Effects Of Different Rice Straw Addition Methods On Iron And Manganese Forms And Reducing Substances In Coastal Saline Paddy Soil

Iron and manganese are high content and active elements in soil.As the main variable chemical valency elements in paddy soil,the forms and transformation of iron and manganese affects the redox reaction process of paddy soil,and also affects the transformation of soil nutrients and their bioavailability.The number of electron donors in the soil is the key factor of affecting the existence and transformation of iron and manganese.The large amount of organic matter in straw returning to the field can provide electron donors for the redox reactions of iron and manganese.It can promote the transformation and migration of iron and manganese in soil and change the bioavailability of iron and manganese.Different methods of rice straw returning to soil can affect the changes of soil pH and redox potential,and the transformation and differentiation of iron and manganese forms and components in different degrees.In this study,in order to explore the reasonable way of straw returning to the field,the typical costal saline paddy soil in northeastern China was used as the research object to study the effects of adding different treatments of rice straw(rice straw biochar,direct returning rice straw,decomposed rice straw)on forms,availability of iron and manganese,and reducing substances in paddy soil.It is to investigate the rules and characteristics for transformation and bioavailability of iron and manganese in paddy soil under the adding different rice straw treatment conditions in an indoor incubation experiment.The results will provide scientific basis and data support for popularizing reasonable rice straw returning method in cold costal saline paddy soil of northern China.The conclusions of the experiment are as follows:1.After 360 days of cultivation,the contents of soluble iron,weak acid iron and oxidizable iron in paddy soil were increased by adding rice straw biochar(S),decomposed rice straw(F)and directly returning rice straw(Z),and the most significant increase was from the rice straw biochar treatment.The content of residual iron under the three treatments was lower than that of the Control check(CK).The lowest content of residual iron was from the treatment of straw biochar.The avairable iron content sequence from high to low was: S> F > Z > CK.Under the test condition,it is advantageous to convert the residue iron to the reducible and weak acid iron.2.The contents of water-soluble manganese,weak acid manganese and oxidizable manganese in paddy soil were increased by the treatments of adding rice straw biochar,decomposed rice straw and directly returning rice straw,and the content of residual manganese in the three rice straw treatment was lower than that of the CK,after the 360 days of cultivation.The content of residual manganese under straw biochar treatment was significantly lower than that of other treatments.The treatment of rice straw biochar,decomposed rice straw and directly returning rice straw also significantly increased the content of available manganese in soil,and the order followed as the decomposed rice straw>rice straw biochar>directly returning rice straw > CK.Under the experimental conditions,weak acid manganese,reducible manganese and oxidizable manganese were transformed into residual manganese.3.There are mutual transformations among different forms of iron or manganese in the tested costal saline paddy soil after adding three kinds straw treatment.Soil soluble iron and reducible iron are the main existential forms of available iron in the soil.Water soluble manganese is the main effective form of soil available manganese.4.The content of total reductive substances and active reductive substances of S treatment in paddy soil were significantly lower than those of CK after 60 ~ 360 days' incubation.Compared with CK,the content of total reducing substances and active reducing substances in paddy soil accumulated at the 30 th day of the training experiment.But during the cultivation from 30 to 360 days,it was gradually reduced.After 360 days of culture,the order for the content of soil total reductive substances and the content of active reductive substances were as follows: decomposed rice straw> CK>directly returning rice straw> rice straw biochar,and CK> decomposed rice straw > directly returning rice straw> rice straw biochar,respectively.