[Soil fertility evaluation of artificial afforestation areas in Tibet, China].

To master the soil fertility situation of afforestation areas, where trees would be planted, the soil samples of 524 afforestation areas were taken to test its nutrients in six prefectures of Tibet, and the soil fertility was analyzed by the method of modified Nemerow synthesis index. The results showed that the synthetic fertility index of afforestation areas was between 0.425 and 1.972 in Tibet. The numbers of afforestation areas with general level, barren level, and fecund level occupied 65.9%, 34.9% and 0.2%, respectively. The mean fertility index of each soil property was in the order of alkalytic nitrogen＞ pH ＞ total nitrogen ＞ available potassium ＞ organic matter ＞ available phosphorus ＞ total phosphorus ＞ total potassium, which was between 0.654 and 2.643. The fertility level of total nitrogen, alkalytic nitrogen was mostly at the fecund and very fecund level. That of available potassium, organic matter, and total phosphorus was mainly at the general level. That of available phosphorus and total potassium was mainly at barren level, and soil pH was at a proper level. The synthetic fertility index in different prefectures was in the order of Nyingchi ＞ Qamdo ＞ Shannan ＞ Lhasa ＞ Shigatse ＞ Ngari, which of afforestation areas was at the barren level in Ngari, Shigatse and Lhasa. The synthetic fertility index of Qamdo and Nyingchi were at general level. The number of afforestation areas at general level or barren level was nearly same in Shannan. The soil fertility of afforestation areas was low in Tibet as a whole. The soil synthetic fertility and sub-fertility of soil properties became gradually good from the northwest (Ngari) to the southeast (Nyingchi), suggesting obvious horizontal zonality.