Effect And Passway Of Winter Cover Crops Regulating Summer Maize Drought In Red Soil

Seasonal drought occurs frequently in subtropical red soil region of China,which is mainly affected by the’root-soil’contradiction of climate,soil and crop growth in red soil region and the lack of agricultural facilities.There are agricultural measures(cultivation,fertilization,tillage,covering measures,modifiers,etc.)and engineering measures(water storage,water transmission and distribution,water-saving irrigation projects,etc.)to prevent and control drought.However,the cost of drought resistance of red soil engineering measures in slope farmland is higher.Seasonal drought in red soil is often characterized by shallow water shortage,deep soil is not water shortage.Crops with strong rooting ability in winter can use their roots to increase deep soil pores,Promote the growth of subsequent crop roots to use more deep water,and thus play a role in regulating drought,its drought resistance effect and the way of action that need further exploration.In this paper,the effects of several cover crops with different characteristics on improving the properties of clay red soil and regulating the seasonal drought of red soil were studied.The response characteristics of different cover crops and post-season maize were compared in order to provide a basis for reasonable drought resistance measures in red soil.The field experiment was carried out at the Field Scientific Observation and Research Station of the Ministry of Education of Heshengqiao Town,Xian’an District,Xianning City,Hubei Province(30°01’45"N,114°21’35"E,altitude of about44.3 m)from 2021 to 2022.The soil is brown red colour developed from quaternary red clay parents materials.Five winter cover crops treatments were set up:common rape(Rape C),annual lucerne(Luc1y),annual vetiver(Vet1y),deep root rape(Rape D)and no winter crop treatment(Control).Cover crops were sown in October or transplanted and harvested in June,and post-season maize was sown in June and harvested in October.During the growth of maize,soil properties,soil,and crop drought indicators,and grain yield were measured to analyze the ways affecting maize drought resistance.The main results are as follows:(1)Cover crops reduced the drought degree of maize and reduced yield loss.The difference in the improvement effect of different treatments in the year with more severe drought was greater.Vet1y had the most obvious effect on the regulation of drought in 20-60 cm soil layer,and the drought degree of maize was the smallest.Luc1y had the best effect on the improvement of drought in 10-20 cm soil layer,and the regulation of maize drought was also better.These two cover crops reduced the proportion of maize yield loss by more than 50%.The more severe the drought,the more the maize yield decreased,but the cover crops treatment reduce the extent of the maize yield loss with Control.(2)There was a positive response relationship between the root characteristics and the organic acids in the rhizosphere exudates of the pre-and post-season crops,and there was no obvious response relationship between the rhizosphere microorganisms.The effect of cover crops on the distribution of maize roots was reflected in the deep soil(20-80 cm).On the one hand,Vet1y and Luc1y treatments could promote the maize roots to penetrate into the 60-80 cm soil layer.On the other hand,the root characteristics(root length density,root surface area,root volume,root diameter)of maize showed Vet1y>Luc1y>Rape D>Rape C in the 40-80 cm soil layer.The increase of organic acid content in cover crops promoted the increase of organic acid secreted by maize roots.Although there was no obvious response relationship between rhizosphere microorganisms,the cover crops also increased the species and abundance of rhizosphere microorganisms during maize drought period.(3)Cover crops improved the water storage and water retention capacity of the soil and improved the water use efficiency of crops.During the drought period from July to October,the soil water loss rate of the cover crops was slower than that of the Control treatment,and the soil moisture content could be maintained for a long time.Compared with Control,Vet1y and Rape D significantly increased the water use efficiency of maize by 16.29%and 11.14%,respectively.(4)Cover crops significantly improved soil physical and chemical properties.The soil bulk density(1.41～1.42 g/cm~3)of Vet1y in 20-60 cm was smaller than that of other treatments(1.45～1.56 g/cm~3).Vet1y had the highest total porosity and capillary porosity,and Rape D had the highest proportion of aeration porosity in 0-40cm soil layer.Vet1y and Luc1y could not only increase the content of water-stable macroaggregates in surface soil(0-20 cm),but also significantly improve the aggregate structure in deep soil.Luc1y increased soil’s available nitrogen content,while Rape C had the best effect on increasing available phosphorus and available potassium,and Vet1y increased soil organic matter content.(5)Maize drought index(root water potential,leaf water potential,crop water stress index,yield)had a significant correlation with soil bulk density,porosity structure,aggregate structure,organic matter content and alkali-hydrolyzable nitrogen content.In the pathway analysis,these soil indicators mainly affected the degree of soil drought during maize growth,total nitrogen of maize plants,root characteristic distribution,rhizosphere microorganisms,and organic acid content.Among them,soil physical indicators have the best effect on improving soil drought,total nitrogen,and root characteristics of maize plants.From a single soil index,the improvement effect of soil organic matter on soil drought degree,nitrogen absorption,and organic acid was the best,and the standard coefficient was above 0.5.The results showed that soil physical properties had the greatest effect on regulating maize drought resistance,and from a single index,the effect of increasing soil organic matter to regulate maize drought resistance was the best.In the selection of cover crops,vetiver is suitable for controlling soil erosion and is suitable for planting in a dry land with ridges and large slopes.Lucerne and deep-rooted rape have high economic value as livestock feed and oil crops respectively,and also have the effect of improving the drought resistance of main crops,so they are more suitable for rotation with main crops to regulate seasonal drought in red soil.