Nitrogen fertilization, irrigation, and harvest times affect biomass and energy value of Helianthus tuberosus L.

This study aimed to determine the effects of delayed harvest, irrigation and nitrogen fertilization on yield and fuel quality of the Jerusalem artichoke (JA) (Helianthus tuberosus L.). The biomass, calorific value, ash content and total calories per hectare of the Jerusalem artichoke were assessed in Inner Mongolia, China, at various harvest times, after irrigation and nitrogen application. The results showed that fresh and dry weights of tubers and underground biomass were higher when harvested after freezing; the dry yields of leaves and stems decreased with harvest time. In addition, irrigation significantly enhanced the yields of underground biomass, aboveground biomass and tubers, compared with non-irrigation conditions (p < 0.05). Interestingly, the highest yield was obtained with irrigation and treatment with nitrogenous fertilizers (20 to 50 kg ha(-1)). The calorific values of tubers and roots were significantly higher for samples harvested after freezing (p < 0.05); the calorific values of leaves and stems significantly decreased with harvest time and without irrigation (p < 0.05). The calorific values of stems and leaves were higher than those of tubers and roots, when JA was harvested before freezing, and the opposite trend was obtained for harvest done after freezing. The highest calories per hectare was obtained in WN2 (585247.42 MJ ha(-1)) on 30 September 2010 harvest. No correlation was found between the effects of water or nitrogenous fertilizers and ash content. However, the ash contents of stems, leafs, tubers and roots were significantly decreased (p < 0.05) with harvest time. Finally, in all treatment conditions, leaves produced the highest ash amounts among all plant parts, including stems, tubers, leaves and roots.