The Fertility Characteristics of the Agricultural Soils from the Inland Plain Region of Shanghai, China

Soil degradation and retrogression have been widely concerned in China in the last several decades due to inadequate utilization, application of various agrochemicals and pesticides, soil pollution, rapid urbanization, and frequent human activities. Degradation of agricultural soils may not only result in some health risks to soil ecosystems, but also affect food quality and safety. This study was mainly aimed at investigating the current status of the soil quality in the Inland Plain Region (IPR) of Shanghai, one of the most developed regions of Changjiang River Delta in China. The soil samples collected from the IPR, the most important agricultural base with prominent inland geomorphy in Shanghai, were analyzed in order to evaluate the fertility characteristics of the soils. According to the soil mineralogical analysis, there were lots of obvious differences of the soil constitutions among the sampling sites for different crop cultivations, although the texture of all the soils was defined as the silt loam (SiL). The molar Si/Al ratio increased with the increase of the depth of soil horizons. The samples with higher value of electrical conductivity, caused by excessive fertilizer application and annual irrigation, were almost for cucumber cultivation in the greenhouses. The pH value correlated positively with the Na
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content to a certain extent. The long-term submersion and saturation of the soils improved the process of the organic matter decomposition, and then increased the cation exchange capacity in the topsoils. The soils in the IPR belonged to the soils with low-grade alkalization and fertility due to the exchangeable sodium percent and base saturation percent values. The content of the organic matter declined 10-15 g kg-1 according to the data analyzed before 1990. Total nitrogen increased by 1.5 times as high as the data investigated during 1979-1988. There was no obvious correlation between total and available phosphorus. Available potassium in the topsoils was much higher than that in the subsoils, while no difference for the total potassium.