Effects Of Different Land-use Types On Nitrogen Balance In Three Gorges Reservoir Area Of China

With abundant of water power resources, the Three Gorges located at the upriver ofYangtze River is one of energy resource centers in China. In recent years many problems,such as seasonal drought, soil and water loss, affected by unreasonable sloping land-useor geography condition exist in this area of the Three Gorges. The quest for long-termsustainability of terrestrial ecosystems is leading to the development of new approaches toprotect nutrients balance. Maintenance of the quantity and quality of nitrogen (N) elementconsidered a critical component of sustainability. The objective of this research was tostudy the effects of different land-use types on N balance in Three Gorges reservoir areaof China.The characteristics of soil & water and N losses under different land-use types(stone/earth dike terrace, hedgerow, sloping field, and fallow) were investigated. Theeffects of different land-use types on N balance were analyzed by comparing the inputways (nitrogen deposition and fertilization) and output ways (N losses, plant utilization,and denitrification). The results showed that:1) The precipitation samples were collected for periods varying from 2005 to 2006 atZigui county. The pH averaged 5.8, and EC averaged 38.9μs.cm^-1. The amounts of Ndeposition averaged 10.5, 10.3 kgN·hm^-2a^-1 in 2005, 2006 respectively. In comparisonwith the level of N deposition in southern area of China, the amount of N deposition wasmoderate in our study and similar with national average level. The amount of phosphorusdeposition averaged 0.246 kgN·hm^-2a^-1 and was lower than national average level. Theconcentrations of ammonium and nitrate decreased with the amount of rainfall increasing.Generally, the concentrations of ammonium are higher than those of nitrate, andammonium made more contributions to nitrogen deposition than nitrate.2) Significant differences were in the amounts of runoff and sediment for differentland-use types. The amounts of runoff and sediment were highest in sloping field andlowest in hedgerow plots and were related to rainfall amount positively.3) The average amounts of different N forms both in runoff and in sedimentdecreased by fallow～sloping field＞dike terrace＞hedgerow, and were all related to rainfall amount positively. The total amounts of N loss were 10.61～36.07 kgN·hm^-2a^-1.4) The total amounts of N losses were highest in sloping field and lowest inhedgerow plots. The result shows agricultural technology of hedgerow was an effectiveway to prevent the soil & water and nutrient losses.5) The annual amount of input was more than output for three cropland plots due tothe fertilization which contributed to the N pool in soil. The annual amount of N lossesfor the plots receiving no fertilizers ranged from 4.31～22.2 kgN·hm^-2a^-1. With the Nlosses increasing, soil N content will ultimately decrease.Based on the results mentioned above, it was concluded that the use of hedgerow orfertilizers is apparently an important consideration for sustainability of soil & waterquality and environment in the Three Gorges reservoir area.