| To evaluate the effect of biochars(made from cotton straw,maize straw and pig manure and made at temperatures 300?C and 500?C)and Cd(II)solutions on early seedling growth,it was compared six biochars with adding Cd(II)solutions.Research was made in 3 parts: soil less Petri dish bioassay,seeds germination in water(soak experiment)and pot experiment.In the first part the influences of biochars and Cd(II)as a contamination on seed germination and early seedling growth of Chinese cabbage(Brassica rapa L.),carrot(Daucus carota L.),wheat(T.aestivum),and maize(Z.mays subsp.Mays)were evaluated under laboratory conditions.The research comprised 4 amount rates(0,0,1,0.5 and 1 g/Petri dish)of 6 types of biochar.Cd(II)was added as chloride salt in solution in 3 concentrations(1,5 and 10 mg/L).Fifty seeds were sown in Petri dishes(8.5 cm diameter)on a layer of filter paper.Each of the six biochar types were added at the rates of 0,0.1,0.5 and 1.0 g/Petri dish(equivalent to 0,2,10,20 t/ha on a volume basis at 10 cm soil depth).20 mL of Cd(II)solutions(1,5 or 10 mg/L)or deionised water was added.Petri dishes were putted in automatic light incubator with the next conditions: temperature 20 ± 2?C,16/8 h of light and humidity 80-90%.The results of sowing seeds in soil less Petri dish bioassay showed that addition of biochar changed such characteristics as pH,electroconductivity,availability of NH4+ and Cd(II).It was determined that germination and root length had been decreased with higher amount of biochar,at the same time lower amount showed increase.A large amount of biochar(1 g/Petri dish)had negative effect on the root length of Brassica rapa L.and Daucus carota L.while fewer biochar(0.1 g/Petri dish)indicated a better result: increased or had no effect,although the percentage of germination did not show a regularity.Wheat and maize showed the same tendency.Root length of seeds gradually decreased with increasing concentration of Cd(II)solution from 1 mg/L to 10 mg/L.Combination of biochars(0.1 and 0.5 g/Petri dish)with Cd(II)solution 1 mg/L showed more high root length than only Cd(II)solution 1mg/L.Pearson's correlation coefficient showed that between root length and germination and main characteristics of biochar and Cd(II)solutions was a very low correlation(r < 0.2).The second part of current study different the influences of 6 types of biochars on seeds germination and root length of wheat and Chinese cabbage in water or Cd(II)solution.Fifty seeds of Chinese cabbage and wheat were sown in plastic glasses.Each of the five biochar types were added at the rates of 0,1% and 2% from water or Cd(II)solutions weight.Tap water or Cd(II)(10 mg/L)solution were added in an amount of 50 ml.These glasses were putted in a room with the next conditions: temperature 19 ± 2?C and humidity >50%.It had the next results.The main characteristics of biochars(pH,EC,NH4+,and Cd2+)changed in difference of added amount of biochars in water or Cd(II)solutions.pH showed the tendency of growing index with growing amount of biochar,but with adding Cd10 solution it goes down.EC increased with adding amount of biochar.Temperature of making biochar also had influence on rising EC index.NH4+ as a nutrient element was presented in practically all rates of biochars,with growing amount of biochar the index increased.In all other types of biochar in mixing with Cd10 solution there were not determined NH4+.Cd2+ was decreased with higher amount of biochar.With increasing amounts of biochar the germination and root length of Chinese cabbage and wheat were decrease.Iincreasing amount of biochar leads to decrease the indicators of germination and length of root,and further mixed with Cd10 has the same trend and gradually fell.Pearson's correlation coefficient indicated that the strength of association between the variables is different: association between pH and Chinese cabbage germination and root length had weak positive relationship,between EC and Cd2+ and root length and germination of both seeds had strong negative relationship,another all had no or had negligible relationship.In the third part of research it was determined influence of biochars on seeds germination and root length in contaminated with Cd(II)soil.The soil was sieved(<2 mm)and homogenized and the test heavy metal(Cd(II))were added as the solutions(10mg/L)of its chloride salt.Fifty seeds of Chinese cabbage(Brassica rapa subsp.chinensis)and wheat(Triticum aestivum L.)were sown in 500 mL soil mixed with Cd(II)solution 10 mg/L in a plastic pot.Each biochar was mixed separately with soil at the rates 0.5(0.5%)10(1%)and 20(2%)t/ha(calculated as soil volume to 10 cm soil depth).Pots were leaved in a laboratory with the next conditions: temperature 19 ± 2?C and humidity >50%,immersed with water or Cd(II)solution and allowed to drain for 24 h before.Germination percentage was recorded on the 12 th day after sowing.On the 12 th day after sowing,roots were washed free of soil,wiped with a paper towel and root lengths was measured using a gridline intercept method,and estimated as cm/pot.The main characteristics of soli with biochars changed with adding different amount of biochars.pH increased with adding amount of biochars or with higher Cd(II)concentrations.EC increased with adding amount of biochar.Temperature of making biochar also had influence on rising EC index.The biochars made at 500?C showed higher results than biochars made at 300?C.Cd2+ was decreased with higher amount of biochar.Root length and germination showed one tendency: with growing amount of biochar added in soil the indexes increased.Pearson's correlation coefficient indicated that the strength of association between the variables is different.So association between pH and germination and root length had weak negative relationship,between EC and Cd2+ and root length and germination of both seeds had strong negative relationship,another all had no or had negligible relationship.The main conclusions are:1)The reaction temperature is an important factor in controlling the nature of the carbon raw material,the higher the temperature,the raw materials decompose more fully,biomass char yield decreased,increasing its carbon content,pore structure formed at high temperatures are relatively stable,pH value also has been increased;2)Biochar contains a large number of elements necessary for plant growth,especially carbon.At the same time,added biomass carbon had no obvious inhibition on seed germination and,from data,some experimental group shoot length and germination rate decreased(in soil less Petri dish experiment and with water).3)All biochars had not significantly affected on seed germination and early growth,suggesting that biochar can be qualified as a soil remediation materials;modified biomass carbon due to surface functional groups added after the adsorption of heavy metals make heavy metal significantly lower toxicity,thereby reducing the toxicity of heavy metals in the soil,which itself has no significant effect on the plant,showing heavy metal contaminated soil good repair effect;Experimental study based on discovery that dry carbon biomass impact on seed germination and root length,but biochar showed both decrease(in soil less Petri dish experiment and with water)and increase(pot experiment with soil)of these indexes.It can be inferred that biochar had both negative and postive impact on the growth of plants,at the same the carbon biomass is qualified as soil remediation agent,it can be applied to the soil and water. |
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