Dynamics Of Soil Carbon And Nitrogen And Its Simulation In Dryland Mulched By Film And Straw

Field trials under the rotation of winter wheat-summer corn in eight-season crop rotations of four years were carried out to study the effects of different mulching measures on surface soil organic carbon?SOC?,total nitrogen?TN?,soil microbial biomass carbon and nitrogen?SMBC and SMBN?,and nitrate-nitrogen accumulation and water distribution in0-200 cm soil profile.The dynamics of soil organic carbon storage and crop yield were also simulated by DNDC model under different long-term mulching conditions,which could provide the theoretical and practical basis for the selection of suitable mulching cultivation measures in the area.The trial set up 4 kinds of mulching treatments such as non-mulching?NM?,straw mulching?SM?,half-film mulching?HFM?,full-film mulching?FM?.The results showed as follow:1)For NM treatment,SOC showed a downward trend,and the SOC content at the harvest stage of the last crop was significantly lower than that of the first two crops under rain-fed dry land conditions?P<0.05?,while TN kept almost stable.For SM treatment,SOC and TN showed a trend of increasing first and then decreasing,and the SOC content at the harvest stage of the last crop was significantly higher than that of the first two crops?P<0.05?.For both of HFM and FM treatments,SOC and TN content showed a fluctuating downward trend as a whole.The average values of SOC and TN at the harvest stage of the eight crops were 8.91 g.kg^-1 and 0.99 g.kg^-1 under NM treatment respectively;those were 9.03 g.kg^-1 and1.03 g.kg^-1 under SM treatment,respectively;those were 8.04 g.kg^-1 and 0.96 g.kg^-1 under HFM treatment,respectively;and those were 8.13 g.kg^-1 and 0.96 g.kg^-1 under FM treatment,respectively.SMBC and SMBN showed fluctuant in rain-fed dry land under all treatments,in which SMBC under NM was the highest with an average value of 274.04 g.kg^-1,and SMBN content under SM was the highest with an average value of 24.46 g.kg^-1.2)The SOC of all treatments remained almost stable except that the SOC of the last crop season decreased significantly in dry land under irrigation condition.TN of HFM and FM treatments showed a downward trend as a whole.For NM treatment,the averages of SOC and TN at the harvest stage of the eight crops were 8.60 g.kg^-1 and 0.95 g.kg^-1,respectively;For SM treatment,those were the highest in 9.50 g.kg^-1 and 1.10 g.kg^-1,respectively;For HFM treatment,those were 8.96 g.kg^-1 and 1.00 g.kg^-1,respectively;For FM treatment,those were9.17 g.kg^-1 and 0.99 g.kg^-1,respectively.The averages of SMBC and SMBN content of NM treatment were the highest in 293.33 g.kg^-1 and 20.11 g.kg^-1,respectively.The results of all mulching treatments under the irrigation conditions were similar to that under the rain-fed conditions,both of which increased the nitrate-nitrogen and water content in 0-20 cm topsoil,and decreased the nitrate-nitrogen content in deep soil.Soil TN,SMBC and SMBN content of HFM and FM treatment gradually decreased with the trial time.SOC and TN in all treatments under irrigation condition were higher than those under rain-fed condition.3)The results of SOC storage,wheat and maize yields under different mulching conditions simulated by DNDC model were in good agreement with the measured ones in rain-fed dry land.The simulated value is significantly related to the measured value,and the NRMSE of the simulated value and the measured value is basically within the acceptable range.It shows that the DNDC model has a good simulation effect on SOC storage and crop yield,and it has higher simulation accuracy for SOC storage.By simulating the results of long-term mulching in rain-fed dry land under the wheat-maize rotation for 30 years,it was found that SOC storage of SM treatment gradually increased first,and then remained stable over time;SOC of FM treatment rised rapidly and then declined slowly that were lower than that of SM treatment overall.HFM and NM treatment decreased SOC storage gradually,in which SOC storage of HFM treatment was slightly higher than that of NM treatment.The results of simulated yield showed that the wheat production showed a large fluctuation and a rising trend.The yield of wheat mulched with FM in early stage was higher than that of other mulching treatments.The yield of wheat mulched with SM increased gradually with the increasing of time,and was higher than other treatments.The yield of corn fluctuated slightly with an increasing tendency gradually,and the differences were not significant in the early period.The yields of SM treatment in the later period were obviously higher than that of other treatments,and that of NM treatment was the lowest.In a long run,SM treatment can increase SOC storage,and wheat and corn yields.It is the most recommended and sustainable mulching cultivation method under the wheat-maize rotation in the region.