|Torbert, Henry - Allen|
Submitted to: Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/4/2002
Publication Date: 7/20/2002
Citation: Torbert, H.A., Daniel, T.C., Lemunyon, J.L., Jones, R.M. Relationship of soil test phosphorus to runoff phosphorus in calcareous soils. Journal of Environmental Quality. 2002. v. 31. p. 1380-1387. Interpretive Summary: Recently, scientists have become concerned the losses of nutrients such as phosphorus in runoff from animal manure application may negatively impact water quality in rivers and lakes. It has been proposed that a soil test for P may be used as a management tool for manure application to help reduce losses of P into water systems. However, the potential relationship between soil test P to runoff losses of P has not been fully developed, especially for calcareous soils. The objective of this project was to examine the relationships between soil test P levels and runoff losses of P for important soil types in the Bosque River watershed and to examine the practical aspects of the data (i.e., depth of sampling and P extractant used) for the potential use in development of a soil test for environmental losses of P. The data presented in this study demonstrate that a soil test P could potentially be utilized for manure management and that there may be chemical or physical characteristics of soils that can be used to develop manure application criteria.
Technical Abstract: A study was initiated to investigate the relationship between soil test P and depth of soil sampling with runoff losses of dissolved molybdate reactive P (DMRP). Rainfall simulations were conducted on four soil types representative of the major soil series in the Bosque River basin of Texas. The soils studied included two non-calcareous soils, a Windthorst sandy loam and a Blanket clay loam, and two calcareous soils, a Purves clay and a Houston Black clay. Soil and runoff samples were collected from each of the four soils in permanent pasture exhibiting a wide range in soil test P levels due to prior manure applications. Soil sampling depths consisted of 0-2.5, 0-5, and 0-15 cm and soil test P levels are determined by Mehlich III and distilled water extraction techniques. Simulated rain was used to produce runoff which was collected for 30 min. Regression equations were developed relating soil test P level to runoff DMRP within each soil type. Good relationships were derived between soil test P and runoff losses of DMRP for all four soil types. The most consistent results were observed with the 0-5 cm sampling depth. The relationship between the level of P in the soil and runoff DMRP losses were shown to be reduced in calcareous soils compared to non-calcareous soils. At the highest soil test P level (360 mg kg**-1 soil), maximum concentrations of 1.73 and 1.63 mg L**-1 DMRP were observed in runoff from the Blanket and Windthorst soils, compared to 0.74 and 0.47 mg L**-1 DMRP in runoff from the Purves and Houston Black soils, respectively. Results indicate that a soil test for environmental P could be developed, but it would require establishing different criteria soil test P levels for different soils or classes of soils.