Seed Phosphorus Effects on Rice Seedling Vigour in Soils Differing in Phosphorus Status

Abstract

A key driver of the current unsustainable global phosphorus (P) cycle is the removal of P from fields in harvested grains. Minimising the concentration of P in grains of staple cereal crops would contribute towards addressing the issue, but it is possible that reducing grain P concentration may impact the vigour of subsequent seedlings. We used a hydroponic method to obtain low- and high-P rice (Oryza sativa L.) seeds from plants grown under near-identical conditions, so that any differences in subsequent seedling growth were likely due to differences in seed P concentrations rather than other seed quality differences that may arise from growing mother plants under different conditions. Seedling biomass production and P uptake were then investigated using high- and low-P seed of four rice genotypes in a P-rich soil and a P-deficient soil in a pot study in a glasshouse. In the P-rich soil, with a history of P fertilisation, with P fertiliser banded below seeds at sowing at 20 kg P ha−1 on a pot surface area basis, seedling biomass and P uptake were significantly affected by genotype (p < 0.05) but not by seed P concentration. In the P-deficient Ferralsol, main effects of seed P concentration, genotype and P fertiliser treatment (nil P, banded P fertiliser, broadcast and incorporated P fertiliser) on seedling biomass were all significant (p < 0.01) with, a significant genotype × P fertiliser treatment interaction. Overall, low-P seed produced less biomass than high-P seed (0.059 vs. 0.067 g plant−1) and nil P fertiliser (0.057 g plant−1) resulted in less biomass than banded P fertiliser and broadcast P fertiliser (0.064 and 0.068 g plant−1, respectively). When two genotypes were re-grown in the P-deficient Ferralsol with P fertiliser banded under the seed at 20 kg P ha−1 there was a significant effect of genotype on shoot biomass (p < 0.001) but only a trend towards lower seedling biomass with low P seed compared to high P seed (p = 0.128). Overall, the results suggest that seed P concentration does not affect seedling vigour when external soil P fertility is sufficiently high, but in P-deficient soils seedling biomass production and P uptake can be reduced by 10–20%. Further research is required to determine whether agronomic interventions including seed P priming or biological seed dressings can mitigate any impacts of lower seed P concentration on seedling vigour in P-deficient soils.