Comprehensive application of bio-char and nitrogen fertilizer in dry-land maize cultivation

Drought stress and the scarcity of nitrogen fertilizer are two of the important abiotic factors affecting maize growth. Bio-char can enhance the maize yield. Therefore, two field experiments were carried out in the 2 years (2019–2020) to study the effects of nitrogen fertilizer at three levels and four levels of bio-char on endogenous protective enzymes, dry matter accumulation, and yield of the maize ‘Xianyu 335’ under two different irrigation methods. A split-plot system in three replications was established to conduct the field trials. Two irrigation methods (Regular irrigation and Irregular irrigation) were in the main plots, three nitrogen fertilization levels (0, 150, 300 kg h(−1) m(2)) were in sub-plots, and four bio-char levels (0, 8, 16, 24 t h(−1) m(−2)) were in the sub-sub plots. Each sub-plot consisted of 9 rows with 5 m length and 0.6 m width, and each sub-plot area was 30 m(2) in the 2 years. The results indicated that the irrigation methods, the nitrogen, and bio-char supply significantly affected the maize endogenous protective enzymes, dry matter accumulation, and yield in the 2 years. Under the same irrigation method, nitrogen fertilizer and bio-char significantly improved the endogenous protective enzyme activity, dry matter accumulation, and yield of maize compared to the treatment without nitrogen fertilizer and bio-char. The above characteristics improved with increased bio-char supply and nitrogen fertilization at 150 kg h(−1) m(−2). The treatment of C24N150 recorded the highest values for the parameters of maize endogenous protective enzymes activity, dry matter accumulation, and yield under different irrigation methods during the two harvest seasons.