Abstract:

A comprehensive analysis was made on the 5 year's successive monitoring findings from the 18 fixed soil erosion monitoring sites of newly established high-yielding timber plantations of 7 main species, such as Larix kaempferi, Cunninghamia lanceolata, Pinus elliottii, Pinus massoniana, Eucalyptus globulus, Pinus caribaea and Eucalyptus urophylla, for the National Afforestation Project loaned by the World Bank, which distributed in 12 provinces or autonomous regions in China.The study showed following conclusions:(1) The afforestation operation would result in soil erosion of the planting site in varing degrees e.g. most(84 %) of the 18 soil erosion monitoring sites show ed extremely slight or slight soil erosion, few (11 %) sites showed middle soil erosion and only one site showed severe soil erosion after the plantation establishment.(2) The site slashing, especially the slash burning, and site preparation, especially the intensive site preparation were the main causes of soil erosion when forest plantation was established.Hence, the runoff and soil loss mainly occurred in the first and second year when planting operation was made.(3) Since the third year (or second year) after the plantation establishment, the soil erosion was significantly reduced to a low level.The runoff decreased to a certain low level and fluctuated in small range with rainfall over years, while the soil loss decreased to an extremely low level and disappeared gradually in the future years.(4) Different site preparation methods would result in soil erosion in different degrees, e.g. the soil erosion occurred at the plantation sites with different site preparation methods varied in the order of overall >strip hole preparation in the first two years after the plantation establishment, with the difference range up to 100 % between overall and strip preparation as well as between strip preparation and hole preparation.(5) The changing pattern of nutrient loss from the plantation land was the same as the soil erosion, i. e. it also occurred mainly in the first and second year after plantation and then decreased or disappeared.Of the total amount of lost nutrients, the loss of soil organic mater and soil total N +P +K took the majority, which were ordered by their lost amount as soil organic mater >soil total N +P +K ≥liquid N +P +K >soil available N +P +K.The to talavailable nutrients carried by the runoff and lost soil, including liquid N, P and K as well as soil available N, P and K.were ordered by their lost amount as total available K >total available N >total available P. However, the total amount of total available nutrient loss was relatively small.It was suggested that site slashing and site preparation methods for plantation establishment should be further improved, such as giving up site slash burning and overall ploughing for site preparation etc., in order to minimize the soil erosion when afforestation operation is conducted.In regard to the lost nutriments caused by soil erosion, a fertilization scheme should be made to replenish the lost available N, P and K to the plantation land.

Key words: High-yielding timber plantations, Long-term fixed soil erosion monitoring, Runoff, Soil loss, Soil nutrient loss