Nutritional root growth promoting agent for dryland crops and preparation method thereof

A nutritional root growth promoting agent for dryland crops is composed of, by mass, 40-60 parts of nitrohumic acid, 20-30 parts of an oxidized peat fulvic acid composite water-retaining agent, 10-30 parts of a chelated nutrient solution and 0.3-5 parts of a disinfectant. A preparation method includes the steps of mixing uniformly the raw materials hereinabove. The nitrohumic acid is composed of low-grade coal, 10-60% of nitric acid, ground phosphate rock, potassium feldspar, agricultural rare earth, an inorganic auxiliary material, an organic auxiliary material and a catalyst. The oxidized peat fulvic acid composite water-retaining agent is composed of oxidized peat fulvic acid, a cationic compound monomer, an anionic compound monomer, a crosslinking agent and an initiator. The chelated nutrient solution is composed of fulvic acid, organic acid, proline, polyaspartic acid, a mid-element compound, a micro-element compound, EDTA and vitamins. The disinfectant is any one selected from mancozeb, validamycins, th