Characteristics Of Nitrogen Transfer And Transformation In Coastal Saline Soil With Different Material Additions

Soil salinization has become one of the most important and widespread land degradation problems in arid,semi-arid,and coastal areas in the world.In today's shortage of land resources,how to improve saline soil has become a hot issue for scholars.Nitrogen is one of the essential nutrient elements for crop growth,and it is of great significance to the continuous and stable increase of crops.Therefore,it is of great significance to study the nitrogen cycle in saline soil.In this study,humic acid,gypsum,and bentonite were applied separately and humic acid and gypsum,humic acid and bentonite were applied to saline soil in a ratio of 5:1,3:1,1:1,1:3,and1:5.Thus,the leaching and culture experiments were carried out to determine the basic physical and chemical properties,nitrogen content,soil respiration,C and N conversion enzyme activities in the soil and leaching solution respectively.Discuss the improvement effect of humic acid,gypsum,and bentonite on saline soil by single application or mixed application and the characteristics of nitrogen transfer and transformation.The main findings are as follows:(1)After mixed application of humic acid and gypsum into saline soil,the soil infiltration rate can be significantly increased,and the maximum increase is when the ratio of humic acid and gypsum is 1:3.Separate application of humic acid or bentonite can significantly increase the soil infiltration rate,but mixed application is not necessarily.Among them,when humic acid is applied more,it can significantly increase the soil infiltration rate,and when more bentonite is applied,it will reduce the soil infiltration rate.(2)The Ca²⁺contained in gypsum and bentonite can increase the cation exchange capacity of saline soil,indicating that both gypsum and bentonite can play a good role in replacing Na⁺in saline soil.Among them,the mixed application of humic acid and gypsum has a positive effect on cations.The increase of exchange capacity is higher than that of single application,but the increase of cation exchange capacity of single application of bentonite is larger than that of mixed application.(3)The combined application of humic acid and gypsum can effectively reduce the migration of nitrogen,reduce the risk of leaching of nitrate nitrogen in saline soil,and play a good role in nitrogen preservation.Among them,when the application ratio of humic acid to gypsum is 1:3 and gypsum is applied alone,the nitrogen retention performance is the best.However,when humic acid is mixed with bentonite,the nitrogen retention performance is better when the application ratio is 5:1and 3:1,but its nitrogen retention capacity is lower than that of humic acid and gypsum mixed treatment,and the other treatments are not effective.Nitrogen may even accelerate the leaching of soil nitrogen to a certain extent.(4)The application of humic acid can increase the total carbon and organic carbon content of the soil,and the mixed application of humic acid and gypsum can increase the C and N convertase activity of the saline soil in the early stage of incubation,and promote soil respiration.When the ratio is 1:3,the enzyme activity is maximized.Also because the application of gypsum will inhibit nitrification to a certain extent,so that the soil nitrate nitrogen content will not increase rapidly to cause the risk of leaching.(5)When humic acid and bentonite are mixed into saline soil,if the application amount of bentonite is higher than that of humic acid,it can increase the activity of C and N convertase in saline soil,and the mixed application of humic acid and bentonite can slow down the decline of ammonium nitrogen.As well as the growth rate of nitrate nitrogen,it is possible that the application of bentonite will also inhibit nitrification,and when the ratio of humic acid to bentonite is 3:1,the decrease of ammonium nitrogen is the lowest,and when the application ratio is 5:1,the increase of nitrate nitrogen is the lowest.However,it will also decrease the soil infiltration rate to a certain extent and accelerate the leaching of nitrate nitrogen.Therefore,if bentonite can be modified and then used to improve saline soil,the effect may be better.