| Currently,crop straw return via mulching is a practice extensively applied in the fluvo-aquic soil zone of the North China Plain,however,the straw returned via mulching is not readily decomposed and hence unable to raise soil fertility and crop yield instantly.Moreover,straw decomposition needs to consume soil N in competition with crop growth,thus making it hard for the two to share the limited N supply harmoniously.A technique of deep burial of straw coupled with application of inorganic or organic nitrogen as primer was presented in this paper,and a continuous five-year(2011-2015)field experiment was conducted to study effects of the technique on soil fertility and wheat yield.The experiment was designed to have 3treatments in straw returning method,i.e.,Treatment NS(No straw returned),Treatment S(Straw returned via mulching,and Treatment IS(straw buried in deep furrows and then covered with crop planted in between the furrows).In addition,Treatment NS consisted of two sub-treatments,Sub-treatment NSF0(No straw returned and no fertilizer applied)and Sub-treatment NSFR(No straw returned,but fertilizer applied at a common rate);and Treatment IS did of three sub-treatments,Sub-treatment ISFR(Deep burial of straw plus conventional fertilization).Sub-treatment ISF(Deep burial of straw applied with chemical fertilizer as primer)and Sub-treatment ISOM(Deep burial of straw applied with organic manure as primer).And Sub-treatments ISF and ISOM was further divided into three Plots ISF1,ISF2 and ISF3,and Plots ISOM1,ISOM2 and ISOM3,corresponding to the proportion of nitrogen consumed by straw decomposition,8%,16% and 24%,respectively.Results show that:In the fluvo-aquic soil zone of the North China Plain,soil mechanical stability aggregates distributed mainly in >2000?m size fraction,there are 41.09%-52.25% in0-10 cm soil layer and 45.47%-62.46% in 10-20 cm soil layer,the number of subsoilaggregates are higher than upper.The content composition of each size fraction aggregates was changed under the effect of straw returning via deep burial coupled with application of fertilizer as primer,which could effectively decrease significantly the distribution of >2000?m aggregates,improve significantly the distribution of250-2000?m and 53-250?m aggregates in the two layer of soil.ISF(Deep burial of straw applied with chemical fertilizer as primer)is better than ISOM(Deep burial of straw applied with organic manure as primer)on the improvement soil structure,this phenomena showed more significantly in the top layer of soil than the subsoil,among all treatments in this experiment,the most significantly improvement is ISOM.Soil water stability aggregates distributed mainly in250-2000?m size fraction,straw returning(SF0 and SFR)and fertilizer application(NSFR)could urge soil aggregate's movement from 53-250?m to 250-2000?m,and the measure of straw returning is more effective.The treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)also could urge soil aggregate's movement from 53-250?m to 250-2000?m,at the same time,could effectively increase significantly the distribution of >2000?m aggregates,this phenomena showed more significantly in the top layer of soil than the subsoil,along with the time increased of this experiment,the effects will be more obvious.The treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)could effectively increase WSAC(>0.25mm),the increased number of soil aggregates in the top soil layer is more than the subsoil,and the increased content mainly from the distribution of 53-250?m.The MWD and GWD in the top soil layer is higher than the subsoil,and different graded aggregates all represented the law of ISOM>ISF>ISFR>SFR>SF0>NSFR>NSF0,were significantly positive correlatived with WSAC(>0.25mm),significant negative correlation was found between Da and WSAC(>0.25mm).All soil stability index indicated that the treatment of ISOM could accelerate soil aggregate stability most effectively.Soil organic carbon mainly consist in 250-2000 ?m and 53-250 ?m water stability aggregates,the treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)could increase the primary soil organic carbon significantly.In the 0-10 cm soil layer,the increasing rate could reach to 31.66%-43.95%,and to 76.72%-112.5% in the 10-20 cm soil layer.The content of soil organic carbon in the subsoil is higher than the top soil layer,ISOM2 is thehighest among all treatments.Referring to the organic carbon content in different graded soil aggregates,the law was represent by Silt + clay fraction(<53?m)> Large macro-aggregate(>2000?m)> Small macro-aggregate(250-2000?m)>micro-aggregate(53-250?m).Soil organic carbon mainly located in Silt + clay fraction(<53?m)and Large macro-aggregate(>2000?m),moreover,the content of soil organic carbon in different graded water stability aggregates in the top soil layer was higher than the subsoil,but the increasing rate was opposite.The treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)mainly increased the soil organic carbon in micro-aggregate(53-250?m)in0-10 cm soil layer and the soil organic carbon in Small macro-aggregate(250-2000?m)in 10-20 cm soil layer.In 0-10 cm soil layer,the treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)mainly increased f POC in Small macro-aggregate(250-2000?m)and o POC in micro-aggregate(53-250?m),and the soil organic carbon mainly consist in MOC.In 10-20 cm soil layer,the treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)mainly increased f POC and o POC in Small macro-aggregate(250-2000?m),and the soil organic carbon mainly consist in o POC and MOC.The treatment of straw returning via deep burial coupled with application of fertilizer as primer(ISOM and ISF)could effectively increase MBC?MBN?soil total nitrogen and soil nitrate nitrogen,the yield of winter wheat was increased significantly.Soil nitrate nitrogen and wheat effective spikes could be increased significantly by priming straw deep returning with chemical fertilizer,while others nutrient indexes were increased significantly by priming straw deep returning with organic fertilizer.The highest wheat yield was appeared in 16% nitrogen used in priming straw deep returning in organic fertilizer. |
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