Characteristics Of Phosphorus Migration And Transformation After Straw Returning Under Flooding Condition

Controlling the concentration of phosphorus in water is an effective way to prevent and control the eutrophication of fresh water.In China,phosphorus mainly comes from agricultural sources,so it is very important to pay attention to phosphorus flow in farmland ecosystem.Straw is rich in phosphorus,and straw returning as a conventional agronomic measure provides the possibility for phosphorus to enter the water.Rice is the main food crop in China,and its special water management makes the risk of phosphorus loss greater.At present,the effect of straw returning on the receiving water and the change of phosphorus in paddy soil are not comprehensive.In order to explore the forms and distribution of phosphorus in soil and water body after straw returning,this study took fluvo-aquic paddy soil(C)and yellow brown paddy soil(H)as the research objects,and set up four treatments of adding straw(C+,H+)and not adding straw(C-,H-)under flooding conditions,and carried out the simulation experiment of straw returning by filling soil column.The changes of various forms of phosphorus in overlying water,leachate and soil layers at different depths in different periods were measured during cultivation,and the migration and transformation rules of phosphorus were analyzed.The main results are as follows:(1)The addition of straw significantly aggravated the loss of phosphorus in the fluvoaquic paddy soil.The total phosphorus loss was 2.45 times,1.06 times,1.32 times,and 1.56 times on the 37 th,54th,71 st and 85 th day,respectively.The addition of straw slightly increased the loss in yellow brown paddy soil.Loss of phosphorus.In the treatment of adding straw,the total phosphorus concentration lost by the overlying water and leachate exceeded 0.02 mg/L.The addition of straw also significantly increased the greenhouse gas emission flux.(2)The addition of straw significantly increased the concentration of particulate phosphorus and soluble organic phosphorus in the overlying water.The average proportions of particulate phosphorus in total phosphorus in the overlying water treated with straw addition in Fluvo-aquic paddy soil and yellow-brown soil were 60.6% and 65.7%,respectively.Among the total soluble phosphorus,the proportions of soluble organic phosphorus were 75.1% and 60%,respectively.The total amount of particulate phosphorus and soluble organic phosphorus in the overlying water is significantly positively correlated with the amount of phosphorus released by straw and the soluble organic carbon content of the upper soil,and is significantly negatively correlated with the phosphorus content of the upper soil microbial biomass.(3)The addition of straw significantly increased the cumulative loss of soluble organic phosphorus in the leachate of the fluvo-aquic paddy soil,resulting in a significant increase in the total phosphorus of the leachate;the addition of straw also increased the soluble organic phosphorus in the yellow-brown soil Cumulative loss,but did not reach the level of significance.Particulate phosphorus is the main form of leachate loss in Fluvo-aquic paddy soil,and soluble phosphorus is the main form in yellow brown paddy soil.The soluble phosphorus in each treatment leachate is mainly organic phosphorus.(4)The addition of straw increased the proportion of organic phosphorus in the two soils.The proportions of the extracted states of the two soils were,in order,inorganic phosphorus extracted by dilute hydrochloric acid,total phosphorus extracted by concentrated hydrochloric acid,total phosphorus extracted by Na OH,total phosphorus extracted by NaHCO3,residual phosphorus,and total phosphorus extracted by water.The proportions of organic phosphorus in Fluvo-aquic paddy soil and yellow brown paddy soil were 8.77%-11.28% and 12.27%-16.80%,respectively,which increased by 0.054% and0.65% after adding straw.The addition of straw has no significant effect on the content of available phosphorus,but significantly affects the content of water-extracted inorganic phosphorus and Na OH-extracted inorganic phosphorus.(5)After adding straw,the content of active organic phosphorus in fluvo-aquic paddy soil increased,and the active organic phosphorus in yellow brown paddy soil decreased.In the changes of different phosphorus components,the fluvo-aquic paddy soil favors the activation of stable phosphorus,and the yellow brown paddy soil favors the fixation of phosphorus.Phosphorus components with higher activity have significant differences in soil layers of different depths.This is due to the higher activity of phosphorus grouping in the soil that has a stronger ability to migrate.Due to insufficient cultivation time and low phosphorus content in the applied straw,there is no significant difference in total phosphorus in different soil layers.(6)Returning straw to the field in the paddy field will aggravate the loss of phosphorus.Adding straw to the fluvo-aquic paddy soil will activate the stable phosphorus in the soil,and further increase the loss of phosphorus in the form of leakage.The addition of straw in the yellow-brown paddy soil will cause the conversion of active phosphorus to stable phosphorus and increase the accumulation of phosphorus in the soil.In paddy fields with frequent irrigation and drainage,returning straw to the field will have a negative impact on the water environment.This study quantified the loss of different forms of phosphorus after returning straw to the field and the distribution of different forms of phosphorus in the soil,observing the negative loss and the corresponding environmental effects,and providing a reference for the prevention and control of agricultural non-point source pollution.