The biocycling of nitrogen and mineral elements of wheat, barley, maize, Sorghum and peanut grown on the calcareous cinnamon soil in Beijing was studied. The results are shown as follows:
1. Analysis shows great differences in the amount of different elements in various crops. It is characteristic that peanut, the legume crop, absorbs large amounts of calcium and magnesium, while grass crops absorb higher amounts of silicon, iron, aluminium, manganese and sodium. The sorghum takes higher amounts of nitrogen, phosphorus, potassium, calcium, magnesium and silicon, and the barley absorbs higher amounts of sodium, manganese and sulfur.
2. Eleven elements returned to soil by roots and stubbles may be grouped into three types:
( 1 ) Type of low returning includes nitrogen, phosphorus and potassium, the ratio of returning is generally lower than 10%.
( 2 ) Type of moderate returning includes magnesium, calcium, sulfur, silicon, sodium and mineral, the ratio of returning is between 10% to 30%.
( 3 ) Type of high returning includes iron, aluminium and manganese, and their ratio of returning is generally higher than 30%.
3. The features of biocycling of different crops has important significance for studying element balances of farm ecosystems, change of fertility in cultivated soils and its forming processes, fertilization and cropping system.