Spatiotemporal Variation Of Soil Salinity And Nutrients In Saline-alkali Land Of Well-facilitated Farmland Construction And Cultivated Land Quality Evaluation

Effected by the special climate,hydrology,geological conditions and farming methods,the saline-alkali cultivated land in Ningxia Yellow River irrigation area is large in area,widely distributed,poor in soil fertility and low in yield,which seriously restricts the protection of local ecological environment and the high-quality development of modern agriculture.The implementation of high standard farmland construction and management and transformation of saline-alkali farmland can enhance the production capacity of cultivated land,which is of great significance to promote the development of modern agriculture and ensure national food security.In order to accurately evaluate the benefits of high-standard farmland construction on the improvement of soil salinity,nutrients and cultivated land quality,this paper takes high-standard farmland construction in Ningxia "Demonstration Area of Salt-alkali Land Comprehensive Utilization Technology in Jiaoji Village,Qukou Town,Pingluo County" as the research object,adopts grid fixed-point sampling survey and spatial analysis method.The temporal and spatial variation of soil salinity and nutrients in saline-alkali land of high-standard farmland construction was discussed and the cultivated land quality was evaluated.The main results are as follows:1,High vertebral farmland construction project area,according to the national standard of the second soil census,in 0～20 cm of soil depth,five kinds of soil nutrient content before and after the project increased,rapidly-available potassium,total nitrogen and alkaline hydrolysis nitrogen nutrient level has increased,and significant differences in different periods,organic matter and effective phosphorus in there is no significant difference before and after the period.From the perspective of variation coefficient,the variation coefficient of soil nutrients ranged from 25.05%to 100.83%.Available phosphorus was of strong variability,while other nutrients were of moderate variability.In the soil depth of 20-40 cm,the nutrient levels of organic matter,available potassium,available phosphorus and alkali-hydrolyzable nitrogen increased before and after the project implementation.There were significant differences in available k,total N and alkali-hydrolyzable N,but no significant differences in organic matter and available P.The coefficient of variation ranged from 28.57%to 76.77%,and all the five nutrients had moderate variability.In the soil depth of 40-60cm,the available potassium level did not change after the implementation of the project,while the levels of organic matter,available phosphorus,alkali-hydrolyzable nitrogen and total nitrogen all increased.There was no significant difference before and after the period of available P,but there was significant difference before and after the period of organic matter,available k,alkali-hydrolyzable N and total N.The coefficient of variation ranged from 32.23%to 152.04%.2,High standard farmland construction project area,at the beginning of the project implementation,the total nitrogen optimal half variance theory model for the spherical model,the optimal semivariance rapidly-available potassium theoretical model for the gaussian model,organic matter,effective phosphorus and alkaline hydrolysis nitrogen optimal half variance theory model for the index model,after the project five kinds of nutrient optimal half variance theory model for the spherical model.The C/(C0+C)ratios of soil nutrients were all higher than 0.75 at the later stage of project implementation,with stronger spatial correlation and little influence by human factors.3.Before and after the implementation of high-standard farmland construction project area,the content of Cl-,Na+,SO42-and total salt decreased in the later period.Before the implementation of the project,the C/(C0+C)ratios of salt ions CO32-HCO3-,K+,Ca2++Mg2+ and total salt content were all higher than 0.75,showing strong spatial correlation.After the implementation of the project,the C/(C0+C)values of CO32-,HCO3-,Cl-and total salt content were all higher than 0.75,showing strong spatial correlation.The results showed that human factors had a greater effect on K+and Ca2++Mg2+.There were significant differences in soil pH in different soil layers and different periods,and the reduction effect was obvious.4.Before and after the implementation of the project,the quality of cultivated land improved by 0.30 grades.In the early stage of the implementation of the project,the cultivated land quality grade is in grade four,grade seven,with an average grade of 5.39.Among them,grade five has the largest area of 197.96 hm2,accounting for 43.51%of the project area,followed by Grade six,with an area of 137.87 hm2,accounting for 30.30%of the project area,grade four and grade seven have the least area.It accounts for 26.19%of the total project area.At the late stage of project implementation,the cultivated land quality grade was in grade four,grade seven,with an average grade of 5.09.The area of grade four was the largest,173.49 hm2,accounting for 38.13%of the total area of the project area,with an increase of 23.67%.The area of grade five and Grade seven both decreased,while the area of grade six increased.