Effect Of Organic Materials On Selenium Form Of Soil And Selenium Absorption Of Wheat

[Objective]Selenium is one of the essential nutrients for animal and human growth and development.In the context of 72%soil selenium def iciency in China and low selenium availability in selenium-enr iched soil areas,increasing the availability of selenium in soil is an important way to increase selenium content in agricultural products.This study included indoor culture experiments as well as field plot experiments.The adsorption-desorption characteristics of Se were studied in soil amended with different organic materials.The effects of these organic amendments on soil Se transformations and Se uptake by wheat were elucidated to provide a basis for producing Se-enriched agricultural products.[Methods]The research was divided into two parts:indoor culture experiments and field plot exper iments.(1)The indoor culture tests included four organic amendments:(i)cotton straw(CS),(ii)humic acid-containing ore(MH),(iii)poultry manure fertilizer(CO),and(iv)ethylenediaminetetraacetic acid(EDTA).Adsorption and desorption experiments were performed by adding different concentrations of Se(IV)to the soil.(2)The field plot exper iment compared four treatments and two application times.The four treatments were(i)biochemical humic acid(BH),(ii)humid acid-containing ore(MH),poultry manure fertilizer(CO),and(iv)unamended soil(CK).The two applications times were basal application and topdress application.The topdress applications were done at the three-leaf stage,at jointing,and at booting.In a second experiment,humic acid-containing ore was applied at four stages during wheat growth.The treatments will be referred to as MH-1,MH-2,MH-3,and MH-4,respectively.Unamended soil was used as a control(CK).[Results](1)The adsorption of Se(IV)reached equilibrium within 24 h in the amended soil.The adsorption amount rapidly increased with the reaction time and then stabilized.The R~2 values of the Langmuir and Freundich equation models were both greater than 0.92.Both equations can describe the isothermal adsorption process of Se(IV)in the amended soil.The initial Se concentration was 8 mg/L.The isothermal equilibrium adsorption capacity and desorption rate were higher in MH than in any other treatment.The isothermal adsorption capacity decreased in the order MH>EDTA>CK>CO>CS.The MH and EDTA treatments increased the isothermal adsorption capacities by 12.51 and 4.45%,respectively,compared with CK.The CO and CS treatments reduced the isothermal adsorption capacities by 6.49 and 13.45%,respectively,compared with CK.The desorption rates in the EDTA,MH,and CO treatments were 18.68,13.69,and 11.53%greater,respectively than that in CK.(2)Soluble Se(as a percent of total Se)increased across time from 1.35 to 3.25%in MH and from1.23 to 4.9%in CO.In comparison,the percentage of exchangeable Se increased across time from 3.96 to10.99%in MH and from 3.15 to 11.89%in CO.In the BH treatment,the percentage of exchangeable Se increased from 3.83 to 10.09%.The percentage of organically bound Se declined across time from 43.72 to35.92%in BH,from 41.72 to 35.52%in MH,and from 44.01 to 35.09%.The organic amendments signif icantly increased both soil available Se and the soil Se activation rate compared with CK.Soil organic matter contents were also greater in the amended soil than in the unamended(CK)soil.The BH and MH treatments reduced soil p H by 0.8 and 0.4 units,respectively,compared with CK.Soil p H was positively correlated with soluble Se.Soil organic matter was signif icantly positively correlated with soluble Se,exchangeable Se,and residual Se,but negatively correlated with organically bound Se and Fe-Mn Se.Soil soluble Se,exchangeable Se,and residual Se were all signif icantly negatively correlated with organically bound Se.(3)The BH treatment increased root Se by 25.58%compared with CK.In contrast,BH had no signif icant effect on the Se content of leaves,stems and grain.The MH treatment signif icantly increased the Se content of roots,leaves,and grain by 9.30,27.12,and 27.59%,respectively,compared with CK.In contrast,MH had no significant effect on the Se content of stems.The CO treatment significantly increased the Se content of roots stems,leaves,and grain by 32.56,38.0,22.03,and 34.48%,respectively,compared with CK.The Se enrichment coefficient of wheat grain was signif icantly greater in BH than in CK.The BH treatment had no significant effect on the Se enrichment coefficient of leaves,stems,and grain.The Se enrichment coefficient of roots,stems,leaves,and grain was significantly greater in MH than in CK.The CO treatment significantly increased the Se enrichment coefficient of roots and grain but not of leaves and stems.The Se transfer coefficients of stems,leaves,and grain were significantly less in BH than in CK.The MH treatment tended(not significant)to increase the Se transfer coefficient of leaves whereas it tended(not significant)to reduce the Se transfer coefficient of stems.(4)The MH-1,MH-2,MH-3,and MH-4 treatments signif icantly increased soluble Se(as a percentage of the total)by 65.68,65.27,33.47,and 23.11%,respectively,compared with CK.The MH-1 and MH-2treatments increased exchangeable Se by 18.83%and 12.81%,respectively,compared with CK.In comparison,MH-1 and MH-2 reduced organically bound Se by 9.77%and 8.27%,respectively,compared with CK.The Se activation rates in MH-1 and MH-2 were 9.09 and 9.58%greater,respectively,than those in CK.The MH-1 and MH2 treatments increased the Se contents of wheat grain by 31.03 and 17.24%,respectively,compared with CK.In contrast,MH-3 and MH-4 had no significant effect on grain Se.When humic acid was applied as a topdressing,the Se contents of roots,leaves and grain were signif icantly positively correlated with soil soluble Se and exchangeable Se.The MH-1 and MH-2 treatments significantly increased wheat yield by 10.01 and 11.99%,respectively,compared with CK.[Conclusion]Humic acid-containing ore and poultry manure fertilizer can(i)increase the desorption rate of Se in soil,and(ii)improve the effectiveness of soil Se.Organic matter can activate organically bound Se in soil and increase both soluble and exchangeable Se.Poultry manure fertilizer and humic acid-containing ore(MH-1 or MH-2)can increase(i)soil available Se,(ii)soil Se activation rate,and(iii)wheat grain Se.