Posted: June 17th, 2015

Phytoremediation of two calcareous soils contaminated with cadmium by Maize and sunflower

Material and method

A greenhouse experiment was designed in a randomized complete block design replicated three times during April to July 2014 inside the Faculty of agriculture and Forestry – university of Duhok – Kurdistan region – Iraq to evaluate phytoremediation of Cd in Cd-pollutes soils.

Soil samples of 0 – 30 cm depth were taken from two locations differing in their CaCO₃ content. The First sample was taken from the field of the Faculty of Agriculture and Forestry –Duhok University with (10.87 % CaCO3), and the second sample was taken from Malta inside the field of agricultural researches directory with (25.23 % CaCO3) in Duhok province.

The following parameters of the two soils were determined prior to the experiment:-

 

parameters	Measuring units	Soil from Sumail	Soil from Malta
PH	1:2 extract	7.75	7.8
EC	Mmohs.cm-1	0.434	0.559
Ca+2	Soluble cations (meq L-1)	2.1	3.2
Mg+2		0.2	0.4
Na+		0.73	0.87
K+		0.11	0.15
TN	g kg-1	1.1
Cd+2	mg kg-1	0.35	0.15
P		4.84	4.80
CO3=	Soluble anions (meq L-1)	Trace	trace
HCO3–		1.8	2.2
CL–		2.7	2.1
SO4=
CaCO3	g kg-1	108.7	252.3
Active CaCO3		98.6	218.7
CEC	Cmol kg-1	29.7	29.1
O.M	g kg-1	10.3	9.5
Sand		64	34
Silt		342	385
Clay		594	581
Soil texture		Clay soil	Clay soil
Bulk density	g cm3-	1.21	1.18
Field capacity	%	36.86	36.34

 

Soil samples were air-dried, passed through a 4 mm sieve, mixed uniformly and were filled in polyethylene pots of   cm height and   cm diameter, each of 6 kg soil capacity after it had been polluted with Cd.

Cd chloride was used in order to create Cd contamination in soils of the pots. Cd in soils includes the following treatments:-

1. Soil without Cd (T1) as control.
2. Soil contaminated with 50 mg/kg Cd (T2).
3. Soil contaminated with 100 mg/kg Cd (T3).
4. Soil contaminated with 200 mg/kg Cd (T4).
5. Soil contaminated with 300 mg/kg Cd (T5).
6. Soil contaminated with 400 mg/kg Cd (T6).

Each 6 kg of soil was spread over a plastic sheet on the ground and 250 ml of CdCl₂ solution containing one of the above concentrations was sprinkled on the soil, in this process good homogeneity in contamination process and contamination period was achieved.

Sunflower peredovic (Helianthus annuus) and Zea mays symiami (Zea mays L.) were used as a test plants, five seeds of each plant were sown in each pot on 23/4/2014 and two plants were left in each pot after germination. The water content was adjusted to 75% of the available water during the experiment period. NPK were applied at a rate of 100 kg per donum to the plant to have optimal conditions for plant growth and reaching suitable limits of phytoremediation. Pots were placed in greenhouse covered with polyethylene to avoid the rainfall for 30 days then placed outside the greenhouse till the end of the experiment.

After 60 days from sowing, the stem gently was cut just above the soil surface and roots were collected, washed carefully with tab water and twice with distilled water to eliminate dust and dirt, and then dried at 65.7C°. After recording the samples dry weight, they were milled with mixer of steel blade and concentration of Cd was measured by wet digestion method with sulfuric acid and Hydrogen peroxide acid using atomic absorption.

Translocation factor indicating hyper accumulation of Cd in plant parts was obtained by dividing Cd concentration in shoots by its concentration in the roots.

Soil samples were also air dried, ground and pass a 2 mm sieve for analysis. 10 g of air dried soil was taken and treated with 20 ml of extracting reagent (AB – DTPA) for extraction of Cd. The contents were shaken for 15 min. and filtrate through whatman No. 42 and analyzed Cd.

 

Laboratory analysis:-

The physical and chemical analyses were done on the 2mm sieving samples.

Soil texture:-

The texture was measured by the hydrometer using the method described by Ryan et al. (2001).

Soil PH:-

The pH of 2:1 extract was measured using a (HI 9023) PH- meter as mentioned by Jackson (1958).

EC (mmohs.cm^-1):-

An EC of 2:1 extract was determined using EC meter (HI 9635) EC- meter according to Wilcox (1950).

Bulk density:-

The Bulk density was determined by core method according to Black (1980).

Field capacity:-

The F.C of soils was measured by equation mentioned by Karim, (1999) as follows:-

F.C =13.28 + (0.397 * % clay)

Organic matter:-

Soil organic matter was determined according to the description of Allison (1965).by the Walkly and Black method using K2Cr2O7 (1N).

 

Available Nitrogen:-

The measurement of available nitrogen was performed by Kjeldahl method following the procedure described by Ryan et al, (2001).

 

Available Phosphate

Soil available phosphorous was determined spectrometrically by (Olsen’s method) according to the description of Rowell (1996), at 880 nm.

 

CEC (cation exchange capacity):-

CEC was measured by using ammonium acetate according to Hesse (1972).

Calcium Ca⁺² and Magnesium Mg⁺² ions:-

Determined by titrimetric methods using (0.01 N) EDTA according to Jackson (1973).

 

Sodium and potassium (Na⁺, K⁺):-

Were measured using flame photometer according to Toth et al. (1948) and Stanford and English (1949).

 

% CaCo3:-

The percentage of CaCO3 was determined using the calcimine method which described by Hesse (1972).

Active CaCO₃

Active calcium carbonate was determined according to Kozhekov and Yakovleva (1977).

 

Statistical analysis:-

The data has been arranged in the form of factorial experiments with randomized complete block design (RCBD). The effect of the studied treatments and their interactions on the parameters was analyzed by analysis of variance (ANOVA). Differences between means were performed according to Duncan’s multiple range tests at P-value <0.05.the statistical analysis was conducted by SAS 9.0 program.