| In recent years,the problem of cultivated land has become more and more serious in our country,which is mainly resulted from the reduced farmland area per person and the decreased land quality.Compared with the former,we should pay more attention to the research about enhancing the land quality.Soil nutrient status is a sensitive parameter to indicate the land quality,therefore,it is very important to study the temporal variability characteristics of the quality of cultivated land.In this research,we studied the evolution characteristics of main nutrients in cultivated land in detail from 1974 to 2012 of Rugao city in Jiangsu province,The results showed that from 1974 to 2012,the soil organic matter content and total nitrogen content decreased firstly and then increased,but the total nitrogen content in soil has been stable in recent years.The averaged soil organic matter content was 11.1 g/kg in 1974 and decreased to 10.7 g/kg in 1981,until 2012,it had been increased to 17.7 g/kg.The total nitrogen content in soil was 0.805 g/kg in 1974 and decreased to 0.786 g/kg in 1981 until 2012,it had benn increased to 1.104 g/kg.The effective phosphorus content in soil increased rapidly in recent years,which was increased from 2.4 mg/kg in 1974 to 20.8 mg/kg in 2012,and the content of effective phosphorus in the local area had been in a state of excess.The available potassium content kept constant at a low level in recent years,in 2012,the averaged available potassium content in the soil of the city was 78 mg/kg,about 77.61%of the land area has a available potassium content less than 100 mg/kg,and 9.83%of the land area has a available potassium content less than 50 mg/kg.In recent 40 years,the highest content of soil nutrition was observed in grey clips wrapped around soil in the eastern of the city,as well as the yellow soil in the southern of the city,while the lowest content of soil nutrition was observed with the high sandy soil in the midwest of the city.The moderate soil nutrition content was observed with clips wrapped around soil in the northeast,the northwest and the south of the city.The soil fertility of the city was in a growing trend in recent 40 years.A slight difference was observed in the variation of the four main soil genus(high sandy soil,clips wrapped around soil,yellow soil and grey clips wrapped around soil).From 1974 to 1981,the soil nutrient of the whole city did not change significantly,and from 1981 to 2012,the soil nutrient of grey clips wrapped around soil and yellow soil in the southern and easterm regions grew slowly while the soil nutrient of high sandy soil in the central region grew rapidly.Although the soil nutrient of this city improved greatly as a whole in recent 40 years,the lack of potassium in soil,therefore,we should pay more attention to balanced management of nutrients in order to improve the quality of cultivated Iand and grain yield. |
