Abstract: To explore the potential for the resource utilization of sediment in the Yellow River and to clarify the physical, chemical and biological responses to improvement measures, we conducted a field experiment with dredged sediment from Wuhai Lake in the Inner Mongolia section of the Yellow River Basin as the research object and maize as the planting crop. The treatments included sediment application, fertilizer application, growth-promoting bacteria application, biochar (rice husk biochar/wheat straw biochar) application, application of microbial agent combined with biochar, and application of microbial agent combined with biochar and covered with hydrophobic sand. Soil samples of the rhizosphere of maize were collected at the pre-planting, seedling, jointing, and maturity stages. Soil moisture, nutrient content and enzyme activity were measured. The results showed that the application of rice husk biochar and wheat straw biochar could improve soil moisture and nutrient content. The improvement effect increased with the increases of dosage (0.5%-4%), and rice husk biochar was superior to wheat straw biochar. Compared with the single application of fertilizers (F), the application of rice husk biochar (with a dosage of 0.5%-4%) increased soil water content by 1.7%-5.5%, 0.3%-5.0%, 0.9%-4.4%, and 0.4%-3.4%, and increased soil organic matter content by 14.0%-156.1%, 18.7%-159.7%, 26.0%-178.6%, and 19.2%-168.9% in the four sampling periods, respectively. An appropriate amount (0.5%) of biochar application significantly enhanced the activities of four enzymes (with rice husk biochar having a better effect), but the enhancement effect was weakened when the dosage increased to 2%. Compared with the application of biochar, the application of microbial agent combined with biochar decreased soil pH, but increased water content, ammonium nitrogen, available phosphorus, and organic matter contents. The hydrophobic sand cover increased the water content, available phosphorus, and organic matter content, but decreased soil pH, conductivity, ammonium nitrogen, and available potassium content. The Pearson correlation analysis and principal components analysis revealed that the improvement of soil physicochemical properties and the increase of nutrient content were conducive to improving enzyme activities, but high soil pH during the maturity stage would inhibit the catalase activity. Therefore, the application of biochar, especially microbial agent combined with biochar treatment, can effectively improve nutrient content and enzyme activity of the sediment, which is an effective way to improve its quality and promote resource utilization.

Key words: biochar, bacteria agent, hydrophobic sand, Yellow River sediment, soil nutrient, soil enzyme activity