Hamid Shahandeh

Plant screening for chromium phytoremediation.

ABSTRACT Thirty-six plant species of different agronomic importance, size, dry matter production, and tolerance to heavy metals were evaluated for Cr(III) and Cr(VI) uptake and accumulation as influenced by rate, form, source, and chelate application to a Cr-contaminated soil. There was a significant difference in the degree of tolerance, uptake, and accumulation of Cr among plant species. Sunflower (Helianthus annuus) was the least tolerant to Cr, and Bermudagrass (Cynodon dactylon) and switchgrass (Panicum virgatum) were the most tolerant. Indian mustard (Brassica juncea, cv 426308) and sunflower accumulated more Cr than other agricultural plant species. There was no inhibition of growth and little Cr accumulation in the presence of Cr(III) in soil, but most of the plant species that were treated with Cr(VI) hyperaccumulated Cr and died. EDTA chelate added to soil enhanced Cr(III) accumulation in some plants. The phytoremediation potential of the plant species tested was limited because Cr was accumulated in the plant roots and a high concentration in the shoots was toxic to plants. The difference in behavior between Cr(III) and Cr(VI) and their importance in soil and environment contamination should be the basis for remediation strategies. The authors acknowledge the support of the Amarillo National Resource Center for Plutonium, 600 South Tyler, Amarillo, TX 79101 under agreement UTA96-0043.

Enhancement of cr(lll) phytoaccumulation

Abstract Chromium (III) accumulation in high biomass agricultural crops, sunflower (Helianthus annum) and Indian mustard (Brassica juncea) was studied using four soils (pH 4.6 to 7.6) contaminated with different rates of CrCl3.6H2O in the presence of synthetic chelate and organic acids. Chromium is essential for normal glucose metabolism in humans and animals, but its contamination and recovery from soils is of environmental concern. Adding ethylenediaminetetraacetic acid (EDTA), citric acid, or oxalic acid to Cr(III)‐contaminated soils significantly increased Cr concentration in plant shoots and roots. Adding Cr(III) complexes of EDTA, citric acid, and oxalic acid to soils dramatically increased (>200‐fold) Cr concentration in shoots and roots. Plant growth was severely decreased but was dependent on soil type, chelate rate, form, and time of chelate application. Chelates and organic acids enhanced Cr(III) accumulation, but its toxic effects were not avoided. Chromium(III) complexes were as toxic to plants as Cr(VI). The phytoaccumulation and recovery of Cr(III) from soils were limited and depended on soil type.

Nutrient Partitioning and Carbon and Nitrogen Mineralization of Switchgrass Plant Parts

Switchgrass (Panicum virgatum L.) is a native warm-season (C4) grass that has the potential to be used as a bioenergy crop and reduce increases in atmospheric carbon dioxide (CO2). Continuous production and removal of switchgrass, however, may deplete soil fertility. A strategy of returning plant components higher in nutrients to the field during harvest may help maintain soil fertility. In this study, nutrient partitioning in switchgrass parts over time and their C and N mineralization patterns in soil were determined. Switchgrass (cv. Alamo) was harvested on a biweekly schedule from June to October, with plants from each harvest separated into six parts (top, middle, and bottom leaves and stems) for mineral and fiber analysis. Plant materials from three harvests were used in an incubation study to determine effects of plant component, age, and composition on carbon (C) and nitrogen (N) mineralization. Results indicated that a strategy of returning specific plant parts to the field would not substantially conserve soil nutrients without proportionally decreasing materials available for bioenergy production. Structural components (cell wall and cellulose) were dominant factors affecting the quantity of C mineralized. Approximately 50% of C added as switchgrass was mineralized after 100 days of incubation. Soil N immobilization was observed in all switchgrass plant part treatments.

Evaluation of soil phosphorus tests for flooded rice soils under oxidized and reduced soil conditions

Abstract Soil tests have had limited success in predicting the response of rice (Oryza saliva, L.) to phosphorus (P) fertilizer. Phosphorus soil test methods have been developed under oxidized conditions without any consideration of changes in available P due to flooding of rice soils. To determine the potential of various P test to predict P availability in flooded soils 28 rice soils were incubated under oxidized and reduced soil conditions and extracted for P with Bray 1, Olsen, ammonium acetate‐ethylenediaminetetraacetic acid (AA‐EDTA) (Texas A&M test), resin, and water. Phosphorus response experiments were conducted on 19 soils in the greenhouse and eight soils under field conditions. Soil extractable P, yield, and plant P were determined. Reducing conditions increased the amount of P removed by AA‐EDTA and Bray 1 soil test methods. AA‐EDTA and Bray 1‐extractable soil P were highly correlated. Resin extracted the highest amount of P under oxidized conditions. The AA‐EDTA soil test method overestimate...

Factors Affecting Mehlich III Soil Test Methodology for Extractable P

ABSTRACT Agronomic and environmental testing laboratories in Texas and elsewhere have adopted Mehlich III (M3) as their official soil test phosphorus (P) methodology. However, M3-P data could be skewed due to non-homogenous soil samples or failure to follow standard protocol which could influence recommendations or restrictions. Twelve agricultural soils with a wide range of properties were collected from across Texas. Exhaustive efforts via multiple methods were made to prepare homogeneous representative soil samples. The standard M3 protocol selected was a 2 g weighed soil sample placed in a 148 ml disposable plastic cup, using a 1:10 soil:M3 solution ratio, shaken on a 200 rpm orbital shaker with a 2.5 cm throw for exactly 5 min, and filtered through Whatman No. 2 filter paper. The standard protocol was compared with nine different protocol variations with variables including soil weighing versus scooping, scooping repeatability of different technicians, soil sample weight, shaking type, speed and time, different filter papers, and varying soil:extractant ratios. Extent of soil pulverization on M3-P results was also evaluated. Tests were performed in four replications for all protocols to assess effects on M3-extractable soil P. Percent recovery of soil during grinding had no effect on M3-extractable P. Little difference in M3-extractable P was observed between scooping and weighing of 2 g soil samples. Shaker type had no effect on extractable P in soils with low clay contents, however, increasing shaking speed and using an orbital shaker resulted in higher extractable P, especially in clayey soils. Both Whatman No. 1 and 2 filter papers were found suitable for M3-P analyses. Different soil:extractant ratios resulted in a highly significant influence on the amount of M3-P extracted. However, when ratios were maintained between 1:9 and 1:11, few differences in extractable P were observed. Using sample weights below 3 g did not significantly alter precision or accuracy of results. However, technician variation in scooping of 2 or 5 g soil samples resulted in significant differences in M3-P.

Linear and Cyclophosphates as Sources of Phosphorus for Corn

Abstract Cyclophosphates are not adsorbed by soil constituents and can be mobile in the soil profile. Mobile phosphorus (P) sources are of interest in soil science and for agronomic practices. Cyclotri (Na3P3O9; C3P), and cyclotetraphosphate (Na4P4O10; C4P) were compared to linear, ortho‐, pyro‐, and tripolyphosphate in four soils with different chemical, physical, and biological properties to determine their mobility and availability to corn (Zea mays, L.) in laboratory and greenhouse experiments. Cyclophosphate (C3P and C4P) hydrolysis products were evaluated by ion chromatography after incubating for 6 to 192 h with 100 and 200 µg P g−1 soil. Phosphorus distribution and mobility, and plant availability and uptake with time, were determined in 45‐cm columns for four soils. Cyclophosphates sorbed less and moved deeper in all soils compared to the linear phosphates. The results showed that after 24 h a large proportion of cyclophosphates (34% of C3P and 37% of C4P) remained unhydrolyzed in Falba sandy acid soil. Split application of C3P and C4P at planting and at booting stage increased corn yield in sandy acid soil. Results of this experiment suggest that P deficiency after plant establishment can be corrected with cyclophosphates in soils with a low potential for cyclo‐P hydrolysis.

Improving of seed quality of black seed (Nigella sativa L.) by increasing seed phosphorus content in a calcareous soil

ABSTRACT Phosphorus (P) sufficiency during seed formation and development can affect the quality of seeds production. For increasing P content of black seed (Nigella sativa) in a calcareous soil, series of experiments were conducted in completely randomized factorial design with 4 replications at the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, in 2012 and 2013. The combinations of vermicompost (V), sulfur (S), and Thiobacillus bacteria (T) were mixed with a calcareous soil fertilized with 0, 30 and 60 kg P ha−1 in pots and incubated for 63 days. At the end of incubation period, black seeds were sown in the pots and plants were grown to maturity. Results showed that S+T and V treatments were significantly increased soil available P, emergence, plant P content, seed yield and vigor of the seeds production. There were positive relationship between soil and plant P concentration with the quality of seeds production.