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Effect of biochar on yield and heavy metals uptake in rice grown on soil amended with sewage sludge.

India has to produce 300 Mt of food grains by 2020 to feed growing population. The net cultivated land (142.5 M ha) is limited and pressure for production of food grains is increasing, therefore, maintenance of soil fertility is a prime issue for farmers. To achieve the above food demand, 45 million tonnes nutrients are required in which 35 Mt is estimated to be supplied by chemical fertilizer and remaining by organic sources (1). The present day agriculture is facing a problem of continuous decline in soil nutrients reserve and decrease in organic matter content of soil. This may be due to intensive cropping system coupled with limited application of FYM, green manure, vermicompost and crop residue in the field. Due to rapid urbanization and industrialization, a huge amount of inorganic and organic wastes are produced in which sewage sludge is one. In India, about 450 cities generate more than 17 x [10.sup.6] [m.sup.3] of raw sewage per day. With available treatment plants, production of sewage sludge is estimated to be around 1,200 tonnes per day, although there exists a potential to produce 4,000 tonnes of sludge per day (2). The nutrient potential of available sewage in India is estimated to be more than 3,50,000 tonnes N, 1,50,000 tonnes P and 2,00,000 tonnes K per year (3).

Sewage sludge and effluents from municipal origin are rich in organic matter and is a good source of plant nutrients (4). Sewage sludge and effluents are frequently disposed off on agricultural lands for irrigation/manures purposes that may prove beneficial because of its organic matter and nutrient content and harmful as it may contain high amount of heavy metals which may limit their long term use in agriculture. The heavy metals may be present in excess amount and prove either phytotoxic (e.g. Zn, Cu, Ni) or hazardous for human health (Cd, Cr, Pb, Hg). For reducing the effect of these metals in food web, the biochar can play a vital role. Biochar refers to a kind of charcoal made from biomass. Unlike charcoal made for fuel, biochar has properties which make it a valuable soil amendment for mitigation of negative effects of heavy metals by sorption (5). Biochar has been found to sorbs a variety of heavy metals, including lead (Pb), arsenic (As) and cadmium (Cd). The global production of biochar (black carbon) has been estimated to be between 50 and 270 Tg [yr.sup.-1], with as much as 80 % of this remaining as residues in the soil (6). Total of 9.5 billion tonnes of carbon could potentially be stored in soils by the year 2100 using a wide variety of biochar application programmes (7).

Rice (Oryza sativa L.) is one of the most important staple food crop for more than half of the world population, especially for south-eastern Asia, where 90% of the world production of rice is grown and consumed. Rice covers about 158.95 Mha areas in world with annual production of 685.01 Mt of grain with average productivity of 4.31 t [ha.sup.-1] globally (1).The country like India has biggest area under rice cultivation, as it is one of the principal food crops. In India, the rice crop occupies 44 million ha of land and produces about 104.32 million tones, which is second in the world after China. In view of increasing use of sewage sludge in crop production and associated potential risk of heavy metals uptake. The present investigation was taken up to study the effect of various levels of biochar on yield and uptake of heavy metals in rice grown soils amended with sewage sludge.

MATERIALS AND METHOD

The pot experiment was conducted on alluvial soil of Varanasi representing an Inceptisol (Typic U stochrept) during July to November 2013, in the net house of the Department of Soil Science and Agricultural Chemistry, Institute of Agriculture Sciences, Banaras Hindu University, Varanasi (U.P.). The experimental soil (0-15 cm) had pH 7.4, EC 0.22 dS [m.sup.-1], organic carbon 0.3 g [kg.sup.-1] and available N, P, K and S to the tune of 126, 18.51, 137.30 and 12.78 kg [ha.sup.-1], respectively. The DTPA-extractable micronutrients Fe, Cu, Zn and Mn in soil were 22.14, 2.25, 1.65 and 8.57 mg [kg.sup.-1] and heavy metals, Cd, Cr, Ni, and Pb were 0.752, 0.164, 2.03 and 0.087 mg [kg.sup.-1], respectively.

Biochar was obtained from a rice mill of village Kollana, Mirzapur (U.P.) where it is considered as a waste material coming form gasifire plant which utilize rice husk as fuel. Farmer of this district has established Rice mills as small scale industries. They burn rice husk under controlled supply of oxygen and obtained smokes are used to mix diesel to get smoke- diesel aerosol. Therefore, the fuel efficiency of diesel engine is increased. The remaining incomplete dark black material of rice husk is known as rice husk Biochar

The Biochar (figure-1, a) use as a heavy metal sorbed material had the colour 2.5 YR 2.5/0 (Black), Bulk density 0.40 (Mg [m.sup.-3]), porosity 72 % and WHC 218 %. The Biochar (BC) had the pH 9.5 ([H.sub.2]O), 9.4 (0.01M Ca[Cl.sub.2]) 1:2.5, 9.3 (0.01M Ca[Cl.sub.2]) 1:5, EC 2.56 (dS[m.sup.-1]), Ca & Mg 0.21 and Na 0.35 mg [kg.sup.-1] respectively (Table 2). The total amount of N, P, K was 0.10, 0.15, 0.20% and DTPA extractable metal was not detected. Six graded levels of biochar were taken i.e. 2.5, 5.0, 7.5, 10, 15, and 20 t [ha.sup.-1] which were equivalent to 11.20 g ([BC.sub.7.5]), 22.40 g ([BC.sub.5.0]), 33.60 g ([BC.sub.7.5]), 44.80 g ([BC.sub.10]), 67.20 g ([BC.sub.13]), and 89.60 g [pot.sup.-1] ([BC.sub.20]), respectively for 10 kg of soil.

The sewage sludge (SS) used as soil amendment had pH 7.2, EC 0.35 dS [m.sup.-1], organic C 8.13 %, total N, P, K and S content as 1.4, 1.3, 0.95 and 2.1%, respectively (Table 3). The DTPA-extractable Fe, Cu, Zn and Mn in SS were 49.56, 13.50, 15.24 and 21.47 mg [kg.sup.-1] and Cd, Cr, Ni and Pb content was 3.2, 4.9, 29.34 and 7.6 mg [kg.sup.-1], whereas total content was 32.2, 44.3, 54.6 and 28.4 mg [kg.sup.-1], respectively.

The constant dose of Sewage sludge (figure-1, b) was taken i.e. 30 t [ha.sup.-1] ([SS.sub.30]) which was equivalent to 131 g [pot.sup.-1]10 for kg of soil. This constant dose of sewage sludge was applied in treatment [T.sub.3] to [T.sub.9]. Required quantities of biochar, sewage sludge and fertilizer for 10 kg soil were calculated. The experiment was conducted in completely randomized block design taking rice as a test crop.

Biochar and Sewage Sludge were thoroughly mixed well with soil. Full dose of fertilizers (accept 1/2 dose Nitrogen) applied in solution through Urea, DAP, and MOP, as source of N, P, and K before transplanting of rice seedlings. Remaining 1/2 recommended dose nitrogen (RDN) fertilizer was applied in two split doses at tillering and flowering initiation stage. The detail of treatment combination is given in Table 1. The experiment was laid out in a completely randomized design with three replications taking rice cv. Swarna as test crop. Grain and straw yield [pot.sup.-1] were recorded after harvesting of crop.

The plants were harvested at maturity, washed sequentially with 0.2% detergent solution, 0.1 N HCl and finally with double distilled water. The plant material was dried at 60+2 [degrees]C for 48 h in a hot air oven. Dry plant tissues were finely ground and digested in a di-acid mixture (HN[O.sub.3]: HCl[O.sub.4] :: 3:1, v/v) and diluted. The content of Fe, Cu, Zn, Mn, Cd, Cr, Ni and Pb in the straw and grain digest was determined by using atomic absorption spectrophotometer (UNICAM-969). Similarly, biochar was also digested and content of Fe, Cu, Zn, Mn, Cd, Cr, Ni and Pb were determined by using atomic absorption spectrophotometer (UNICAM-969). Sewage sludge was also digested in di-acid and analyzed for P, K and total micronutrients (Fe, Cu, Mn, Zn) and heavy metals (Cd, Cr, Ni and Pb), however, for the determination of total N sludge was digested in concentrated [H.sub.2]S[O.sub.4]. The soil samples were analyzed for pH in 1:2.5 soil: water suspension; EC (dS[m.sup.-1]) organic carbon (8); DTPA-extractable Cd, Cr, Ni and Pb by methodusing Atomic Absorption spectrophotometer (AAS) (9).

RESULTS AND DISCUSSION

Grain Yield

The grain yield of rice (Table 4) increased significantly by applying sewage sludge along with biochar. The application of 100% RDF ([T.sub.2]) resulted in significantly higher grain yield by 23.49%, 35.05% and 2 time over [T.sub.3] ([SS.sub.30]), [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) and control ([T.sub.1]), respectively. The maximum grain yield was observed in [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) which was 8.5% higher over the treatment [T.sub.2] (100% RDF). Lowest grain yield (19.3 g [pot.sup.-1]) recorded in control which was two times lower than the [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) and [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]). Increase in grain yield of rice with application of sewage sludge (10). The bean yield increased by 46% and biomass production by 3 9% over the control at 60 g [kg.sup.-1] biochar (11). A significant increase in straw and grain yields of rice with application of sewage sludge (12).

Straw Yield

The straw yield of rice (Table 4) ranged between 76.1 to 143 g [pot.sup.-1]. The application of 100% RDF resulted in significantly higher straw yield by 87.91% than the straw yield obtained from [T.sub.1] (control). The maximum straw yield (143 g [pot.sup.-1]) was recorded in the [T.sub.2] (100% RDF) which was higher than [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) by 7.5% [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) by 9.1%, [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5], [SS.sub.30] [RN.sub.50]) by 13.4%. The treatment [T.sub.3] ([SS.sub.30]) was 66.8 % higher over the control ([T.sub.1]) and 12.5 % lower from the [T.sub.2] (100% RDF). Significant increase in straw yield might be due to the availability of all essential elements to the rice crop in sufficient amount by the sewage sludge application. A significant increase in straw yield of wheat and rice was also reported (13).

Test Weight

The test weight of rice (Table 4) ranged from 16.5 to 22.2 g 1000 [grains.sup.-1] and it increased significantly with application of graded level of biochar and constant level of sewage sludge. The maximum test weight (22.2 g) was recorded with treatment [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) which was 34.54 % higher over control ([T.sub.3]) followed by 33.3 % [T.sub.2] (100% RDF). Minimum test weight (16.50g) was recorded in control ([T.sub.3]). The increase in test weight might be the result of improvement in the soil fertility due to sewage sludge application. Similar findings also reported (14). The higher thousands seed weight of dry been grown at 2, 4, and 6 kg [m.sup.2] sewage sludge amendment rates as compared to unamended soil (15). A significant increase in test weight, grain and straw yield of rice crop with conjoint application of sewage sludge and fertilizer (13).

Harvest Index

The highest harvest index (Table 4) was registered (34.5%) in [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) which was 8.02% higher over 100% RDF ([T.sub.2]). The harvest index ranged from 20.2 to 34.9% and the treatment [T.sub.3] ([SS.sub.30]), [T.sub.4]([BC.sub.7.5] [SS.sub.30] [T.sub.5] ([BC.sub.5] [SS.sub.30] [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]), [T.sub.7] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) were found statistically at par to each other. The minimum harvest index was recorded in the control ([T.sub.1]), which decreased 78.37% from the [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]).

Heavy Metals Concentration and Heavy Metals Uptake

Cadmium content in grain and straw

The data pertaining to Cd content in grain (Table 5) showed a significant effect with graded application of biochar and constant level of sewage sludge. The maximum (1.59 mg [kg.sup.-1]) was recorded in[T.sub.3] ([SS.sub.30]) which was 4 times higher over the [T.sub.1] (Control) followed by 3 times in [T.sub.4] and [BC.sub.7.5] [SS.sub.30] [RN.sub.50][T.sub.5]. The minimum (0.31 mg [kg.sup.-1]) was observed in [T.sub.1] Control. The treatment [T.sub.3] ([SS.sub.30]) was 75.47 % higher than the [T.sub.2] (100% RDF) followed by treatment [T.sub.4] (69.04%), [T.sub.5] (68.8 %), [T.sub.6] (62.13%), [T.sub.7] (61.00%) and [T.sub.9] (41%). Treatment [T.sub.4] ([BC.sub.25] [SS.sub.30] [RN.sub.50]) was found at par with [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]). The data pertaining to Cd content in rice straw (Table 5) experienced significant decrease with graded application of biochar. The Cd content in rice straw increased from 0.69 to 2.74 mg [kg.sup.-1]. Maximum (2.74 mg [kg.sup.-1]) being in [T.sub.3] ([SS.sub.30]) and minimum (0.69 mg [kg.sup.-1]) in [T.sub.3] (Control).Treatments [T.sub.3] ([SS.sub.30]) was almost 3 times higher than the control([T.sub.1]) followed by [T.sub.5] (2.68 times), [T.sub.6](2.63 times), [T.sub.7](2.31 times),[T.sub.8] (2.30 times) and [T.sub.9] (1.68 times). Treatment [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) was at par with [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]).

The increase in Cd content of straw and grain of rice in [T.sub.3] ([SS.sub.30]) may be due to addition of Cd present in sewage sludge, however a significant decrease in content and uptake of Cd with the application of biochar ([T.sub.4] to [T.sub.8]) may be due to the adsorption of Cd by biochar.

Cadmium uptake in grain and straw

A significant variation in uptake of Cd (Table 5 & Figure 2) with the straw and grain with the application of biochar and sewage sludge was noticed. The Cd uptake by grain varied from 0.01 to 0.09 mg [pot.sup.-1]. The maximum uptake (0.09 mg [pot.sup.-1]) was observed in [T.sub.3] ([SS.sub.30]) which increased by 8 times over control ([T.sub.3]). The minimum Cd uptake by rice grain (0.01 mg [pot.sup.-1]) was observed in control ([T.sub.1]). Application of 30 t [ha.sup.-1] sewage sludge alone resulted in 8 times increase in uptake of Cd in rice grain over control. The uptake of Cd was found maximum (0.09) in [T.sub.3] ([SS.sub.30]) followed by [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]). The treatment [T.sub.3] ([SS.sub.30]) increased Cd uptake by 5 times over the [T.sub.2] (100% RDF) followed by [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 5714%- [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) and [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]): 50% and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]):40 %. Treatment [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) and [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) and [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) were at par. The Cd uptake by straw varied from 0.05 to 0.35 mg [pot.sup.-1]. The maximum uptake (0.35 mg [pot.sup.-1]) was observed in [T.sub.3] ([SS.sub.30]) followed by [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]): 0.32 mg [pot.sup.-1] [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 0.31 mg [pot.sup.-1] and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 0.30 mg [pot.sup.-1]. Both Chicken Manure and Green Waste were very effective in reducing Cd and Pb concentrations of Indian mustard shoots (16, 17). Application of sewage sludge along with fertilizers also increased Cd content and uptake in rice straw and grain (13).

Chromium content in grain and straw

The data pertaining to of Cr content in grain (Table 5) showed a significant effect with graded application of biochar and constant level of sewage sludge. The maximum (2.15 mg [kg.sup.-1]) was recorded in[T.sub.3] ([SS.sub.30]) which showed an increase of 1.3 times over the [T.sub.1] (Control) followed by [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) and [T.sub.5] ([BC.sub.5.0] [SS.sub.30] [RN.sub.50]). The minimum Chromium content was in [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50] which was 9.7 % lower than control. The content of chromium in [T.sub.3] ([SS.sub.30] was 59.06% higher than [T.sub.2] (100% RDF).

The data pertaining to Cr content in rice (Table 5) revealed that the maximum content of chromium was (2.37 mg [kg.sup.-1]) in [T.sub.3] ([SS.sub.30]) which was 53.16% higher than [T.sub.2] (100% RDF) and minimum content was found in [T.sub.1] (Control). Treatment [T.sub.3] ([SS.sub.30]) found 1.96 times higher than the [T.sub.1] (Control). The treatment [T.sub.2] (100% RDF), was at par with treatment [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]). A significant decreased Cr content by (53.16%) in [T.sub.2] (100% RDF) over [T.sub.3] ([SS.sub.30]) followed by [T.sub.4] (40.32%), [T.sub.5] (22.37%) and [T.sub.6] (10.48%) was noticed. The normal range of Cr in plants is considered 0.03-14.00 mg [kg.sup.-1], while the toxic concentrations fall between 5-30 mg [kg.sup.-1] (18). This suggests that plant Cr in this study was in the normal range. The concentration of chromium in rice grain and straw significantly decreased due to biochar application which may be due to the slow release pattern of heavy metal adsorption biochar. Green waste-derived biochar (GW) immobilized Cd, Cu, and Pb by 30.3, 22.9 and 36.8%, respectively, for spiked soil, and by 42.7, 0.901 and 72.9% for naturally contaminated soil (16).

Chromium uptake in grain and straw

The Cr uptake in rice grain (Table 5 & Figure 2) varied from 0.02 to 0.12 mg [pot.sup.-1]. The maximum uptake (0.12 mg [pot.sup.-1]) was recorded in [T.sub.3] ([SS.sub.30]) which was about 5 times higher than control ([T.sub.1]). The chromium uptake by rice grain was maximum in [T.sub.3] ([SS.sub.30]) which showed an increase of 5 times over control followed by [T.sub.4] ([BC.sub.25] [SS.sub.30] [RN.sub.50]): 3.5 times, [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 2.5 times,[T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) and [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]): 2 times. Treatment [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) was at par with [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]), [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]).

The uptake of Cr in rice straw varied from 0.06 to 0.30 mg [pot.sup.-1]. The maximum Cr uptake (0.30 mg [pot.sup.-1]) was observed in [T.sub.3] ([SS.sub.30]) and minimum 0.06 mg [pot.sup.-1]in control. The treatment [T.sub.3] ([SS.sub.30]) had Cr uptake 4 times higher over control ([T.sub.1]) followed by [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 2.8 times, [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]): 2 times, [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) & [T.sub.2] (100% RDF): 1.6 times, [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) & [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]): 1.5 times and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]): 1.3 times. Nickel content in grain and straw

The Ni content in grain (Table 5) significantly affect by application of graded dose of biochar along with of sewage sludge. The maximum nickel content (7.99mg [kg.sup.-1]) in grain was in [T.sub.3] ([SS.sub.30]) which was 1.2 times higher than the [T.sub.3] (Control), and the minimum content (5.00 mg [kg.sup.-1]) was in treatment [T.sub.1] (Control). The treatment [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) was at par with [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]). The [T.sub.2] (100% RDF), registered 59.08 % increase in Ni content over control ([T.sub.1] ) followed by [T.sub.9] (40.90%), [T.sub.8] (41.16%), [T.sub.7] (31.84%) and [T.sub.6] (6.5%).

Similar results were observed in Ni content of straw. It ranged from 7.10 to 19.61 mg [kg.sup.-1]. The maximum (19.61 mg [kg.sup.-1]) was observed in [T.sub.3] ([SS.sub.30]) and the minimum (7.10 mg [kg.sup.-1]) in control ([T.sub.1]). Treatments [T.sub.2] (100% RDF) showed a significant decrease in Ni content by 59.71% from [T.sub.3] ([SS.sub.30]) followed by [T.sub.4] (47.12%), [T.sub.5] (43.36%), [T.sub.6] (40.82%), [T.sub.8] (28.63%) and [T.sub.9] (21.07%). A significant decrease in Ni content was noticed with the application of biochar in combination with sewage sludge. Concentration of chromium in rice grain and straw significantly decreased by 20 to 40 % over 100% RDF which may result due to the slow release pattern of heavy metal adsorbed on biochar. Significant increase in Ni concentration in seed at 4 kg [m.sup.-2] sewage sludge amendment in both years in dry bean (15).

Nickel uptake in grain and straw

The Ni uptake in rice grain ranged between 0.10 to 0.61 mg [pot.sup.-1] (Table 6). The maximum uptake (0.61 mg [pot.sup.-1]) was recorded in [T.sub.3] ([SS.sub.30]) which was 5 times Ni uptake over control ([T.sub.1]). The minimum (0.10 mg [pot.sup.-1]) was found in control. Application of 30 t [ha.sup.-1] sewage sludge with biochar ([T.sub.3]) resulted 11.47% increase in uptake of Ni by rice grain over [T.sub.2] (100% RDF). The Treatments [T.sub.3] ([SS.sub.30]) showed 5 times higher over control ([T.sub.1]) followed by [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]): 4.1times [T.sub.4] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) & [T.sub.9] ([BC.sub.20] [SS.sub.30] 3.8 times, [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 3.2 time and [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) & [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]): 2.5 times. Thus a significant decrease in Ni uptake was noticed with increase in doses of biochar.

The Ni uptake in rice straw ranged between 0.54 to 2.48 mg [pot.sup.-1] (Table 6). The maximum uptake (2.48 mg [pot.sup.-1]) was recorded in [T.sub.3] ([SS.sub.30]) and the minimum was observed in control ([T.sub.1]). Treatments [T.sub.3] ([SS.sub.30]) showed 3.5 times increase in Ni uptake over control ([T.sub.3]) followed by [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]): 2.5 times, [T.sub.4] ([BC.sub.2], [SS.sub.30] [RN.sub.50]):2.3 times, [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]): 2.2 times and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]) : 2.2 times. Treatment [T.sub.2] (100% RDF) was found 38.25 % decreased over [T.sub.4] ([BC.sub.2.5] [SS.sub.30] [RN.sub.50]) followed by [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]): 35.79%, [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 34 680% [T.sub.7] ([BC.sub.10] [SS.sub.30] 40.21%, [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]): 23.64 and [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]): 18.11 %. A significant decrease in Ni uptake with addition of Biochar was also reported (16).

Lead content in grain and straw

The data pertaining to Pb content in rice grain revealed that its content varied from 0.10 to 0.63 mg [kg.sup.-1] (Table 6). The maximum (0.63 mg [kg.sup.-1]) was observed in [T.sub.3] ([SS.sub.30]) and minimum (0.10 mg [kg.sup.-1]) in [T.sub.1] (Control).The Pb content in grain is increased by 5.3 times over control in [T.sub.3] ([SS.sub.30]) followed by 1.7 times in [T.sub.2] (100% RDF), [T.sub.4] (60%) and [T.sub.7] (60%) [T.sub.6] (40%), [T.sub.8] (30%) and [T.sub.9] (20%). The data pertaining to Pb content in rice straw also showed similar significant effect. Its content ranged from 0.21 to 1.15 mg [kg.sup.-1](Table 6). The maximum of 1.15 mg [kg.sup.-1] was observed in [T.sub.3] ([SS.sub.30]) and the minimum 0.21 mg [kg.sup.-1] in [T.sub.9] (0.21mg [kg.sup.-1]) followed by [T.sub.8] (0.23 mg[kg.sup.-1]), [T.sub.7] (0.27 mg [kg.sup.-1]),[T.sub.6] (0.30 mg [kg.sup.-1]) and [T.sub.5](0.37 mg [kg.sup.-1]). Chicken manure-derived biochar (CM) dramatically reduced N[H.sub.4]N[O.sub.3] extractable Cd and Pb concentrations from 0.95 and 11.3 mg [kg.sup.-1] to 0.11 (88.4%) and 0.73 (93.5%) mg [kg.sup.-1], respectively (16).

Lead uptake in grain and straw

The uptake of Pb was very less in rice straw (Table 6) as well as grain. The uptake of Pb in straw and grain was increased with application of sewage sludge. The minimum Pb uptake by grain was 0.01 mg [kg.sup.-1] in all treatment except [T.sub.2] (100% RDF), [T.sub.3] ([SS.sub.30]) treatment and maximum uptake of lead was found in [T.sub.3] ([SS.sub.30]) 0.03 mg [kg.sup.-1] followed by [T.sub.2] (100% RDF) 0.02 mg [kg.sup.-1]. The Pb uptake in rice straw ranged between 0.03 to 0.14 mg [pot.sup.-1]. The maximum value for uptake (0.14 mg [pot.sup.-1]) was recorded from [T.sub.3] ([SS.sub.30]) and the minimum 0.03 mg [kg.sup.-1] was observed in control ([T.sub.1]) as well as also m[T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]),[T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) ,[T.sub.9] [BC.sub.20] [SS.sub.30] [RN.sub.50]) due to the application of biochar. The treatment [T.sub.3] ([SS.sub.30]) was increased Pb uptake by 50 % over [T.sub.2] (100% RDF).Study clearly indicated that application of sewage sludge increased the concentration and uptake of heavy metal. However addition of biochar reduced its uptake. Edible part of wheat plants (grains) from test samples presented high concentration of Cd, Cr, Cu, Ni, Pb and Zn with the application of sewage sludge (19).

Application of sewage sludge along with fertilizers also increased Ni, Cr, Cd and Pb content in rice straw and grain. There was about 7, 5, 5 and 10 times increase in Cd, Cr, Ni and Pb content, respectively, in rice grain and about 7, 3, 7 and 2 times increase in rice straw over control13. Sewage sludge amendment increased the content and uptake of Cd, Cr, Pb, Ni, and Zn in shoot. Some [IBI.sup.5] members (Joshep) also reported the application of biochar reduce the heavy metal content in both shoot and root (20).

Properties of post harvest soils

Soil reaction (pH)

The data pertaining to pH of the soil (Table 7) showed that it varied from 7.3 to 8.0. The maximum pH 8.0 observed in treatments [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) and the minimum [T.sub.1] (Control) followed by [T.sub.2] (100% RDF). Application of fertilizer and sewage sludge resulted a decrease in pH [T.sub.2] (100% RDF) and [T.sub.3] ([SS.sub.30]). The application of biochar did not show significant increase in pH. The maximum soil pH 8.0 was found in treatment [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) followed by [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]): 7.9, [T.sub.8] (BCU [SS.sub.30] [RN.sub.50]) & [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]): 7.8 and [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]):7.7. It has been reported that chemical properties of biochar after addition in soil cause changes in pH, electrical conductivity (EC), cation exchange capacity (CEC) and nutrient levels (21, 22, 23 & 24).

Electrical conductivity (EC)

There was significant increase in the EC of soil with application of biochar and sewage sludge was observed (Table 7) The EC of soil ranged between 0.18 to 0.25 dS [m.sup.-1]. The minimum of EC (0.18 dS [m.sup.-1]) was recorded in control ([T.sub.1]) and the maximum (0.25dS [m.sup.-1]) in treatment [T.sub.7] ([BC.sub.10] [SS.sub.30] [RN.sub.50]) where biochar was applied along with sewage sludge. An increase in EC was found in [T.sub.7]([BC.sub.10] [SS.sub.30] [RN.sub.50]) followed by [T.sub.8] ([BC.sub.15] [SS.sub.30] [RN.sub.50]) and [T.sub.6] ([BC.sub.7.5] [SS.sub.30] [RN.sub.50]X[T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) and [T.sub.3] ([SS.sub.30]). Sewage sludge application Increase in EC was also reported (14, 25 & 26).

Organic Carbon

There was a significant increase in soil organic carbon content with application of biochar and sewage sludge (Table 7). The organic carbon content in soil ranged from 0.30 to 0.51 %. The minimum organic carbon content (0.30%) was observed in control ([T.sub.1]) and the maximum (0.51 %) in [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) which was 70% higher over control followed by [T.sub.8] (60%), [T.sub.7] (53.33%), [T.sub.6] (46.66%) and [T.sub.4] (36.66%). The treatment [T.sub.2] (100% RDF), had 37.25 % lower organic carbon content to [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) followed by [T.sub.8] (33.33%), [T.sub.7] (30.48%), and [T.sub.6] (27.30 %) (27 & 28).

DTPA extractable heavy metal in post-harvest soil

The heavy metal Cd (Table 7 & figure 3) content of soil range from 0.64 to 2.59 mg [kg.sup.-1]. The minimum content (0.64 mg [kg.sup.-1]) was recorded in treatment where sewage sludge was not applied. However, Maximum content (2.59mg [kg.sup.-1]) was recorded in the treatment [T.sub.3] ([SS.sub.30]) which showed 3 times increase in DTPA extractable Cd over control (0.64 mg [kg.sup.-1]). DTPA extractable Cr in soil ranged between 0.15 to 1.0 mg [kg.sup.-1]. The maximum (1.0 mg [kg.sup.-1]) was recorded in [T.sub.3] ([SS.sub.30]) followed by [T.sub.9] (0.84 mg [kg.sup.-1]),[T.sub.8] (0.72mg [kg.sup.-1]) [T.sub.7] (0.60mg [kg.sup.-1]). The maximum chromium content in [T.sub.3] ([SS.sub.30]) was 5 times higher over control ([T.sub.1]) followed by [T.sub.9] (4.6times), [T.sub.8] (3.8times), [T.sub.7] (3.0times), [T.sub.6] (2.4 times), [T.sub.5] (2.1times) and [T.sub.4] (1.5times). The concentrations obtained in this study were very low as compared to the maximum permissible limit of 25 mg [kg.sup.-1] set for extractable Cr in soil by UK Department of Environment (Alloway and Ayers, 1997). The DTPA extractable Ni ranged between 1.80 to 5.19 mg [kg.sup.-1]. The maximum (5.19 mg [kg.sup.-1]) was recorded in [T.sub.3] ([SS.sub.30]) which showed about 3.5 times increase over control (1.80 mg [kg.sup.-1]). Application of 30 t [ha.sup.-1] sewage sludge with no fertilizer and biochar had shown 1.8 times increase over control (5.78 mg [kg.sup.-1]) followed by [T.sub.9] ([BC.sub.20] [SS.sub.30] [RN.sub.50]) 1.3 times. The treatment [T.sub.5] ([BC.sub.5] [SS.sub.30] [RN.sub.50]) was statistically at par with [T.sub.4] ([BC.sub.2.5] [SS.sub.30] [RN.sub.50]). The Ni concentration in soil was lower than maximum permissible limit of 20 mg [kg.sup.-1] for toxicity as suggested by UK Department of Environment (Alloway and Ayers, 1997). There was a significant increase in DTPA extractable Pb in soil with graded application of biochar and sewage sludge. The DTPA extractable Pb in soil varied between 0.19 to 2.04 mg [kg.sup.-1] with the maximum (2.04 mg [kg.sup.-1]) in [T.sub.3] ([SS.sub.30]) which was 9.7 times more over control (0.19 mg [kg.sup.-1]) followed by [T.sub.9] (5 times),[T.sub.7] (4.7 times), and [T.sub.2] (52.63%). The increasing levels of sewage sludge composts addition increased the extractable heavy metal status (Cd, Cr, Ni, and Pb) in the soil but did not increase to the toxic limits (29).

CONCLUSION

A significant increase in grain and straw yield of rice could be achieved by application of biochar and sewage sludge. Sole application of lower doses of biochar has no significant effect on grain yield of rice in alluvial soils of Varanasi. However, combined application of sewage sludge and biochar resulted in significant increase in yield. Among the various treatments, the highest grain yield was obtained with combined application of 20 t [ha.sup.-1] biochar and 30 t [ha.sup.-1] sewage sludge, which was 2.8 times higher over control ([T.sub.1]) and 8.5% higher over 100% RDF. Biochar application increased the grain yield of rice, soil organic carbon content with a significant sorption of heavy metals in biochar reduced the uptake of heavy metals by rice.

ACKNOWLEDGEMENTS

The author is thankful to B SER Ajmer and Ministry of Human Resource Development, Government of India for providing Central Sector Scholarship for M. Sc (Ag.) studies.

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H.S. Jatav *, S.K. Singh, Y.V Singh, Alpana Paul, Vipin Kumar, Preeti Singh and Hemant Jayant

Department of Soil Science and Agricultural Chemistry, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi--221 005, India.

(Received: 21 December 2015; accepted: 03 February 2016)

* To whom all correspondence should be addressed.

E-mail: hanumaniasbhu@gmail.com

Caption: Fig. 1. Experimental material a) Rice husk Biochar and (b) Sewage Sludge

Caption: Fig. 2. Effect of biochar application on Cd and Cr uptake in rice grown in soil amended with sewage sludge

Caption: Fig. 3. Effect of Biochar application on Cd and Cr concentration in post harvest soil amended with sewage sludge
Table 1. Treatment combination

                                      Applied Biochar

Treatment    Fertilizer           Pots             Equivalent
                          (g [kg.sup.-1] soil)   ton [ha.sup.-1]

[T.sub.1]        0                 0                    0
[T.sub.2]     100% RDF             0                    0
[T.sub.3]     50% RDN              0                    0
[T.sub.4]     50% RDN            11.20                 2.5
[T.sub.5]     50% RDN            22.40                 5.0
[T.sub.6]     50% RDN            33.60                 7.5
[T.sub.7]     50% RDN            44.80                 10
[T.sub.8]     50% RDN            67.20                 15
[T.sub.9]     50% RDN            89.60                 20

                 Applied Sewage Sludge

Treatment        Pots          Equivalent
             (g kg-1 soil)   ton [ha.sup.-1]

[T.sub.1]          0                0
[T.sub.2]          0                0
[T.sub.3]         131              30
[T.sub.4]         131              30
[T.sub.5]         131              30
[T.sub.6]         131              30
[T.sub.7]         131              30
[T.sub.8]         131              30
[T.sub.9]         131              30

Table 2. Physico-chemical characteristics
of Rice husk biochar

Properties                                       Biochar

Colour                                    2.5 YR 2.5/0 (Black)
Bulk density (Mg [m.sup.-3])                      0.40
Porosity                                           72%
Particle density (Mg [m.sup.-3])                  1.40
Available WHC (Using keens box)                   218%
pH (H2O) 1:2.5                                     9.5
pH (0.01M Ca[Cl.sub.2]) 1:2.5                      9.4
pH (0.01M Ca[Cl.sub.2]) 1:5                        9.3
EC (dS[m.sup.-1])                                 2.56
Organic carbon (%)                                4.80
Ca & Mg (mg [kg.sup.-1])                          0.21
Na (mg [kg.sup.-1])                               0.35
Total N (%)                                       0.10
Total P (%)                                       0.15
Total K (%)                                       0.20

DTPA Extractable Metal (mg [kg.sup.1])
Ni                                            Not Detected
Cr                                            Not Detected
Pb                                            Not Detected
Cd                                            Not Detected

Table 3. The physico- chemical characteristics
of Sewage Sludge

Properties                               Sewage sludge

Colour                                     7.5YR 4/2
                                         (Light brown)
Bulk density (Mg [m.sup.-3])                 1.65
Available WHC (Using keens box)              48.37
pH ([H.sub.2]O) 1:2.5                         7.2
EC (dS[m.sup.-1])                            0.35
Organic carbon (%)                           8.13
C/Nratio                                    16.03:1
Total N (%)                                   1.4
Total P (%)                                  1.30
Total K (%)                                  0.95
Total S (%)                                   2.1

DTPA Extractable Metal (mg[kg.sup.1])
Ni                                           29.34
Cr                                            4.9
Pb                                            7.6
Cd                                            3.2

Table 4. Effect of biochar application on test weight,
harvest index, grain yield and straw yield of rice
grown in soil amended with sewage sludge

Treatment           Test weight        Harvest index
                (Wt. of 1000 grains)        (%)

[T.sub.1]               16.5               20.2
[T.sub.2]               22.0               32.1
[T.sub.3]               19.3               30.2
[T.sub.4]               17.7               29.0
[T.sub.5]               19.1               29.1
[T.sub.6]               19.0               30.0
[T.sub.7]               20.1               30.7
[T.sub.8]               21.4               31.8
[T.sub.9]               22.2               34.9
SEm [+ or -]            0.74               0.67
CD (P=0.05)             2.14               1.95

Treatment         Grain yield        Straw yield
                (g [pot.sup.-1])   (g [pot.sup.-1])

[T.sub.1]             19.3               76.1
[T.sub.2]             67.8               143
[T.sub.3]             54.9               127
[T.sub.4]             50.2               122
[T.sub.5]             51.8               126
[T.sub.6]             55.5               129
[T.sub.7]             58.0               131
[T.sub.8]             62.2               133
[T.sub.9]             74.1               138
SEm [+ or -]          1.63               2.38
CD (P=0.05)           4.74               6.92

Treatments: [T.sub.1]-Control, [T.sub.2]-100% RDF,
[T.sub.3]-30 t [ha.sup.-1] SS, [T.sub.4]-2.5 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.5]-5.0 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.6]-7.5 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.7]-10 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.8]-15 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.9]-20 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN

Table 5. Effect of biochar application on Cd, Cr
Concentration and uptake in rice grown in soil
amended with sewage sludge

                                                 Concentration

Treatment          Biochar           Sewage        Grain   Straw
               (t [ha.sup.-1])       Sludge
                                 (t [ha.sup.-1])

[T.sub.1]           0                 0          0.31    0.69
[T.sub.2]           0                 0          0.39    0.85
[T.sub.3]           0                30          1.59    2.74
[T.sub.4]          2.5               30          1.26    2.54
[T.sub.5]          5.0               30          1.26    2.51
[T.sub.6]          7.5               30          1.25    2.29
[T.sub.7]          10                30          1.03    2.28
[T.sub.8]          15                30          1.00    1.99
[T.sub.9]          20                30          0.67    1.46
SEm [+ or -]                                     0.04    0.09
CD (P=0.05)                                      0.13    0.26

Treatment      Grain          Cd          Total
                       (mg [pot.sup.1])
                            Uptake
                            Straw

[T.sub.1]      0.01          0.05         0.06
[T.sub.2]      0.03          0.12         0.15
[T.sub.3]      0.09          0.35         0.43
[T.sub.4]      0.06          0.31         0.37
[T.sub.5]      0.07          0.32         0.38
[T.sub.6]      0.07          0.30         0.37
[T.sub.7]      0.06          0.30         0.36
[T.sub.8]      0.06          0.27         0.33
[T.sub.9]      0.05          0.20         0.25
SEm [+ or -]   0.01          0.01         0.01
CD (P=0.05)    0.01          0.04         0.04

                         Cr (mg [pot.sup.-1])

               Concentration

Treatment      Grain   Straw   Grain   Uptake   Total
                                       Straw

[T.sub.1]      0.92    0.80    0.02     0.06    0.08
[T.sub.2]      0.88    1.11    0.06     0.16    0.22
[T.sub.3]      2.15    2.37    0.12     0.30    0.42
[T.sub.4]      1.86    1.86    0.09     0.23    0.32
[T.sub.5]      1.43    1.43    0.07     0.18    0.25
[T.sub.6]      1.27    1.24    0.07     0.16    0.23
[T.sub.7]      0.99    1.11    0.06     0.15    0.20
[T.sub.8]      0.94    1.10    0.06     0.15    0.21
[T.sub.9]      0.83    1.01    0.06     0.14    0.20
SEm [+ or -]   0.07    0.04    0.001    0.01    0.01
CD (P=0.05)    0.20    0.11    0.01     0.02    0.03

Treatments: [T.sub.1] -Control, [T.sub.2] - 100% RDF,
[T.sub.3] - 30 t [ha.sup.-1] SS, [T.sub.4] - 2.5 t
[ha.sup.-1] BC+30 t [ha.sup.-1] SS +50% RDN,
[T.sub.5] - 5.0 t [ha.sup.-1] BC+30 t [ha.sup.-1] SS +50%
RDN, [T.sub.6] -7.5 t [ha.sup.-1] BC+30 t [ha.sup.-1] SS +
50% RDN, [T.sub.7] -10 t [ha.sup.-1] BC+30 t [ha.sup.-1]
SS +50% RDN, [T.sub.8] -15 t [ha.sup.-1] BC+30 t [ha.sup.-1]
SS +50% RDN, [T.sub.9] -20 t [ha.sup.-1] BC+30 t
[ha.sup.-1] SS +50% RDN

Table 6. Effect of biochar application on Ni, Pb Concentration
and uptake in rice grown in soil amended with sewage sludge

                                               Concentration

Treatment          Biochar          Sewage     Grain   Straw
               (t [ha.sup.-1])    Sludge (t
                                [ha.sup.-1])

[T.sub.1]            0               0         5.00    7.10
[T.sub.2]            0               0         7.99    7.90
[T.sub.3]            0               30        11.01   19.61
[T.sub.4]           2.5              30        9.55    14.94
[T.sub.5]           5.0              30        9.80    13.95
[T.sub.6]           7.5              30        7.50    13.35
[T.sub.7]           10               30        6.06    14.47
[T.sub.8]           15               30        5.66    11.07
[T.sub.9]           20               30        5.67    10.01
SEm [+ or -]                                   0.23    0.51
CD (P=0.05)                                    0.66    1.48

               Cd (mg [pot.sup.-1])     Cr (mg [pot.sup.-1])

                                        Concentration

Treatment     Grain   Uptake    Total   Grain   Straw
                       Straw

[T.sub.1]     0.10     0.54     0.64    0.10    0.46
[T.sub.2]     0.54     1.13     1.67    0.27    0.49
[T.sub.3]     0.61     2.48     3.09    0.63    1.15
[T.sub.4]     0.48     1.83     2.31    0.16    0.44
[T.sub.5]     0.51     1.76     2.27    0.14    0.37
[T.sub.6]     0.42     1.73     2.14    0.14    0.30
[T.sub.7]     0.35     1.89     2.24    0.16    0.27
[T.sub.8]     0.35     1.48     1.83    0.13    0.23
[T.sub.9]     0.42     1.38     1.80    0.12    0.21
SEm [+ or -]  0.02     0.06     0.07    0.02    0.02
CD (P=0.05)   0.06     0.19     0.22    0.05    0.06

              Cr (mg [pot.sup.-1])

Treatment     Grain   Uptake   Total
                      Straw

[T.sub.1]     0.01    0.03     0.04
[T.sub.2]     0.02    0.07     0.09
[T.sub.3]     0.03    0.14     0.18
[T.sub.4]     0.01    0.05     0.06
[T.sub.5]     0.01    0.05     0.05
[T.sub.6]     0.01    0.04     0.05
[T.sub.7]     0.01    0.03     0.04
[T.sub.8]     0.01    0.03     0.04
[T.sub.9]     0.01    0.03     0.04
SEm [+ or -]  0.001   0.003    0.003
CD (P=0.05)   0.004   0.01     0.01

Treatments: [T.sub.1] -Control, [T.sub.2] - 100% RDF,
[T.sub.3] - 30 t [ha.sup.-1] SS, [T.sub.4] - 2.5 t
[ha.sup.-1] BC+30 t [ha.sup.-1] SS +50% RDN,
[T.sub.5] - 5.0 t  [ha.sup.-1] BC+30 t [ha.sup.-1]
SS +50% RDN, [T.sub.6] -7.5 t [ha.sup.-1] BC+30 t
[ha.sup.-1] SS +50% RDN, [T.sub.7] -10 t [ha.sup.-1]
BC+30 t [ha.sup.-1] SS +50% RDN, [T.sub.8] -15 t
[ha.sup.-1] BC+30 t [ha.sup.-1] SS +50% RDN,
[T.sub.9] -20 t [ha.sup.-1] BC+30 t
[ha.sup.-1] SS +50% RDN

Table 7. Effect of Biochar application on pH, EC,
Organic Carbon and Heavy metals (Cd, Cr, Ni, Pb)
in post harvest soil amended with sewage sludge

Treatment       pH       EC(dS      OC (%)
                      [m.sup.-1])

[T.sub.1]      7.3       0.18        0.30
[T.sub.2]      7.3       0.23        0.32
[T.sub.3]      7.4       0.21        0.36
[T.sub.4]      7.6       0.23        0.41
[T.sub.5]      7.7       0.22        0.41
[T.sub.6]      7.8       0.23        0.44
[T.sub.7]      7.9       0.25        0.46
[T.sub.8]      7.8       0.22        0.48
[T.sub.9]      8.0       0.24        0.51
SEm [+ or -]   0.16      0.01        0.01
CD (P=0.05)     NS        NS         0.03

                      Heavy metals
                  in post harvest soil
                    (mg [kg.sup.-1])

Treatment       Cd     Cr     Ni     Pb

[T.sub.1]      0.64   0.15   1.80   0.19
[T.sub.2]      1.09   0.25   2.59   0.29
[T.sub.3]      2.59   1.00   5.19   2.04
[T.sub.4]      1.36   0.38   2.93   0.77
[T.sub.5]      1.11   0.47   3.09   0.91
[T.sub.6]      1.14   0.51   3.22   0.88
[T.sub.7]      1.57   0.60   3.19   1.10
[T.sub.8]      1.85   0.72   3.92   0.87
[T.sub.9]      2.00   0.84   4.19   1.16
SEm [+ or -]   0.15   0.03   0.09   0.05
CD (P=0.05)    0.45   0.09   0.26   0.13

Treatments: [T.sub.1] - Control, [T.sub.2] - 100% RDF,
[T.sub.3] - 30 t [ha.sup.-1] SS, [T.sub.4] - 2.5 t
[t.sup.-1] BC+30 t [ha.sub.-1] SS +50% RDN,
[T.sub.5] - 5.0 t [t.sup.-1] BC+30 t [t.sup.-1] SS +
50% RDN, [T.sub.6] -7.5 t [t.sup.-1] BC+30 t [t.sup.-1]
SS +50% RDN, [T.sub.7] -10 t [t.sup.-1] BC+30 t [t.sup.-1]
SS +50% RDN, [T.sub.8] -15 t [t.sup.-1] BC+30 t [t.sup.-1]
SS +50% RDN, [T.sub.9] -20 t [t.sup.-1] BC+30 t [t.sup.-1]
SS +50% RDN
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Author:Jatav, H.S.; Singh, S.K.; Singh, Y.V.; Paul, Alpana; Kumar, Vipin; Singh, Preeti; Jayant, Hemant
Publication:Journal of Pure and Applied Microbiology
Article Type:Report
Date:Jun 1, 2016
Words:9610
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