Characteristics Of Fertility And Nitrogen Mineralization Of The Foreshore Reclamation Paddy Soils

In the present study,a series of foreshore paddy soils and upland soils reclaimed at six typical periods(Western Han dynasty,Song dynasty,Yuan dynasty,Ming dynasty, Qing dynasty and Present age,and the corresponding cultivation chronosequence was 2000,1000,700,500,300 and 50 years,respectively) at Cixi City Zhejiang province were selected to investigate the characteristics of fertility,and nitrogen minilization based on chemical analysis combined with a Stanford culture experiment under the control condition.Results were as follows:(1) Significant differences of element concentration,pH,and organic matter in foreshore paddy soils were determined in dependence on foreshore reclaimation period, element itself and their available.The early reclaimed foreshore paddy solids tended to have lower total Na,Mg,Ca,Mn,Fe,P and S relative to the later reclaimed paddy soils. Soil OM and total N were significant higher in paddy soils reclaimed at Western Han dynasty than these at other periods.Paddy soil pH tended to decrease along with reclaimation period from present age to Western Han dynastry,and the pH of paddy soils reclaimed at Western Han dynastry decreased to 4.22,which was obviously lower than these reclaimed at other periods.The content of alkaline-hydrolysed N in paddy soils reclaimed at Western Han dynasty was significant higher than these reclaimed at other periods.Content of available K in paddy soils reclaimed at five periods followed the decreasing order as bellow: Present age>Song,Yuan,Ming dynasty>>Western Han dynasty.(2) Contents of OM,Total N,alkaline-hydrolysed N,S,total Mn,total Mg and total Ca were significant higher in foreshore paddy soils than those in upland soils,but no remarkable difference of pH,P,K,total Al,total Fe and total Na were observed between in paddy soils and in upland soils.(3) There were no difference of the nitrogen mineralization potential(N₀) and the accumulative mineralized nitrogen(N_t) for 119d in paddy soils reclaimated at five periods, but the differences of nitrogen mineralization process were determined in dependence on paddy soil reclaimation periods.The proportion of the accumulative mineralized nitrogen for 14d in these for 119d in paddy soils reclaimed at five typical periods followed the increasing order as bellow:Western Han dynasty<0) in foreshore paddy soils reclaimated at five periods,their k₀ followed the increasing order as bellow: Western Hart dynastyt and N₀ between in foreshore paddy soils and in upland soils reclaimed at same period.The proportions of N₀ in total N,and N_t for 119d in total N were lower in foreshore paddy soils than in upland soils reclaimed at the same period.The proportation of the N mineralized for 14d in these for 119d was larger in foreshore paddy soils than in upland soils reclaimed at same period.These results indicated the foreshore paddy soils had a relative lower proportion of tolerable mineralized nitrogen,but exhibited a higher proportation of fast mineralized nitrogen compared to the upland soils reclaimed at the same period.The N mineralization rates(k₀) was significant larger in foreshore paddy soils than these in upland soils.It could be concluded that the N active was higher in foreshore paddy soils than that in the upland soils.To sum up,the foreshore paddy soils showed a higher potential of N and C fixation compared to the foreshore upland soils reclaimed at same period,the earlier foreshore reclaimation period,the more nitrogen cumulation in foreshore paddy soils,the weaker active of nitrogen in foreshore paddy soils.The foreshore paddy soils had a lower proporttation of the tolerable mineralized nitrogen,but higher proportation of fast mineralized nitrogen compared to foreshore upland soils reclaimed at same period.The earlier foreshore reclaimation period,the lower available K in the foreshore paddy soils, and the lower pH in the foreshore paddy soils.Therefore,acidification and imbalance of nutrients in the early reclaimated foreshore paddy soils shall be paid more attentation.