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Effect of Balanced Fertilization on Arsenic and Other Heavy Metals Uptake in Rice and Other Crops

S M Imamul Huq
Bangladesh-Australia Centre for Environmental Research (BACER-DU), Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

J C Joardar
Bangladesh-Australia Centre for Environmental Research (BACER-DU) Department of Soil, Water and Environment, University of Dhaka, Dhaka-1000, Bangladesh.

Abstract/ Executive Summary:

Balanced fertilization of low land rice culture has not proven to be effective in avoiding arsenic accumulation. Accumulation of As has been found to be higher in BRRI dhan29 than in BRRI dhan28 grown under similar condition. The accumulation of a few heavy metals also indicated that balanced fertilization does not play any significant role in their accumulation. On the other hand, excess P over the required amount could help decrease accumulation of As in an upland crop of kangkong. When amaranthus was grown with balanced fertilizer, half that of balanced and one and a half times more than the balanced fertilizer, the balanced fertilizer could keep the accumulation of the heavy metals in the minimum. It seems that cropping system has a role to play in the accumulation of As and heavy metals when they are fertilized. The paper presents some findings in this regards.

Keywords: Fertilization, Arsenic, Heavy metals, Rice

Location: Bangladesh Department of Soil, Water and Environment, University of Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Rice, Fertilizer

Objectives:

To highlight the necessity and effect of balanced fertilization on plant quality particularly as it concerns accumulation of arsenic and a few heavy metals.

Methodology:

The area where groundwater As contamination has not been reported was sought. As such a farmer’s field in Dhamrai Thana near Dhaka, Bangladesh was selected for soil sampling. The georeference of the sampling site is 23^o54.776′ N and 90^o10.938′ E. The soil thus selected belongs to the Dhamrai soil series; general soil type is Non-Calcareous Grey Floodplain soil (GST No. 6); USDA soil taxonomy is Typic Andoaquept and FAO- UNESCO Legend is Chromi-Eutric Gley Sol. The bulk soil samples representing 0-15 cm depth from the surface were collected by composite soil sampling method as suggested by the soil survey staff of the United States Department of Agriculture (USDA 1951). The collected soil samples were air dried; visible roots and debris were removed from the soil samples and discarded. Then a portion of the larger and massive aggregates were broken by gently crushing them by a wooden hammer and were screened through a 0.5 mm stainless steel sieve. The sieve ed samples were then mixed thoroughly for making the composite sample. These soil samples were used for various laboratory analyses. The bulk soil samples were screened through a 2 mm sieve and used for pot experiment. Environment, University of Dhaka, Bangladesh. In one experiment, arsenic at the rates of 0, 10, 20 and 40 mg/kg soil was mixed with the soils before one week from sowing of the rice seeds. Clay pots of 5L sizes were used. The pots were filled with 5 kg of soil. The pots were arranged randomly in the net house. Two different varieties (BRRI dhan-28 and BRRI dhan-29) of rice seeds were collected from Bangladesh Rice Research Institute (BRRI). The other experiment was carried out with four imposed treatments of As at the rates of 0, 0.5, 1.0 and 2.0 mg As/L in irrigation water. In this experiment only BRRI dhan-28 was used. The soils used were sterilized in an autoclave (at 15 psi, 121? temperatures for 15 minutes) in batches of 5 kg. The pots were inoculated with a green and blue green algae cultivated in the laboratory. Treatments of arsenic were applied with irrigation water. Algal samples of 90 days aged were inoculated to each pot in equal amount (15 ml). The background level of As in soil was 1.6 mg/kg. This was taken as control. Sodium meta- arsenite was used as source of arsenic. All experiments were done in triplicates. The nutritional (N, P, K and S) requirement was calculated on the basis of “Soil Test Value Interpretation” as recommended by the Bangladesh Agriculture Research Council. This means that the soils were balanced fertilized. According to this recommendation the required amount of N, P, K and S for the given soil were met from the fertilizer sources urea, TSP, MOP and ZnSO₄ respectively. The whole of TSP, MOP, ZnSO₄ , and 1/3 of the urea fertilizer were applied at time of soil preparation. Rice seeds were dipped in water and kept over night and then kept 2 to 3 days in dark condition for germination. The germinated seeds were sown directly in pots and were allowed to grow. The pots were thinned to 3 plants after seedling were established. Of the rest 2/3 urea fertilizer, 1/3 was applied after 35 days from seed sowing and the final 1/3 was applied during the panicle initiation stage of rice plant. Various cultural operations were made whenever necessary. Weeds were removed manually. Different agronomic characters of the plants were observed during the growth period. Various physical, chemical and physiochemical properties of the soils were determined. Soil, plant and algae were analyzed for total arsenic by hydride generation atomic absorption spectrometry (HG-AAS). Other heavy metals were analyzed by atomic absorption spectrometry (AAS). Arsenic of the plant and algae samples was extracted with HNO₃ and of the soil with aquaregia solution. Certified reference materials were used through the digestion and analyzed as part of the quality assurance/quality control protocol. Reagent blanks and internal standards were used where appropriate to ensure accuracy and precision in the analysis of arsenic and other heavy metals. Each batch of 10 samples was accompanied with reference standard samples to ensure strict QA/QC procedures. The experimental data were statistically analyzed by using the common statistical software MINITAB 13.0. The amount of uptake (mg/100 plants) by different plant parts and the plant as a whole were calculated. The uptake was calculated using the concentration in dry matter and dry weight of plant parts and the result is expressed as mg/100 plants: Uptake = Concentration in dry matter × dry weight of plant part.

Source of Information: Bangladesh J. Agric. and Environ. 4: 177-191, Special Issue 2008

Article Link (Online Journal): http://www.ipipotash.org/udocs/SPECIAL_ISSUE_BJAE-2008.pdf#page=137

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It is apparent from the above observations that balanced fertilization in low land rice culture, though is necessary to keep the yield levels at optimum, can not avoid the accumulation of As and other heavy metals in them. On the other hand, upland crops like kangkong and amaranthus behave differently to balanced fertilization. Balanced fertilization can improve the crop nutrient quality vis-à-vis As and other heavy metal accumulation in them. Further research is underlined to investigate in depth of these phenomena in fields.

Knowledge Management: Journal