Master of Science (MS)


Plant, Environmental Management and Soil Sciences

Document Type



Runoff of sediments and nutrients, particularly phosphorus (P) from agricultural fields is considered as one of the main causes of water quality impairment. Very little research has been done on relating suspended solids in runoff to soil test information. This two-part study was aimed at:1) evaluating the relationship between total suspended solids (TSS), P forms in runoff, and soil salinity measurements, particularly electrical conductivity (EC), and 2) establishing the relationships between runoff P forms and the various soil test P measures, across a variety of selected Louisiana calcareous and acid soils. In the first part of the study, five Louisiana soils with clay content of 27 to 44% were selected, treated with different concentrations of salt solution (7.5 to 30 dS m-1), subjected to simulated rainfall, and various runoff parameters were measured. The TSS, total phosphorus (TP), and particulate phosphorus (PP) in runoff were found to decrease with consecutive simulated rainfall event. A highly significant relationship existed between TSS and turbidity of the runoff water (R2 = 0.92, P < 0.001). Each of TSS, turbidity, TP and PP negatively correlated to soil EC (R2 = 0.22-0.29, P < 0.05). A very significant relationship was observed between TP and TSS in runoff (R2 = 0.73, P < 0.001). In the second part of the study, nine soils of varying chemical and physical properties (pH, % clay, CaCO3 etc.) were used. The results revealed that among the measures of soil P examined, only water extractable P and Mehlich III P were reliable indicators of DP losses, explaining about 86% and 57% respectively, of the variability in runoff DP. The study showed that Olsen P (R2 = 0.73, P < 0.01), NH4-oxalate P (R2 = 0.50, P < 0.05), and NaOH P (R2 = 0.50, P < 0.05), reasonably correlated with runoff TP. Among the calcareous soils, Bray II P, NH4-oxalate P and NaOH P each explained about 40% of the variability associated with TP in runoff water. Along with soil test P measures, soil EC relationship with TSS could be useful in predicting P losses in runoff and hence requires further examination.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jim J. Wang