Aims The study was to explore the effects of different ratios of straw to N-fertilizer on growth of Malus hupehensis seedlings and 15 N absorption, distribution and utilization in them.
Methods Using 15N trace technique, we measured growth parameters (plant height, basal stem diameter and dry weight) and 15N parameters (absorption, N derived from fertilizer, distribution and utilization) of two-year-old M. hupehensis seedlings and C/N ratio in soil organic matter under different straw-nitrogen fertilizer treatments.
Important findings Seedlings grew best under the condition of 45 : 1 of soil to straw and 300 mg·kg–1 N addition, showing the greatest height, basal stem diameter and total dry weight: 85.33 cm, 8.05 mm and 74.68 g, respectively. Total nitrogen, the 15N uptake and 15N utilization were also greatest: 0.938 g, 29.2 mg and 9.7%, respectively. The root/shoot ratio of seedlings without addition of straw (the control treatment) was 1.54, higher than those of other treatments. The 15N derived from fertilizer (Ndff) values of the aboveground parts for all the treatments were higher than those of the belowground parts, and the control showed the highest Ndff values in both aboveground and belowground parts, which were 7.94% and 4.69%, respectively. The 15N distribution ratios of the aboveground parts were higher than those of belowground parts in all treatments except the control. Straw additions could obviously increase the contents of organic matter and total nitrogen in soil and increase C/N ratio of soil organic matter. The correlation analysis showed that the C/N ratio of soil organic matter was significantly negatively correlated with the Ndff value of the belowground parts, as well as in the whole plant. Our findings suggest that it is better to apply nitrogen at rates between 200 and 300 mg·kg–1 when corn straw is added into orchard soil.