Nitrate Accumulation as Affected by Nitrogen Fertilization and Foliar Application of Micronutrients in Rocket Plant

Field experiment was carried out in season 2007/2008 in a special farm near El-Mansoura City Dakahlya Governorate, Egypt to estimate the effect of N fertilization levels (0, 70, 105 and 140 kg N· ha

−1

) in the form of NH

4

NO

3

33.5% N as soil application and foliar application of Fe-EDTA at the rate of 300 mg · kg

−1

, Mo as sodium molybdate at the rate of 50 mg · L

−1

and their mixture (Fe + Mo) at the same used rates, each treatment was replicated three times. The results can be summarized as follow: Increasing N levels from 70, 105 and 140 kg N · ha

−1

significantly increased all growth parameters i.e. plant height (cm), fresh and dry weight (g · plant

−1

) for rocket plant at marketing stage as compared to the control treatment. Foliar spraying of Fe or Mo either as a solely addition or in combination together on plants fertilized by N rates (70, 105 and 140 kg N · ha

−1

) significantly increased plant height, fresh and dry weight of rocket as compared to the untreated one. The average values of all growth parameters under study with foliar spraying of micronutrients were higher than that obtained without spraying under any level of N fertilization. Nitrate and nitrite concentrations in the fresh leaves of rocket plant were gradually and significantly increased due to increasing N level from 0 up to 140 kg N · ha

−1

. On the contrary of this trend, the activity of nitrate reductase enzyme (μ · NO

2

·min

−1

· g

−1

· FW) was sharply and significantly decreased as the level of N fertilization was increased. Foliar application of Fe or Mo either in a single form or combined together in the presence of N levels under investigation significantly decreased the mean values of NO

3

-N and NO

2

-N mg · kg

−1

in the leaves of rocket plant than those obtained for the plants treated with the same N levels only. As for the activity of nitrate reductase enzyme, foliar spraying of (Fe + Mo) was superior for increasing the mean values of this parameter at any level of N fertilization. Applying nitrogen at the rates of 70, 105 and 140 kg N · ha

−1

resulted in significantly increase the values of N% over the control treatment. Foliar spraying of Fe or Mo in single form combined with the same N rates under study led to an increase in the average values of N% rocket leaves compared with those obtained from the same N rates without Fe or Mo in foliar way. Such effect of Fe or Mo spraying was realized when (Fe + Mo) were foliarly applied tell the rate of 105 kg N · ha

−1

. Increasing the rate of N addition from 105 to 140 kg·ha

−1

in the presence of (Fe+Mo) had no significant effect on the values of N% in rocket leaves. The mean values of Fe and Mo in rocket leaves significantly decrease as the level of N fertilization was increased. The mean values of Fe and Mo in rocket leaves significantly decrease as the level of N fertilization was increased. An adversely effect was realized due to spraying of (Fe + Mo) combined with the investigated N rates, whereas the mean values of Fe and Mo in rocket leaves significantly increased as the level of N fertilizer was increased. The calculate values of N/Fe and N/Mo ratios did not increase due to an increase of N rates in the presence of (Fe + Mo) foliar addition, but it tended to be constant around (18 × 10

−2

) and (19 × 10

−3

) for N/Fe and N/Mo, respectively.