[Effects of maize and rice straw amendment on the pH, CO2, and exchangeable NH4+ of submerged soil].

A greenhouse incubation test was conducted to study the effects of amendment with different amounts of maize and rice straws on the soil pH, CO2, and exchangeable NH4+ under continuous flooded condition. The results showed that in a near-neutral soil, straw amendment could decrease soil pH, with a significant difference (P < 0.05) between the treatments of 4 g straws x kg(-1) and control (CK), but no significant difference (P > 0.05) between the treatments of 1 g straws x kg(-1) and CK. The CO2 content in soil solution increased with increasing rate of straw amendment, with the peak value being 35.9% and 31.9% (v/v) in the treatments of 1 g maize straw x kg(-1) and 1 g rice straw x kg(-1), respectively. These two treatments had significantly higher CO2 contents (P < 0.05) than CK, but no obvious difference between themselves (P > 0.05). In treatments 4 g maize straw x kg(-1) and 4 g rice straw x kg(-1), the peak value of CO2 content was 54.2% and 41.8% (v/v), respectively, being significantly higher than that of CK (P < 0.01), and significantly different between themselves (P < 0.05). Under non-N fertilization, soil NH4+-N concentration decreased after straw amendment, and the increase of the amendment rate caused a further decrease of soil NH4+-N concentration, with a significant difference (P < 0.05) between the doses of 1 and 4 g straw x kg(-1). Under N fertilization, soil NH4+-N concentration increased after 1 g straw x kg(-1) amendment, but decreased after amendment with 4 g straw x kg(-1). No significant differences were observed between maize straw and rice straw amendment regardless with or without N fertilization (P > 0.05).