Characteristics Of Rhizosphere Process And Farmland Phosphorus Balance In Response To Dairy Cattle Slurry Returning Of Spring Maize In Northeast Of China

The combined application of organic-inorganic manure and urine after harmless treatment can effectively reduce the input of fertilizer,promote the utilization of fecal waste resources,and realize the important way of rural revitalization and agricultural green development.In this study,spring corn was selected as the research object for two consecutive years from 2021 to 2022 under field conditions,and anaerobic fermentation dairy cattle slurry was used as the main material.N:200 kg·hm^-2,P₂O₅:100 kg·hm^-2,K₂O:80 kg·hm^-2was the total nutrient input,and six treatments were set up,including no fertilizer（CK）,conventional fertilizer（F）for farmers,and fertilizer combined with dairy cattle slurry,which were 30,60,90,120 t·hm^-2（FL30,FL60,FL90,FL120）according to the amount of cow manure.The effects of combined application of liquid cow dung and fertilizer on maize root growth,rhizosphere soil organic acid concentration,rhizosphere soil acid phosphatase activity,mycorrhizal infection,plant phosphorus absorption and transport,grain yield and economic benefits,phosphorus fertilizer utilization rate,soil phosphorus depletion and leaching were discussed,providing theoretical basis for dairy cattle slurry return to field and green production of maize.The results are as follows:（1）Combined application of dairy cattle slurry with fertilizer could promote root growth,increase root biomass,root length per plant,expand root surface area,adjust root diameter and optimize root morphology.Compared with F treatment,the root length,average root diameter,root surface area and root biomass of maize increased by 0.42%to 98.87%,1.73%to 81.07%,2.12%to142.92%and 2.59%to 134.15%respectively.Comprehensive analysis showed that the application of 90 t·hm^-2dairy cattle slurry combined with chemical fertilizer was more beneficial to promote the growth of root system.（2）In the process of rhizosphere regulation,dairy cattle slurry combined with chemical fertilizer can promote root secretion of organic acids,reduce rhizosphere soil pH,improve rhizosphere acid phosphatase activity and maintain stable mycorrhizal infection rate,so as to promote the phosphorus absorption of maize roots.Rhizosphere acid phosphatase activity and organic acid secretion of maize were affected by above-ground P concentration,and there was a significant positive correlation with P concentration.There was a significant negative correlation between arbuscular mycorrhizal infection and soil Olsen-P.When soil Olsen-P<64.09 mg·kg^-1,it decreased with the increase of Olsen-P content.When soil Olsen-P>64.09 mg·kg^-1,the arbuscular mycorrhizal infection rate remained stable at 23.33%.The combined application of 60～90 t·hm^-2dairy cattle slurry with chemical fertilizer was more favorable to the rhizosphere process and mycorrhizal regulation.（3）The combined application of dairy cattle slurry and fertilizer could improve the corn grain yield and the utilization rate of phosphorus fertilizer.Compared with F treatment,the corn grain yield was increased by 15.61%to 32.14%.The maize yield was the highest when 90～120 t·hm^-2liquid manure was combined with fertilizer,which increased by 22.87%to 32.14%compared with F treatment.Combined application of dairy cattle slurry and fertilizer could promote dry matter accumulation and above-ground P accumulation,and phosphorus transport efficiency and contribution rate in vegetative organs of maize.Compared with F treatment,plant height increased by 1.53%to 7.95%,leaf area increased by 4.76%to 48.49%,total dry matter accumulation increased by 5.37%to 14.50%and above-ground phosphorus accumulation increased by 2.23%to21.94%.Comprehensive analysis showed that 60～90 t·hm^-2dairy cattle slurry combined with chemical fertilizer was more favorable to above-ground dry matter and phosphorus accumulation.（4）Combined application of dairy cattle slurry and chemical fertilizer can increase the soil available P content,reduce the apparent soil P deficit in the current season,increase the soil P accumulation in 0～100 cm depth,significantly higher than the single application of chemical fertilizer,promote the migration of phosphorus to deep soil,soil phosphorus in a short time into the deep soil,that is,under the condition of dairy cattle slurry returning to the field,Based on the correlation analysis between Olsen-P and calcium chloride and phosphorus,the critical value of phosphorus leaching in soil of the experimental base was determined to be 48.99 mg·kg^-1,that is,when the application of dairy cattle slurry exceeded 90 t·hm^-2,the content of Olsen-P in soil exceeded the critical value of phosphorus leaching,and the risk of phosphorus leaching in soil increased.In conclusion,optimizing the amount of liquid cow dung returned to the field under the condition of 60～90 t·hm^-2can effectively improve the root growth and rhizosphere physiology of maize,coordinate root morphology,physiology and mycorrhizal symbiosis to promote plant phosphorus uptake and dry matter accumulation,improve the utilization efficiency of phosphorus fertilizer,reduce soil phosphorus surplus and reduce phosphorus loss caused by phosphorus leaching.Finally,higher grain yield was obtained.Therefore,under the application mode of dairy cattle slurry combined with fertilizer,the recommended application amount of dairy cattle slurry should be controlled within the range of 60～90 t·hm^-2,which can reasonably utilize livestock and poultry manure resources to reduce environmental harm,meet crop nutrient requirements and achieve crop economic benefits,which is conducive to green crop production and efficient nutrient management.