Effects of AMF inoculation on summer maize production, soil enzymes and nitrogen balance in salinized fluvo-aquic soil area

Maize is one of the most important grain crops in the Heilonggang region of the Huang-Huai-Hai Plain, playing a pivotal role in food security. The soil in this region is classified as fluvo-aquic soil and exhibits varying degrees of salinization. Maize is a moderately salt-sensitive crop. Salinized environments disrupt its salt tolerance mechanisms, which are established through ion balance regulation, osmotic adjustment, and antioxidant defense, leading to physiological drought, soil structure compaction, and nutrient fixation. As a result, the normal growth and metabolism of maize are hindered, and nutrient use efficiency is significantly reduced. Arbuscular mycorrhizal fungi (AMF) and plant roots can form a mutualistic symbiosis with specific structure and function. They enhance plant tolerance to saline-alkali stress by modifying root morphology, promoting water and nutrient uptake, alleviating the toxic effects of salt ions, strengthening osmotic regulation, and altering plant hormone levels. To reduce the negative effects of saline-alkali stress on summer corn production and improve corn yield, quality and nitrogen use efficiency in salinized fluvo-aquic soil areas, a field experiment was conducted in moderate to severe salinized fluvo-aquic soil in Cangzhou, Hebei Province, using a randomized block design with ‘Zhengdan 958’ as the test material. Four treatments were set: CKA- (non-inoculated with AMF + no fertilization), CKA+ (inoculated with AMF + no fertilization), NPKA- (non-inoculated with AMF + conventional fertilization), and NPKA+ (inoculated with AMF + conventional fertilization). The results showed that under conventional fertilization conditions, inoculation with AMF significantly increased the maize root colonization rate by 148.30% compared with the non-inoculated treatment. It also significantly improved maize grain yield (an increase of 9.12%), as well as nitrogen accumulation in grains and straw (increases of 10.44% and 4.66%, respectively). Furthermore, AMF inoculation significantly enhanced soil catalase and urease activities (increases of 57.38% and 37.27%, respectively), reduced soil ammonium nitrogen and nitrate nitrogen contents (decreases of 14.86% and 9.38%, respectively), thereby improving nitrogen use efficiency and reducing the apparent nitrogen surplus and actual nitrogen surplus by 43.64% and 11.85%, respectively. Although the contents of crude protein, crude starch, and crude fat in maize grains increased after AMF inoculation, the differences were not significant compared with the non-inoculated treatment. Therefore, AMF can establish a mycorrhizal symbiosis system to achieve yield and quality improvement of summer maize in salinized fluvo-aquic soil areas, stimulate soil enzyme activity, optimize soil nitrogen balance, and reduce nitrogen environmental risks, providing theoretical support and practical pathways for the improvement of salinized cultivated land and stress-resistant, high-yield maize cultivation.