Effects Of Straw Returning On Greenhouse Gas Emissions And Nitrogen Components Of Rice Planting In Tropical Areas

Straw returning is an important measure to reduce environmental pollution and improve the utilization efficiency of agricultural resources.Based on the paddy soil treated by different management measures for four years,four treatments were set up:no nitrogen application（CK）,conventional nitrogen application（CT）,straw application without nitrogen（ST）and straw application with nitrogen（CTST）.Through pot experiment,we studied the effects of straw returning on greenhouse gas emissions,soil nitrogen composition and content,plant nitrogen absorption and fertilizer nitrogen fate in tropical soil rice system under the condition of equal amount of nitrogen input,and analyzed the nitrogen composition characteristics of rice planting system under the condition of straw returning.In order to provide theoretical basis for reducing agricultural environmental pollution and improving nitrogen utilization in paddy field.The main results are as follows:1.Straw application increased CH₄emission in rice planting system,the cumulative emissions of CH₄in treatments with straw application were significantly higher than that in treatments without straw application（P<0.05）,and CTST treatment was 27.53 times of CT treatment.Straw application increased the CO₂emission in the system,and the CO₂absorption of CTST treatment was 27.14%lower than that of CT treatment.Nitrogen application significantly increased N₂O emission,and the cumulative emissions of N₂O in treatments with nitrogen application were significantly higher than that in treatments without nitrogen application（P<0.05）,while straw application reduced N₂O emission,the cumulative N₂O emission of CTST treatment was 49.11%lower than that of CT treatment（P<0.05）.The global warming potentials of nitrogen treatments were significantly higher than that of no nitrogen treatments,the CTST treatment was 68.78%less than that of CT treatment.2.Straw application promoted the increase of p H and the decrease of inorganic nitrogen concentration in surface water.Compared with CT treatment,CTST treatment significantly reduced the content of soil dissolved inorganic nitrogen（DIN）（P<0.05）,and increased the ratio of dissolved organic nitrogen（DON）to total dissolved nitrogen（TDN）.The content of dissolved nitrogen components in ST treatment decreased significantly at maturation stage of rice.The content of DON decreased first and then increased in all treatments,and it in CTST treatment was significantly higher than that in other treatments（P<0.05）.CTST treatment significantly increased the content of total hydrolysable nitrogen（THN）and its proportion in soil total nitrogen.In addition to ST treatment,the content and proportion of non-acid hydrolysable nitrogen（NHN）decreased evidently.Straw application promoted the increase of amino acid nitrogen（AAN）,and the content of AAN in CTST treatment was higher than ST treatment at all growth stages.Nitrogen application promoted the increase of hydrolysable ammonium nitrogen（HAN）at tillering and heading stages,but the content of HAN in CTST treatment was significantly lower than CT treatment.Nitrogen application promoted the decrease of amino sugar nitrogen（ASN）at heading stage,but promoted its increase at maturity stage,and the content of ASN CTST treatment was higher than CT treatment.The content of hydrolysable unidentified nitrogen（HUN）increased gradually in each treatment,and nitrogen application promoted the increase of it,the content of HUN in CTST treatment at maturation stage was significantly higher than that of other treatments.3.The biomass of stem,leaf and root was the highest in ST treatment.Nitrogen application significantly increased the nitrogen accumulation at the maturation stage of rice stem and leaf,and CTST treatment was higher than CT treatment.Compared with CTST treatment,the amount of accumulated nitrogen from fertilizer in stem and leaf of CT treatment was increased by14.97%.Compared with CT treatment,CTST treatment significantly reduced the proportion of accumulated nitrogen from fertilizer nitrogen in stem,leaf and root,and the decreasing in stem and leaf increased with the growth of rice.4.According to ¹⁵N fate analysis,the average proportion of nitrogen loss in fertilizer nitrogen was 54.66%,rice plant absorption was 23.87%,and soil residue was 21.47%.Compared with CT treatment,the uptake of fertilizer nitrogen by rice increased by 17.44%and the loss of fertilizer nitrogen decreased by 8.22%in CTST treatment.