Effect of late-season N fertilization on photosynthesis and yield of transplanted and direct-seeded tropical flooded rice. II. A canopy stratification study uri icon

abstract

  • Grain-yields of broadcast-seeded tropical semidwarf lowland rices (Oryza sativa L.) frequently fall short of potential yield because of excessive vegetative growth and subsequent N deficiency in the foliage during the reproductive phase. A field experiment was conducted during the 1989 dry season in the Philippines to determine relationships between canopy structure and CO2 assimilation rates at anthesis with yield and yield components at maturity. Canopies of broadcast-seeded flooded rice had greater leaf area index (L), dry matter, N uptake, and tiller number than had canopies of transplanted rice. Grain-yields were equal for both planting methods. Early and midseason N fertilization increased dry-matter, L and tiller number, whereas late-season foliar N application increased foliar N concentration and delayed senescence. The N status of leaves affected stomatal conductance, CO2 assimilation and leaf width. Despite N content being greater in the uppermost than in lower leaf positions, N limited photosynthesis for all leaves. Potential canopy CO2 assimilation rates (P(n)) depended linearly on L, whereas actual P(n) was little affected by L. High tiller number was detrimental to P(n), possibly because of shading by panicles, whereas high N uptake and flag-leaf N concentration promoted P(n). The P(n) at anthesis was linearly correlated with grain-yield, whereas the harvest index (HI) was high at a combination of high P(n), low L, and high flag-leaf N content. Late-season foliar N application favored these canopy characteristics, thus improving grain-yields and HI. It is concluded that late-season foliar N application can improve yields of tropical semidwarf rices, particularly for direct-seeded culture. Future breeding efforts for rices adapted to direct seeding should reduce L and tillering activity while increasing the N concentration of the uppermost leaves during the reproductive growth phase.

publication date

  • 1992
  • 1992
  • 1992