Background and aims

This study aims to investigate the effect of nitrogen (N) on grain phosphorus (P) accumulation in japonica rice.

Methods

Six cultivars with contrasting agronomic traits were grown for 3 years (from 2008 to 2010) of field experiments under seven N treatments and 1 year (in 2010) of pot experiments with five N treatments to study the effect of N on grain phosphorus accumulation and to explore its physiological foundation.

Results

Grain total P and phytic acid concentration showed a clearly decreasing trend as N rate increased for both field and pot experiments. Pot experiment revealed that application of N increase plant biomass but tended to lower plant P uptake especially for the split topdressing treatments. Both harvest index (HI) and P harvest index (PHI) increased with N rate but PHI was consistently higher than HI indicating the larger proportion of P translocation to grain than that of dry matter by N. Further ratio of PHI-HI differed significantly among genotypes but was stable across contrasting N treatments.

Conclusions

The combination of decreased plant P uptake and dilution effect of increased grain yield by N is proposed as underlying mechanism of the decreased grain P concentration by high N.