Effects of co-composted cow manure and poultry litter on the extractability and bioavailability of trace metals from the contaminated soil irrigated with wastewater

It is generally recognized that agricultural soils accumulate toxic metals after long-term wastewater irrigation. The removal of trace metals (TMs) from the soil is not possible. Therefore, this study investigated the effects of the addition of manure on the extractability and bioavailability of TM from the contaminated soil after wastewater irrigation. Soils samples were treated with co-composted cow manure (CM) and poultry litter (PL) at 10 and 20 t ha (cid:1) 1 . The study showed that addition of manure enhanced fenugreek biomass and reduced TM uptake depending on the combination of composted manures used. TM concentrations in the fenugreek shoots varied in the order of Pb > Ni > Zn > Cu > Cd. A higher amount of manure mixture especially composted with the privet and cypress residues decreased the extractability of TM from the contaminated soil. Soils amended with PL reduced TM concentrations more than CM; this is also true for the plant uptake. The variation of TM in plants was positively associated with their concentrations in the soil and adversely related to the plant biomass. This study con ﬁ rmed that the combined use of composted manure with plant residues can be an effective addition for ameliorating the TM pollution in soils and crops.


INTRODUCTION
The benefits of treated wastewater reuse for integrated water resources management and its role for water cycle management and solving water scarcity issues have been emphasized (Kalavrouziotis et al. ). The metal pollution in soils and vegetation has become a significant environmental and ecological issue of the world (Satashiya ).
Wastewater irrigation, the disposal of solid waste, the application of sludge, vehicle emissions and industrial activities have been reported among major contributors of trace metals (TMs) in soil (Majeed et al. ) and impaired the quality and safety of food (Alghobar & Suresha ).
Edible crops in the Hattar industrial area of Pakistan were found to be accumulated with TMs, and these metals were present beyond permissible limit in agricultural soils (Irshad et al. ). Sarwar et al. () reported the importance of TM monitoring in the environment due to foodchain contamination.
Abdel-Shafy & Mansour () reported the successful remediation of contaminated soils using phytoremediation technology. However, the remediation of the soil contaminated particularly with TMs has also been reported a complicated phenomenon (Liu et al. ). TMs cannot be removed from soils, but can only be changed from one state to another oxidation state (Ullah et al. ). Plants are unable to uptake the total pool of metals that exist in the growth medium. The fraction of the metal which a plant can uptake and absorb is known as a bioavailable fraction.
The accumulation of TM in plant tissues depended on the type of plant species and the ability of different plants to uptake metals had been assessed by the uptake of plant and the transfer factor of metal ions from soil to plant (Abbaslou & Bakhtiari ). In soils and bio-waste, TMs exist in variable forms such as exchangeable metals, organic matter-associated metal, metals associated with secondary minerals, phosphates, carbonates and oxides, and ions present on the crystals of primary minerals (Theobald ).  ). However, metals from polluted soils and their bioavailability to a crop after the application of co-composted manures have not been well reported. Therefore, the current study was conducted to investigate the extraction of metals and the uptake response of fenugreek in the contaminated soil after discrete treatment with composted cow manure (CM) and poultry litter (PL) with privet and cypress residues.

MATERIALS AND METHODS
Polluted soil samples were collected (0-20 cm) randomly from 10 adjacent wastewater-irrigated fields of the Hattar area, District Haripur, Pakistan. Samples were air-dried, sieved and then kept in plastic bags. These samples were thoroughly mixed and analyzed for the physico-chemical properties (texture, total carbon, electrical conductivity (EC), pH and extractable TM). Total carbon content was measured by using a dry combustion method (Nelson & Sommers ). The pH of compost suspension with soil: water at the ratio of 1:5 was measured by using a pH meter (Model: HANNA HI 8520). The EC of the soil suspension was determined with an EC meter (Model: 4320 JENWAY). Soil texture was determined using a pipette method (Gee & Bauder ). Selected properties of soil are given in Table 1. Industrial wastewater samples collected from the drain (used for irrigation) were also analyzed for chemical properties (Table 1

Soil incubation
Polluted soil samples were amended with the addition of manure at two levels: 10 and 20 t ha À1 (based on 2 million kg soil per plow layer in ha). A 500 g sample of soil was weighed and mixed with manure samples. The experiment was a factorial combination of 2 × 2 × 3 × 2 (two manure types, two types of plant residues, three mixing ratios and two application rates) replicated three times arranged into a completely randomized design. The moisture content of the soil was kept at 30% in plastic buckets. Samples were incubated for 8 weeks at room temperature. Concentrations of extractable metals, namely lead (Pb), nickel (Ni), zinc (Zn), copper (Cu) and cadmium (Cd) in the manure-amended soils, were determined by a modified procedure of Amacher (), i.e., metals were extracted with 0.1 mol L À1 Mg(NO 3 ) 2 and shaken for 2 h at about 80 cycles/min. Soil weighing 5 g was extracted.
After extraction, the solution was centrifuged and filtered and finally used for the determination of TM concentrations using an atomic absorption spectrophotometer (AAS) (Model: Analyst 700, Perkin Elmer).

Greenhouse study
Fenugreek (Trigonella foenum-graecum) was grown in a greenhouse. For this purpose, plastic pots were filled with the contaminated soil (5 kg per pot). Soil samples were brought from the Hattar industrial estate area. The contaminated soil was treated with the above-composted manures.
An equal number of seeds was sown in each pot at a depth of 2 cm. After 1 week of germination, plants were

Parameters
Unit Present study (mean) NSDWQ-Pak US irrigation water quality Soil properties pH -9.20 ± 0.3 6.5-8.5 6.5-8.4 thinned to 20 seedlings per pot. A basal dose of nitrogen and phosphorus at the rate of 100 kg ha À1 in the form of urea and diammonium phosphate was applied to boost the initial plant growth. Experimental setup for the pot experiment consisted of the amended treatments as detailed above.
The experiment was a factorial combination of 2 × 2 × 3 × 2 (two manure types, two types of plant residues, three mixing ratios and two application rates) units. It was arranged into a randomized complete block design with three replications. Irrigation was applied according to the

Soil incubation
Soil samples contained higher concentrations of TM due to long-term wastewater irrigation (Table 1). Extractable TM concentrations in the soil varied as Pb > Ni > Cu > Cd > Zn. Results showed that the application of composted material to soil reduced the extractability of TM depending upon the type and ratio of composted manure applied (Table 2). TM concentration in soils reduced significantly as compost application rates increased and decreased as the amount of privet and cypress wastes in the compost increased. Mixing of soil with manure containing cypress residues reduced TM concentrations more than the composted material containing privet residues. PL combined with plant residues was found more effective in mitigating the concentrations of TM in soil than CM treatments.

Lead (Pb)
Soil samples treated with manure apparently reduced the concentration of Pb in the soil extract. Both CM and PM cocomposted with cypress reduced Pb concentration in the soil extract when compared with manure þ privet residues. At an application rate of 10 t ha À1 , the composted CM þ privet at the ratio of 1:2 reduced Pb by 12.5% as compared to CM (1:0), i.e., without plant residues. The soil treated with composted CM along with privet at the ratio of 1:2 obviously reduced Pb concentration by 21% than control soil. It was noticed that the composted CM and PM combined with

Nickel (Ni)
Significant changes in the Ni concentration of soil samples applied with composted CM and PM were observed (Table 2). A higher concentration of Ni was found (6.9 mg kg À1 ) in soil treated with CM samples without plant residues. Nickel concentration apparently decreased due to the addition of manure mixture with plant residues. For instance, composted CM with privet residues at the application of 10 t ha À1 showed the Ni concentration of 6.9, 6.6 and 5.7 mg kg À1 at the ratio of 1:0, 1:1 and 1:2, respectively. Nickel concentrations were 5.8 and 4.8 mg kg À1 in the soil treated with CM þ cypress residues at the ratio of 1:1 and 1:2, respectively.
Increasing the manure application rate also reduced more Ni concentration from the soil. Composted manure with plant waste relatively decreased the release of Ni than manure without plant waste. It has been reported that organic matter after a composting process supported binding sites in soil, which reduced TM uptake by plants (

Copper (Cu)
The concentration of Cu reduced in the amended soil according to the manure application (Table 2). Increasing the application rate of manure reduced more Cu concentration in the soil. The concentrations of Cu in soil treated with CM þ privet residues were 6.5, 5.0 and 3.9 mg kg À1 in 1:0, 1:1 and 1:2 ratios, respectively, at 10 t ha À1 . The

Cadmium (Cd)
Changes in the extractable Cd were observed when the soil was treated with CM and PL composted with or without plant residues (Table 2)

Zinc (Zn)
Reduction in Zn concentration was observed in the soil after the addition of manure (Table 2). In other words, composted manure with privet and cypress residues immobilized Zn in the soils. Zinc concentration in the soil decreased by 42.1% and 10.5% when treated with CM þ privet (1:2) and CM þ cypress residues, respectively, at 10 t ha À1 than CM without

pH and EC
The pH of the soil was higher with composted manure added with plant residues (Table 2). pH values of soil were higher in cypress þ CM/PL treatments than privet þ manure mixtures. Overall, the pH values of CM containing soil were higher than the PM-amended soil. The PL þ privet compost amended soil showed pH that ranged from 6.73 to 6.85, while pH values of soil were 6.82 and 6.86 after amendments with 1:1 and 1:2 mixture of PL þ cypress residues. It showed that the pH of the soil slightly increased due to the addition of composted CM with plant residues.
Soil higher pH was reported after the application of composted animal manures (Scharenbroch ). Loper et al.
() also reported soil lower pH after compost amendment. Incubating the soil with different animal manures resulted an increased in soil pH (Roy & Kashem ).
The EC of soil enhanced with a higher application rate of composted manure (

Plant growth and TM concentration
The application of composted manure significantly (P <      The BAC for TM also showed that TM accumulation in fenugreek plants was ameliorated with the addition of  manure after the co-composting process (Table 3). The regression analysis showed that shoot Pb concentration was related to the Pb concentration of soil by the following equations: y ¼ 0.28, x þ 1.08 and R 2 ¼ 0.76. Nickel concentration in fenugreek shoots was related to the Ni concentration of soil by the equations: y ¼ 0.49, x À 0.55 and R 2 ¼ 0.72 (Figures 9 and 10). The higher values of