Effect of Controlled-release Fertilizer and Irrigation Method on Seedling Quality and Outplanting Performance of Quercus variabilis

Objective To investigate the effects of fertilizer rate and irrigation method on morphological attributes, nutrient status, medium electrical conductivity (EC) and 2-years' outplanting performance of containerized Quercus variabilis seedlings.

Method Seedlings were raised with 5 fertilizer rates (25, 75, 125, 175, and 225 mg·plant^-1) and 2 irrigation methods (overhead irrigation (O) and subirrigation (S)). The experiment was a two-factor completely randomize design. Morphological attributes, nutrient status, root growth, medium EC, and 2-years' outplanting performance were measured.

Result Interaction of fertilizer rate and irrigation method significantly affected seedling growth. The root-collar diameter, root and total biomass of seedling reached maximum value with 225-O treatment. There was no significant difference on root and total plant biomass among 225-O, 125-S, and 175-O. The height, stem biomass, and S/R ratio of seedling reached maximum value with 225-S treatment. There was no significant difference on stem biomass among 225-S and 225-O. The nutrient concentration and content were improved with increasing fertilizer rate. There was no significant difference on root N, P content and total P content among 125, 175, and 225 mg·plant^-1. Increasing fertilizer rate promoted root growth. There was no significant difference on root surface area and volume among 125, 175, and 225 mg·plant^-1. Fertilization resulted in high medium EC. Subirrigation significantly increased medium EC in upper and bottom layer. The highest medium EC reached 4.69 dS·m^-1 but did not have harmful effect on seedlings. Subirrigation improved the height and root-collar diameter of seedlings 1 year after outplanting. 2 years after outplanting, the height and root-collar diameter of seedlings grew greatly with increasing fertilizer rate, but there was no significant difference on height and root-collar diameter of seedlings among 125, 175, and 225 mg·plant^-1.

Conclusion Subirrigation improves nutrient content and 1-year's outplanting performance. Controlled-release fertilizer increased seedlings quality, and 2-years' outplanting performance. Considering seedling quality, economic benefits and environmental value, fertilizer rate of 125 mg·plant^-1 and subirrigation was the optimum combination for container seedling production of this species.