Consequences of Excessive Overhead Irrigation on Runoff during Container Production of Sweet Viburnum

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/m 2 (2380 gal/100 ft 2 ) for IRR1 and 2220 liters/m 2 (5450 gal/100 ft 2 ) 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/m 2 ) but decreased nutrient concentrations (mg/liter) in runoff.