Impact of nitrogen management strategies on yield, N-use efficiency, and Rhizoctonia diseases of Irish potato.

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Title: Impact of nitrogen management strategies on yield, N-use efficiency, and Rhizoctonia diseases of Irish potato.
Author: Meyer, Karen Michelle
Advisors: Dr. David Shew, Committee Co-Chair
Abstract: An interdisciplinary approach, integrating aspects of plant pathology, soil science and horticulture, were used to study tuber initiation, plant density, N-use efficiency, Rhizoctonia disease development of Irish potatoes influenced by N management strategies. The impact of N rate and seed piece spacing on tuber yield and N uptake efficiency in the potato varieties Atlantic and Superior was examined in a field project conducted at the Tidewater Research Station in Plymouth, NC. A split-split field design was used with urea applied to main plots at rates of 0, 56, 112, or 168 kg N ha-1, seed piece spacing varied in the sub-plot at 23 or 30 cm, and potato variety in the sub sub-plot. In 2000 and 2001, Atlantic produced a greater total yield than Superior at the 23 and 30 cm spacing, and both varieties yielded higher at a 23 cm spacing compared to a 30-cm spacing. Total and marketable yield in plots with 56, 112, or 168 kg N ha-1 urea were not different, but the two highest N rates had significantly (P=0.05) greater yield than the 0 N treatment. Averaged across variety and spacing, total N uptake was 58 kg N ha-1 with 0 N, and increased to 100 Kg N ha-1 with 168 N ha-1. Data suggests that growers could apply N at rates of 56-112 kg N ha-1 with optimal seed piece spacing for Atlantic and Superior to produce high quality yields and reduce the potential of polluting surface and ground water reservoirs. The form and rate of nitrogen can affect the incidence and severity of many plant disease. The effects of N rate and form on hyphal growth of Rhizoctonia solani anastomosis group 3 (AG3), development of Rhizoctonia diseases, and the yield of Irish potato were determined in growth chamber, laboratory, and field studies. A significant interaction of N form and N rate on mycelial growth in-vitro was observed with R. solani grown on minimal slats culture medium with selected N sources supplying nitrate or ammonium N at rates of 0, 50, 100, and 150 ppm. High rates of ammonium sulfate and urea (ammonium N sources) produced the greatest mycelial dry weight than nitrate N sources. To evaluate the effect of N form and rate in the field, three field experiments (two in Plymouth and on in Lewiston, NC) were arranged in a split plot design to evaluate the effects of N rate (0, 84, or 168 kg N ha-1) and form (nitrate vs. ammonium) supplied as NaNO3 or urea on potato yield of Atlantic and Rhizoctonia disease incidence and severity. At the Plymouth location in 2000 and 2001, the highest total yields were similar for the 84 and 168 kg N ha-1 and the 0 N treatments. A significant effect of R. solani was observed at Plymouth, with greater total and marketable yields in the non-infested compared to infested plots for both years. Stolon infection was significantly greater in the 168 kg N ha-1 urea treatment than in the 84 kg N ha-1 NaNO3 plots at Plymouth 2001. A Phytotron experiment was conducted to determine effects of N form (supplied as NaNO3 and urea) and rate (0, 0.25, and 0.50 g N L-1) applied to either infested or non-infested pots R. solani. In two experiments, the highest and lowest incidence of stem and stolon canker occurred at the high rate of urea and the low rate of Sodium nitrate, respectively. The use of reduced rates of NaNO3 in potato production may reduce the incidence of Rhizoctonia disease, give optimum yields and reduce the risk of undesirable environmental effects.
Date: 2002-08-26
Degree: MS
Discipline: Plant Pathology

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