Cyclic Irrigation Increases Irrigation Application Efficiency and Decreases Ammonium Losses

Abstract

Abstract Cyclic irrigation using pressure compensated drip emitters was evaluated for irrigation application efficiency, nutrient efficacy, and plant growth. The experiment, a RCBD with four replications was conducted in a simulated nursery using high volumes of irrigation which are common in container-grown ornamental nurseries in the southeastern United States. A container-grown plant production area, subdivided into 16 separate plots, allowed for the collection of all irrigation water leaving each plot. Rudbeckia fulgida Ait. ‘Goldsturm’ and Cotoneaster dammeri Schneid. ‘Skogholm’ plants were potted into 3.8 liter (#1) containers in a pine bark: sand substrate (8:1 by vol) and irrigated with either 900 ml (1.2 in) of water applied once a day [900 ml (1×)], 450 ml (0.62 in) applied in two cycles [450 ml (2×)], 300 ml (0.41 in) applied in three cycles [300 ml (3×)], or 150 ml (0.21 in) applied in six cycles [150 ml (6×)]. A cycle consisted of a one-hour rest interval between each irrigation allotment. At 8:00 AM daily, volume of effluent from each plot was measured and a sub-sample of the effluent was analyzed for NO3-N, NH4-N, and P. Cycled irrigation (2×, 3×, 6×) reduced volume of effluent, increased irrigation application efficiency [(irrigation volume applied-volume leached) ÷ volume applied], and decreased total NH4-N (mg) losses compared to the 900 ml (1×) application. Cycled irrigation (2×, 3×, 6×) did not differ in effluent volume or irrigation application efficiency. However, the 450 ml (2×) treatment had greater total NH4-N losses compared to 300 ml (3×) and 150 ml (6×) treatments. Irrigation treatments did not affect NO3 or P losses. Irrigation application efficiency over the course of the experiment averaged 0.52 for cyclic irrigation applications (2×, 3×, 6×), a 38% improvement over the 900 ml (1×) standard application. Depending on irrigation treatment, 89% to 104% of the 3.0 g of N applied was recovered. Nitrogen efficiency averaged 89% and 88% for cotoneaster and rudbeckia, respectively. Of the 0.34 g of P applied, 43.4% was recovered. Phosphorus efficiency averaged 29% for both species. Growth, nutrient concentration, and nutrient content of cotoneaster or rudbeckia were not affected by irrigation treatments.