Acta Geographica Sinica ›› 2017, Vol. 72 ›› Issue (11): 2032-2046.

• Surface Process and Ecological Environment •

### Cropland quality evolution following coastal reclamation at the prograding tidal flats of Jiangsu Province, China

Yan XU1,2,3(), Lijie PU1,2(), Runsen ZHANG1, Ming ZHU1,2, Xueying LI1, Hongyun SHEN1, Tianying MAO1, Chenxing XU1

1. 1. School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China
2. The Key Laboratory of the Coastal Zone Exploitation and Protection, Ministry of Land and Resources, Nanjing 210023, China
3. School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, Jiangsu, China
• Received:2017-04-10 Revised:2017-08-08 Online:2017-11-20 Published:2017-11-16
• Supported by:
National Natural Science Foundation of China, No.41230751;Postdoctoral Program of Jiangsu Province, No.1601067B

Abstract:

Coastal prograding tidal flats are important wetlands and reserve resources of cropland in China, which provide the services of ecological protection, society security, and economic development. Taking the reclamation zones on the prograding coast of Jiangsu as a case study, this paper analyzed soil quality at the reclamation zones with a duration of 0-40 years to indicate the evolution of cropland quality following reclamation for sustainable use of cropland, by using the method of "space for time substitution". The results show that cropland soils had high salinity but low nutrients. The variation of soil physical and chemical properties is high in the coastal reclamation zones, and the soil particle sizes had obvious gradients of North-South and Land-Sea. The factors such as topography, vegetation status, and the path of tidal flats to cropland had significant impacts on cropland quality evolution following coastal reclamation. The path of tidal flats to cropland were jointly decided by physical condition of reclamation zones, development entity, and development scale in the coastal area of Jiangsu. The cropland trajectories have changed from "halophytes→aquaculture pond→cropland" to "halophytes→cropland" in the central part of the province's coastal area. This change shortened the period of tidal flats to cropland, but led to idle tidal flats after reclamation. The soils of coastal tidal flats have gradually transferred into soils of cropland. The changing trends of soil properties were divided into four types. The first one was the type of increase, such as soil total phosphorous, available phosphorous, and clay content. The second one was the type of decrease, such as sand content. The third one was the type of increase then decrease, such as soil salinity and pH. The fourth one was the type of decrease then increase, such as soil organic matter, total nitrogen, available nitrogen, and capacity of exchange cations. At the initial period of reclamation, soil organic matter showed a declining trend because of the process of mineralization. The soil salinity and pH increased due to transpiration and evaporation. At the middle period of reclamation, soil organic matter and nutrients increased because of the fertilization and organic matter input via human cultivation. Soil salinity and pH decreased as a result of precipitation and water resource facilities. At the later period of reclamation, the factors of soil quality fluctuated under the effect of cultivation management. The quality of cropland at the reclamation zones was fragile and sensible to cultivation management, because of the relatively short history of coastal reclamation.