Effect Of Tillage And Drought On Water Relations Of Maize Root In A Red Soil

Red soil is widely distributed in the south of our country and is an important source of land production.Due to the weak holding capacity,the low content of available water,and high temperature,strong evaporation,less rainfall in the summer and autumn season,red soil is prone to seasonal drought.Soil moisture content is relatively high in deep layer when drought occurred,but crop roots are shallower and cannot directly use it.Reasonable tillage can increase the soil moisture content,promote the crop roots extending to the depths,and reduce the risk of drought to crop.Therefore,the water relationship of root-soil is the key to study the effects of tillage on crop growth in drought stress.The objectives of thesis were to study the change of soil moisture temporal and spatial dynamics and root growth morphology,spatial distribution on the effect of tillage and drought in maize growth period through field experiment,and analyzed the water relation of root-soil system and yield under tillage measurement in different drought conditions,to explore the relationship between soil drought and crop drought and analyze the effect of seasonal drought on maize growth.It's hope to find an appropriate and effective tillage measures to mitigate drought farming,so as to effectively guide the agricultural production.Field experiment in red soil experiment station of Huazhong Agricultural University in Heshengqiao Hubei were conducted from June to September in 2016.Experiment set up deep plowing D,conventional tillage C,no-tillage N and compaction P,totally 4 farming treatments.Each tillage was divided into three drought levels,ie,sufficient irrigation CK,mild drought S,moderate drought M.Each treatment had 2 replicates,a total of 24 plots.The tested soil was red soil developed from the Quaternary red clay,and planted maize variety was Zhengdan 958.Drought treatment began in the period of corn V8.The soil water content of the mild drought plots were monitored by the automatic moisture probe(WaterScout SMEC300)instrument,and the remaining plots were determined by the drying weighing method with repeated three times in the critical growth period of maize.In the V8 and VT period,the maize growth index,root index and harvest were measured.The main results are showed as follows:The distribution of soil water content was affected by tillage and drought.With the soil depth increasing the water content increased,but there were difference between tillage management.Soil moisture content were active in the 20 ~ 30 cm layer;With the increase of drought,The daily variable quantity of soil water storage in deep plowing and conventional tillage were higher than other treatments,especially 10 ~ 30 cm soil layer;Accumulation of the variation of soil water storage in deep plowing at 10 ~ 30 cm layer was 11.92 and 12.42 mm higher than no-tillage and compaction.The consumption in tillage treaments were increased with the aggravation of drought stress,and deep plowing and conventional tillage evapotranspiration were higher than others.The evapotranspiration of the 0 ~ 20 cm upper layer were higher than the 20 ~ 40 cm lower layer.The evapotranspiration of deep tillage and conventional tillage in 10 ~ 20 cm layers were significantly higher than other treatments.No-tillage and compaction were the largest in the 0 ~ 10 cm layers.Tillage and drought treatments had an effect on root growth and architecture.In terms of root microcosm,cortical thickness and cortical cells number of different tillages significantly reduced with increasing of drought degree,no-tillage were opposite.The ratio of cortical thickness to root radius decreases and the area of vascular bundle increases.With the deepening of the soil depth,deep tillage and conventional tillage occurred cortical cells deformation,and no-tillage and compaction were deformed in any droughts and soil depth.In terms of roots macro aspects,the longitudinal distribution of root dry weight in the soil layer were negative exponent y = ae curve "S" type distribution,where the smaller the value of the decreasing rate | b |,the greater the root of the soil.In the mild drought condition,the root dry weight and root diameter increased,the root length and root surface area decreased;Root dry weight,root length and root surface area were reduced,root diameter became thicker and root growth was restricted in moderate drought.The root length,root surface area and root weight under deep plowing were distinctly higher than others.The root length and root surface area of no-tillage severely reduced in moderate drought,and roots were seriously damaged.The growth of maize roots were related to soil moisture transformation in different tillage and drought treaments.There was a significant relationship between root length density,root mass density,root surface area and soil water content(P<0.01)in the soil profile.The relationship were optimized by the quadratic equation,but the r value decreased with the increase of drought,indicating that there were other factors affect root growth in addition to moisture;.The water content in 10 ~ 20 cm layer had a significant correlation with the roots,and the root characteristics of this layer were related to the roots in 0 ~ 40 cm layers.The relationship between root length density,root mass density,root surface area and water content in total soil layer were fitted with y = ae curve.Total root length under tillage and drought treatments and consumption had a significant positive correlation(P <0.01),as similar as total root surface area.The average root diameter was negatively correlated with the water consumption(P <0.01).Tillage and drought significantly effected on maize yield(P<0.01).The variation rule of maize yield under different drought conditions were D>C>N?P.Yield were severely reduced as drought increased.The yield of no-tillage significant reduction was respectively by 44.19% and 85.40% when suffered from drought stress.The root mass,root length,root surface area and yield were significantly correlated in the 10 ~ 20 cm layers.Simultaneously,root length and root surface area of fine roots were a significant positive correlation with yield(P<0.01).The formation of yield,root growth characteristic and soil water change were showed closely relevant relation.Tillage and drought treatments significantly affected the moisture relationship of maize root in red soil.Root growth and water relations were complex,where tillage changed soil moisture migration and affected root growth and yield.Deep plowing improved the soil moisture content of drought,especially in 10 ~ 20 cm soil layer.And it adjusted root system and promoted deep root growth,what increased yield and enhanced drought resistance.While no-tillage in red soil had a detrimental effect on maize roots and yield,which was not conducive to alleviating crop drought stress.