Effects of long-term straw return on corn yield, soil nutrient contents and en-zyme activities in dryland of the Loess Plateau, China

Incorporation of straw in soil plays an important role in nutrient management, maintenance of crop productivity, and improvement of soil quality, which is considered to be an effective measure as a substitute for chemical fertilization. Understanding the effects of long-term straw incorporation on soil properties and corn yield in the dryland of the Loess Plateau are essential to provide scientific evidence for sustainable utilization and soil quality improvement of cropland. Here, based on a long-term (24 years) straw return field experiment, effects of different straw return regimes, i.e., straw mulching (SM), direct straw return (DS), animal-digested straw return (AS), and non-straw return (CK) on soil chemical properties, enzyme activities, and corn yield were studied. Results showed that the cumulative corn yield under SM, DS, and AS treatments were 1.885×10⁵ kg·hm^-2, 1.854×10⁵ kg·hm^-2 and 2.001×10⁵ kg·hm^-2, respectively; the yields increased by 10.1%, 8.6% and 15.3%, respectively, compared to CK treatment (1.695×10⁵ kg·hm^-2). Besides, the three long-term straw incorporation treatments enhanced soil organic carbon by 6%-14% in 0-20 cm soil layer, whereas they had no significant effect on soil organic carbon in 20-40 cm soil layer. Compared to CK, soil total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus and available potassium contents were significantly increased under AS treatment; whereas DS treatment enhanced soil total nitrogen, total potassium, available nitrogen and available potassium contents; and SM treatment increased soil available nitrogen and potassium content. In addition, soil invertase activity was the highest under AS treatment, followed by SM and DS, and the lowest under CK treatment. Soil cellulase activity under DS treatment was 2.2 and 1.3 times higher in 0-20 cm and 20-40 cm soil layers, respectively, than that under CK treatment. Furthermore, AS treatment enhanced soil urease activity by 13.0% and soil alkaline phosphatase by 20.5% compared to CK, while SM and DS treatments had no significant effect on soil urease and alkaline phosphatase activities. Soil activities of invertase, urease and alkaline phosphatase showed a greater response to animal-digested straw return treatment, whereas soil cellulose activity had a greater response to direct straw return treatment. Furthermore, there was a significant positive correlation between corn yield and soil invertase activity. In conclusion, long-term continuous animal-digested straw return and direct straw return had a profound impact on soil nutrients and enzyme activities. Particularly, the increase in soil invertase activity by straw return is closely related to the promotion of corn yield.