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United States Department of Agriculture

Agricultural Research Service

Title: Nutrient content and yield in relation to top breakover in onion developed from greenhouse-grown transplants

Author
item Russo, Vincent

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2008
Publication Date: February 12, 2009
Citation: Russo, V.M. 2009. Nutrient content and yield in relation to top breakover in onion developed from greenhouse-grown transplants. Journal of the Science of Food and Agriculture. 89:815-820.

Interpretive Summary: The nutrient content of edible plant parts can change as the plant ages. Onion (Allium cepa L.) bulbs are generally harvested when 50% of the tops of plants in the field breakover. It is not clear if harvest at 50% breakover maximizes bulb nutrient content. To determine if plant development stage affects nutrient content bulbs of the onion cultivars Candy and Texas Grano 1015 Y were harvested at 10, 20, 30, 40 and 50% top breakover. Contents of total nitrogen, nitrate-N, nitrite-N, potassium, total phosphorus, phosphate, calcium, magnesium, sodium, sulfate and soluble solids were determined. Measures of plant development, bulb size and weight, were also determined. Bulb size and weight did not change from the 20% breakover point, and most nutrients, with the exception on nitrate- and nitrite-N, were highest below the 30% breakover. It appears that a harvest occurring soon after breakover begins would be beneficial in terms of nutrient content without loss of bulb size or weight.

Technical Abstract: Onions (Allium cepa L.) generally are harvested based on percentage of tops broken over. Since plant metabolism changes over time, percentage of tops broken over may be used to determine a harvest time to deliver marketable bulbs with the best nutrient content. The cultivars Candy and Texas Grano 1015 Y were harvested at 10, 20, 30, 40 and 50% breakover in 2006 and 2007. Larger and heavier bulbs were produced by 'Candy' and in 2006, the year with near normal precipitation. There was little difference in bulb size and weight due to percent breakover. Bulb nutrient content was affected by year with the majority of nutrients being higher in 2006, and there were either no differences due to cultivar, or where differences were found nitrate-N, phosphate and sulfate contents were lower in 'Candy.' Soluble solids content was lower in 2006 and higher in 'Candy.' Content of nitrogen and phosphorous in a Kjeldahl digest; nitrate-N, phosphate, potassium and sulfate were either linearly or quadratically distributed over percent breakover. Nitrite-N, calcium, magnesium, sodium and soluble solids were randomly distributed over percent breakover. Bulb size and weight did not change from the 20% breakover point, and most nutrients, with the exception on nitrate- and nitrite-N, were highest below the 30% breakover. It appears that a harvest occurring soon after breakover begins would be beneficial in terms of nutrient content without loss of bulb size or weight.

Last Modified: 10/24/2014
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