Slow-release fertilizer and water management with container-grown Ligustrum texanum

Abstract

Tests were performed to assess the relative benefit of 4 slow-release fertilizers (Osmocote 18-6-12, resin-coated urea 40-0-0, resin-coated urea 41-0-0 and Notroform 38-0-0) on the growth of privet ( Ligustrum texanum) in 2.8-1 containers at 2 irrigation rates. Rates of N applied were 0.6, 1.2, 1.8 and 2.4 kg N m −3, and irrigation regimes were leaching-fraction (LF) = 0.1 or 0.4. After 6 months, yields were highest for 18-6-12, and peaked between 1.2 and 1.8 kg N m −3, with 40-0-0 producing yields consistently about 80% of those produced by 18-6-12. Yields for 38-0-0 were about 25% of those with 18-6-12, and increased gradually with increasing rate of N application. The high rates of 41-0-0 killed a number of plants. Although LF = 0.1 resulted in higher N and P concentrations in tissue, growth was generally poorer than at LF = 0.4. Concentrations of N in plant tops were consistently lower for 40-0-0 than for 18-6-12, suggesting that the plant had some difficulty in acquiring sufficient N from this source. Optimum tissue N concentrations were between 18 and 20 mg N g −1 dry matter (whole tops). At maximum plant-growth rates (achieved between 1.2 and 1.8 kg N m −3), 32 and 29% of the N was leached from containers of 18-6-12 and 40-0-0, respectively. Water-use efficiency was approximately 1 g dry matter per 450 ml H 2O, or 20 1 per plant. The average leachate N concentration corresponding to maximum yield was between 100 and 200 mg N l −1. Leachate pH was generally greater for urea-based material than for 18-6-12. The resin-coated urea appears to have good potential for use in potting-media for container-grown plants.