| Abstract: | Few research studies have examined the influence of delayed filtration on sample stability or runoff nutrient loss assessments. Runoff samples from irrigation furrows were each split into four volumes: two were filtered (45 μm) in the field and two were filtered 10 days later, with or without boric acid treatment, and stored at 4 °C. Sample dissolved reactive P (DRP), nitrate nitrogen (NO3-N), and ammonium (NH4)-N concentrations were measured in all filtered samples 10 and 107 days after collection. Samples filtered in the field and those with a 10-day delayed filtration had similar dissolved DRP, NO3-N, and NH4-N concentrations, whether or not boric acid was added. Boric acid stabilized DRP and NH4-N sample concentrations, but not NO3-N, during the 107 days of storage (relative to field-filtered samples). The effect of treatments on computed furrow stream concentration and runoff mass losses was similar to that for sample concentrations, except that furrow NH4-N parameters were unaffected by treatments. The field-filtered or 10-d delayed filtration without boric acid treatments provided the best dissolved nutrient measurements for comparing agricultural management effects at the field edge; however, results suggest that an incubation-type test for field-edge runoff water may provide a more accurate estimate of field management effects on dissolved nutrient loads in downstream aquatic ecosystems. |
