Effects Of Fallow Rotation On Soil Aggregates And Its Nutrients In Maize Land Under Straw Returning To Field

Through the analysis of 0~10 cm soil samples under fallow rotation and conventional tillage,using dry sieving method to isolate five soil aggregates,determination of various soil aggregate quality percentage and soil nutrient contents in different particle soil aggregates.The specific objectives were to determine the distribution of soil aggregates,characteristic of soil nutrient contents and its influence of seasonal changes under different tillage methods.The following are the mainly results of this paper:The contents of >0.25 mm aggregate in the mulching zone,leisure zone and planting zone of fallow rotation was higher than that under conventional tillage in Changchun and Dehui pilot site.>2.0 mm aggregates were dominant in both the mulching zone and the planting zone,accounting for more than 35% of the total grain size respectively,while aggregates with 1.0-0.5 mm grain size were dominant in the traditional farming tillage.The MWD and GMD of fallow rotation under straw returning to the field were both larger than that of conventional tillage,which indicated that fallow rotation under straw mulching was beneficial to the improvement of soil aggregate and the stability of soil structure to some extent.The contents of soil aggregate organic carbon,total nitrogen,available nitrogen,available potassium in fallow rotation were higher than conventional tillage in both pilot site.The growth of soil aggregate organic carbon under fallow rotation in Dehui experimental zone(13 years)was greater than that in Changchun(7 years),and microaggregate was more significant(32.99%);The aggregates of 0.5-0.25 mm and <0.25 mm had more total nitrogen content.In 2.0-1.0 mm,1.0-0.5 mm and <0.25 mm,the contents of available nitrogen were significantly different between two tillage methods(p<0.05).The contents of available K were distributed evenly in different aggregate size,indicating that available K was less affected by particle size.The total phosphorus(TP)contents in >0.25 mm were lower than that in <0.25 mm.The cultivation method in Dehui had little effect on available phosphorus.The content of available phosphorus in the two managements in Changchun pilot site presented significant difference(p<0.05),and available phosphorus was mainly concentrated in microaggregate.The contents of soil aggregate organic carbon except >2 mm aggregate first increased and then decreased with the change of time,which was opposite to the conventional tillage in Changchun pilot site.This might be explained that all residues retaining in the field were effective in improved SOC.The contents of soil aggregate AN,AP,AK under fallow rotation and AP and AK under traditional tillage showed a trend of increase after the first decrease seasonal change,which could be explained that maize need to absorb a large number of nutrients during the growth periods.It is difficult to maintain the balance nutrient elements,which resulted in the rapidly decrease of AN,AP and AK in soil aggregate.