耕作红壤改水田后磁化率动态的研究

BEHAVIOR OF SOIL MAGNETIC SUSCEPTIBILITY IN THE RECLAIMATION OF RED EARTH INTO RICE FIELD

耕作红壤改水田6年中,磁化率逐年下降,平均下降速率为5×10^(-6)CGSM/g,3种稻作制的下降速率差异不大,绿肥处理对土壤磁化率有较大影响,用量愈大,磁化率波动幅度愈大,不施绿肥的处理则一直平缓下降,6年后不施绿肥处理土壤磁化率高于施绿肥处理,不同地下水位对植稻土壤表层(0～20cm)磁化率影响很小,而对底层(20～40cm)影响大。磁化率动态和无定形铁有负相关性,而和游离铁之间相关性差,不同绿肥用量及不同地下水位处理6年后磁化率和无定形铁及铁活化度之间反相关明显,植稻6年后土壤磁化率为稻地同母质老水稻土的8倍,比幼年水稻土也高得多,估计红壤旱改水后至少连续种植10年以上才能形成幼年水稻土,结合其它性状考察,磁化率可能作为鉴定水稻土的重要指标之一。

Soil magnetic susceptibility (MS) of rice field reclaimed from red earth since 1982 under the treatments of three cropping systems,three levels of green manure application and two water tables (20 and 80cm)was measured co-ntinually. As a whole, the MS kept decreasing after reclaimation, but different treatments affected the MS vibrating with different amplitudes in the trend of decreasing, The dynatic change of MS had a negative relation to amorphous iron (Feo) and the MS in all treatments showed a negative relation to the activation coefficient of iron (the ratio of amorphous and free iron) significantly.Acc-ording to the decreasing rate of MS observed, it was estimated that the recla-imation of red earth into amorphous paddy soil needed over 10 years at least. The MS might be used as one of the indexes in affirming paddy soil and in its classification.