Root Drilling Performance Of Different Preceding Crops And Its Improvement Effects On A Clayey Red Soil

Seasonal drought occurs frequently in the red soil region of China.Red soil water shortage often occurs on the surface of the soil while the deep layer is not dried.However,the high intensity of the sticky red soil restricts the distribution of field crops under the root system,so it is impossible to utilize and absorb the deep soil water.Some plants have strong drilling ability and their roots can penetrate deep into the soil,which not only provides a pore channel for the growth of the crop roots in the latter season,but also may improve the porosity and improve the drought resistance of subsequent crop.In this paper,through indoor and field experiments,explored the drilling performance of several preceding crop roots on the clay red soil and its effect on soil physical properties,in the hope of finding suitable drilling plants for rotation and providing scientific basis and possible ways to prevent the seasonal drought in the red soil.The field experiment was conducted at the Field Science Observation Station of the Ministry of Education in the middle reaches of the Yangtze River in Xian Ning,Hubei Province from July 2018 to August 2019.The field experimental plot is a clay red soil developed from the Quaternary red clay parent material.A total of 6 treatments were set up in the field trials,namely,fallow?plant-free?land Land F,common rape Rape C,deep root rape Rape D,1 annual Lucerne Luc1Y,1 annual vetiver Vet1Y and 5 annual vetiver Vet5Y.The distribution characteristics of the root system and its effect on the soil physical properties were measured during the plant harvest period.The soil samples for the indoor pot experiment were taken from the above-mentioned fields,and three bulk density treatments?1.2 g/cm3,1.4 g/cm3,and 1.6 g/cm3?were set,and the same four plants as the field experiment were planted,which were ordinary rape?Hua Shuang 4?,Deep-rooted rape?xinan28?,Lucerne?radio?and vetiver?Wild?.after 12 days of growth in the growth box,the geometric morphological characteristics and growth status of the plant root system under different bulk densities were determined.The following main results are obtained:?1?Different plant roots have different geometric characteristics and different drilling capabilities.In the pot experiment,Vet1Y had the largest root length density,root volume,and number of root tips,respectively 0.16 cm/cm3,286.94 cm³,and 63,followed by Luc1Y,while Rape D and Rape C had no significant differences and were the smallest.As the soil bulk density increases,the total root length density and root volume of several plants decrease,while the root diameter and root tip angle gradually increase.In field trials,the extension depths of Vet5Y,Vet1Y,Luc1Y,Rape D,and Rape C were 100 cm,100 cm,80 cm,60 cm,and 40 cm,respectively,and 95%root depth of deep-rooted plants?the depth of root cumulative length?is significantly greater than Rape C,further verifying that Vet1Y's drilling ability is the strongest,followed by Luc1Y,and finally Rape D and Rape C.Plant root elongation?rate of root elongation per unit time?decreases with decreasing root length density,root volume,and number of root tips,and decreases with increasing root diameter and root tip angle.Vet1Y has the largest root elongation and the smallest apex angle(spherical apex shape factor i SF_spheroid).?2?The distribution characteristics of different root systems on the soil profile are significantly different.The root system is more concentrated at a depth of 0?40 cm,20 cm depth of root length density?cm/cm3?were Rape D?1.82?>Rape C?1.70?>Vet1Y?1.34?>Vet5Y?1.23?>Luc1Y?1.16?,and the depth at 40 cm is Vet5Y?1.62?>Luc1Y?1.60?>Vet1Y?1.17?>Rape D?1.06?.The root diameter and root volume density decrease gradually with the increase of soil depth.In terms of varieties,Vet5Y is the largest,followed by Vet1Y and Luc1Y,and the smallest is Rape D and Rape C.The root surface area density is the largest in Vet5Y,while there was no significant difference in the remaining annual plants.With the increase of soil depth,the root mass and root number density decreased.Vetiver?Vet1Y and Vet5Y?had the highest root number density,while Luc1Y had the highest root mass density and the lowest Rape D and Rape C.Different plants have different root diameter gradation distribution.The main root crops rape has a large proportion of fine roots and medium roots,the sum of the two is up to 90%,while the same main root plant luc1Y has a larger root ratio than rape;The fibrous root vetiver?Vet1Y and Vet5Y?accounted for a large proportion in the middle root?37%?and coarse roots?11%?.In addition,the growth years significantly affect the root size distribution of plants.Vet5Y's fine roots?14%?and coarse roots?19%?account for more than Vet1Y's fine roots?8%?and coarse roots?11%?.?3?The root system improved the pore structure and water conductivity of the clayey red soil.Compared with the control,the soil bulk density of the land with root system decreased,and the total porosity and aeration porosity increased.In the shallow soil?0?40 cm?,except for the small Vet5Y porosity,the total soil porosity is in order of Luc1Y>Vet1Y>Rape D>Rape C>Land F,while in the deep soil??40 cm?,the total porosity of Vet5Y and Luc1Y is significantly greater than that of Vet1Y,Rape D and Land F.The order of unsaturated hydraulic conductivity K?h?in the soil surface is Rape C>Vet5Y>Vet1Y>Rape D>Luc1Y>Land F,while K?h?in deep soil is represented as Vet5Y>Luc1Y>Vet1Y>Rape C>Land F.It shows that plants with strong drilling ability have better effect on improving water conductivity of deep soil.Plant roots also reduce soil mechanical resistance?soil strength?,especially at a depth of 20 cm,the mechanical resistance of the soil?MPa?of Land F is 1.77,which is higher than that of Rape C?1.29?,Rape D?0.41?,Luc1Y?0.57?,Vet1Y?0.40?,Vet5Y?1.57?,Coarse root plants are better at reducing soil strength.The results show that the geometric characteristics of plant roots?root diameter and root tip angle?affect its drilling ability and distribution in clayey red soil,and have different effects on soil properties.Vet5Y and Luc1Y are deep-rooted and have more coarse roots,which significantly increases the soil aeration porosity and improves the water conductivity of the soil,which is beneficial to the growth and drought resistance of the latter crops.