The Effect Of Tidal Flat Reclamation On Grain Production Capacity In The Jiangsu Coastal Zone

Agriculture is the founding of the nation and ensuring the food security is the basic task for economic development.Rapid globalization,urbanization and industrialization make more prime croplands transferred to the construction land.Therefore,since 1990,the China government has complemented the most strict cropland protection policy and focused on land consolidation project.The coastal tidal flat sediment is one of the basins of cropland reserve resources for securing the national food safety.The length of coast in Jiangsu province accounts for 5 percent of that in the whole country.The coast type of Jiangsu is simple,and most of which is tidal flat.Agriculture is the main development in the Jiangsu coastal zone.In 2009,the planning of coastal development was becoming the national development planning.The study on the effect of reclamation on grain production capacity has greatly practical significances to coastal development planning,alleviating the contradiction between people and land,and promoting land use more sustainably.This paper analyzes the effect of coastal reclamation and development on grain production capacity by the method of statistics,the method of space for time,the soil laboratory analysis,the AEZ model and the Maas-Hoffman model based on the technology of GIS,RS and GIS.This paper aims to understand the changes of cropland area and quality following coastal reclamation,indicates the relationship of reclamation time and cropland area and quality,and designs the land productivity model in the coastal reclamation zones.This research has four important conclusions as follows.We analyzed the changes of agricultural reclamation zones following reclamation and development.The coastal reclamation in Jiangsu province has the temporal and spatial characteristics.From 1948,there are two peaks,which are before 1984 and after 1995.The reclamation zones in the first period lie at the whole coastal area,and that in the second period at the south and central area.The areas of cropland are different in the reclamation zones with different development types.The area of cropland is large in the agricultural reclamation zones,and that is small in the reclamation zones developed for aquaculture,saltpan,port,urban,and industry.From 1990s,the development types transferred from agriculture to aquaculture,port,urban and industry.The percentage of agriculture reclamation zones before 1999 is 49.5%,and that after 2000 is 2.9%.The contribution of reclamation and development of tidal flat to grain production become more and more small.Based on the analysis of all reclamation zones,we further understood the temporal changes of cropland area in the agricultural reclamation zones following reclamation and development.In the initial stage of reclamation,the government built canal,ditch and road,and improved coastal saline soil by plants and aquaculture ponds until the crops can grow in the soil.The crop areas of different reclamation zones with different years are different.The proportion of cropland in the reclamation zones with long time(about 30 years)is high and that in the new reclamation zones is low.We took a case study in the Rudong reclamation zones.The proportion of agriculture land is highest after 30 to 50 years and that decreases after 50 years.We also analyzed the cropland proportion in all agriculture zones,and found that the cropland proportion is highest after 30 to 50 years and that decreases after 50 years because of urbanization.The quality of cropland soil reached a stable level for 30 to 40 years,and the soil salinity was the key limit factor.The soil qualities in the different reclamation zones are different.Therefore,land use types in different reclamation zones area different.The land use types in the new reclamation zones are saline plants,bare flat,and pond;that in the reclamation zones with long time are cotton,corn,bean,rice and so on.Based on the soil samplings in the reclamation zones with different years,the soil salinity reach the un-saline level after 38 years;the soil fertility increases following reclamation and is in the stable level after 30 years.The soil quality is improving following reclamation and reaches the stable level after 38 years.We found that the time of soil evolution from tidal sediment to crop soil is 30 to 40 years.From the correlation among soil physic-chemical properties,we found that soil salinity has significantly positive correlation with soil pH(P<0.01),and has significantly negative correlation with soil particle size fraction,soil organic matter,soil nutrients(P<0.01).Soil salinity is the most important factors to soil quality in the agricultural reclamation zones.Lastly,we calculated the grain production capacity of coastal reclamation zone in 2012 and 2020.We designed the land potential productivity model using soil salinity correction coefficient based on the AEZ model and Maas-Hoffman model.The results show that the rice production changes from 13886 to 21469 kg/hm2.The wheat production in the 1982,1974 and 1951 reclamation zones is 10329 kg/hm2.The grain production capacity of the coastal reclamation zones in 2012 is 1472 thousand ton,and accounts for 11.03 percent of total grain production in Jiangsu coastal cities.The grain productivity capacity of the coastal reclamation zones in 2020 is 1642 thousand ton,and increases 152.2 thousand ton comparing to it in 2012.To sum up,due to the long evolution period of agriculture land and relatively low benefits,the development type has changed from agriculture to urban and industrial development and aquaculture since 1990s.Soils are always improving following reclamation.The grain potential production needs more exploitation.In the future study,we should understand the mechanism of land use to increase more cropland,shorten the soil improvement time.