Ulla E. Gertsson

Organically Fertilized Onions (Allium cepa L.): Effects of the Fertilizer Placement Method on Quercetin Content and Soil Nitrogen Dynamics

Field-cured onions cv. Hyskin ( Allium cepa L.) supplied with organic nitrogen fertilizer were studied. The fertilizer was applied by broadcasting and harrowing, broadcasting and rotary cultivation, or placement between rows. Nitrogen dynamics were monitored throughout the growing season by soil sampling. Variation in quercetin content in the onion scales was analyzed by HPLC. The organically fertilized onions were compared with inorganically fertilized onions grown in the same field. Inoculation with arbuscular mycorrhizal fungi (AMF) in the row at sowing or during commercial transplant production was tested but did not significantly affect mycorrhizal root colonization levels in the field. Onions that received no fertilizer at all or that had fertilizer placed between rows had better establishment, probably due to more favorable soil nitrogen concentrations for seedling emergence. Broadcast application led to higher nitrogen concentration in the root zone, resulting in fewer but larger individual onions. Quercetin levels were not significantly altered as a result of nitrogen fertilizer source (inorganic or organic), application method, or mycorrhizal inoculation. However, variation between years was significant, with quercetin levels in 2004 almost twice as high as those in 2005.

Shallot yield, quality and storability as affected by irrigation and nitrogen

Summary Field experiments were conducted to evaluate growth, yield and quality of shallot (Allium cepa var. ascalonicum Baker) under three levels of irrigation and nitrogen fertilization, on a clay soil in the sub-humid tropical climate of eastern Ethiopia from 1999 to 2002. Treatments comprised furrow irrigation at three moisture levels (75, 50 and 25% available soil moisture) and three nitrogen levels (0, 75 and 150 kg ha–1), using two local shallot cultivars. Bulb yield and mean bulb weight of both cultivars were higher at irrigation levels of 75% than at 50% or 25% available soil moisture. Total weight and rotting losses of bulbs were highest at the irrigation level of 75% and least at 25% available soil moisture in the cultivar ‘DZ-sht-91’, while in cultivar ‘Fedis’ irrigation treatments did not affect storability. The best irrigation water-use efficiency was obtained with irrigation at 50% available soil moisture. Nitrogen at 75 or 150 kg ha–1 increased the pyruvic acid content of bulbs. Application of nitrogen tended to increase mean bulb weight in ‘Fedis’ while ‘DZ-sht-91’ receiving no nitrogen had heavier bulbs. No significant effects were observed on the yield, dry matter, soluble solids and storability of bulbs due to the nitrogen fertilization. No interaction effects were observed between N and irrigation treatments. Irrigation at 75% available soil moisture is suggested for shallots destined for immediate use.

Season, and Nitrogen Source and Rate Affect Development and Yield of Shallot

ABSTRACT Three field experiments were conducted in 1999 and 2000 to assess the response of shallots (Allium cepa var. ascalonicum Backer) to nitrogen fertilizer sources and rates in eastern Ethiopia. Treatments comprised three nitrogen sources, urea, ammonium nitrate and ammonium sulphate, each at 0, 50, 100, 150 and 200 kg ha−1 N. Bulb yield was significantly increased with nitrogen fertilization up to 150 kg ha−1 in the main rainy season of 2000 when supplemental irrigation was applied. However, fertilization significantly reduced growth and yield of shallot in the main rainy season of 1999 and the short rainy season of 2000 under rain-fed conditions. Fertilization tended to increase bulb number per plant while reducing mean bulb weight. The dry matter and total soluble solids of bulbs from fertilized plots were either higher than or similar to those of unfertilized shallots. Ammonium nitrate produced significantly higher yields of shallots than ammonium sulphate, but did not differ from urea. Nitrogen source did not have significant effects on plant height, leaf number, bulb weight or bulb diameter. Higher nitrogen levels increased leaf and bulb nitrogen contents at harvest. The results indicated that nitrogen fertilizer should not be used for rain-fed shallots under low moisture regimes. Supplemental irrigation is essential in order to achieve high yields with nitrogen fertilization practices.

Model analysis of shoot elongation in Chrysanthemum × morifolium

Abstract A prediction model is presented describing the effect of light integral and temperature on side shoot elongation in Chrysanthemum × morifolium cultivar ‘Garland’. Daily increment in side shoot length is calculated by multiplying maximum daily increment with a light index ( F 1 ) and a temperature index ( F T ). The F T is related to the day/night heat sum ratio ( Q dn ). The model simulated the effect of seasonal variations in light integral and of day/night temperature regimes with an r 2 value of 0.97 in relation to the data used for parameter estimation. In validation trials, the model overestimated the shoot elongation of plants grown in daylight growth chambers, while it underestimated the elongation of plants grown in a greenhouse environment ( r 2 = 0.91). The model can also be used to simulate the effect of daylength on shoot elongation but further work is needed to develop and validate this feature.

Effect of temperature, daylength and light intensity on growth and development of Dipladenia sanderi Hemsl. ‘Rosea’

Abstract Dipladenia sanderi Hemsl. ‘Rosea’ (syn.: Mandevilla sanderi (Hemsl.) Woodson ‘Rosea’) was grown in a glasshouse at 12, 15, 18 and 21°C, daylengths of 8 or 20 h, natural daylight, and natural daylight supplemented with cool-white fluorescent lamps (10 W m−2). Time from propagation to unfolded flower decreased with increasing temperature, and at 12°C there were relatively few flowers in the inflorescences. The time to flower opening was not influenced by daylength, but with 20 h there were more buds in the first developed inflorescence and the petals were larger than with 8 h. In addition, the vegetative growth was favoured by 20 h. Supplementary lighting shortened the developmental time to unfolded flower, but the flowers were smaller than in natural light only. The growth and development varied according to the time of year. Dipladenia was able to bloom all year round, except in January and February. The low light intensity in November and December probably made it impossible for the buds to develop into flowers in January and February.