Effect of crop residue returns on N2O emissions from red soil in China.

For a long time, farmers in the red soil region of southern China have returned crop residues to the soil, but how various crop residues influence nitrous oxide ( N₂ O) emissions is not well understood. We compared the influence of returning different crop residues [rapeseed cake (RC), maize straw, rice straw and wheat straw (WS)] in combination with different levels of nitrogen ( N) fertilizer (nil, low and high) on red soil N₂ O emissions. Results confirmed the inverse relationship between cumulative N₂ O emissions and residue C:N ratio in red soil under different levels of N fertilizer. However, N-fertilizer application did not significantly influence N₂ O emissions in the WS (which had the highest C: N ratio) and corresponding control treatments, while it enhanced N₂ O emissions in the RC (which had the lowest C: N ratio) treatment and displayed significantly higher cumulative N₂ O emissions with low N fertilizer application. This phenomenon may be attributed to the poor nutrient content in red soil, which leads to 'Liebig's Law of the Minimum' on available C. N fertilizer application provided sufficient available N, while the readily available C, which was mainly dependent on the degradability of the residue, became the crucial factor influencing N₂ O emissions. Additional experiments, which showed that the addition of glucose and sucrose could increase N₂ O emissions when N ( [ABSTRACT FROM AUTHOR]