Evaluation of yield and nitrogen utilisation with urease and nitrification inhibitors in sweet potato crop (Ipomoea batatas L.)

Sweet potato (Ipomoea batatas L.) is a new tuber crop grown in Greece. It constitutes an innovative dietary component for both humans and animals, due to its nutritional properties. The cultivation of sweet potato focuses on the growth of both tubers and plants. Nitrogen is considered an essential element for almost all crops. This study set out to compare the effect of nitrogen inhibitors on yield components of sweet potato. In the literature, it is stated that in sweet potato cultivation nitrogen mainly affects the plants’ growth such as the tuber's yield and some quality characteristics such as dry matter and protein content. To furthermore explore this particular area, field experiments took place in West Greece, during the years 2018 and 2019. Several urea combination treatments were used in the experimental process. The treatments were urea (46-0-0), urea with urease inhibitor (UI), urea with nitrification inhibitor (NI), urea with double inhibitors (UI + NI) and control (without fertilizer) in a randomised complete block design. Leaf area index (LAI) was significantly affected by the fertilizer marking the highest value of 5.35 under urea + UI + NI treatment. Marketable yield was profoundly affected by the fertilizer in the experimental years and ranged from 18,180 to 23,230 Kg · ha−1 whereas non-marketable yield was not affected by the fertilizer. A considerable impact of fertilizers was noticed on yield where the highest value was 30,923 Kg · ha−1 under urea + NI + UI treatment. The percentage of nitrogen on tubers and upper parts was significantly affected by the fertilizers. Nitrogen markers, such as nitrogen use efficiency (NUE), nitrogen harvest index and nitrogen agronomic efficiency (NAE), were used to evaluate nitrogen release. A significant positive correlation was noticed between marketable yield and NUE (0.774). Also, the significant increase in yield showed a positive correlation with NAE (0.727). For yield components of sweet potato, the highest values were observed in urea with double inhibitors treatment in both experimental years.