Phosphorus sorption and desorption as impacted by long-term cover cropping at two soil surface depths

Authors: DADA, ADEBUKOLA - Purdue University; ARMSTRONG, SHALAMAR - Purdue University; Smith, Douglas

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Agricultural phosphorus losses degrade water quality in lakes and estuaries worldwide. Improved management strategies are needed to reduce the environmental footprint of agriculture related to phosphorus and water quality. Cover crops have been used effectively to decrease erosion and nitrate leaching; however, reports of phosphorus losses related to cover cropping in the scientific literature have been contradictory. This study was conducted by collecting soils from a field with a history of four cover crop treatments (cereal rye, annual rye, oat/radish and control with no cover crop) for the previous nine years. Phosphorus sorption characteristics were measured on these surficial soil samples (0-1 and 1-2 inch soil depth). It was observed that cover cropping with cereal rye and annual rye resulted in the soil having a greater affinity to sorb phosphorus, which in turn may decrease the amount of phosphorus lost to runoff water. These two cover crops may help improve water quality in regions where phosphorus losses have severely impaired important water bodies.

Technical Abstract: Phosphorus loss from agricultural land is a persistent environmental challenge and a better understanding of the impact of cover crop management practices on soil phosphorus sorption and desorption characteristics is needed to inform mitigation strategies. The objectives of this study were to investigate the impact of cover crop species on soil phosphorus pools, sorption characteristics, and dissolved reactive P after 9 years of cropping history. Soil samples were collected at 0 – 2 and 2 – 4 cm depth from a silty clay loam Mollisol and treatments included cereal rye (Secale cereal L.), annual ryegrass (Lolium multiflorum), oats/radish, (Raphanus sativus L/Avena sativa) and control having no cover crop. Adsorption was by batch experiment with varying phosphorus concentrations for 24 hours and sorption parameters were estimated by applying Langmuir model to sorption isotherms. The dissolved reactive phosphorus was estimated using sequential soil extraction by 0.01M CaCl2 for 5 hours. Long-term cover crop significantly decreased Smax but increased K at both soil depths. Annual ryegrass significantly decreased soil water extractable phosphorus, Mehlich 3 phosphorus, and degree of phosphorus saturation relative to oat/radish and control at 0 – 2 cm depth. Annual ryegrass and cereal rye significantly decreased dissolved reactive phosphorus by an average of 42 and 45% relative to control and oat/radish respectively at 0 – 2 cm soil depth. These results demonstrate that long-term grass species decreased the concentration of surface soil dissolved reactive phosphorus loss by decreasing the soil labile phosphorus pool and increasing the soil phosphorus retention capacity. Therefore, we recommend that planting annual rye and cereal rye should be promoted in fields susceptible to dissolve reactive phosphorus losses.