淹水土壤有机酸积累与秸秆碳氮比及氮供应的关系

ACCUMULATION OF ORGANIC ACIDS IN RELATION TO C:N RATIOS OF STRAWS AND N APPLICATION IN FLOODED SOIL

有机酸积累和毒害是稻田秸秆还田中受到广泛关注的问题。本文以水稻与小麦秸秆为材料,采用淹水培养研究了甲酸、乙酸、丙酸及丁酸在土壤中的积累及其与秸秆碳氮比、氮肥添加量的关系。结果表明,在不施用氮肥的情况下,随秸秆用量的增加,秸秆处理的有机酸积累均显著增多。与稻秸处理相比,麦秸处理的有机酸(尤其是丙酸)积累量显著较高,土壤溶液中NH4+浓度显著较低。加入尿素明显减少有机酸积累,促进CH4排放,但对CO2的排放无显著影响;氮素的影响在麦秸处理中表现的尤为明显。上述结果说明麦秸的高碳氮比增加了无机氮的生物固定,抑制有机酸向CH4转化,从而导致麦秸处理有机酸积累量高于稻秸处理。施用氮肥是减少麦秸还田后有机酸积累的有效措施之一,但此措施将可能促进CH4的排放。

Accumulation of organic acids and their phytotoxicity in paddy rice fields incorporated with crop straws have been widely concerned. Laboratory incubation was conducted to investigate the accumulation of organic acids, including formic, acetic, propionic and butyric acid in soil solution under flooded conditions and the effects of C ： N ratios of straw materials and N application. Results showed that the concentration of organic acids in soil solution increased with the rate of straws incorporated. The overall accumulation of organic acids （especially propionic acid） was significantly higher in soil incorporated with wheat straws than with rice straws, while NH4^＋ concentration in the soil solution was the other way round due to wider C ： N ratio in wheat straw. Addition of urea significantly reduced concentration of organic acids in soil solution and enhanced CH4 flux but had no obvious influence on CO2 flux in the wheat straw treatment, while in the rice straw treatment, the concentration of organic acids and CH4 flux were less sensitive to N addition. Results obtained in this study indicated that wider C ： N ratio of wheat straw enhanced the immobilization of inorganic N and inhibited the transformation of organic acids to CH4 which led to higher accumulation of organic acids. N application can serve as one of the effective ways to reduce the accumulation of organic acids in rice fields incorporated with wheat straw, but may enhance CH4 emission.