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

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Abstract
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 ✕ 104 lux or 3.23 ✕ 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 ✕ 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 ✕ 104 lux contained more K than tissue grown at 3.23 ✕ 104 lux.Any factor which increased the total N concentration of the tissue resulted in a corresponding increment in the NO3 concentration.

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