In conclusion, significant differences in soil fertility of paddy
soils in the red soil region of southern China among different
fertilization treatments were found in our study. Application of
OM and NPK resulted in a substantial increase of SOC, TN, C/N
ratios, AN and AP contents relative to the other fertilization
treatments. Thus, it is likely that the OM and NPK application
improves soil fertility. Meanwhile, the application of NPK would
increase soil AK, leading to the highest AK contents. Continuous
application of SR also had a positive effect in sustaining SOC, TN
and C/N ratios. However, the effect of GM application on soil
fertility was not remarkable compared to CK. Hence, organic
manure should be recommended to improve soil fertility in this
region and K fertilizer should be simultaneously applied considering
the soil K contents. Moreover, in terms of the long-term
fertilizer efficiency, annual straw returning application year by
year could be adopted in this trail region.