| In order to clarify the best rotation mode of "three advance" water storage and soil conservation techniques,it provides important theoretical and practical significance for high quality and high yield cultivation of wheat in dryland area of Loess Plateau.The effects of different tillage patterns on soil physical structure,available nutrients,organic carbon components and microbial biomass were studied under field test conditions in 2015-2016.The main results are as follows:(1)The results showed that fallow rotation could improve the soil bulk density during sowing,wintering,returning and harvest stages,and with the growth process showed an increasing trend.Three years of no-tillage increased soil bulk density by 1.31 to 1.53 g/cm3.Before sowing of deep plowing and subsoiling soil bulk density was significantly lower than that of no tillage,and the soil bulk density was reduced by ST/DT/ST of.19?1.26 g/cm3 in the wintering,returning and harvest stage,the soil was loose,the gap was more and the air permeability was good.Fallow tillage can increase soil porosity,ranging from 42.1%to 59.4%,is conducive to water conservation and moisture.The effect of ST/ST/ST and ST/DT/ST rotation was better before sowing,and ST/DT/ST was better in wintering,returning and harvesting stages.There was a difference in soil microaggregates with different grain sizes.Before sowing and after harvest,the NT/NT/NT pattern promoted the formation of micro-aggregates with 0.01-0.005 mm particle size,the percentage was 9.3%to 16.3%.The ST/DT/ST pattern promoted the formation of micro-agglomeration in 0.25-0.05 mm,the percentage was 31.5%to 51.5%.(2)The results showed that fallow rotation tillage increased 3 m soil nitrate nitrogen accumulation of dryland wheat by 1.7 to 33.0 kg/hm2 before sowing,but after the harvest of dryland wheat under 1 m soil nitrate nitrogen accumulation decreased significantly.The soil nitrate accumulation decreased gradually during the wintering to anthesis period,and before sowing,harvest stage and different growth stages by ST/DT/ST pattern is better,reaching 0.8?33.0 kg/hm2.Before sowing and harvest 3 m soil ammonium nitrogen accumulation decreased gradually with the increase of soil depth,but the decline is different,the deep leveled off,the growth period soil ammonium nitrogen accumulation increased gradually from wintering to maturity,due to the fallow rotation tillage improved soil structure,soil ammonium nitrogen accumulation in the topsoil.In the later stage of the growth period accumulation,and the effect of ST/DT/ST pattern was significant before sowing,harvest stage and at different growth stages,reaching 2.3?26.5 kg/hm2.Fallow rotation can increase 0-40 cm soil layer available P and available K content of topsoil was higher,the ST/DT/ST pattern had the best effect,and it is 2.8%?159.8%and 4%?139%higher than that of other farming models,which can increase the content of sufficient phosphorus and potassium for the growth of wheat.(3)The results showed that fallow rotation was beneficial to improve the TOC and various carbon content before sowing and after harvest stage,and then increased a certain extent after the harvest.Compared with other tillage patterns,the TOC,ROC,WSOC,POC and LFOC contents were increased by the DT after 2 years,and increased from 4%to 61.4%,11.3%to 107.6%,1.4%to 536.5%,2.6%to 294.5%and 8.8%to 410.6%respectively,while DT and other farming methods were used to improve HFOC content before sowing.NT/NT/DT,DT/DT/NT,ST/DT/ST pattern is beneficial to increase the soil HFOC content after harvest.(4)Fallow rotation tillage can improve the growth period in SMBC,SMBN and SMBP content were by ST/DT/ST pattern better than other tillage were increased by 11.1%?143.1%,1.1%?233.5%and 0.7%?396.4%.SMBC showed a gradual upward trend from wintering stage to maturity stage and outstanding performance during turning green,jointing,booting,flowering and maturity stage.SMBN showed a gradual decrease from wintering to jointing stage,booting to maturity stage gradually increased,and there was a significant difference between other stages of growth and other rotation patterns.SMBP showed a gradual increase from wintering to flowering stage,and maturity stage showed different degrees of decrease,there was a significant difference between fertilization and no fertilization at jointing stage and maturity stage.(5)The correlation analysis showed that significantly positive correlation with the porosity of soil nutrient and microbial biomass and available,the correlation coefficient reached 0.63?0.85,<0.001 mm particle size of micro aggregates and soil nutrients showed significant or extremely significant negative correlation,the correlation coefficient reached 0.46?0.72;soil porosity was positively correlated with HFOC,the correlation coefficient is 0.43.0.05-0.01 mm size fractions of micro aggregates with TOC,WSOC,POC,HFOC were positively correlated,the correlation coefficient reached 0.47?0.59,and the<0.001 mm size fractions of micro aggregates with TOC,POC,HFOC showed a significant negative correlation,the correlation coefficient reached 0.48?0.61.In short,fallow rotation improve the soil structure,reduce soil bulk density,increase soil porosity,promote microaggregate formation.It is beneficial to improve the NO3--N,NH4--N,available phosphorus and available potassium,both ST/DT/ST pattern is better;Fallow rotation tillage could also improve the content of soil total organic carbon and carbon group,including NT/NT/DT could improve TOC,ROC,WSOC,POC and LFOC,and DT and other farming methods with the help of improving the soil HFOC content;Fallow rotation was also helpful to improve the content of soil microbial biomass carbon,nitrogen and phosphorus,and the effect of ST/DT/ST was better. |
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