Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

During a two-year held study, an annual nutrient budget and cycles were dev eloped for a small agricultural watershed. The study emphasized the integra ted unit of the watershed in understanding the biogeochemistry. It was foun d that the total nutrient input was 39.1 x 10(4) kg nitrogen and 3.91 x 10( 4) kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7 x 10(4 ) kg (676 kg/ha) nitrogen and 3.88 x 10(4) kg (76 kg/ha) phosphorus. The to tal nutrient output from the watershed was 13.55 x 10(4) kg nitrogen and 0. 40 x 10(4) kg phosphorus, while the largest output of nitrogen was denitrif ication, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutr ient surplus within the watershed, a surplus which may become a potential s ource of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitroge n are key ways of nitrogen loss from the watershed. This suggests that care ful management of fertilizer application will be important for the sustaina ble development of agriculture. The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutr ients, benefiting the water, nutrient and sediment recycling in the terrest rial ecosystem and helping to reduce a,agricultural nonpoint pollution at i ts source. Therefore, this unique watershed system should be recommended du e to its great potential relevance for sustainable agricultural development .