Physicochemical mechanisms underlying soil and organic amendment effects on runoff P losses

Abstract

Phosphorus depletion from cultivated lands by runoff is a significant contributor to soil chemical degradation. Our objective was to elucidate the mechanisms through which soil and organic matter amendments affect rain-induced runoff P losses in Mediterranean soils. Clay, loam, and loamy sand mixed with noncomposted activated sludge (AS), manure compost (MC), industrial humic acid (HA), orthophosphate (Pi), or inositol hexaphosphate (IHP) were subjected to six consecutive artificial rainstorms. Adding amendments significantly increased runoff available Pi loss (the sum of solution and sediments bicarbonate extractable Pi) for all soils. The order of loss (Pi, mg m −2) was soil dependent; greatest and lowest in the loam and loamy sand, respectively (loam: Pi[270] > IHP[128] > AS[108] > MC[97] > HA[49] > Control[33], and loamy sand: AS[42] > HA[23] > Pi[22] > IHP[18] > MC[13] > Control[4]), although order of runoff and soil loss were clay > loam > loamy sand. Treating with IHP and Pi at a similar total P level led to comparable cumulative total-P runoff losses, but runoff available Pi loss was much greater in the Pi treatment of soils with higher clay content (clay > loam > loamy sand). A derived isotherm relating sediment Olsen Pi to dissolved reactive Pi (DRP) concentration in runoff was found useful for estimating runoff Pi losses from measured DRP, runoff volume, and sediment concentration. The results could be explained by the impact of the amendments on soil structure stability, sealing, runoff, and erosion levels associated with soil physical and chemical degradation.

Soil Structure Stability under Different Land Uses in Association with Polyacrylamide Effects

“…Soil structure and aggregation are central physical properties of soil that control a wide array of soil properties and functions including water retention and infiltration [1], susceptibility to erosion and the movement of associated contaminants [2], aeration, gaseous exchanges, and greenhouse gas emission [3], C sequestration, soil organic carbon (SOC) protection [4], soil organic matter mineralization [5], and biogeochemical cycling of essential elements such as macro-and micronutrients [6]. Hence, monitoring of soil structure and stability is vital in determining the sustainability of land use and management practices in both agricultural and natural ecosystems [7].…”