Short-term Effects Of Exogenous Ferrihydrite And Glucose On The Paddy Soil Available Phosphorus Under Waterlogged And Non-waterlogged Conditions

Previous studies have shown that the seasonal redox cycles caused by repeated drying and wetting conditions in the rice-wheat cropping system facilitate the redox transformation of iron(Fe)oxides while application of organic fertilizers further enhanced the transformation and the accumulation of active iron oxides in soil.We assumed that the transformation of iron oxides and accumulation of reactive iron oxides in soil might also changed the availability of soil phosphorus(P),which is a key essential nutrient necessary to optimize healthy plant growth and yields.In this paper,the soil fertility indicators of long-term application of different fertilizers under the rice-wheat rotation system were firstly analyzed.Then,laboratory incubation experiments were conducted by using the soil,in which no fertilizers was applied for a long term,with addition of exogenous an active iron oxide(ferrihydrite)and organic substance(glucose)to explore the effects of exogenous ferrihydrite and glucose on the availability of P and microsite distribution of Fe and P.Main results were gained as follows.1.The soil sample analysis results of the different fertilizer treatments from the long-term field location experiment site in Jintan,Changzhou,Jiangsu,showed that the treatments of different application of fertilizers had significant effect on soil fertility indicators,As compared with no fertilizer control(T1),all treatments including application of chemical,organic,and chemical-organic complexed fertilizers as well as straw return to soil significantly decreased soil pH,and the high level chemical-organic complexed fertilizer treatments(T16 and T17)acidified soil most significantly by more than 1.2 pH unit of reduction.As compared with T1,the treatment(T5)of a high level organic fertilizer and treatments(T10,T11,T12 and T13)of straw returning with application of organic fertilizers and chemical compound fertilizers significantly increased soil organic matter,total nitrogen ant total phosphorus(TP)contents.All treatment excepting the sole chemical fertilizer treatment significantly increased the soil TP,while no significant difference in total potassium was determined among all treatments.Some treatments of straw returning with application of organic fertilizers and chemical compound fertilizers coul significantly increased soil available nitrogen(treatments T11 and T13),SAP(treatments T12 and T13)and soil available potassium.(treatment T11,T12 and T13)as compared with T1.All fertilizer treatments significantly increased rice and wheat yields as compared with T1,but no significant difference in yield was determined among fertilizer treatments.This suggested that replacing a portion of chemical fertilizers by organic fertilizer,straw returning,and application of organic-inorganic complexed fertilizer were practicable in production of rice and wheat.2.The results from laboratory incubation experiments showed that addition of ferrihydrite or glucose or both could significantly decrease SAP within 192h.Exogenous ferrihydrite decreased the SAP by 30.9%and 25.8%,while exogenous glucose decreased SAP by 40.5%and 26.8%,respectively,under waterlogged and non-waterlogged conditions.For treatments with both ferrihydrite and glucose amendments,SAP were decreased by 61.5%and 45.3%,respectively,under waterlogged and non-waterlogged conditions.Thus,SAP of waterlogged soil was more affected than that of nonwaterlogged soil.These results suggested that chemical fixation of P by active iron oxides and microbiological immobilization of P by carbon induction might co-exist and the adsorption sites of P on active iron oxides might little be affected by active organic substances,which can be used by microbes.3.Synchrotron radiation infrared micro-imaging analysis showed that addition of either ferrihydrite or glucose or both could break the balance of interaction between iron and phosphorus by changing the spatial distribution of Fe and P in microsite.These results suggested that exogenous addition of ferrihydrite and glucose might disturb the original relationship of Fe and P in soil especially more evident in the waterlogged condition than in the non-waterlogged condition.In conclusion,application of fertilizers is the main reason that leads to P accumulation in rice-wheat rotation systems.Exogenous application of ferrihydrite and glucose can decline SAP in short stages.This is consistent with the increase of active iron(Fe)oxides and organic matter and total phosphorus content under long-term fertilization.The above results have important reference values and application potentials in soil phosphorus nutrient management and non-point source phosphorus pollution control.