Effects Of Tillage And Residue Returning On Root Spatial Distribution And Water Use Efficiency Of Summer Maize

To explore the effects of different tillage methods and residue returning on yield and water use efficiency of summer maize,and further explore the conservation tillage measures suitable for North China Plain.In this experiment,the yield and water use efficiency were studied in2018-2019,and in 2020,the"3D space method"was used to study the distribution characteristics of the root and the rhizosphere environment,and systematically discussed the effects of deep ploughing(PT),subsoiling(ST),rotary tillage(RT)on the spatial distribution of summer maize root system and water use efficiency under the conditions of the residue returning(1)and without residue(0).The main results are as follows:The root length,root dry weight,root surface area and root radius all increased with residue and at the filling period increased by 33.75%,17.58%,21.75%and 8.78%,respectively,compared with no residue.Residue returning significantly promoted the development of root systems.The different tillage methodes showed similar spatial configuration under the conditions of residue and without sresidue.In the jointing stage,the root length density of RT1and PT1 in the horizontal direction were 13.85%and 10.23%higher than that of ST1,respectively.ST1 significantly increased the vertical root length density of 30-60 cm,which was 86.38%higher than that of RT1;the RL/RB at 10-20 and 20-30 cm away from the plant in PT1 and RT1 wer significantly higher ST1.The root radius of 0-40 cm soil at the jointing stage of rotary tillage treatment increased by 22.01%,and the root radius of 40-60 cm in subsoil was significantly increased by 36.37%,compared with plow treatment.The distribution of ST1jointing stage presents the characteristics of"narrow horizontally,deep vertical,and thick lower layer";RT1 presents the characteristics of"wide horizontally,shallow vertically,thin lower layer",and the spatial configuration of PT1 is somewhere in between.The tillage treatment at filling stage and jointing stage showed similar spatial distribution characteristics.The root length and root dry weight were significantly increased compared with the jointing stage.The root length density of 0-20 cm in the RT1 at filling stage increased by 51.75%compared with the jointing stage,and the upper root system was more crowded.The horizontal radiation in ST1 range becomes larger at filling stage.ST1 and RT1 significantly increased root dry weight and root length during the filling stage,which were 28.61%,29.59%,5.72%and 20.99%higher than PT1,respectively.Residue returning significantly improves the soil structure and increases soil nutrients and water content.Compared with no residue,the total porosity of 0-40 cm soil and the number of large water-stable aggregates under residue returning increased by 4.46%and 11.88%,respectively,and the soil water content,organic carbon,total nitrogen and available phosphorus of 0-20 cm increased by 5.74%,18.47%,16.62%and 51.97%respectively.RT1 treatment significantly increased the total porosity,soil moisture and available phosphorus of the 0-10 cm soil layer,which were increased by 14.68%,16.06%and 206.05%respectively compared with PT1.Compared with RT1,ST1 and PT1 significantly increased the total porosity,capillary porosity and non-capillary porosity of the soil layer by 10-40 cm.The soil water content of 10-60 cm during the filling period increased by 9.51%and 8.76%,respectively.Compared with RT1,the organic carbon and total nitrogen of ST1 and PT1 in the 0-30 cm soil layer increased by 18.97%,14.98%,16.62%and 12.53%,respectively.It is found that the soil water content has a significant binomial distribution relationship with root length density during the filling period,and a significant linear relationship with root dry weight(p<0.01)through correlation analysis;soil organic carbon,total nitrogen,available phosphorus,total porosity and MWD has a very significant positive correlation with root length density and root dry weight,and a very significant negative correlation with soil bulk density(p<0.01).Compared with no residue,residue returning can significantly increase leave area and dry matter above the ground,thereby increasing summer maize yield and water use efficiency.The two-year average summer maize yield was significantly increased by 6.70%compared with that without residue,and the water use efficiency was increased by 7.29%.ST1 significantly increased the summer maize yield,with an average two-year yield of 8.81 t hm~2,and was 5.19%and 3.23%higer than PT1 and RT1.In 2018,there was a lot of precipitation in the year,which significantly improved the water use efficiency,and in the dry year of 2019,the use of soil moisture was increased.Correlation analysis showed that root length at jointing stage and root dry weight,root surface area and root radius at filling stage are significantly positively correlated with summer maize yield(p<0.05).In summary,residue returning significantly improves the soil water and fertilizer environment,promotes root extension and development,thereby increasing leave area and photosynthetic rate,which is conducive to the accumulation of dry matter above the ground and the transfer of assimilation to the grain.The formation of the root system spatial distribution in a subsoil environment shows the characteristics of"narrow horizontal,deep vertical,and thick lower layer",which is beneficial to the formation of high-yield populations and thus improves water use efficiency;the bulk density in RT1 hinders the rooting of the root system,presenting a spatial distribution of"wide horizontal,shallow vertical,and fine lower layer".It mainly uses the upper soil resources and has a greater risk of yield reduction in drought years.Therefore,the recommended conservation tillage measure is subsoil with residue returning.