Nutrient management practices, such as optimum fertilizer addition rate and co-addition of inorganic fertilizers and organic amendments (compost and biochar), were investigated to enhance crop production and nitrogen (N) use efficiency. However, how these practices improve the defense system, N use efficiency, yield quantity and quality, and physio-biochemical constituents of maize (Zea mays L.) plants grown on an alkaline soil under different irrigation levels (well-watered conditions, mild drought, and severe drought) remains unclear. A two-year field trial was carried out in a split–split plot with a randomized complete block design with three irrigation levels (100% evapotranspiration (ET), 80% ET, and 60% ET) as the main plots, two amendments (5 Mg ha–1 biochar or compost) as subplots, and three regimes of inorganic fertilization (119-16-69, 179-24-99, and 238-31-138 kg N-phosphorus (P)-potassium (K) ha−1) as sub-subplots. We found that maize yield, oil, starch, protein, carbohydrates, and NPK uptake significantly decreased with increasing drought levels, but catalase, peroxidase, superoxide dismutase, and proline contents significantly increased. The addition of organic amendments (compost or biochar) with inorganic fertilizers was more effective in enhancing the above attributes than inorganic fertilizers alone, but these attributes were positively related to inorganic fertilizer rates. The treatment of compost or biochar plus 238-31-138 kg N-P-K ha−1 was the best treatment. The agronomic efficiency of applied fertilizer N (NAE) significantly decreased with increasing drought levels by 28.4–34.7%. The addition of biochar with inorganic fertilizers significantly enhanced NAE by 11.6% compared to inorganic fertilizers alone. Comparing the effect of inorganic fertilizer rates across all irrigation levels, the treatment of 119-16-69 kg N-P-K ha−1 gave the highest NAE. Thus, the addition of optimum NPK fertilizer rate with biochar or compost is suitable to enhance the yield quantity and quality of maize plants grown on alkaline soils by improving its defensive system and N use efficiency, especially under the expected increase in aridity response to climate change.