| Black soil region of Northeast China is an important grain production base in China with fertile soil and sufficient light.However,in recent years,soil fertility decreased rapidly owing to unreasonable farming and straw utilization.In order to solve the technical problems of the construction of tillage layer and the effective straw returning in the northeast black soil area,the effects on the physical properties of black soil and the growth of corn root system under different tillage methods and straw returning were studied,and the effects on improving the physical properties in different tillage layers and the growth of corn root system were clarified.This can provide a scientific basis for the construction of deep and mature tillage layer in the northeast black soil area.Based on the in-situ experiments?from 2015 to 2018?of the thin layer black soil in Gongzhuling City of Jilin Province and the deep layer black soil in Keshan County of Heilongjiang Province,the root length density,root tip number and other main root growth characteristics by the minirhizotron method were monitered in 2018,and the important soil physical indexes affecting root growth were measured.The main results are as follows:1.Compared with rotary tillage when the straw was not returned,soil bulk density and soil compactness of subsoiling and deep ploughing decreased by 7.8%and 6.4%,and soil temperature increased by 0.55%-4.23%on average in each growth period;subsoiling,deep ploughing and no-tillage treatment are beneficial to increase the field water holding capacity and soil moisture content of 0-30cm soil layer in jointing period,meanwhile subsoiling and deep ploughing treatment are beneficial to increase the saturated water conductivity and the soil moisture content of 30-100cm soil layer in the whole growth period.2.Compared with simple tillage,tillage+straw returning mode's the soil bulk density and soil compactness of each soil layer decreased by 3.4%-46.3%,increased the field water holding capacity,saturated hydraulic conductivity and soil moisture content of 0-30cm soil layer.Among them,the soil bulk density,compactness and water condition under subsoiling straw returning and deep ploughing straw returning mode were better than that of no-tillage straw returning mode and rotary tillage straw returning mode.Compared with tillage+straw returning,tillage+straw returning combining manure mode's soil bulk density and compactness of each soil layer were further reduced by 2.2%-18.8%and the field water holding capacity and soil saturated hydraulic conductivity were increased by 3.7%-22.9%.Subsoiling and deep ploughing+straw returning combining manure can fully mix the straw and manure with the soil on the plough layer,so the soil compaction and water condition of subsoiling and deep ploughing+straw returning combining manure were the best,which played an important role in soil and water conservation.3.Compared with rotary tillage when the straw was not returned,subsoiling,deep ploughing and no-tillage's the root length density,root surface area density,root tips number and root volume of maize were all increased,and the increase range of subsoiling and deep ploughing in 15-45cm soil layer was the largest?7.1%-63.6%?,which indicated that subsoiling and deep ploughing were beneficial to the root system;compared with simple tillage,tillage+straw return mode's the root length density,root surface area density and root volume of each soil layer were increased.Root tips and volume increased by 22.5%,25.4%,30.0%and 23.8%respectively,meanwhile subsoiling straw returning and deep ploughing straw returning had the best effect on the improvement of each index of roots.The average diameter of roots in each treatment was no obvious change in 0-15cm soil layer,and the soil layer of 15-45cm was reduced.Compared with tillage+straw returning,tillage+straw returning combining manure mode further promote the growth of corn roots.Among which,0-15cm soil layer had the best effect of no-tillage straw returning with manure,while 15-45cm soil layer had the best effect of subsoilibg and deep ploughing+straw returning combining manure.The correlation analysis showed that soil bulk density and soil compactness were significantly or extremely significantly negatively correlated with root length density,root surface area density,root volume and root tip number,respectively.When the soil compactness value is more than 2000 KPa,or the soil bulk density is more than 1.4 g·cm-3,it has a significant inhibitory effect on the root length density of maize.4.The dynamic changes of maize root growth were different under different tillage and straw returning.With the development of the growth stage,the root length density and tips number of each soil layer gradually increased from jointing stage to trumpet stage,and reached the maximum value at the tassel stage.In terms of different tillage methods,compared with no-tillage and rotary tillage,the root length density,root tips number and net growth rate in soil layer of 15-45cm were significantly increased under subsoiling and deep ploughing from bellmouth stage to grouting stage.Compared with simple tillage,tillage+straw returning mode's the root length density and root tips number from bellmouth stage to grouting stage were significantly increased,and subsoiling straw returnin and deep ploughing straw returning mode's effect of improving root length density and root tips number was better than that of no-tillage straw returning and rotary tillage straw returning.Compared with tillage+straw returning,tillage+straw returning combining manure was significant on root length density,root tips number and net growth rate in the period of higher nutrient demand,tasselling and filling stage,which promoted the growth of a large number of fine roots with smaller diameter class.Deep ploughing+straw returning combining manure was the best way to improve the root density,root tips number and the net growth rate,and promote the root growth and increase the root growth activity.On the whole,the mode of subsoiling and deep ploughing+straw returning or the mode of subsoiling and deep ploughing+straw returning combined combining manure can effectively amend the soil compaction and water condition of the black soil in Northeast China,alleviate the problem of thickening and hardening of the bottom of plough,promote the growth of corn root system to a large extent,and make the corn root system obtain a good spatial distribution form. |
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