Variation in productivity of Ipomoea batatas at various rates of nitrogen fertilization

Currently, the cultivation of sweet potato (Ipomoea batatas (L.) Lam.) is gaining more and more popularity. The aim of the present study was to investigate the effect of different nitrogen (N) fertilization levels on the parameters related to the efficiency of the photosynthetic apparatus, plant photosynthetic productivity, tuber yield and tuber dry matter yield of f. batatas. The study also aimed to identify phenotypic variation in the physiological measures and tuber yield traits off. batatas. To achieve these objectives, a field experiment was carried out during the period 2013-2015 in Uhnin (51.5833 degrees N, 23.0333 degrees E), central-eastern Poland. The experimental factor was different nitrogen fertilization rates (0, 50, 100, 150 and 200 kg ha(-1) N). The conditions in the experimental years had the strongest effect on tuber dry matter content and yield and on minimum chlorophyll fluorescence yield and chlorophyll a content. The fertilization x year interaction had the lowest percentage contribution to the total variance, while its highest contribution was observed for chlorophyll b. Nitrogen fertilization had the lowest percentage contribution to the physiological measures of chlorophyll fluorescence, but a quite high contribution to tuber dry matter content and yield. Nitrogen fertilization up to a level of 150 kg ha(-1) N beneficially affected electron flow at successive plant growth stages, beginning from the 6-leaf stage until physiological maturity. Nitrogen fertilization was also shown to have a stimulating effect on the photosynthetic efficiency of f. batatas at the end of the growing season. A decreasing trend was observed in the maximum chlorophyll fluorescence yield (F-m) as affected by increasing N rates. A significant increase in actual photochemical efficiency of photosystem (PS) II (Y) and in the photochemical fluorescence quenching coefficient (q(P)) was observed up to a level of 100 kg ha(-1) N. The minimum chlorophyll fluorescence yield (F-0), non-photochemical fluorescence quenching coefficient (qN) and electron transport rate (ETR) were most favourable in the plots fertilized at a rate of 150 kg ha(-1) N.