Change of soil organic matter
The soil organic matter was important basic substance in soil fertility. The soil organic matter was increased except control after five years fertilization (Fig.5). Comparing with initial soil organic matter content, it increased by 6.5% in NPK treatment, and was significantly less than that in NPKM (18.5%) and M (37.1%) treatments. Therefore, application of organic manure or organic manure combined with chemical fertilizer was propitious to the increase of soil organic matter
and improvement of soil fertility. The soil organic matter in M treatment (34.0 g kg-1) was higher than in NPKM (29.4 g kg-1), NPK (26.4 g kg-1), and PK (24.7 g kg-1) treatments under five years fertilization. The soil organic matter with no fertilization was decreased slightly under five years plantation.