Changes in soil chemical properties following afforestation of cropland with Robinia pseudoacacia in the southeastern Loess Plateau of China

•Nitrogen fixation by leguminous Robinia pseudoacacia was not obvious.•Soil organic carbons stocks in the 16- and 49-year-old plantations were similar.•Soil organic carbon was negatively correlated with soil pH.•Robinia pseudoacacia plantations showed soil acidification across entire profiles.