Abstract: To explore the ecophysiological mechanism underlying the effects of straw returning on maize seedling growth, three types of soils (black soil, loess and acid soil) were selected, two methods of straw returning to the field (straw mulching and straw mixing) and two stone treatments (stone covering and stone mixing) in black soil were set up. The morphological changes of aboveground and belowground parts and the physiological indices of stress resistance under different treatments were compared. The results showed that straw returning significantly increased plant height, leaf area, dry matter weight, chlorophyll fluorescence parameters, root length, root surface area, root tip number, and active absorption area of roots at seedling stage. The straw mixing treatment performed better than straw mulching treatment. Straw returning decreased superoxide dismutase and catalase activities and malondialdehyde content, with mulching treatment performing better than mixing treatment. Although the fertility of loess was different from that of black soil and acid soil, the effects of straw returning were the same. Both stone treatments inhibited root growth. Straw returning treatments (either mulching or mixing) performed better than stone treatments. Therefore, straw returning promoted root growth and nutrient absorption mainly by changing soil biochemical properties, and thus enhanced the growth of aboveground parts.

Key words: maize, straw mulching, straw mixing, stone covering, stone mixing.