Kentucky State University

Poster Title

Row Cover Weight Influences Nitrate Content of Kale Grown in Solar Greenhouses

Institution

Kentucky State University

Abstract

Vegetables account for most human nitrate intake. Nitrates may accumulate in vegetables produced under low light conditions because nitrate reductase requires sufficient light to function. Row covers used to protect plants from low winter temperatures can reduce light transmission to winter-grown vegetables. To test this effect, and its impact on nitrate accumulation, Siberian kale (Brassica napus var. pabularia) was grown in a solar greenhouse, called a high tunnel, near Frankfort, KY, between September 2011 and January 2012. The kale was grown without row covers, or under one of three weights of translucent polyester row cover: light, medium, or heavy. Air and soil temperatures were recorded hourly throughout the experiment. Kale was harvested on clear mornings in November and January, immediately after measuring photosynthetically active radiation at canopy height. Young leaves were picked from the center of representative plants for nitrate analysis using nitrate-specific probes. Increasing row cover weight was positively correlated with warmer nighttime temperature, reduced light penetration, and higher leaf nitrate content. Yields ranged from 2.2 kg per square meter under heavy row covers to 3.8 kg per square meter without row covers. Leaf nitrate content ranged from 330 mg/kg without row covers to 1,850 mg/kg with heavy row covers. Although row covers had a clear impact on nitrate accumulation in kale leaves, none of the observed nitrate levels were sufficient to warrant health concerns in adults.

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Row Cover Weight Influences Nitrate Content of Kale Grown in Solar Greenhouses

Vegetables account for most human nitrate intake. Nitrates may accumulate in vegetables produced under low light conditions because nitrate reductase requires sufficient light to function. Row covers used to protect plants from low winter temperatures can reduce light transmission to winter-grown vegetables. To test this effect, and its impact on nitrate accumulation, Siberian kale (Brassica napus var. pabularia) was grown in a solar greenhouse, called a high tunnel, near Frankfort, KY, between September 2011 and January 2012. The kale was grown without row covers, or under one of three weights of translucent polyester row cover: light, medium, or heavy. Air and soil temperatures were recorded hourly throughout the experiment. Kale was harvested on clear mornings in November and January, immediately after measuring photosynthetically active radiation at canopy height. Young leaves were picked from the center of representative plants for nitrate analysis using nitrate-specific probes. Increasing row cover weight was positively correlated with warmer nighttime temperature, reduced light penetration, and higher leaf nitrate content. Yields ranged from 2.2 kg per square meter under heavy row covers to 3.8 kg per square meter without row covers. Leaf nitrate content ranged from 330 mg/kg without row covers to 1,850 mg/kg with heavy row covers. Although row covers had a clear impact on nitrate accumulation in kale leaves, none of the observed nitrate levels were sufficient to warrant health concerns in adults.