Temporal And Spatial Variability Of Available Nitrogen,Phosphorus And Potassium Status In Cropland Topsoil In Jilin Province

Understanding the temporal and spatial variability of nutrients status in cropland soil could provide an important foundation to optimize crop precise nutrient management,resource high-efficiency use,soil fertility improvement and agri-ecological environmental protection.In this study,the spatial variability of nitrogen(N),phosphorus(P)and potassium(K)status across the different regions and soil types in cropland topsoil of Jilin province were evaluated,based on the data of topsoil total N,alkali-hydrolyzable N,olsen P and exchangeable K in the program of soil testing and recommended fertilization during 2005-2013.Moreover,the historic changing trend of topsoil N,P and K status in cropland topsoil were also investigated by comparing with the data obtained during the second national soil survey.(1)The total N content ranged between 0.4 and 3.9 g/kg with a mean of 1.62 ± 0.60 g/kg,and alkali-hydrolyzable N content ranged between 15 and 360 mg/kg with a mean of 145.0 ± 59.5 mg/kg in the present cropland topsoil of Jilin province.Total N and alkali-hydrolyzable N contents in topsoil showed same sequences among the various soil types,which were highest in dark brown soil with the values of 2.02 ± 0.57 g/kg and 190.2 ± 72.8 mg/kg,and followed by albic soil,paddy soil,black soil,meadow soil,chernozem and aeolian sandy soil.In view of the province as a whole,the spatial distribution of N status in topsoil was characterized by being high in the east and low in the west,and a positive and significant correlation was obsevred between total N content and alkali-hydrolyzable N content on the county scale.Compared with the date in second soil survey,total N and alkali-hydrolyzable N contents in topsoil showed obviously ascending trends in the scale of whole Jilin province,the change magnitude of topsoil N status were greatest in central region but lower relatively in west region.Obvious differeces were also observed in change trends of topsoil N status among the various soil types.Of which,black soil,chernozem,meadow soil and aeolian sandy soil showed increasing trends,while dark brown soil,albic soil and paddy soil showed decreasing trends.Compared with other soil types,the highest increasing magnitude was observed in aeolian sandy soil and the highest decreasing magnitude was found in dark brown soil.(2)The olsen P content ranged between 1.6 and 84.2 mg/kg with a mean of 25.4 ± 13.0 mg/kg in the present cropland topsoil of Jilin province.The olsen P contents in topsoil showed different among the various soil types,these were highest in albic soil with the values of32.5 ± 15.1 mg/kg,and followed bydark brown soil,black soil,paddy soil,meadow soil,aeolian sandy soil and chernozem.In view of the province as a whole,the spatial distribution of P status in topsoil was characterized same as N by being high in the east and low in the west.Compared with the date in second soil survey,olsen P contents in topsoil showed obviously ascending trends in the scale of whole Jilin province,the change magnitude of topsoil P status were most significant in east region but relatively lower in west region.The great discrepancies were also observed in the change trends of topsoil P status among various soil types.Of which,chernozem,albic soil,meadow soil,paddy soil and aeolian sandy soil showed increasing trends,while dark brown soil and,black soil showed decreasing trends.Compared with other soil types,the highest increasing magnitude was observed in aeolian sandy soil and the highest decreasing magnitude was found in dark brown soil.(3)The exchangeable K content ranged between 24 and 299 mg/kg with a mean of 123.6 ± 33.1 mg/kg in the present cropland topsoil of Jilin province.The exchangeable K contents in topsoil showed different among the various soil types,these were highest in black soil with the values of 138.2 ± 39.2 mg/kg,and followed by meadow soil,chernozem,dark brown soil,albic soil,aeolian sandy soil and paddy soil.In view of the province as a whole,the spatial distribution of K status in topsoil was characterized by being high in the northwest and low in the southeast.Compared with the date in second soil survey,exchangeable K contents in topsoil showed obviously decreasing trends in the scale of whole Jilin province,the increase magnitude of topsoil K status were slightly higher in Changchun City,Jilin City,Tonghua City and Baishan City,but other regions have greatly reduced.The great discrepancies were also observed in the change trends of topsoil K status among various soil types.Of which,chernozem,albic soil,paddy soil and aeolian sandy soil showed increasing trends,while black soil,dark brown soil and meadow soil showed decreasing trends.Compared with other soil types,the highest increasing magnitude was observed in aeolian sandy soil and the highest decreasing magnitude was found in dark brown soil.In conclusion,there were enormous differences in spatial distribution and historic change in N,P and K status in the cropland topsoil of Jilin province.Based on the temporal and spatial characteristics of topsoil nutrient status,we suggested that N and P fertilizer rates in crop production should be strictly controlled in the central grain producing region of Jilin province,aiming to improve N and P fertilizer use efficiency and reduce environmental risk.Meanwhile,K fertilizer should be applied reasonably with straw returning to field in this region to maintainsoil K balance.In the east and west regions of Jilin province,crop fertilizer management should be improved according to local natural climatic conditions,soil fertility status and cultivation measures to enhance cropland productivity and achieve crop high yield and nutrient high use efficiency.