Human interactions with the critical zone through land use can alter soil phosphorus (P) cycling and distribution. These P changes occur through both time and space as P is taken up by plants, and as added P fertilizer is translocated downslopes and throughout the soil profile by erosion and leaching. In the southeastern US Piedmont, one hundred years of forest clearing and farming that included P fertilization caused severe surface erosion prior to reforestation. Previous research has demonstrated elevated surface soil P in farmed ridge tops even after 70 years of reforestation, but little data exists on P redistribution downslope of down profile during these 70 years. Based on this history of land uses, the objective of this study is to investigate the effect of different land use on P losses over time. Combined with multiple years of current site data on soils, soil solutions, and stream waters, we use the soil and water assessment tool (SWAT) to simulate different land use trajectories (Mature deciduous forest, upland agriculture and lowland forest, farmland, afforestation, and mixed-forest) to assess the land use effects on P movement. SWAT is calibrated and validated for two small watersheds in the Calhoun Critical Zone Observatory in South Carolina, USA. This validated model is used for simulating the effect of different land uses on P movement to surface water and vertical re-distribution into soil. We expected that P movement in watersheds during long-term farming and fertilizing is higher relative to other land use structures, but that P loss continues over decades. Results indicates the annually total P loss in farmland was six times greater than forest land cover (0.6 kg ha-1); even though, the P fractions enriched when watershed was under cultivation. This study demonstrated how historical land use impact on soil P over time.
Foroughi, Maryam, John Mallard, Daniel Markewitz (2019): Modeling Phosphorus Losses and Distribution in Different Land Uses over Time. ASA-CSSA-SSSA International Annual Meeting, 10-13 Nov. 2019, San Antonio, Texas.
This Paper/Book acknowledges NSF CZO grant support.