Exponential nitrogen fertilization of Quercus robur seedlings in County Carlow, Ireland

Justin L Schmal, Purdue University

Abstract

Nursery production of broadleaved seedlings, especially pedunculate oak (Querus robur L.), and the amount of land area planted with them has increased dramatically in Ireland along with concerns over environmental contamination caused by nitrogen (N) leaching losses. In addition, a need exists to establish methods that allow production of seedlings in Ireland meeting morphological specifications in one year (vs. the conventional two or more years) possible. Exponential fertilization has been shown to improve fertilizer nutrient use efficiency (NUE) for species of both conifers and oaks in North America and maintains stable internal N concentrations in plant tissue over time. Exponential nutrient loading induces luxury nutrient uptake and results in seedlings that are both morphologically and physiologically superior to those grown under conventional methods and have improved growth upon outplanting. In Chapter 2, we investigated the effects of a wide range, 0.10-1.0 g N seedling-1 yr-1, of E fertilization rates on seedling morphology, physiology, and nutrition of Quercus robur L., as well as soil nutrient status and N budget during one growing season. A primary objective was to identify points of N deficiency, sufficiency, and toxicity to refine optimal N fertilization rates. Significant N losses occurred over the course of the study due to high precipitation (215% of summer normals) precluding symptoms of nitrogen toxicity, especially in the highest fertilizer treatments. Seedlings receiving the 0.5 E rate were morphologically and nutritionally superior to all other treatments; however, 0.10 E seedlings achieved the highest nitrogen use efficiency (NUE). In Chapter 3, we expanded on the range of rates used from 0.5-3.5 g N seedling-1 yr-1 because the lack of toxicity in the previous study suggested that we may not have attained optimal N loading. The same parameters analyzed in the Chapter 2 study were revaluated under increased exponential rates in this study, but soil sampling was less intensive and both NO3 and NH4 were included in the nitrogen budget. Significant N losses occurred at the two highest exponential rates (2.5 E and 3.5 E), again attributable to significant precipitation (194% of summer normals). However, N losses in lower treatments were offset by a significant addition of N to the system via mineralization. Despite the sharp increase in N application rates, seedling N toxicity was still not observed. This may be associated with yet another season of very high rates of precipitation and the ecology of Quercus robur. Seedlings receiving the 1.5 E rate exhibited the best combination of morphological and nutritional gains paired with reduced N losses. High NUEs and low residual N in plots of the 0.5 E treatment further substantiated the suitability of this rate for optimal seedling production paired with reduced N losses. Results from both studies indicate that it may be possible to produce 1-0 bareroot seedlings meeting target specifications in Ireland and other countries of northern latitudes by using an exponential fertilization rate between 0.5-1.5 g N seedling -1 yr-1.

Degree

M.S.

Advisors

Jacobs, Purdue University.

Subject Area

Agronomy|Forestry

COinS