Effect of net terrace biological bank on soil nutrients distributions along slope

As a new slope protection technique, net terrace biological bank combines biological measures with engineering practices for soil/water conservation. They significantly influence soil nutrient contents and distribution patterns along slope. The technique has made it possible to realize full uses of land resources and ensure maintenance of ecological and economic benefits under insufficient supply of arable land resources against vast slope of varying lengths. To study soil nutrients distributions in different slope positions and to provide theoretical basis to further promote net terrace biological bank and artificial regulation of slope-protection economic vegetation, this article analyzed the impact of net terrace biological bank on soil nutrient distribution patterns on slope. It also determined the soil nutrients contents in net terrace biological bank with different construction years using field investigation and indoor experimental methods. The results showed that: (1) net terrace biological bank significantly changed soil pH and organic matter content. Also while soil pH decreased with increasing construction years, organic matter content significantly increased. The distribution pattern of organic matter along slope changed significantly, with that of the upper part > middle part > lower part of slope in all construction period. However, the trend of organic matter content change under the control (bare slope) tracked the reverse pattern. (2) With the increasing construction years of net terrace biological bank, total nitrogen content increased after an initial period of decrease. The improvement in nitrogen content in the upper part of slope was stronger than that in the middle and lower parts of slope. Alkali-hydrolysis nitrogen content was significantly related to total nitrogen content. The differences among different construction years were more significant in the upper and lower parts of slope. (3) In the first three construction years, differences were noted in the distribution patterns of total phosphorus on different slope positions. In the fourth year of development, however, the distribution pattern of total phosphorus along slope were in the reverse order to the control. The distribution pattern of total phosphorus along slope followed the order of lower part > middle part > upper part, with significant (P=0.000) difference among different slope positions. Furthermore, soil available phosphorus exhibited some degree of volatility with construction years of net terrace biological bank. Although the coefficient of variation was reached 31.37%, the average content of available phosphorus increased to 1.15 3.30 times compared with the control, where no obvious distribution patterns were noted on the slopes. (4) Compared with the control, total potassium content increased by 9.7% 28.2%. With increasing construction years of net terrace biological bank, however, total potassium decreased. Net terrace biological bank also improved soil available potassium content. The differences in available potassium content in different slope positions were enhanced after an initial year of construction of net terrace biological bank.