Profile Changes Of Soil Phosphorus Storage Capacity And Environmental Risk Assessment In Red Upland Soil And Paddy Field

Profile soil samples?0?120 cm?were collected from the peanut upland?PU?and paddy field?PF?under the different slope,which located at the typical red soil small watershed in Sunjia,Yingtan,Jiangxi Province.Soil total phosphorus?P?,available P?Bray-P?and P sorption index?PSI?,P saturation ratio and soil P storage capacity?SPSC?were analyzed in lab.The conversion relationships of different SPSC values were calculated through the P,aluminum?Al?,iron?Fe?extracted by the ammonium oxalate,Mehlich 1,HCl-NH₄F?Bray?and Na HCO₃?Olsen?solutions also were compared and discussed.The theoretical framework and application model of SPSC for the environmental risk assessment of P loss in red soil peanut upland and paddy field was established based the exogenous P addition experiment.The results are as follows:?1?Soil TP and Bray-P of peanut upland?PU?and paddy field?PF?decreased with the increase of soil profile depth.Compared with PU on the top of slope?PU-T?,the TP contents of PU located in the middle of slope?PU-M?and at the bottom of slope?PU-B?significantly increased by 30%and 29%,but the Bray-P significantly decreased by 57%and 58%, respectively.Compared with new paddy field in the middle of slope?PF-M?,the TP contents of paddy fields on the top of slope?PF-T?and at the bottom of slope?PF-B?significantly increased by 74%and 103%,but the Bray-P decreased by 9%and 6%,respectively.The PSI of in PU and PF ranged in 621?2156 mg kg^-1and 561?1849 mg kg^-1,respectively;and both increased with the increasing of soil profile depth.?2?The PSR of PU and PF ranged in 0.01?0.13 and 0.07?0.18,respectively;and the PSR of PU,PF-T and PF-B all decreased with the increase of soil profile depth,but the PF-M was the opposite.Compared with PU-B,the PSR of PU-M and PU-T significantly decreased by 52%and 89%,respectively.Compared with PF-M,the PSR of PF-T and PF-B significantly increased by 15%and 7%,respectively.The threshold PSR calculated by the P,Al,and Fe in acid ammonium oxalate,Mehlich 1,Bray method,and Olsen method extracting solutions were in order of 0.09,0.09,0.04,and 0.85.?3?The SPSC of PU and PF ranged in-172?99 mg kg^-1and-76?295 mg kg^-1, respectively,and all decreased with the increase of soil profile depth?except for the PF-M?.Compared with PU-B,the SPSC of PU-M and PU-T significantly increased by 750%and1264%,respectively.Compared with PF-M,SPSC of PF-T and PF-B significantly increased and decreased by 47%and 40%.The SPSC calculated by ammonuim oxalate exctraction method ranged in-172 to 295 mg kg^-1,and was the 2.82,3.10,and 3.52 times of SPSC calculated by the Mehlich 1,Bray method,and Olsen method,respectively.Based on the correlation relationship between SPSC and Ca Cl₂-P,PSI,DPS,when SPSC<0 or Ca Cl₂-P>0.5 mg kg^-1,PSI<892 mg kg^-1,DPS>15.8%,the environmental risk of P loss in the soil profiles of PU and PF will be increased.?4?The soil TP,Bray-P and PSR all significantly increased with the addition of exogenous P,but the SPSC significantly decreased.The threshold PSR of PU,PF-M and PF-B were 0.10,0.08,and 0.10,respectively;and the safe amount of P applied was 455 mg P kg^-1soil^-1,418 mg P kg^-1soil^-1,and 388 mg P kg^-1soil^-1,respectively.?5?According to the relationship of SPSC and Bray-P,there was four phases for the soil P management in PU and PF:When SPSC>239 mg kg^-1or Bray-P?20 mg kg^-1,soil was P sink,and continued application of P could increase the crop yield;when 189 mg kg^-1<SPSC?239 mg kg^-1or 20 mg kg^-1<Bray-P?47 mg kg^-1,soil was P sink,continuous application of P fertilizer still also be needed to ensure crop high-stable yield;when 0<SPSC?189 mg kg^-1or 47 mg kg^-1<Bray-P?151 mg kg^-1,soil was P sink,continuous application of P not only could not increase crop yield but also could increase the potential risk of soil P loss;when SPSC?0 or Bray-P>151 mg kg^-1,soil was P source,P application must be stopped and the environmental protection measures must be implemented immediately.?6?According to the changes of SPSC in surface horizon?a?and spodic horizon?b?, there was four types of profile soil P loss in PU and PF:when SPSC_a<0 and SPSC_b<0,soil was P source and was releasing P into the surrounding environment;when SPSC_a>0 and SPSC_b>0,soil was P sink and continued P application was permitted;when SPSC_a<0 and SPSC_b>0,soil surface horizon was P source,but profile P leak was relatively weaker,the P application program should be adjusted and the soil surface P storage should be monitored;when SPSC_a>0 and SPSC_b<0,soil surface horizon was P sink,continued P application was permitted,but there existed P loss risk in soil spodic horizon,and the change of P in groundwater should be monitored as well as the groundwater level should be raised.