Effects Of Burning Straw On Season Dynamics In Soil Available Nitrogen And Its Mineralization

Straw is one of the main wastes produced in the agricultural production process.Although some straw has been comprehensively utilized,a large amount of straw is still treated by open burning.Open burning straw is an important human disturbance that pollutes the atmosphere and causes soil degradation.However,current research pays more attention to the impact of burning straw on the atmospheric environments,and few on the soil environments,especially soil nitrogen dynamics.In this study,field sampling and laboratory analysis methods were used to examine the relationships between different factors?e.g.,burning season,soil type,crop type?and soil nitrogen availability,and to explore the seasonal changes in soil inorganic nitrogen?N?after burning straw.Additionally,using the effects of adding straw and its ash on soil nitrogen mineralization were studied using laboratory culture experiments,and further revealed the effects of burning straw on soil nitrogen fertility.The main conclusions were as follows:?1?After burning straw in the autumn and spring,soil moisture content significantly increased by 24%due to the melting of frozen soil water.Soil available phosphorus and sulfur significantly decreased by 30%and 19%,respectively.After burning straw in the autumn,the total phosphorus content of the soil was 100%lower than that of spring,and the urease was 43%higher than that of spring.Soil types affected the responses of soil properties to burning straw.The available phosphorus contents of the clay sand soil decreased by 49%after burning.The water content of the sand soil was reduced by 28%.Soil depth and crop types showed no significant effects on the response of soil properties to burning straw?2?Burning straw affected the soil inorganic nitrogen contents.Burning straw significantly increased soil NH₄⁺-N by 100%and decreased NO₃^--N by 68%.The soil NO₃^--N contents were 80%lower after burning in the autumn than that burning in the spring,and the soil NH₄⁺-N contents after burning in the autumn were 43%higher than burning in the spring.Soil depth affected the responses of soil inorganic nitrogen to burning straw.After burning straw,NH₄⁺-N increased by 114%in the depth of 0-5 cm,while NO₃^--N decreased by 69%;there was no significant change in the 5-10 cm depth.Soil type affected the responses of soil inorganic N to burning straw.After burning straw,NH₄⁺-N of the oil sand soil increased by 62%and the NO₃^--N decreased by 57%;NH₄⁺-N of the sand soil increased by 57%.Burning Crop types affected the responses of soil inorganic N to burning.After burning rice and corn straw,soil NH4+-N increased by 62%and 38%,respectively.After burning corn straw,the soil NO₃^--N decreased by 60%.The results of variance partitioning showed that burning straw was the most important for soil NH₄⁺-N,and the burning season was the most important for soil NO₃^--N.?3?Compared with the control,adding straw,ash and their mixture significantly increased the soil pH,but adding straw showed no significant effect on soil properties.Adding ash showed no significant effect on soil urease activity,NH₄⁺-N and NO₃^--N contents.Adding straw and the mixture of the straw and ash?MSA?significantly increased soil urease activity by 300%and 130%,respectively,and decreased soil NH₄⁺-N and NO₃^--N by 47%and 49%,respectively.The soil NH₄⁺-N reduced with the culture time and reached equilibrium on the 9th d.The soil NO₃^--N increased with the culture time and decreased after reaching the peak on the21st d.After Adding straw or MSA,the trend of soil urease activity was opposite to that of soil NO₃^--N.In the control,NO₃^--N was significantly negatively correlated with the soil water content.After adding straw,soil NH₄⁺-N was significantly negatively correlated with urease activity,and NO₃^--N was significantly positively correlated with soil pH.After only adding ash or MSA,soil NO₃^--N was negatively correlated with soil,pH and urease activity.The results of variance partitioning showed that the adding straw was the most important factor in affecting soil ammonization,while soil water content was the most important factor for soil nitrification.