Abstract

An experiment with two leaching fractions (LF = volume of water leached ÷ volume of water applied) and two fertilizer rates was conducted to evaluate the effects of reduced irrigation volume in combination with reduced fertility on irrigation use efficiency, nutrient efficacy (retention), and plant growth. Rooted cuttings of Cotoneaster dammeri Schneid. ‘Skogholm’ were potted into 3.8 liter (#1) containers in a pine bark: sand substrate (8:1 by vol). Osmocote 24N-1.7P-5.8K (24-4-7) was topdressed at 3.5 g N or 1.75 g N per container at treatment initiation. The experiment, a RCBD with four replications was conducted for 100 days on a container-grown plant production area subdivided into 16 separate plots that allowed for the collection of all irrigation water leaving each plot. Twenty containers were placed in each plot. Irrigation water was applied daily to attain either a high LF of 0.4 to 0.6 or a low LF of 0.0 to 0.2. Irrigation water was applied in two cycles with a two hour rest interval between each application via pressure compensated spray stakes at a rate of 200 ml/min (0.28 in/min). Volume of effluent from each plot was measured daily and analyzed for NO₃, NH₄, and P. Low LF decreased irrigation volume and effluent volume by 44% and 63%, respectively, compared to high LF. Irrigation use efficiency [total plant dry weight (volume applied-volume leached)] by plants irrigated with low LF was 29% greater than high LF. Compared to high LF, low LF decreased cumulative NO₃ and NH₄ contents in effluent by 66% and 62%, respectively, for containers fertilized with 3.5 g N. Low LF also reduced cumulative P content in the effluent by 57% compared to high LF. Shoot and total plant dry weights produced with low LF were reduced 8% and 10%, respectively, compared to plants grown with high LF. Root dry weight was not effected by LF. Shoot, root, and total plant dry weights with 1.75 g N were reduced by 26%, 26%, and 28%, respectively compared to 3.5 g N. Nitrogen efficiency was higher when plants were fertilized with 3.5 g N regardless of LF. To maximize N absorption and minimize N losses requires a combination of maintaining an adequate N supply which is this study was 3.5 g N per 3.8 liter container in combination with a low LF.