A field experiment was carried out during the two successive summer seasons of 2019 and 2020 in a Private Farm at Meet Faris Village, Dekarns, District Dakhlia Governorate, Egypt to study the effect of irrigation intervals (15 and 30 days) and some soil application treatments (humic acid at 20 kg /fad. and fulvic acid at 10 kg/fad.) and foliar application treatments (without, trehalose at 1 g/l, potassium silicate at 1ml/l and algae extract at 1g/l) on growth, plant water relationships, yield and its components as well as tuber roots quality of sweet potato plants cv. Beauregard grown under clay soil conditions using follow irrigation system .
The obtained results showed that, the interaction treatment between irrigation sweet potato plants cv Beauregard grown in clay soil during summer seasons conditions every 15 or 30 days and treated plants with fulvic acid at 10 kg /fad. as soil application + spraying with potassium silicate at 1 ml/l increased main vine length , both fresh and dry weight of shoots/ plant, average tuber root weight , total yield/fad. and K contents in tuber roots. In addition, the interaction between irrigation every 15 and treating with fulvic acid at 10 kg /fad. as soil application+ foliar spray with potassium silicate at 1 ml/l increased number of branches/plant, marketable yield and total carbohydrates in tuber roots. Also the plants grown under the same irrigation intervals (every 15 days) and treating with fulvic acid at 10 kg /fad.+ spraying with trehalose at 1 g/l significantly increased total , free water in leaf tissues , however , the interaction between irrigation every 15 days intervals and treating with fulvic acid at 10 kg /fad. as soil application+ spraying with algae extract at 1 g/l increased N and P in shoots and tuber roots as well as tuber root diameter. On the other hand, the interaction between irrigation every 30 days and treated plants with FA at 10 kg /fad.+ spraying with potassium silicate at 1 ml/l increased K contents in shoots , tuber root length and dry matter contents in tuber roots. The interaction between irrigation every 30 days and treating with humic acid only at 20 kg /fad increased bound water (%) , osmotic pressure and proline amino acid in leaves of sweet potato in both growing seasons
Conclusively, it could be concluded that, irrigation sweet potato plants grown in clay soil during summer seasons every 15 or 30 days and treated plants with fulvic acid at 10 kg /fad. soil application + spraying with potassium silicate at 1 ml/l or with algae extract or trehalose at 1 g/l of each to obtain high productivity and best tuber root quality.