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Nitrate Accumulation in Table Beets and Spinach as Affected by Nitrogen, Phosphorus, and Potassium Nutrition and Light Intensity¹

The objective of this research was to determine the effects of varying levels of N, P, and K fertilizer and light intensity on nitrate accumulation in species grown for human consumption. In greenhouse experiments, table beets (Beta vulgaris L.) and spinach (Spinacia oleracea L.) were grown in fine sandy loam soil at three levels of N, P, and K fertilizer in a 3³ factorial design. Plants were grown under two light intensities, 1.08 x 10⁴ lux or 3.23 x 10⁴ lux. Nitrate, total N, P, and K were determined on freeze dried table beet leaf blades and roots and on spinach leaves.

Fertilizer N had the greatest influence on NO₃ accumulation in all three tissues studied. Varying the rate of fertilizer P had no effect on NO₃ accumulation. Plants of both species grown with the highest rate of K and under the lower light intensity accumulated significantly more NO₃-N than other plants receiving less K. Table beet leaf blades contained three times more NO₃ than roots. Lowering the light intensity from 3.23 to 1.08 x 10⁴ resulted in a significant increase in NO₃-N in all tissues tested.

Total N concentration increased in all tissues with an addition of N fertilizer or by a reduction in light intensity. In spinach, total N was lower in plants receiving K fertilizer. P and K were lower in beet and spinach leaves that received N fertilizer. Light intensity had no influence on P concentration, while all tissues grown at 1.08 x 10⁴ lux contained more K than tissue grown at 3.23 x 10⁴ lux.

Any factor which increased the total N concentration of the tissue resulted in a corresponding increment in the NO₃ concentration.

Key Words: Total N • Nitrate poisoning • P concentration • K concentration

² Former Research Associate, Department of Vegetable Crops. (now Research Scientist, Horticultural Research Institute of Ontario, Horticultural Experiment Station, Simcoe, Ontario, Canada).

Received for publication November 29, 1972.