Effects of two perennials, fallow and millet on distribution of phosphorous in soil and biomass on sloping loess land, China

Soil erosion causes sequential eco-environmental problems in the Loess Plateau of China. Therefore, vegetation restoration measures were adopted in this area by converting steep cropland into alternative land uses in order to remedy the erosion problem and alleviate land degradation. As part of the effort to understand the potential of this management practice in sequestering nutrients, the present study assessed the impact of vegetation restoration on the distribution of phosphorus (P) and aboveground biomass on a sloping land in this area. The study compared four land uses, Korshinsk Peashrub (KOP), alfalfa (ALF), natural fallow (NAF), and millet (MIL). KOP, ALF and NAF were adopted as vegetation restoration patterns, while MIL was an example of crop land. For the sampling time the average aboveground P pools of KOP, ALF, and MIL were 1.118, 0.406, and 0.091 g m− 2, respectively. The magnitudes of the aboveground biomass and tissue P concentration of the three land uses followed the same order. Both vertical and horizontal distributions of soil Olsen P of KOP were relatively uniform. Soil Olsen P of ALF accumulated significantly at the down-slope position within the surface 60 cm soil profile. The down-slope accumulation of soil Olsen P was significant at the depth of 80 to 100 cm and 0 to 20 cm for NAF and MIL, respectively. The soil Olsen P concentrations in deeper soil layers of KOP and ALF were clearly lower than that of NAF, while MIL had apparent higher concentrations of soil Olsen P in the 0 to 20 cm layer of soil. Generally, the vegetation restoration did not present a significant effect on total soil P level, with the average values of 0.722, 0.751, 0.747, and 0.729 kg m− 2 for KOP, ALF, NAF, and MIL, respectively. However, an apparent accumulation of total soil P at the down-slope position was observed for NAF and MIL treatments. For ALF and KOP, the soil Olsen P and the soil moisture content were correlated positively to the aboveground P pool. For MIL, however, the higher aboveground P corresponded to a higher soil Olsen P but to a lower soil moisture content. Results from the four years of data suggest that ALF is the fastest absorber of soil P, while KOP is the best vegetation to sequester soil P of the soil–plant systems in this study.