Nitrate Accumulation in Vegetable Crops As Affected by Photoperiod and Light Duration1

Abstract

No NO₃ accumulated at any photoperiod in leaves or roots of table beets when N was not added to the soil. When N was applied at rates from 100 to 400 lb./acre less NO₃ accumulated in both plant parts as photoperiod was extended from 8 to 20 hr. Addition of N to the soil increased the total N content of leaves and roots. Larger total N concn were observed in plants grown under an 8-hr photoperiod than in plants grown under longer photoperiods. Various radish, spinach, and snap bean cultivars were grown at different soil N rates and harvested 0, 6, and 12 hr after the initiation of the light period. Radish leaves and snap bean pods contained less NO₃-N as the plants were harvested further into the light period. Nitrate concn of radish roots and spinach leaves were not changed by harvesting at 6 AM, 12 noon or 6 PM. The addition of N fertilizer increased the NO₃-N concn of radish and spinach but decreased the NO₃-N concn of snap bean pods. Cultivars differed in their capacity to accumulate NO₃ in all 3 species. Nitrite accumulation was proportional to the quantity of NO₃ in the tissue.