[Objective] The effects of wood-source biochar on the soil aggregate structure were studied to find a suitable biochar addition and to provide a scientific basis for improving the soil structure and increasing crop yield for solar greenhouse soil in Yangling District

Shaanxi Province.[Methods] Five biochar treatments of 10

30

50

70 and 90 t/hm2

and a control treatment without any biochar

were set up. For all treatments

soil aggregate mean weight diameter

geometric mean diameter

damage rate and fractal dimension were calculated through the dry sieve method and the wet sieve method. And

crop yields under different biochar additions were also analyzed. Finally

an appropriate biochar addition was concluded both in considering soil aggregates and crop yields.[Results] The results showed that the mechanically stable dry aggregates significantly increased by 0.6~4.6 mg/kg and the dry microaggregates decreased by 4.0%~32.6% compared with that of control treatment. Further

after adding biochar

3~2 mm

2~1 mm and 1~0.5 mm water stable large aggregates increased by 25.3%~41.2%

22.7%~74.2%

9.1%~46.4% respectively; however 0.5~0.25 mm water stable large aggregates decreased by 2.1%~18.1%. Biochar could promote the formation of small size microaggregates

but have a non-significant effect on microaggregate stability and microaggregates. Additionally

biochar had a positive effect on the spinach fresh weight with an increase of 68.8%~214.9%.[Conclusion] Biochar can ameliorate the soil aggregate structure. Taking soil aggregates and crop fields into account

the 70 t/hm2 biochar has the optimal effect in greenhouse.