Influence of plant growth regulators and humic acid on the phytoremediation of lead by maize in a Pb-polluted calcareous soil

Phytoremediation is a cleanup technology for the removal of contaminants from polluted soils. The influences of humic acid (HA) and four plant growth regulators, i.e. gibberellic acid, salicylic acid, 3-indoleacetic acid, and 6-benzylaminopurine on the phytoremediation of Pb by maize were investigated in a pot trial on a Pb-contaminated soil. Foliar spray of 6-benzylaminopurine and salicylic acid significantly increased mean root dry matter but none of growth regulators had a significant effect on that of shoot. Addition of HA decreased root dry matter and had no significant effect on that of shoots. Application of all growth regulators except gibberellic acid significantly increased root Pb uptake. Application of salicylic acid significantly increased mean uptake efficiency and shoot Pb concentration and uptake. Although addition of HA significantly increased mean phytoextraction and translocation efficiencies, these responses were mainly attributed to the role of HA in the reduction of both root dry weight and Pb uptake, meaning that HA is not promising in Pb phytoremediation by maize. Among the four plant growth regulators evaluated, salicylic acid was the most effective in enhancing phytoremediation through phytostabilization of Pb.     

Improvement of biochar capability in Cr immobilization via modification with chitosan and hematite and inoculation with Pseudomonas putida

ABSTRACT

Modification of biochar using chitosan and hematite made the biochar product more effective for hexavalent chromium (Cr (VI)) reduction in contaminated soils. Release experiment was conducted to examine Cr (VI) reduction in different treatments (control, unmodified biochar and two modified biochars with chitosan or hematite). The results indicated that the application of all treatments significantly decreased the release rate of Cr in comparison to the control treatment. Chitosan-modified biochar application increased Cr (VI) reduction from 28.53% (biochar) to 46.23%. In the case of hematite-modified biochar, it increased Cr (VI) reduction from 28.55% (biochar) to 38.95%. Two kinetic equations including pseudo-first-order and pseudo-second-order models employed to describe the time-dependent Cr release data. Between the kinetic equations estimated, the pseudo-second order best fitted to experimental data. In the presence of Pseudomonas putida, cumulative Cr release rate decreased by 2.38 mg kg^?1 (50.29%) in hematite–biochar and 1.768 mg kg^?1 (39.73%) in unmodified biochar as compared with control (4.43 mg kg^?1). According to results reported herein, modification of biochar with chitosan or hematite is promising since made biochar more effective in removing Cr from Cr-polluted calcareous soils.     

Simulation of 1D surface and 2D subsurface water flow and nitrate transport in alternate and conventional furrow fertigation

Increasing water and fertilizer productivity stands as a relevant challenge for sustainable agriculture. Alternate furrow irrigation and surface fertigation have long been identified as water and fertilizer conserving techniques in agricultural lands. The objective of this study was to simulate water flow and fertilizer transport in the soil surface and in the soil profile for variable and fixed alternate furrow fertigation and for conventional furrow fertigation. An experimental data set was used to calibrate and validate two simulation models: a 1D surface fertigation model and the 2D subsurface water and solute transfer model HYDRUS-2D. Both models were combined to simulate the fertigation process in furrow irrigation. The surface fertigation model could successfully simulate runoff discharge and nitrate concentration for all irrigation treatments. Six soil hydraulic and solute transport parameters were inversely estimated using the Levenberg–Marquardt optimization technique. The outcome of this process calibrated HYDRUS-2D to the observed field data. HYDRUS-2D was run in validation mode, simulating water content and nitrate concentration in the soil profiles of the wet furrows, ridges and dry furrows at the upstream, middle and downstream parts of the experimental field. This model produced adequate agreement between measured and predicted soil water content and nitrate concentration. The combined model stands as a valuable tool to better design and manage fertigation in alternate and conventional furrow irrigation.     

Influence of zinc sulfate and municipal solid waste compost on chemical forms of zinc in calcareous soils

Zinc (Zn) is an essential micronutrient for crop growth. This metal can be found in chemical forms or fractions in the soil. The objective of this study was to investigate the distribution of Zn in special chemical forms using the sequential extraction method after treating eight calcareous soils by zinc sulfate and municipal solid waste (MSW) compost. Zn was separated in seven defined forms as exchangeable (Ex), carbonate (Car), organic (Om), manganese oxide bound (MnOX), amorphous iron oxide bound (FeAOX), crystalline iron oxide bound (FeCOX), and residual (Res). According to the results, the mean concentrations of Zn in chemical forms in untreated soils from higher to lower were 31.84, 8.13, 2.64, 2.57, 0.45, 0.39, and 0.16?mg?kg^?1 for the Res, FeCOX, Car, FeAOX, Om, MnOX, and Ex forms, respectively. The total applied Zn to the studied soils from both the sources of zinc sulfate and MSW compost after incubation for 30 days was converted to chemical forms in the following order: Car?>?Res?>?FeCOX?>?Om?>?FeAOX?>?MnOX?>?Ex. On average, 30.3% of total Zn from zinc sulfate and 28.8% of total Zn in the MSW compost were converted into the Car form. The high content of calcium carbonate (CaCO₃) in the studied soils is an important factor affecting the conversion of Zn forms, mostly in the Car form through the application of both the inorganic and the organic sources of Zn.     

Assessing environmental impacts of major vegetable crop production systems of East Azerbaijan province in Iran

In the present study, environmental effects of carrot, tomato, potato and onion production systems were evaluated using the quantitative indices of energy efficiency, global warming potential (GWP), economic indicators, pesticide risk (field environmental impact quotient – FEIQ), tillage impact (TI), fertilizer, land and water use efficiency, and the eco-efficiency index (ratio of gross production to environmental impact for GWP, FEIQ and TI). Data was collected from 110 farmers by survey to determine crop production in the region. The results showed that the energy index for the potato production system was the most efficient; however, the carrot production system was the best in terms of the economic and environmental indices of GWP, FEIQ and TI. For irrigation water productivity (IWP) and land production efficiency (LPE), the potato production system was superior. The carrot production system had the highest values for economic irrigation water productivity (EIWP), economic land production efficiency (ELPE) and phosphorous and potassium use efficiency. The tomato production system recorded the lowest nitrogen use and highest nitrogen use efficiency. It can be concluded that the onion production system was furthest from sustainability goals based on the aforesaid indices.