Influence Of Different Drying-Re Wetting Frequency On Soil Respiration And Available Nutrients

In order to explore the mechanism of the effects of different drying-rewetting frequency on soil respiration,available nutrient and DOC(Dissovoled organic carbon),measuring soil respiration was combined with cultivating soil by controlled experiment method and indoor simulation experiment method.Control of other variables,exposing soil to a series of different frequency that 0,1,2,3,4,6,8 drying-rewetting cycles in total 58 days,including 10 days pre-incubation period and 48 days incubation period,soil respiration was measured by alkali absorption and acid-base titration method every 24h and main soil fertility indexes,such as available nutrient,DOC were tested to observe changes in different drying-rewetting frequency after the 1st and the last drying-rewetting cycle(day 58)in each frequency treatment.The conclusions can be drawn as follows:(1)Rewetting in drying-rewetting can cause a sudden increase in soil respiration,and the rate of increase become weakened with increase cycle number of drying-rewetting.There was a high correlation between soil cumulative respiration in 6 drying-rewetting cycles,8 drying-rewetting cycles and constantly moist.As the frequency of drying-rewetting increased,drying-rewetting cycles were more likely to reach the same level of constantly moist.(2)The shorter the cycle,the higher the frequency of a drying-rewetting cycle,resulted in the lower the soil cumulative respiration.Soil cumulative respiration during incubation period was not evenly distributed to each cycle.When the frequency was less than or equal to 6 cycles,soil cumulative respiration generated by each cycle decreased as the number of times increases.In the 48 days incubation period,when the frequency was less than or equal to 4 cycles,soil cumulative respiration generated by rewetting period in drying-rewetting cycle can not compensate for the drying period.When the frequency was greater than 4 cycles,soil cumulative respiration produced by rewetting period may compensate.(3)Drying and rewetting days(the day of drying and rewetting for a total of 24 days respectly)dispersing in 48 days differed in different drying-rewetting frequency.With the increase of frequency,the total soil cumulative respiration produced by rewetting period decreased.The total soil cumulative respiration in 8 drying?rewetting cycles(6 days in each cycle)was higher than the other groups.Soil cumulative respiration generated by rewetting period was greater than that produced by drying period in the same cycle.With the increase of the number of times,soil cumulative respiration in rewetting period and the drying period were gradually reduced;when the degree of 8 drying-rewetting cycles(which frequency more than 6 cycles)reduction slowed down.The release of soil CO2 in drying-rewetting occured mainly in the first half of the rewetting period.(4)During soil moisture decrease in drying period process,when soil moisture decreased,soil respiration rate was reduced.Soil respiration rate and soil moisture can be fitted by quadratic equation.(5)Soil nitrate nitrogen significantly increased,when Available K,ammonium nitrogen,available P,pH and DOC significantly reduced in drying-rewetting.In 48 days,as drying-rewetting frequency increase(from 1 cycle to 2,3,4 cycles)and drying-rewetting period(from 48d to 24,16,12d)and last time of each drying or wetting period(from 24d to 12,8,6d)shorten,nitrate nitrogen,available K had increasing trends to constantly moist level.Low drving-rewetting frequency will lead to the loss of available K of soil and potassium releasing may appear in late period of high drying-rewetting frequency.With drying-rewetting frequency increased,available K of drying-rewetting treatment increase.4 drying-rewetting cycles is critical cycles of potassium releasing.