Influence of different drying-rewetting frequencies on available soil nutrients and DOC

To investigate the mechanism of influence of different drying-rewetting frequencies on available soil nutrients and DOC,in this study,we collected cinnamon soil at a depth of 0-10 cm below the surface in Beijing and manipulated soil water stress in the laboratory by exposing soil to 0,1,2,3,or 4 drying-rewetting cycles for 58 days,including a 10 day pre-incubation period and a 48 day treatment period. After 58 days,principal soil fertility indexes such as available nutrients and DOC were tested to observe changes as a result of different drying-rewetting frequencies. Data were analyzed using single-factor variance analysis and the Least Significant Difference method( LSD) for the dependent groups. Available K and nitrate nitrogen were lower in the drying and rewetting treatments than in the constantly moist treatment( CM). Low drying-rewetting frequency might lead to the loss of available K,while K release might appear in the late stages of high drying-rewetting frequency conditions. As drying-rewetting frequency increased,the available K also increased. Four drying-rewetting cycles were critical for K release. Increasing the drying-rewetting frequency would result in frequent perturbations to the balance between various forms of nitrogen,and the mineralization rate would increase at the lowest drying-wetting frequency( DW1,1 drying-rewetting cycle) and the highest drying-wetting frequency( DW4,4 drying-rewetting cycles).As drying-wetting frequency increased,nitrate nitrogen of drying-rewetting treatment become closer to that of constantly moist( CM). Soil nitrate nitrogen significantly increased,while available K,ammonium nitrogen,and DOC significantly decreased,with drying-wetting frequency,and available P and p H were relatively insensitive to drying-rewetting frequency.In 48 days,with increase in drying-rewetting frequency( from 1 cycle to 2,3,and 4 cycles) and decrease in dryingrewetting period( from 48 d to 24,16,and 12 d) and the last period of each drying or wetting period( from 24 d to 12,8,and 6 d),nitrate nitrogen and available K tended to increase to levels close to those of the constantly moist condition.