Spatio-temporal Dynamics And Correlations Between Soil Salinity And Nutrient In Reclamated Tidal Flats

With the advancement and deep going of "LOICZ" plan, the study about interactions between land and ocean in the coastal zone has become a hot topic which is paid much attention by the scholars. As the most important part of coastal zone and basilic mothball resources of cultivated land to human, tidal flat is not only valuable to offer ecological service function, but also play an important role to alleviate the increasingly acute contradictions between human and cultivated land by maintaining the national food security, especially in the countries where there is large population with relatively limited land resources. With the implementation of coastal strategy, the state gradually pays much attention to the development and the planning of tidal flat resources in the coastal area.The coastal area of Jiangsu province in China is a typical deposit type flat, where the area is largest and the land use types are most complete in mid-latitudes of the world. Reclamation for decline of soil salinity has been a main human activity and primary method to use the tidal flat in this place for many years. As the most important resource of supplementary to cultivated land in coastal province, the nutrients play a decisive role to the utilization of the reclamation. At the same time, the improvement of soil salinity is the foundation to the effective use of soil with significant characteristics of salinity. However, whether the nutrient is also affected by soil salinity just like that in inland in this special area? As two important factors affecting the utilization of land and the growth of plants, the study on the spatio-temporal dynamic and correlation between soil salinity and nutrient in this special area is very valuable to reveal the evolution of soil salinity and nutrients under the different influence of intensive human activity and the correlation of them under the natural condition. At the same time, it can provide reference for the utilization and management of tidal flat in future. In this article, the Parameters such as Cluster Coefficient, Coefficient of Variance and the methods of principal component analysis, scatter diagram and correlation analysis are used. The results are as follows:Firstly, with the increase of reclamation years and the acceleration of humans’ interference, the average soil salinity in tidal flats decreases gradually. The desalination in the center of farmland where crop grows is apparently better and faster than that of the edge of farmland without plants. There is a process of "even distribution profiles (EDP) — surface accumulation profiles (SAP) — oscillation profiles (OP) — bottom accumulation profiles (BAP) — oscillation profiles (OP) — even distribution profiles (EDP)" for the change of soil salinity in soil profile of tidal flats under the different reclamation years, which shows the conversion from the salinity is affected by natural factors mainly to that is affected by humans’activities.Secondly, with the increase of reclamation years and the acceleration of humans’ interference, the integrated nutrient in tidal flats increases gradually, and the speed of increasing suffers the conversion from fast to slow. There is an opposite process from even distribution profiles (EDP) to surface accumulation profile (SAP) for the change of integrated nutrient in soil profile of tidal flats under the different reclamation years. The contents of nutrient indexes show different trends. Among them, the trends of organic matter, total nitrogen and available nitrogen are almost similar. The contents of them are relatively barren, but they all increase gradually, and the peed is decreasing gradually. The contents of Total potassium and available phosphorus are relatively stable, which show a minor change in the whole cycle. The content of the available potassium is most abundant which is the only index decreasing with the reclamation years.Thirdly, there is a breakthrough point where the content of soil salinity and nutrients is relatively stable, but the time when nutrient is relatively stable is later than that of salinity. When the tidal is reclaimed by 20 years, the soil salinity is relatively stable, which is about 0.8-1.0 g/kg. Besides the available phosphorus and total potassium whose content is relatively stable in whole cycle and the Total phosphorus whose content is affected by humans’ activities obviously, the trends of other nutrient indexes are almost similar too, which is stabilize at around 9-10 g/kg (CM),7-8 g/kg (TN),50 mg/kg (AN) and 150 mg/kg (AP) after reclamation for 30 years.Fourthly, the effect of soil salinity to the nutrient is very outstanding, and all of the nutrients indexes are decreasing with the increase of soil salinity except for available potassium. The effect of salinity to nutrient can be roughly divided into 4 categories:firstly, negative influence with strong elastic and critical point, which include organic matter and alkali hydrolysable nitrogen; secondly, negative influence with weak elastic and critical point, which include integrated nutrient and total nitrogen; thirdly, negative influence with wake elastic, which consist of the total phosphorus, total potassium and available phosphorus; finally, positive influence with strong elastic, which include available potassium. All of the four types have their own characteristics.Fifthly, the correlations between soil salinity and total N, available K are very significant at 1% level, and the correlation between soil salinity and alkaline hydrolysis nitrogen, comprehensive nutrient are also significant at 5% and 10% level respectively. Although organic matter didn’t pass the significant test, the correlation between it and soil salinity is higher than that of others, and their relationship is also credible at 15% level. All of the above illustrate that the effect of salinity on nutrient is mainly achieved by affecting the organic matter content, total nitrogen and available nitrogen.Finally, according to the results of analysis, the soil type is divided into 3 types: low salinity and high nutrient; low salinity and low nutrient; high salinity and low nutrient. And the relevant suggestions of land use are also put forward according to the results of classification and the characteristics of each type.