Phosphorus Associated With Sediments in Irrigation and Drainage Waters for Two Large Tracts in Southern Idaho

Abstract

Phosphorus was measured in irrigation and surface drainage waters for two large irrigation tracts, and inorganic, water‐soluble PO4‐P and total P inputs and outputs were computed. The present irrigation practices on both irrigation tracts conserve P by removing more P from the Snake River in irrigation water than is returned in drainage water. Even greater P conservation could be attained by implementing new practices. Approximately 90% of the P in waters diverted to irrigate the Northside Tract remained in the tract. About 50% of the amount diverted remained in the Twin Falls Tract. Particle size segregation takes place in some drainage streams and the finer sediments returning to the river contain higher total and NaHCO3‐extractable P concentrations than the soils from which they were eroded. The importance of defining sampling methods and procedures for P analyses is illustrated by comparative data on irrigation and drainage waters. The PO4‐P concentration in samples filtered through a 0.45 µm membrane filter was independent of the sediment concentration in waters, whereas the total P concentration of unfiltered samples was proportional to the sediment concentration.

Water Balance for a Predominantly Surface Irrigated District in Southern Idaho

“…In 1971 the TFCC diverted 1690 mm , or about 30% more than we measured in the mainline canal in 2005. Return flow volume measured in 1971 (456 mm) was similar to this study (408 mm), which indicates that Carter et al (1974) may have under measured return flow and/or that seepage losses within the irrigation district have decreased. Although TSS concentrations in canal water were similar between these two studies (55 and 30 mg L-1 ), diverting additional water in 1971 resulted in an additional 580 kg ha-1 TSS in inflow compared to 2005.…”

Controlling Sprinkler Irrigation Runoff, Erosion, and Phosphorus Loss With Straw and Polyacrylamide

“…However, applying PAM to straw-covered soil decreased sediment concentrations for irrigations 1 and 2 compared to untreated bare soil or untreated strawcovered soil. Typically sediment and total-P concentrations are directly related (Andraski et al, 1985;Carter et al, 1974). Significant relationships (P < 0.01) between sediment concentration and total-P concentration occurred for both PAM-treated and untreated soil, but sediment concentration only explained 37 and 18% of the total-P concentration variability, respectively ( fig.…”

Polyacrylamide for Surface Irrigation to Increase Nutrient-Use Efficiency and Protectwater Quality

“…Large increases in runoff inorganic-N concentrations occur when fertilizers are applied to fields in irrigation water, but not all high N-loss events are associated with such operations (Fitzsimmons et al, 1972). Carter et al (1971Carter et al ( , 1974 reported that south-central Idaho surface irrigated tracts were a net sink for total P and ortho-P loads entering the tracts in irrigation source water. Irrigation runoff had higher P concentrations than source water but return flow volumes were a small fraction (14%) of the total source water volume diverted from the Snake River, and P concentrations in the groundwater-derived return flow contributions (13% of tract supply flow volume) were lower than that of the source water.…”

“…Total P and organic-N forms are largely associated with transported sediment and organic particles or colloids in furrow runoff (Carter et al, 1974;Carter and Bondurant, 1976). Furrow erosion and transport processes and runoff sediment load substantially determine the concentrations of these nutrient components in runoff (Carter et al, 1974;Brown, 1985;Bjorneberg et al, 1999). Clay and organic matter adsorb more P than other soil materials.…”

“…Clay and organic matter adsorb more P than other soil materials. The stream sediment clay : soil ratio, also called the enrichment ratio, and the total sediment load largely determine the total P in runoff (Carter et al, 1974). The P enrichment ratio increases as the proportion of clay and organic matter in the sediment load increases, and declines as sediment increases, owing to the decrease in the proportion of fine to coarse particles in sediments produced from escalating erosion regimes (Logan, 1982).…”