Potato tubers contamination with nitrate under the influence of nitrogen fertilizers and spray with molybdenum and salicylic acid

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Abstract
A field trial was conducted through 2015 and 2016 growing seasons to study the effect of nitrogen fertilizer sources and foliar spray with molybdenum (Mo), salicylic acid (SA) and their combination on tubers yield, some chemical constituents, nutrients uptake, nitrate accumulation and nitrate reductase activity in potato tubers. N source was added at a rate of 350 kg N ha−1in five equal doses as two different forms, the first is urea and the second is ammonium sulfate plus calcium nitrate equally. SA was sprayed with three rates of 0, 75 and 150 mg l−1. Also, Mo as ammonium molybdate was sprayed using three rates 0, 50 and 100 mg l−1Mo. Both treatments of SA and Mo were applied separately as well as with each other, at three successive times 30, 50 and 70 days after planting of potato plants. Results indicated that the addition of 350 kg N ha−1 as ammonium sulfate and calcium nitrate equally caused a significant elevation (P > 0.05) in fresh weight, chlorophyll b, carotenoids, chlorophyll a, nitrate reductase activity, dry weight and NPK uptake by potato tubers compared with the same amount of nitrogen in the form of urea only. All the aforementioned characteristics were improved with increasing concentration of Mo and/or SA. The highest accumulation of nitrate was recorded under the addition of 350 kg N ha−1 as urea alone. The highest average of all the aforementioned characteristics was observed at the treatment of 350 kg N ha−1 as ammonium sulfate and calcium nitrate equally plus spraying with 100 mg l−1Mo and 150 mg l−1 SA. In contrast, this treatment gave the lowest accumulation of nitrates in potato tubers.

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