Conclusions

• Applying alum to return flow water reduced soluble P concentrations up to 95%.

• Suspended sediment in water (<1000 mg L^-1) did not affect soluble P reductions.

• The model developed to predict soluble P reductions suggests that applying alum at a rate of 20 mg L^-1 would reduce soluble P concentrations by 53% (lowers P levels below TMDL thresholds).

• Although alum effectively reduces soluble P, the cost of applying alum may be too high for routine use in irrigation districts.

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