Straw retention decreased the available P concentration in
the soil solution, although it did not alter the trend of
available P concentration in the soil solution during plant
growth. In addition, in the 10–20-day period after
transplantation, the available P concentration in the soil
solution was high, although it decreased thereafter. The
available P concentration in the soil solution increased with
the amount of applied P fertilizer, and the rice yield also
increased with increasing applications of P fertilizer. The
results of experiments A and B showed that straw retention
had no significant impact on the rice yield; however, years
of continuous observation are required to verify these
results. In this study, P (inorganic and organic form) content
in the soil did not produce a significant effect on the
rice yield. Application of P may be absorbed by the soil
and result in increased P concentrations in the soil.
Therefore, continuous experiments should be conducted at
this experimental site to observe the long-term effects.