Changes in Soil Hot-Water Extractable C,N and P Fractions During Vegetative Restoration in Zhifanggou Watershed on the Loess Plateau

The study was conducted in Zhifanggou Watershed, Shaanxi Province, China, to evaluate the effect of different vegetation types on hot-water extractable C, N and P fractions, with the aim to determine whether hot-water extractable fractions could be used as indicators of soil quality change in Loess Plateau. The six vegetation types established in 1975 were (i) Robinia pseudoacacia L., (ii) Caragana korshinkii Kom., (iii) Pinus tabulaeformis Carr., (iv) P. tabulaeformis-Amorpha fruticosa L., (v) R. pseudoacacia-A. fruticosa, and (vi) grassland. A cropped hillslope plot and a Platycladus orientalis L. native forest plot were used as references. The results indicated that the conversion of native forest to cropland resulted in a significant decline in the hot-water extractable C, N and P fractions. Hot-water extractable C, N, and P increased when cultivated land was revegetated, but after 30 years the amount of hot-water extractable C, N, and P in revegetated fields was still much lower compared to native forest. Hot-water extractable fractions increased more under mixed-forest than under pure-forest stands. Furthermore, there was a significant correlation between the hot-water extractable fractions and soil chemical and microbiological properties. The results showed that hot-water extractable fractions could be used as indicators of soil quality change on the Loess Plateau.