Effect of Nitrogen Fertilizer Forms on Growth, Photosynthesis, and Yield of Rice Under Cadmium Stress

ABSTRACT

A pot experiment was conducted to study the influence of four nitrogen (N) fertilizer forms [Urea; calcium nitrate, Ca(NO₃)₂; ammonium sulfate, (NH₄)₂SO₄; and organic N] on growth, photosynthesis, and yield of rice under two cadmium (Cd) levels (0 and 100 mg Cd kg⁻¹ soil). Cadmium addition significantly reduced photosynthetic rate, and the reduction varied with N fertilizer form, with ammonium (NH₄ ⁺)-N and urea treated plants having more reduction. Nitrogen form had a distinct effect on SPAD value, and the effect was also dependent on Cd level and growth stage. Cadmium-stress significantly reduced flag leaf area, but for the second leaf, only the plants supplied with organic N showed the reduction. There was a significant difference in plant height among four N forms, with NH₄ ⁺- and nitrate (NO₃ ⁻)-treated plants having the highest and lowest height, respectively. Cadmium stress caused significant reduction in grains per panicle and total plant weight, and the reduction varied with N form, with organic N treatment showing more reduction. There were significant differences among N forms in N and Cd concentrations of the plants subjected to Cd stress, with NH₄ ⁺-N treated plants having highest N and lowest Cd concentrations and NO₃ ⁻-treated plants having lowest N and highest Cd uptake. The results showed that the inhibition of Cd stress on growth and yield formation of rice is closely related to N fertilizer form.

Keywords:

• cadmium
• growth
• nitrogen
• photosynthesis
• rice
• Oryza sativa L

ACKNOWLEDGMENT

We are greatly grateful of Zhejiang Natural Science Foundation (Z304104) for its financial support to this research program.

Notes

¹The same letter after data within a column represents no significant difference at 95% probability;

²NS, ∗ and ∗∗ represent no significance, significant at 95% probability and highly significant at 99% probability respectively.

¹The same letter after data within a column represents no significant difference at 95% probability;

²NS, ∗ and ∗∗ represent no significance, significant at 95% probability and highly significant at 99% probability respectively.

¹The same letter after data within a column represents no significant difference at 95% probability;

²NS, ∗ and ∗∗ represent no significance, significant at 95% probability and highly significant at 99% probability.

¹The same letter after data within a column represents no significant difference at 95% probability;

²NS, ∗ and ∗∗ represent no significance, significant at 95% probability and highly significant at 99% probability.