Mixed and Conventional Nitrogen Fertilizers Impacts on Yield, quality and nutrient uptake of Potato.

Selecting the appropriate form of nitrogen fertilizer is one of the important limitation factors for potato yield and quality, which depends primarily on the availability and cost of fertilizers. The aim of this study was to compare the effect of conventional N-fertilizer forms (urea "U", ammonium nitrate "AN" and ammonium sulphate "AS') with mixed fertilizers (six MF: as a mixture percent's of AS with U or AN of the added N) on growth, yield, quality, nutrients uptake, N use efficiency (NUE) and profitability of potatoes grown in clayey loam soils. Two field experiments were carried out at Batra, Talkha, Dakahlia Governorate, Egypt (30° 16' 72"N; 31° 46' 25.80"E) during successive seasons; 2015/2016 and 2016/2017 on two potato varieties; Spunta and Diamant. Treatments were arranged in Complete Randomized Blocks Design with three replicates. The obtained results showed that mixed nitrogen fertilizers treatments enhanced plant growth, tuber yield, quality, nutrient uptake and NUE compared to sole application of conventional forms, with superiority of MF: 75%AN+25%AS, 50%AN+50%AS and 50%U+50%AS. The highest yield of dry matter and starch was obtained by adding MF of 50%AN+50%AS. However, the accumulation of NO3- in tuber is inversely proportional to dry matter; the highest content obtained with 100%Uea, but the lowest content obtained with MF of 25%AN+75%AS. The greatest percentage of NUE was obtained with MF of 50%AN+50%AS in both experiments. These results referred to the importance of AS application along with AN or U as a mixed fertilizer to maximize potato yield and quality, NUE and profitability.