Evaluation of Humic Acid on Chromium Toxicity, Accumulation and Translocation in Lettuce (Lactuca sativa L. var. longifolia)

IntroductionChromium pollution of the soil due to natural processes or industrial activities such as metal refining, chrome plating, stainless-steel production, leather tanning, and chemical dye production is a globle environmental issue. Excessive soil Cr levels cause detrimental effects on plant physiological processes including photosynthesis, water relations and mineral nutrition as well as the growth of roots, stems and leaves, which may decrease the biomass and yield of plants. Currently, soil application of organic amendments particularly humic acid seems to be an effective procedure to enhance relative plant tolerance to Cr stress. Humic acids are complexes of heterogeneous poly electrolytes with abundant functional groups that act as a weak poly electrolytic acid. Their structures, the degree to which these functional groups are protonated or ionized and environmental conditions influence the interaction between HA and soil pollutants. The complex compounds form by interaction of HA and heavy metals that cannot be uptaken by plants. Humic acid may play a significant role in the mobility and uptake of Cr which leads to a significant increase in plant biomass and growth. The aim of this research was to investigate the ability of humic acid to reduce Cr uptake and translocation by lettuce (Lactuca sativa L.) from Cr-contaminated soil. Materials and MethodsThe present study through a greenhouse pot experiment was conducted in the greenhouse of Ferdowsi university of Mashhad. The experiment was arranged in a factorial manner in a randomized complete design with three replications and treatments consisted of 3 levels of Cr (0, 25, and 50 mg kg-1as K2Cr2O7) and 3 rates of HA (0, 5 and 10 %). The soil samples were dried at room temperature, ground and sieved with a 2-mm mesh screen for further analysis. The bioavailable concentrations of Cr in the soils were assessed by DTPA. Three lettuce seedlings were grown in each pot containing five air-dried soil and watered to a near field capacity with distilled water as needed. After 100 days plant tissues were harvested, carefully washed with deionized water and the leaf, stem and root parts separated. All of them were oven-dried at 65-75 °C to constant weight and the dry weight of lettuce tissue samples was recorded. To determine the Cr concentrations, the tissues were ground, passed through a 0.3-mm sieve and digested in di-acid mixture (HNO3:HClO4). Concentrations of Cr in the digested solutions and soil extractions were determined using an Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). Translocation factor (TF) is determined from the ratio of the concentration of Cr in the plant’s shoots compared to that in the plant’s roots. Bioaccumulation factor (BAF) was evaluated as defined as the accumulated concentration of Cr in plant divided by concentration to that in respective soil. A two-way analysis of variance was done by using a statistical package, JMP version 8.0. The differences between the treatments were determined using LSD multiple range tests at significance level of P ≤ 0.05 and P ≤ 0.001.Results and DiscussionThe results of the present study clearly demonstrate that all Cr treatments significantly reduced leaf, stem, shoot and root dry weights. In unamended soils, both Cr treatments alone reduced leaf, shoot, stem and root dry weights 83%, 101%, 207% and 65% (for Cr 25 mg kg-1) and 194%, 219%, 355% and 92% (for Cr 50 mg kg-1) respectively as compared to control. Using HA (5 and 10%) and Cr treatments (25 and 50 mg kg-1), showed that leaf, shoot, stem and root dry weights were significantly increased as compared to Cr contaminated control. The lowest values of these parameters were recorded in Cr treatments without addition of HA, whereas at each Cr level, the highest values of them were obtained with application of 10% HA. The Cr concentrations in shoot and root samples significantly were affected by adding HA and Cr levels in soil. It was observed that Cr contents in shoots and roots, transfer factor and bioaccumulation factor of shoots and roots significantly increased by increasing soil Cr levels. Moreover, HA application negatively affected Cr content in shoot compared to Cr treatment alone. The interaction of chromium and humic acid caused a significant decrease in the concentration of chromium in the aerial parts, the shoot accumulation factor and a significant increase in the concentration of chromium in the roots and consequently reduced translocation factor. The highest value of Cr in shoot (47.7 mg kg-1) was obtained in those plants grown in soil with addition of 50 mg kg-1 Cr alone, whereas at each Cr level the lowest value of Cr in shoot was found in those plants grown in soil with the application of 10% HA. HA application in soil increased Cr concentration in root compared with Cr contaminated control. The maximum Cr concentration in the root (367 mg kg-1) and root bioaccumulation factor (28.5) was obtained after exposure to 50 mg kg-1 Cr +10% HA treatment. Also, the regression models showed that the transfer factor and shoot bioaccumulation factor decreased significantly and linearly with increasing shoot dry weight. Moreover, the regression model of shoot dry weight and shoot bioaccumulation factor was able to predict traslocation factor and shoot bioaccumulation factor with Adjusted R2 = -0.78** and R2 = -0.93**, respectively. ConclusionResults demonstrated that Cr toxicity markedly reduced plant growth parameters for instance leaf, stem, shoot and root dry weight and enhanced the concentration of Cr in shoot and root as compared to control. Humic acid application in Cr contaminated soil induced increased plant biomass, root bioaccumulation factor, Cr contents in roots and reduced Cr concentration in leaves, translocation factor and shoot bioaccumulation factor. Therefore, the application of HA specially at higher dose (10%) seems to be a cost-effective and environmentally friendly method for the restriction of Cr accumulation and its transfer from contaminated soil to edible parts of lettuce, thus helping to enhance food security

Evaluating the effect of organic matter on soil quality score functions

Soil quality is important for evaluating the soil fertility and physical condition. Soil physical and chemical indicators should be regarded for determining the soil quality. This research was conducted to study the effect of organic matter on quantitative value of soil quality. Three level (15, 30, and 60 ton/ha) of different organic compounds including municipal waste compost, sewage sludge, cattle manure, and wheat straw to gether with control treatment in three replications were applied into loamy soil. The treated soils were kept for 6 months at 70% of field capacity moisture in greenhouse condition. Then soil quality determined based on non-linear score function by using of 14 physical and chemical indicators. The results showed that the score of control treatment was 52.7, which it belong to class 4, i.e. low quality. Addition of different organic matter into studied soil led to improve soil quality score and soil quality class was increased one to 2 degrees. Among the studied treatments, the highest score of soil quality was obtained in 60 ton/ha sewage sludge and 30 and 60 ton/ha compost. Also, addition the other organic treatments cause to increase the quantitative soil quality score in relation to control, and soil quality class increased one degree. Among the studied indicators, iron (Fe), Manganese (Mn), zinc (Zn) micro-nutrients, aeration porosity (AC), and mean weight diameter of aggregates (MWD) were the important limiting indictors in degrading the soil quality in control treatment, and applying the compost and sewage sludge increased their scores

Using satellite data for soil cation exchange capacity studies

This study was planned to examine the use of LandSat ETM+ images to develop a model for monitoring spatial variability of soil cation exchange capacity in a semi-arid area of Neyshaboor. 300 field data were collected from specific GPS registered points, 277 of which were error free, to be analysed in the soil laboratory.The statistical analysis showed that therewas a small R-Squared value, 0.17, when we used the whole data set. Visual interpretation of the graphs showed a trend among some of the data in the data set. Forty points were filtered based on the trends, and the statistical analysis was repeated for those data. It was discovered that the 40 series were more or less in the same environmental conditions; most of them were located in disturbed soils or abandoned lands with sparse vegetation cover. The soil was classified into high and medium salinity, with variable carbon (1.0 to 1.6%), heavy textured and with high silt and clay. Finally it was concluded that two different models could be fitted in the data based on their spatial dependency. The current models are able to explain spatial variability in almost 45 to 65% of the cases

Using satellite data for soil cation exchange capacity studies

This study was planned to examine the use of LandSat ETM+ images to develop a model for monitoring spatial variability of soil cation exchange capacity in a semi-arid area of Neyshaboor. 300 field data were collected from specific GPS registered points, 277 of which were error free, to be analysed in the soil laboratory.The statistical analysis showed that therewas a small R-Squared value, 0.17, when we used the whole data set. Visual interpretation of the graphs showed a trend among some of the data in the data set. Forty points were filtered based on the trends, and the statistical analysis was repeated for those data. It was discovered that the 40 series were more or less in the same environmental conditions; most of them were located in disturbed soils or abandoned lands with sparse vegetation cover. The soil was classified into high and medium salinity, with variable carbon (1.0 to 1.6%), heavy textured and with high silt and clay. Finally it was concluded that two different models could be fitted in the data based on their spatial dependency. The current models are able to explain spatial variability in almost 45 to 65% of the cases

Spatio-temporal Soil Quality Assessment under Crop Rotation Irrigated with Treated Urban Wastewater using Fuzzy Modelling

Quantifying soil quality is important for asses- sing soil management practices effects on spatial and temporal variability of soil quality at the field scale. We studied the pos- sibility of defining a simple and practical fuzzy soil quality index based on biological, chemical and physical indicators for assessing quality variations of soil irrigated with well water and treated urban wastewater during two experimental years. In this study 6 proper- ties considered as minimum data set were selected out of 18 soil properties as total data set using the principal component analysis. Treated urban wastewater use had greater impact on biological and chemical quality. The results showed that the studied minimum data set could be a suitable representative of total data set. Significant correlation between the fuzzy soil quality index and crop yield (R 2 = 0.72) indicated the index had high biological significance for studied area. Fuzzy soil quality index approach (R 2 = 0.99) could be effectively utilized as a tool leading to better understanding soil quality changes. This is a first trial of creation of a universal index of soil quality undertaken

Effect of Municipal Solid Waste Compost and Sewage Sludge on yield and Yield Components of Black Cumin (Nigella sativa L. )

Abstract In order to investigate the effect of municipal solid waste compost (MSWC) and sewage sludge (SS) on yield and yield components of black cumin (Nigella sativa L.) an experiment was conducted in greenhouse of Faculty of Agriculture, Ferdowsi University of Mashhad. Municipal solid waste compost at 0, 15, 30 ton/ha (C0, C15 and C30) and sewage sludge at 0, 15, 30 ton/ha (S0, S15 and S30) were used in a factorial experiment based on completely randomized design with three replications. Results showed that municipal solid waste compost and sewage sludge and their interaction effects had significant effects on plant height, number of capsule per plant, number of seeds per capsule, number of seeds per plant, seed yield, biomass and 1000 seed weight. Increasing of sewage sludge amount from 15 to 30 ton/ha increased all measured parameters. But with increasing of municipal solid waste compost from 15 to 30 ton/ha, plant height, number of capsule per plant, number of seeds per capsule, number of seeds per plant, seed yield, biomass and 1000 seed weight were decreased. Interaction effects of municipal solid waste compost and sewage sludge showed that yield and yield components in all treatments were increased with the exception of treatment that contained 30 ton/ha municipal solid waste and 0 ton/ha sewage sludge (C30S0). Use of high amounts of municipal solid waste compost (>15 ton/ha) had a detrimental effect on yield and yield components of black cumin. Keywords: Nigella sativa, Municipal solid waste compost, Sewage sludge, Yield and yield component

Spatio-temporal soil quality assessment under crop rotation irrigated with treated urban wastewater using fuzzy modelling

Quantifying soil quality is important for asses- sing soil management practices effects on spatial and temporal variability of soil quality at the field scale. We studied the pos- sibility of defining a simple and practical fuzzy soil quality index based on biological, chemical and physical indicators for assessing quality variations of soil irrigated with well water and treated urban wastewater during two experimental years. In this study 6 proper- ties considered as minimum data set were selected out of 18 soil properties as total data set using the principal component analysis. Treated urban wastewater use had greater impact on biological and chemical quality. The results showed that the studied minimum data set could be a suitable representative of total data set. Significant correlation between the fuzzy soil quality index and crop yield (R 2 = 0.72) indicated the index had high biological significance for studied area. Fuzzy soil quality index approach (R 2 = 0.99) could be effectively utilized as a tool leading to better understanding soil quality changes. This is a first trial of creation of a universal index of soil quality undertaken