Different Forms of Organic Nitrogen Loss in Soil by Runoff in Slope Land of Loess Plateau

Under natural rainfall condition, the regular pattern of soil organic nitrogen loss by runoff was investigated. The results showed that except for that the content of amino sugar reduced in sediment, the other forms of organic N were increased compared with local soil. With slope gradient falling, the contents of hydrolyzable-N, amino acid-N, and ammonia-N were increased. The hydrolyzable-N, amino acid-N, ammonia-N, and unidentified-N existed in enriching phenomenon in sediment, the enrichment ratios of these organic nitrogen were increased with slope gradient falling, but, the amino acid-N has a higher enrichment ratio than other organic N, on the contrary, the content of amino sugar-N in sediment was lower than local soil. The loss amounts of hydrolyzable-N were 1135.0 in 25°, 763.7 in 20°, 485.5 in 15°, 313.0 in 10°and 154.4 kg/km² in 5°. The loss amounts of amino acid-N were 234.8, 182.7, 121.1, 76.8 and 33.9 kg/km² separately, accounting for 20.5%～24.9% of hydrolyzable-N. The loss amounts of ammonia-N were 742.5, 505.3, 322.2, 208.9 and 97.4 kg/km² respectively, accounting for 63.1%～66.7% of hydrolyzable-N. The loss amounts of amino sugar-N accounted for 1.1%～2.9% of hydrolyzable-N. The loss amounts of unidentified-N accounted for 5.8%～12.6% of soil total N.