Abstract

The effects of irrigation rate on volume and nutrient content of runoff were investigated. Runoff (leachate plus un-intercepted irrigation and rain) was collected weekly for 20 weeks during production of trade #1 (2.7-liter) sweet viburnum [Viburnum odoratissimum (L.) Ker-Gawl.] fertilized with a resin-coated, controlled-release fertilizer [Osmocote 18N–2.6P–10K (18–6–12), 8–9 month 21C (70F)]. Treatments were a factorial arrangement of two irrigation rates [1 (IRR1) or 2 (IRR2) cm/day (0.39 or 0.79 in)] and two fertilizer rates [15 (FRT15) or 30 (FRT30) g/container (0.53 or 1.06 oz)]. Total runoff volume was 970 liters/m² (2380 gal/100 ft²) for IRR1 and 2220 liters/m² (5450 gal/100 ft²) for IRR2 which was 49 and 69%, respectively, of total irrigation plus rainfall. Increasing the irrigation rate from 1 to 2 cm/day increased leaching losses of N, P, and K 34, 38, and 45%, respectively, with FRT15 and 21, 28, and 23%, respectively, with FRT30. Increasing the irrigation rate increased nutrient loads (g/m²) but decreased nutrient concentrations (mg/liter) in runoff.