0, 5 and 10%. Pre and post soil heavy metal analysis were carried out on the soil samples. At harvest, plant tissues were analysed for heavy metals using AAS method. The results showed that heavy metals were present in high concentration in the stream water sample. The values of the heavy metals in the stream water sample used for watering were Iron – 138.15 mg/L, Zinc – 68.4 mg/L, Lead – 7.89 mg/L and Copper – 8.98 mg/L. Heavy metal analysis of the soil and all the treatments revealed that treatments with P. aeruginosa inoculation had the lowest level of Iron, Copper, Zinc and Lead followed by treatments inoculated with T. harzianum. The study concluded that the use of contaminated stream water for irrigation could be a potential source of heavy metals in tomato. However, inoculation of microorganisms for the treatment of the heavy metal contaminated sites was effective Phytoremediation,for increased health, growth and yield of tomato fruits.

Sulfur (S) deficiency is becoming one of the soil health challenges in the Ethiopian crop production systems. However, visual identification of its deficiency, especially in cereals is difficult, because the symptoms are nearly identical with those of nitrogen. Hence, deficiency indicators are necessary for balancing fertilizer use. For this purpose, 18 sulfur response experiments conducted in 2012-14 were considered. Major aim was identifying more suitable indices of S supply and setting their critical thresholds. The treatments were: absolute control (CK); nitrogen (N); nitrogen and sulfur (NS); and nitrogen, phosphorus and sulfur (NPS). The levels of nutrients tested were: S (0 and 20 kg S/ha), P (0 and 20 kg P/ha) and N (0 and 69 kg N/ha) in the form of gypsum, triple-super phosphate (TSP) and urea, respectively. Treatments were arranged in randomized complete block (RCB) design and replicated 3 times. In the study, from the selected indices: N/S-ratio and S concentration in wheat at booting showed better sensitivity as indicators of S deficiency than the organic carbon (OC) in native soils. Critical levels (CLs) were set at 90% relative yield (RY), using the Cate and Nelson model, and estimated to be 16.5:1(N/S-ratio), and 0.16% (S concentration); and 2.07% (for the soil OC). Therefore, sulfur responsive soils/treatments in wheat at booting can be separated from un-responsive ones, in which case much sulfur response is expected for sites/treatments with N/S-ratio >16.5:1; TS <0.16%; and the soil OC <2.07%. This study further affirmed that, plant analysis could be used as a better tool for assessing sulfur deficiency in wheat than soil analysis. Thus, the results could be used as provisional recommendations for wheat growing and as the basis for further sulfur research in Ethiopia. However, differences between the estimated values and those reported in literature have been observed. Therefore, the follow-up research should focus in identifying/standardizing a more reliable index of S deficiency and CLs, through a more reliable research condition.

Field experiments were conducted to determine the effects of micronutrients application on soil properties of sapota (Achras sapota L.) cv. Kalipatti at Kittur Rani Chennamma College of Horticulture, Arabhavi, India, during the year 2015-2016. Zinc and iron sulphates were used for soil and foliar application, whereas the boron in the form of sodium tetraborate (Jai bore) for soil and solu-bore for foliar application were used. The results revealed that foliar application of 0.5% ZnSO₄+ 0.5% FeSO₄ + 0.3% B lead to maximum utilization of N, P and K by the plant which resulted into reduced concentration of (123.50 kg ha^-1), (11.59 kg ha^-1) and (103.50 kg ha^-1) as well as exchangeable micronutrient content boron (1.70 mg/kg) in the soil.