Effect Of Residue Retention And No-till On Soil Respiration Of A Rainfed Crop Field On The Loess Plateau

On the Loess Plateau of northwest China,conservation tillage is popularized to reduce soil emissions,increase carbon sequestration and maintain agricultural sustainable development.However,little is known about the controlling mechanisms of no-till and residue management to soil respiration under conservation tillage in the rainfed farmland.Winter soil respiration is also becoming a significant component of annual carbon budgets with greater change of temperature in winter than summer.A long-term conservation tillage experiment was established in a maize/ winter wheat/ vetch rotation field in 2001.Continuous measurement of soil respiration was taken with an automated soil respiration system(LI-8100 A equipped with an LI-8150 multiplexer and LI-104 chambers,which also recorded synchronous soil moisture and soil temperature data)from 2014 to 2016,to investigate the causes of soil respiration(Rs)dynamics during the growing season and non-growing season.Results showed that:1.From July 2014 to August,four treatments were included in the experiment: conventional tillage(T),no-tillage(NT),conventional tillage with half amount of the previous crop's stubble retention the plots(TS)and no-tillage with half amount of the previous crop's stubble retention the plots(NTS),conducted to compare the effect of tillage treatments on soil respiration during a drying and rewetting cycle.Common vetch existed in the field during the measurement.The mean soil respiration rates of T,TS,NT and NTS were 2.16,3.56,2.26 and 2.45 ?mol/(m2�s),respectively,before the rewetting of soil,and those values were 2.09,5.31,2.80 and 3.56 ?mol/(m2�s1),respectively,after the rewetting.Soil respiration of the TS,NT and NTS rose rapidly after the rainfall while that of the treatment T only showed an insignificant increase.Soil respiration was positively related to soil moisture and negative related to temperature before the rewetting of soil,however,it had an opposite relationship with these parameters after the rewetting.The sensitivity of soil respiration to soil moisture and temperature was reduced by no tillage and stubble retention practices.2.From March 2016 to september,we made continuous measurements of annual soil respiration in four tillage treatments(no-till(NT),no-till with half amount of the previous crop's stubble(NTS),no-till with whole amount of the previous crop's stubble(NTSW),conventional tillage with half amount of the previous crop's stubble(TS),to evaluate the effect of different conservation tillage treatments on soil respiration.During growing season,mean soil temperature values for NT,NTS,NTSW and TS were 20.74?,18.63?,19.93? and 20.44?,respectively,mean soil water content were 23.71%,23.84%,25.78% and 21.41%.CO2,respectively release elevated with quantity of residue increased under no-till,and no-till released more compared with conventional tillage under whole amount of the previous crop's stubble.Mean soil respiration for NT,NTS,NTSW and TS were 4.63,4.46,4.37 and 3.16 ?mol CO2 m-2�s-1 during the growing season.Q10 value ranged from 2.05 to 2.38,and it was lower under whole amount of the previous crop's stubble treatments(TS and NTSW).3.During non-growing season(from December 2015 to March 2016),mean soil respiration rates for NT,NTS,NTSW and TS were 0.26,0.36,0.30 and 0.40 ?mol CO2 m-2�s-1 and Q10 value were 3.88,3.80,3.00 and 5.38,respectively,accounting for 7.49%,7.50%,5.99% and 8.11% of annual soil respiration.Winter Rs in farmlands was sensitive to soil temperature(Ts)and Ts-induced freeze-thaw cycle.Mean soil temperature of NT,NTS,NTSW and TS were-0.92?,-0.04?,-0.30? and-0.84?,mean soil water content was 21.14%,22.43%,18.08% and 22.72%,respectively,the relative contribution of freeze-thaw cycle RS to annual RS were 1.27%,0.45%,0.35% and 0.97% with 20,10,11 and 17 days in non-growing season respectively.Q10 value was higher during frozen days(57.40,9.91,9.39 and 24.89)than freeze-thaw cycles(4.89,7.19,4.08 and 6.43).In conclusion,no-till and residue retention can thermal insulation and buffer temperature fluctuations,and also reduced the Q10 value,led to RS of NTS was lower than TS under the same quantity of residual.Soil temperature stability was affected by the interaction of no-till and residue retention,and its impact on Rs varied among residue management.Annual RS of NT was lowest(NTSW>TS>NTS>NT),during growing season RS increased with increasing quantity of residual,with highest in NTSW.But during non-growing season,RS was highest in TS.Drying and rewetting events and freeze-thaw cycles may become more important to soil respiration as the climate is continuously getting warmer.