Variation law of nitrate content of celery during growth period under water and fertilizer coupling

In order to determine the effect of water and fertilizer coupling on the variation law of nitrate content in celery at the growth stage, a 3×5 orthogonal block design experiment was conducted under rain-free condition in the semiarid cold region of Northwest Hebei Province. Results show that celery nitrate content increases at early growth stage and then decreases at late growth stage, reaching its lowest at harvest under different combinations of high, moderate and low water and fertilizer. However, the nitrate content order is different for low water and fertilize treatment and also in the control treatment. Of all the treatments, only 7 (N_109.5P₃₆W₅₆₉₂) and 20 (N₂₇₀P₉₀W₄₅₀₀) treatments, low fertilizer and high water treatment, and moderate fertilizer and water treatments meet safe standards for public health. The one-factor, two-factor and three-factor effect on nitrate content under different combinations show that the effect of N increases, that of P is uncertain while that of water decreases. Unreasonable N, P, water combination restricts normal growth of celery, increases nitrate accumulation.