Acta Geographica Sinica ›› 2003, Vol. 58 ›› Issue (1): 147-154.

### Losses of Nitrogen Nutrient in Overland Flow from Farmland in Beijing under Simulated Rainfall Conditions

HUANG Manxiang, ZHANG Shen, ZHANG Guoliang, ZHANG iumei

1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
• Received:2002-06-08 Revised:2002-10-11 Online:2003-01-25 Published:2003-01-25
• Supported by:

National Natural Science Foundation of China, No.397901000

Abstract:

Rainfall simulation experiments were performed to evaluate the contribution of both particulate N and dissolved N to losses of nitrogen by comparing the difference of the N concentrations and the yields in runoff from three tilled plots A, B and C, and the effect of fertilizer applications on them. The catchment area of the plot is 2 m × 5 m each with a slope of 5 degrees. A and B were bare and unfertilized, and C was fertilized with granular urea (360 N kg/ha) idle 35%. These results indicate that: (1) higher rainfall intensity results in higher discharge, sediment yield and losses of N, even lower cover rate significantly reduces discharge, and sediment yield and loss of N; (2) particulate N was the dominative form of N loss in surface runoff, added fertilizer N may suffer loss by runoff dissolved N form. Mechanism of soil aggregates detachment by rainfall and loss by runoff was investigated to seek explanation for the enrichment of PN in eroded sediment to original soil. The results showed that the aggregate size distribution of the eroded sediment was drastically different to that of the original soil. Aggregates smaller than 0.25 mm constituted more than 81% of the sediment as compared with only 16% in the original soil. More than 99% of total N transported by runoff was in the particulate form, whereas 78% of particulate N lost with finer aggregates smaller than 0.25 mm. About 44% of particulate N lost with finer aggregates smaller than 0.045 mm. ERN decreased as the erosion process continued. A higher percentage of aggregates smaller than 0.25 mm, especially the enrichment of aggregates smaller than 0.045 mm which has a high concentration of nitrogen is responsible for the enrichment of N in eroded sediment.